[RESEND,V16,4/6] libxl: add pvusb API

Commit Message

Chunyan Liu March 8, 2016, 1:37 a.m. UTC

Add pvusb APIs, including:
 - attach/detach (create/destroy) virtual usb controller.
 - attach/detach usb device
 - list usb controller and usb devices
 - some other helper functions

Signed-off-by: Simon Cao <[e-mail]>
Signed-off-by: George Dunlap <[e-mail]>
Signed-off-by: Chunyan Liu <[e-mail]>
---
Changes:
  * Address George's comments

 tools/libxl/Makefile                 |    3 +-
 tools/libxl/libxl.c                  |   18 +
 tools/libxl/libxl.h                  |   77 ++
 tools/libxl/libxl_device.c           |    5 +-
 tools/libxl/libxl_internal.h         |   18 +
 tools/libxl/libxl_osdeps.h           |   13 +
 tools/libxl/libxl_pvusb.c            | 1620 ++++++++++++++++++++++++++++++++++
 tools/libxl/libxl_types.idl          |   46 +
 tools/libxl/libxl_types_internal.idl |    1 +
 tools/libxl/libxl_utils.c            |   18 +
 tools/libxl/libxl_utils.h            |    5 +
 11 files changed, 1822 insertions(+), 2 deletions(-)
 create mode 100644 tools/libxl/libxl_pvusb.c

Comments

George Dunlap March 8, 2016, 5:14 p.m. UTC | #1

On 08/03/16 01:37, Chunyan Liu wrote:
> Add pvusb APIs, including:
>  - attach/detach (create/destroy) virtual usb controller.
>  - attach/detach usb device
>  - list usb controller and usb devices
>  - some other helper functions
> 
> Signed-off-by: Simon Cao <[e-mail]>
> Signed-off-by: George Dunlap <[e-mail]>
> Signed-off-by: Chunyan Liu <[e-mail]>

Reviewed-by: George Dunlap <[e-mail]>

Good work!

 -George

> ---
> Changes:
>   * Address George's comments
> 
>  tools/libxl/Makefile                 |    3 +-
>  tools/libxl/libxl.c                  |   18 +
>  tools/libxl/libxl.h                  |   77 ++
>  tools/libxl/libxl_device.c           |    5 +-
>  tools/libxl/libxl_internal.h         |   18 +
>  tools/libxl/libxl_osdeps.h           |   13 +
>  tools/libxl/libxl_pvusb.c            | 1620 ++++++++++++++++++++++++++++++++++
>  tools/libxl/libxl_types.idl          |   46 +
>  tools/libxl/libxl_types_internal.idl |    1 +
>  tools/libxl/libxl_utils.c            |   18 +
>  tools/libxl/libxl_utils.h            |    5 +
>  11 files changed, 1822 insertions(+), 2 deletions(-)
>  create mode 100644 tools/libxl/libxl_pvusb.c
> 
> diff --git a/tools/libxl/Makefile b/tools/libxl/Makefile
> index 789a12e..8fa7b87 100644
> --- a/tools/libxl/Makefile
> +++ b/tools/libxl/Makefile
> @@ -105,7 +105,8 @@ LIBXL_OBJS = flexarray.o libxl.o libxl_create.o libxl_dm.o libxl_pci.o \
>  			libxl_stream_read.o libxl_stream_write.o \
>  			libxl_save_callout.o _libxl_save_msgs_callout.o \
>  			libxl_qmp.o libxl_event.o libxl_fork.o \
> -			libxl_dom_suspend.o libxl_dom_save.o $(LIBXL_OBJS-y)
> +			libxl_dom_suspend.o libxl_dom_save.o libxl_pvusb.o \
> +                        $(LIBXL_OBJS-y)
>  LIBXL_OBJS += libxl_genid.o
>  LIBXL_OBJS += _libxl_types.o libxl_flask.o _libxl_types_internal.o
>  
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index 2ab5ad3..1e68688 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -4102,6 +4102,8 @@ out:
>   * libxl_device_vkb_destroy
>   * libxl_device_vfb_remove
>   * libxl_device_vfb_destroy
> + * libxl_device_usbctrl_remove
> + * libxl_device_usbctrl_destroy
>   */
>  #define DEFINE_DEVICE_REMOVE_EXT(type, remtype, removedestroy, f)        \
>      int libxl_device_##type##_##removedestroy(libxl_ctx *ctx,           \
> @@ -4159,6 +4161,10 @@ DEFINE_DEVICE_REMOVE(vfb, destroy, 1)
>  DEFINE_DEVICE_REMOVE(vtpm, remove, 0)
>  DEFINE_DEVICE_REMOVE(vtpm, destroy, 1)
>  
> +/* usbctrl */
> +DEFINE_DEVICE_REMOVE_CUSTOM(usbctrl, remove, 0)
> +DEFINE_DEVICE_REMOVE_CUSTOM(usbctrl, destroy, 1)
> +
>  /* channel/console hotunplug is not implemented. There are 2 possibilities:
>   * 1. add support for secondary consoles to xenconsoled
>   * 2. dynamically add/remove qemu chardevs via qmp messages. */
> @@ -4174,6 +4180,8 @@ DEFINE_DEVICE_REMOVE(vtpm, destroy, 1)
>   * libxl_device_disk_add
>   * libxl_device_nic_add
>   * libxl_device_vtpm_add
> + * libxl_device_usbctrl_add
> + * libxl_device_usbdev_add
>   */
>  
>  #define DEFINE_DEVICE_ADD(type)                                         \
> @@ -4205,6 +4213,12 @@ DEFINE_DEVICE_ADD(nic)
>  /* vtpm */
>  DEFINE_DEVICE_ADD(vtpm)
>  
> +/* usbctrl */
> +DEFINE_DEVICE_ADD(usbctrl)
> +
> +/* usb */
> +DEFINE_DEVICE_ADD(usbdev)
> +
>  #undef DEFINE_DEVICE_ADD
>  
>  /******************************************************************************/
> @@ -6750,6 +6764,10 @@ int libxl_retrieve_domain_configuration(libxl_ctx *ctx, uint32_t domid,
>  
>      MERGE(pci, pcidevs, COMPARE_PCI, {});
>  
> +    MERGE(usbctrl, usbctrls, COMPARE_USBCTRL, {});
> +
> +    MERGE(usbdev, usbdevs, COMPARE_USB, {});
> +
>      /* Take care of removable device. We maintain invariant in the
>       * insert / remove operation so that:
>       * 1. if xenstore is "empty" while JSON is not, the result
> diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
> index 0859383..5cc3ce3 100644
> --- a/tools/libxl/libxl.h
> +++ b/tools/libxl/libxl.h
> @@ -123,6 +123,12 @@
>  #define LIBXL_HAVE_DOMAIN_NODEAFFINITY 1
>  
>  /*
> + * LIBXL_HAVE_PVUSB indicates functions for plugging in USB devices
> + * through pvusb -- both hotplug and at domain creation time..
> + */
> +#define LIBXL_HAVE_PVUSB 1
> +
> +/*
>   * LIBXL_HAVE_BUILDINFO_HVM_VENDOR_DEVICE indicates that the
>   * libxl_vendor_device field is present in the hvm sections of
>   * libxl_domain_build_info. This field tells libxl which
> @@ -1536,6 +1542,77 @@ int libxl_cdrom_insert(libxl_ctx *ctx, uint32_t domid, libxl_device_disk *disk,
>                         const libxl_asyncop_how *ao_how)
>                         LIBXL_EXTERNAL_CALLERS_ONLY;
>  
> +/*
> + * USB
> + *
> + * For each device removed or added, one of these protocols is available:
> + * - PV (i.e., PVUSB)
> + * - DEVICEMODEL (i.e, qemu)
> + *
> + * PV is available for either PV or HVM domains.  DEVICEMODEL is only
> + * available for HVM domains.  The caller can additionally specify
> + * "AUTO", in which case the library will try to determine the best
> + * protocol automatically.
> + *
> + * At the moment, the only protocol implemented is PV.
> + *
> + * One can add/remove USB controllers to/from guest, and attach/detach USB
> + * devices to/from USB controllers.
> + *
> + * To add USB controllers and USB devices, one can adding USB controllers
> + * first and then attaching USB devices to some USB controller, or adding
> + * USB devices to guest directly, it will automatically create a USB
> + * controller for USB devices to attach.
> + *
> + * To remove USB controllers or USB devices, one can remove USB devices
> + * under USB controller one by one and then remove USB controller, or
> + * remove USB controller directly, it will remove all USB devices under
> + * it automatically.
> + *
> + */
> +/* USB Controllers*/
> +int libxl_device_usbctrl_add(libxl_ctx *ctx, uint32_t domid,
> +                             libxl_device_usbctrl *usbctrl,
> +                             const libxl_asyncop_how *ao_how)
> +                             LIBXL_EXTERNAL_CALLERS_ONLY;
> +
> +int libxl_device_usbctrl_remove(libxl_ctx *ctx, uint32_t domid,
> +                                libxl_device_usbctrl *usbctrl,
> +                                const libxl_asyncop_how *ao_how)
> +                                LIBXL_EXTERNAL_CALLERS_ONLY;
> +
> +int libxl_device_usbctrl_destroy(libxl_ctx *ctx, uint32_t domid,
> +                                 libxl_device_usbctrl *usbctrl,
> +                                 const libxl_asyncop_how *ao_how)
> +                                 LIBXL_EXTERNAL_CALLERS_ONLY;
> +
> +libxl_device_usbctrl *libxl_device_usbctrl_list(libxl_ctx *ctx,
> +                                                uint32_t domid, int *num);
> +
> +void libxl_device_usbctrl_list_free(libxl_device_usbctrl *list, int nr);
> +
> +
> +int libxl_device_usbctrl_getinfo(libxl_ctx *ctx, uint32_t domid,
> +                                 libxl_device_usbctrl *usbctrl,
> +                                 libxl_usbctrlinfo *usbctrlinfo);
> +
> +/* USB Devices */
> +
> +int libxl_device_usbdev_add(libxl_ctx *ctx, uint32_t domid,
> +                            libxl_device_usbdev *usbdev,
> +                            const libxl_asyncop_how *ao_how)
> +                            LIBXL_EXTERNAL_CALLERS_ONLY;
> +
> +int libxl_device_usbdev_remove(libxl_ctx *ctx, uint32_t domid,
> +                               libxl_device_usbdev *usbdev,
> +                               const libxl_asyncop_how *ao_how)
> +                               LIBXL_EXTERNAL_CALLERS_ONLY;
> +
> +libxl_device_usbdev *
> +libxl_device_usbdev_list(libxl_ctx *ctx, uint32_t domid, int *num);
> +
> +void libxl_device_usbdev_list_free(libxl_device_usbdev *list, int nr);
> +
>  /* Network Interfaces */
>  int libxl_device_nic_add(libxl_ctx *ctx, uint32_t domid, libxl_device_nic *nic,
>                           const libxl_asyncop_how *ao_how)
> diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
> index a356e2a..b7a6a13 100644
> --- a/tools/libxl/libxl_device.c
> +++ b/tools/libxl/libxl_device.c
> @@ -676,7 +676,10 @@ void libxl__devices_destroy(libxl__egc *egc, libxl__devices_remove_state *drs)
>                  aodev->action = LIBXL__DEVICE_ACTION_REMOVE;
>                  aodev->dev = dev;
>                  aodev->force = drs->force;
> -                libxl__initiate_device_generic_remove(egc, aodev);
> +                if (dev->backend_kind == LIBXL__DEVICE_KIND_VUSB)
> +                    libxl__initiate_device_usbctrl_remove(egc, aodev);
> +                else
> +                    libxl__initiate_device_generic_remove(egc, aodev);
>              }
>          }
>      }
> diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> index 082f656..f78cb72 100644
> --- a/tools/libxl/libxl_internal.h
> +++ b/tools/libxl/libxl_internal.h
> @@ -2587,6 +2587,14 @@ _hidden void libxl__device_vtpm_add(libxl__egc *egc, uint32_t domid,
>                                     libxl_device_vtpm *vtpm,
>                                     libxl__ao_device *aodev);
>  
> +_hidden void libxl__device_usbctrl_add(libxl__egc *egc, uint32_t domid,
> +                                       libxl_device_usbctrl *usbctrl,
> +                                       libxl__ao_device *aodev);
> +
> +_hidden void libxl__device_usbdev_add(libxl__egc *egc, uint32_t domid,
> +                                      libxl_device_usbdev *usbdev,
> +                                      libxl__ao_device *aodev);
> +
>  /* Internal function to connect a vkb device */
>  _hidden int libxl__device_vkb_add(libxl__gc *gc, uint32_t domid,
>                                    libxl_device_vkb *vkb);
> @@ -2619,6 +2627,13 @@ _hidden void libxl__wait_device_connection(libxl__egc*,
>  _hidden void libxl__initiate_device_generic_remove(libxl__egc *egc,
>                                                     libxl__ao_device *aodev);
>  
> +_hidden int libxl__device_from_usbctrl(libxl__gc *gc, uint32_t domid,
> +                               libxl_device_usbctrl *usbctrl,
> +                               libxl__device *device);
> +
> +_hidden void libxl__initiate_device_usbctrl_remove(libxl__egc *egc,
> +                                                   libxl__ao_device *aodev);
> +
>  /*
>   * libxl__get_hotplug_script_info returns the args and env that should
>   * be passed to the hotplug script for the requested device.
> @@ -4014,6 +4029,9 @@ static inline void libxl__update_config_vtpm(libxl__gc *gc,
>  #define COMPARE_PCI(a, b) ((a)->func == (b)->func &&    \
>                             (a)->bus == (b)->bus &&      \
>                             (a)->dev == (b)->dev)
> +#define COMPARE_USB(a, b) ((a)->ctrl == (b)->ctrl && \
> +                           (a)->port == (b)->port)
> +#define COMPARE_USBCTRL(a, b) ((a)->devid == (b)->devid)
>  
>  /* DEVICE_ADD
>   *
> diff --git a/tools/libxl/libxl_osdeps.h b/tools/libxl/libxl_osdeps.h
> index d9661c9..802c762 100644
> --- a/tools/libxl/libxl_osdeps.h
> +++ b/tools/libxl/libxl_osdeps.h
> @@ -24,6 +24,8 @@
>  #define _GNU_SOURCE
>  
>  #if defined(__NetBSD__)
> +#define SYSFS_USB_DEV          "/sys/bus/usb/devices"
> +#define SYSFS_USBBACK_DRIVER   "/kern/xen/usb"
>  #define SYSFS_PCI_DEV          "/sys/bus/pci/devices"
>  #define SYSFS_PCIBACK_DRIVER   "/kern/xen/pci"
>  #define NETBACK_NIC_NAME       "xvif%ui%d"
> @@ -31,6 +33,8 @@
>  #elif defined(__OpenBSD__)
>  #include <util.h>
>  #elif defined(__linux__)
> +#define SYSFS_USB_DEV          "/sys/bus/usb/devices"
> +#define SYSFS_USBBACK_DRIVER   "/sys/bus/usb/drivers/usbback"
>  #define SYSFS_PCI_DEV          "/sys/bus/pci/devices"
>  #define SYSFS_PCIBACK_DRIVER   "/sys/bus/pci/drivers/pciback"
>  #define NETBACK_NIC_NAME       "vif%u.%d"
> @@ -38,6 +42,8 @@
>  #elif defined(__sun__)
>  #include <stropts.h>
>  #elif defined(__FreeBSD__)
> +#define SYSFS_USB_DEV          "/dev/null"
> +#define SYSFS_USBBACK_DRIVER   "/dev/null"
>  #define SYSFS_PCI_DEV          "/dev/null"
>  #define SYSFS_PCIBACK_DRIVER   "/dev/null"
>  #define NETBACK_NIC_NAME       "xnb%u.%d"
> @@ -45,6 +51,13 @@
>  #include <sys/endian.h>
>  #endif
>  
> +#ifndef SYSFS_USBBACK_DRIVER
> +#error define SYSFS_USBBACK_DRIVER for your platform
> +#endif
> +#ifndef SYSFS_USB_DEV
> +#error define SYSFS_USB_DEV for your platform
> +#endif
> +
>  #ifndef SYSFS_PCIBACK_DRIVER
>  #error define SYSFS_PCIBACK_DRIVER for your platform
>  #endif
> diff --git a/tools/libxl/libxl_pvusb.c b/tools/libxl/libxl_pvusb.c
> new file mode 100644
> index 0000000..5f92628
> --- /dev/null
> +++ b/tools/libxl/libxl_pvusb.c
> @@ -0,0 +1,1620 @@
> +/*
> + * Copyright (C) 2015 SUSE LINUX Products GmbH, Nuernberg, Germany.
> + * Author Chunyan Liu <[e-mail]>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU Lesser General Public License as published
> + * by the Free Software Foundation; version 2.1 only. with the special
> + * exception on linking described in file LICENSE.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU Lesser General Public License for more details.
> + */
> +
> +#include "libxl_osdeps.h" /* must come before any other headers */
> +
> +#include "libxl_internal.h"
> +#include <inttypes.h>
> +
> +#define USBBACK_INFO_PATH "/libxl/usbback"
> +
> +#define USBHUB_CLASS_CODE 9
> +
> +static int libxl__device_usbctrl_setdefault(libxl__gc *gc, uint32_t domid,
> +                                            libxl_device_usbctrl *usbctrl)
> +{
> +    int rc;
> +    libxl_domain_type domtype = libxl__domain_type(gc, domid);
> +
> +    if (!usbctrl->version)
> +        usbctrl->version = 2;
> +
> +    if (!usbctrl->ports)
> +        usbctrl->ports = 8;
> +
> +    if (usbctrl->type == LIBXL_USBCTRL_TYPE_AUTO) {
> +        if (domtype == LIBXL_DOMAIN_TYPE_PV) {
> +            usbctrl->type = LIBXL_USBCTRL_TYPE_PV;
> +        } else if (domtype == LIBXL_DOMAIN_TYPE_HVM) {
> +            /* FIXME: See if we can detect PV frontend */
> +            usbctrl->type = LIBXL_USBCTRL_TYPE_DEVICEMODEL;
> +        }
> +    }
> +
> +    rc = libxl__resolve_domid(gc, usbctrl->backend_domname,
> +                              &usbctrl->backend_domid);
> +    return rc;
> +}
> +
> +int libxl__device_from_usbctrl(libxl__gc *gc, uint32_t domid,
> +                               libxl_device_usbctrl *usbctrl,
> +                               libxl__device *device)
> +{
> +    device->backend_devid   = usbctrl->devid;
> +    device->backend_domid   = usbctrl->backend_domid;
> +    device->backend_kind    = LIBXL__DEVICE_KIND_VUSB;
> +    device->devid           = usbctrl->devid;
> +    device->domid           = domid;
> +    device->kind            = LIBXL__DEVICE_KIND_VUSB;
> +
> +    return 0;
> +}
> +
> +/* Add usbctrl information to xenstore.
> + *
> + * Adding a usb controller will add a new 'vusb' device in xenstore, and
> + * add corresponding frontend, backend information to it. According to
> + * "update_json", decide wether to update json config file.
> + */
> +static int libxl__device_usbctrl_add_xenstore(libxl__gc *gc, uint32_t domid,
> +                                              libxl_device_usbctrl *usbctrl,
> +                                              bool update_json)
> +{
> +    libxl__device *device;
> +    flexarray_t *front;
> +    flexarray_t *back;
> +    xs_transaction_t t = XBT_NULL;
> +    int i, rc;
> +    libxl_domain_config d_config;
> +    libxl_device_usbctrl usbctrl_saved;
> +    libxl__domain_userdata_lock *lock = NULL;
> +
> +    libxl_domain_config_init(&d_config);
> +    libxl_device_usbctrl_init(&usbctrl_saved);
> +    libxl_device_usbctrl_copy(CTX, &usbctrl_saved, usbctrl);
> +
> +    GCNEW(device);
> +    rc = libxl__device_from_usbctrl(gc, domid, usbctrl, device);
> +    if (rc) goto out;
> +
> +    front = flexarray_make(gc, 4, 1);
> +    back = flexarray_make(gc, 12, 1);
> +
> +    flexarray_append_pair(back, "frontend-id", GCSPRINTF("%d", domid));
> +    flexarray_append_pair(back, "online", "1");
> +    flexarray_append_pair(back, "state",
> +                          GCSPRINTF("%d", XenbusStateInitialising));
> +    flexarray_append_pair(back, "type",
> +                          (char *)libxl_usbctrl_type_to_string(usbctrl->type));
> +    flexarray_append_pair(back, "usb-ver", GCSPRINTF("%d", usbctrl->version));
> +    flexarray_append_pair(back, "num-ports", GCSPRINTF("%d", usbctrl->ports));
> +    flexarray_append_pair(back, "port", "");
> +    for (i = 0; i < usbctrl->ports; i++)
> +        flexarray_append_pair(back, GCSPRINTF("port/%d", i + 1), "");
> +
> +    flexarray_append_pair(front, "backend-id",
> +                          GCSPRINTF("%d", usbctrl->backend_domid));
> +    flexarray_append_pair(front, "state",
> +                          GCSPRINTF("%d", XenbusStateInitialising));
> +
> +    if (update_json) {
> +        lock = libxl__lock_domain_userdata(gc, domid);
> +        if (!lock) {
> +            rc = ERROR_LOCK_FAIL;
> +            goto out;
> +        }
> +
> +        rc = libxl__get_domain_configuration(gc, domid, &d_config);
> +        if (rc) goto out;
> +
> +        DEVICE_ADD(usbctrl, usbctrls, domid, &usbctrl_saved,
> +                   COMPARE_USBCTRL, &d_config);
> +    }
> +
> +    for (;;) {
> +        rc = libxl__xs_transaction_start(gc, &t);
> +        if (rc) goto out;
> +
> +        rc = libxl__device_exists(gc, t, device);
> +        if (rc < 0) goto out;
> +        if (rc == 1) {
> +            /* already exists in xenstore */
> +            LOG(ERROR, "device already exists in xenstore");
> +            rc = ERROR_DEVICE_EXISTS;
> +            goto out;
> +        }
> +
> +        if (update_json) {
> +            rc = libxl__set_domain_configuration(gc, domid, &d_config);
> +            if (rc) goto out;
> +        }
> +
> +        libxl__device_generic_add(gc, t, device,
> +                          libxl__xs_kvs_of_flexarray(gc, back, back->count),
> +                          libxl__xs_kvs_of_flexarray(gc, front, front->count),
> +                          NULL);
> +
> +        rc = libxl__xs_transaction_commit(gc, &t);
> +        if (!rc) break;
> +        if (rc < 0) goto out;
> +    }
> +
> +out:
> +    libxl__xs_transaction_abort(gc, &t);
> +    if (lock) libxl__unlock_domain_userdata(lock);
> +    libxl_device_usbctrl_dispose(&usbctrl_saved);
> +    libxl_domain_config_dispose(&d_config);
> +    return rc;
> +}
> +
> +/* AO operation to add a usb controller.
> + *
> + * Generally, it does:
> + * 1) fill in necessary usb controler information with default value
> + * 2) write usb controller frontend/backend info to xenstore, update json
> + *    config file if necessary.
> + * 3) wait for device connection. PVUSB frontend and backend driver will
> + *    probe xenstore paths and build connection between frontend and backend.
> + *
> + * Before calling this function, aodev should be properly filled:
> + * aodev->ao, aodev->callback, aodev->update_json, ...
> + */
> +void libxl__device_usbctrl_add(libxl__egc *egc, uint32_t domid,
> +                               libxl_device_usbctrl *usbctrl,
> +                               libxl__ao_device *aodev)
> +{
> +    STATE_AO_GC(aodev->ao);
> +    libxl__device *device;
> +    int rc;
> +
> +    rc = libxl__device_usbctrl_setdefault(gc, domid, usbctrl);
> +    if (rc < 0) goto out;
> +
> +    if (usbctrl->devid == -1) {
> +        usbctrl->devid = libxl__device_nextid(gc, domid, "vusb");
> +        if (usbctrl->devid < 0) {
> +            rc = ERROR_FAIL;
> +            goto out;
> +        }
> +    }
> +
> +    if (usbctrl->type != LIBXL_USBCTRL_TYPE_PV) {
> +        LOG(ERROR, "Unsupported USB controller type");
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    rc = libxl__device_usbctrl_add_xenstore(gc, domid, usbctrl,
> +                                            aodev->update_json);
> +    if (rc) goto out;
> +
> +    GCNEW(device);
> +    rc = libxl__device_from_usbctrl(gc, domid, usbctrl, device);
> +    if (rc) goto out;
> +
> +    aodev->dev = device;
> +    aodev->action = LIBXL__DEVICE_ACTION_ADD;
> +    libxl__wait_device_connection(egc, aodev);
> +    return;
> +
> +out:
> +    aodev->rc = rc;
> +    aodev->callback(egc, aodev);
> +    return;
> +}
> +
> +static int libxl__device_usbdev_list_for_usbctrl(libxl__gc *gc, uint32_t domid,
> +                                                 libxl_devid usbctrl,
> +                                                 libxl_device_usbdev **usbdevs,
> +                                                 int *num);
> +
> +static int libxl__device_usbdev_remove(libxl__gc *gc, uint32_t domid,
> +                                       libxl_device_usbdev *usbdev);
> +
> +/* AO function to remove a usb controller.
> + *
> + * Generally, it does:
> + * 1) check if the usb controller exists or not
> + * 2) remove all usb devices under controller
> + * 3) remove usb controller information from xenstore
> + *
> + * Before calling this function, aodev should be properly filled:
> + * aodev->ao, aodev->dev, aodev->callback, ...
> + */
> +void libxl__initiate_device_usbctrl_remove(libxl__egc *egc,
> +                                           libxl__ao_device *aodev)
> +{
> +    STATE_AO_GC(aodev->ao);
> +    libxl_device_usbdev *usbdevs = NULL;
> +    int num_usbdev = 0;
> +    int i, rc;
> +    uint32_t domid = ao->domid;
> +    int usbctrl_devid = aodev->dev->devid;
> +    libxl_device_usbctrl usbctrl;
> +    libxl_usbctrlinfo usbctrlinfo;
> +
> +    libxl_device_usbctrl_init(&usbctrl);
> +    libxl_usbctrlinfo_init(&usbctrlinfo);
> +    usbctrl.devid = usbctrl_devid;
> +
> +    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
> +    if (rc) goto out;
> +
> +    if (usbctrlinfo.type != LIBXL_USBCTRL_TYPE_PV) {
> +        LOG(ERROR, "Unsupported USB controller type");
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    /* Remove usb devices first */
> +    rc = libxl__device_usbdev_list_for_usbctrl(gc, domid, usbctrl_devid,
> +                                               &usbdevs, &num_usbdev);
> +    if (rc) goto out;
> +
> +    for (i = 0; i < num_usbdev; i++) {
> +        rc = libxl__device_usbdev_remove(gc, domid, &usbdevs[i]);
> +        if (rc) {
> +            LOG(ERROR, "libxl__device_usbdev_remove failed: controller %d, "
> +                "port %d", usbdevs[i].ctrl, usbdevs[i].port);
> +            goto out;
> +        }
> +    }
> +
> +    libxl_device_usbctrl_dispose(&usbctrl);
> +    libxl_usbctrlinfo_dispose(&usbctrlinfo);
> +
> +    /* Remove usbctrl */
> +    libxl__initiate_device_generic_remove(egc, aodev);
> +    return;
> +
> +out:
> +    libxl_device_usbctrl_dispose(&usbctrl);
> +    libxl_usbctrlinfo_dispose(&usbctrlinfo);
> +    aodev->rc = rc;
> +    aodev->callback(egc, aodev);
> +    return;
> +}
> +
> +static const char *vusb_be_from_xs_fe(libxl__gc *gc, const char *fe_path,
> +                                      uint32_t tgt_domid)
> +{
> +    const char *be_path;
> +    int r;
> +    uint32_t be_domid, fe_domid;
> +
> +    r = libxl__xs_read_checked(gc, XBT_NULL, GCSPRINTF("%s/backend", fe_path),
> +                               &be_path);
> +    if (r || !be_path) return NULL;
> +
> +    /* Check to see that it has the proper form, and that fe_domid ==
> +     * target domid */
> +    r = sscanf(be_path, "/local/domain/%d/backend/vusb/%d",
> +               &be_domid, &fe_domid);
> +
> +    if (r != 2 || fe_domid != tgt_domid) {
> +        LOG(ERROR, "Malformed backend, refusing to use");
> +        return NULL;
> +    }
> +
> +    return be_path;
> +}
> +
> +libxl_device_usbctrl *
> +libxl_device_usbctrl_list(libxl_ctx *ctx, uint32_t domid, int *num)
> +{
> +    GC_INIT(ctx);
> +    libxl_device_usbctrl *usbctrls = NULL;
> +    char *path = NULL;
> +    char **entry = NULL;
> +    unsigned int nentries = 0;
> +
> +    *num = 0;
> +
> +    path = GCSPRINTF("%s/device/vusb",
> +                     libxl__xs_get_dompath(gc, domid));
> +    entry = libxl__xs_directory(gc, XBT_NULL, path, &nentries);
> +
> +    if (entry && nentries) {
> +        usbctrls = libxl__zalloc(NOGC, sizeof(*usbctrls) * nentries);
> +        libxl_device_usbctrl *usbctrl;
> +        libxl_device_usbctrl *end = usbctrls + nentries;
> +        for (usbctrl = usbctrls;
> +             usbctrl < end;
> +             usbctrl++, entry++, (*num)++) {
> +            const char *tmp, *be_path, *fe_path;
> +            int ret;
> +
> +            libxl_device_usbctrl_init(usbctrl);
> +            usbctrl->devid = atoi(*entry);
> +
> +#define READ_SUBPATH(path, subpath) ({                                  \
> +        ret = libxl__xs_read_checked(gc, XBT_NULL,                      \
> +                                     GCSPRINTF("%s/" subpath, path),    \
> +                                     &tmp);                             \
> +        if (ret) goto out;                                              \
> +        (char *)tmp;                                                    \
> +    })
> +
> +#define READ_SUBPATH_INT(path, subpath) ({                              \
> +        ret = libxl__xs_read_checked(gc, XBT_NULL,                      \
> +                                     GCSPRINTF("%s/" subpath, path),    \
> +                                     &tmp);                             \
> +        if (ret) goto out;                                              \
> +        tmp ? atoi(tmp) : -1;                                           \
> +    })
> +
> +            fe_path = GCSPRINTF("%s/%s", path, *entry);
> +            be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
> +            if (!be_path) goto out;
> +            usbctrl->backend_domid = READ_SUBPATH_INT(fe_path, "backend-id");
> +            usbctrl->version = READ_SUBPATH_INT(be_path, "usb-ver");
> +            usbctrl->ports = READ_SUBPATH_INT(be_path, "num-ports");
> +            libxl_usbctrl_type_from_string(READ_SUBPATH(be_path, "type"),
> +                                           &usbctrl->type);
> +
> +#undef READ_SUBPATH
> +#undef READ_SUBPATH_INT
> +       }
> +    }
> +
> +    GC_FREE;
> +    return usbctrls;
> +
> +out:
> +    LOG(ERROR, "Unable to list USB Controllers");
> +    libxl_device_usbctrl_list_free(usbctrls, *num);
> +    GC_FREE;
> +    *num = 0;
> +    return NULL;
> +}
> +
> +int libxl_device_usbctrl_getinfo(libxl_ctx *ctx, uint32_t domid,
> +                                 libxl_device_usbctrl *usbctrl,
> +                                 libxl_usbctrlinfo *usbctrlinfo)
> +{
> +    GC_INIT(ctx);
> +    const char *dompath, *fe_path, *be_path, *tmp;
> +    int rc;
> +
> +    usbctrlinfo->devid = usbctrl->devid;
> +
> +#define READ_SUBPATH(path, subpath) ({                                  \
> +        rc = libxl__xs_read_checked(gc, XBT_NULL,                       \
> +                                    GCSPRINTF("%s/" subpath, path),     \
> +                                    &tmp);                              \
> +        if (rc) goto out;                                               \
> +        (char *)tmp;                                                    \
> +    })
> +
> +#define READ_SUBPATH_INT(path, subpath) ({                              \
> +        rc = libxl__xs_read_checked(gc, XBT_NULL,                       \
> +                                    GCSPRINTF("%s/" subpath, path),     \
> +                                    &tmp);                              \
> +        if (rc) goto out;                                               \
> +        tmp ? atoi(tmp) : -1;                                           \
> +    })
> +
> +    dompath = libxl__xs_get_dompath(gc, domid);
> +    fe_path = GCSPRINTF("%s/device/vusb/%d", dompath, usbctrl->devid);
> +    be_path = READ_SUBPATH(fe_path, "backend");
> +    usbctrlinfo->backend = libxl__strdup(NOGC, be_path);
> +    usbctrlinfo->backend_id = READ_SUBPATH_INT(fe_path, "backend-id");
> +    usbctrlinfo->state = READ_SUBPATH_INT(fe_path, "state");
> +    usbctrlinfo->evtch = READ_SUBPATH_INT(fe_path, "event-channel");
> +    usbctrlinfo->ref_urb = READ_SUBPATH_INT(fe_path, "urb-ring-ref");
> +    usbctrlinfo->ref_conn = READ_SUBPATH_INT(fe_path, "urb-ring-ref");
> +    tmp = READ_SUBPATH(be_path, "frontend");
> +    usbctrlinfo->frontend = libxl__strdup(NOGC, tmp);
> +    usbctrlinfo->frontend_id = READ_SUBPATH_INT(be_path, "frontend-id");
> +    usbctrlinfo->ports = READ_SUBPATH_INT(be_path, "num-ports");
> +    usbctrlinfo->version = READ_SUBPATH_INT(be_path, "usb-ver");;
> +    tmp = READ_SUBPATH(be_path, "type");
> +    libxl_usbctrl_type_from_string(tmp, &usbctrlinfo->type);
> +
> +#undef READ_SUBPATH
> +#undef READ_SUBPATH_INT
> +
> +    rc = 0;
> +
> +out:
> +    GC_FREE;
> +    return rc;
> +}
> +
> +int libxl_devid_to_device_usbctrl(libxl_ctx *ctx,
> +                                  uint32_t domid,
> +                                  int devid,
> +                                  libxl_device_usbctrl *usbctrl)
> +{
> +    libxl_device_usbctrl *usbctrls;
> +    int nb = 0;
> +    int i, rc;
> +
> +    usbctrls = libxl_device_usbctrl_list(ctx, domid, &nb);
> +    if (!usbctrls) return ERROR_FAIL;
> +
> +    rc = ERROR_FAIL;
> +    for (i = 0; i < nb; i++) {
> +        if (devid == usbctrls[i].devid) {
> +            libxl_device_usbctrl_copy(ctx, usbctrl, &usbctrls[i]);
> +            rc = 0;
> +            break;
> +        }
> +    }
> +
> +    libxl_device_usbctrl_list_free(usbctrls, nb);
> +    return rc;
> +}
> +
> +static void *zalloc_dirent(libxl__gc *gc, const char *dirpath)
> +{
> +    size_t need = offsetof(struct dirent, d_name) +
> +                  pathconf(dirpath, _PC_NAME_MAX) + 1;
> +
> +    return libxl__zalloc(gc, need);
> +}
> +
> +static char *usbdev_busaddr_to_busid(libxl__gc *gc, int bus, int addr)
> +{
> +    DIR *dir;
> +    char *busid = NULL;
> +    struct dirent *de_buf;
> +    struct dirent *de;
> +
> +    /* invalid hostbus or hostaddr */
> +    if (bus < 1 || addr < 1)
> +        return NULL;
> +
> +    dir = opendir(SYSFS_USB_DEV);
> +    if (!dir) {
> +        LOGE(ERROR, "opendir failed: '%s'", SYSFS_USB_DEV);
> +        return NULL;
> +    }
> +
> +    de_buf = zalloc_dirent(gc, SYSFS_USB_DEV);
> +
> +    for (;;) {
> +        char *filename;
> +        void *buf;
> +        int busnum = -1;
> +        int devnum = -1;
> +
> +        int r = readdir_r(dir, de_buf, &de);
> +        if (r) {
> +            LOGE(ERROR, "failed to readdir %s", SYSFS_USB_DEV);
> +            break;
> +        }
> +        if (!de)
> +            break;
> +
> +        if (!strcmp(de->d_name, ".") ||
> +            !strcmp(de->d_name, ".."))
> +            continue;
> +
> +        filename = GCSPRINTF(SYSFS_USB_DEV "/%s/devnum", de->d_name);
> +        if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
> +            devnum = atoi(buf);
> +
> +        filename = GCSPRINTF(SYSFS_USB_DEV "/%s/busnum", de->d_name);
> +        if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
> +            busnum = atoi(buf);
> +
> +        if (bus == busnum && addr == devnum) {
> +            busid = libxl__strdup(gc, de->d_name);
> +            break;
> +        }
> +    }
> +
> +    closedir(dir);
> +    return busid;
> +}
> +
> +static int usbdev_busaddr_from_busid(libxl__gc *gc, const char *busid,
> +                                     uint8_t *bus, uint8_t *addr)
> +{
> +    char *filename;
> +    void *buf;
> +
> +    filename = GCSPRINTF(SYSFS_USB_DEV "/%s/busnum", busid);
> +    if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
> +        *bus = atoi(buf);
> +    else
> +        return ERROR_FAIL;
> +
> +    filename = GCSPRINTF(SYSFS_USB_DEV "/%s/devnum", busid);
> +    if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
> +        *addr = atoi(buf);
> +    else
> +        return ERROR_FAIL;
> +
> +    return 0;
> +}
> +
> +static int get_assigned_devices(libxl__gc *gc,
> +                                libxl_device_usbdev **list, int *num)
> +{
> +    char **domlist;
> +    unsigned int ndom = 0;
> +    int i, j, k;
> +    int rc;
> +
> +    *list = NULL;
> +    *num = 0;
> +
> +    domlist = libxl__xs_directory(gc, XBT_NULL, "/local/domain", &ndom);
> +    for (i = 0; i < ndom; i++) {
> +        char *path;
> +        char **usbctrls;
> +        unsigned int nc = 0;
> +        uint32_t domid = atoi(domlist[i]);
> +
> +        path = GCSPRINTF("%s/device/vusb", libxl__xs_get_dompath(gc, domid));
> +        usbctrls = libxl__xs_directory(gc, XBT_NULL, path, &nc);
> +
> +        for (j = 0; j < nc; j++) {
> +            libxl_device_usbdev *tmp = NULL;
> +            int nd = 0;
> +
> +            rc = libxl__device_usbdev_list_for_usbctrl(gc, domid,
> +                                                       atoi(usbctrls[j]),
> +                                                       &tmp, &nd);
> +            if (rc) goto out;
> +
> +            if (!nd) continue;
> +
> +            GCREALLOC_ARRAY(*list, *num + nd);
> +            for (k = 0; k < nd; k++) {
> +                libxl_device_usbdev_copy(CTX, *list + *num, tmp + k);
> +                (*num)++;
> +            }
> +        }
> +    }
> +
> +    return 0;
> +
> +out:
> +    LOG(ERROR, "fail to get assigned devices");
> +    return rc;
> +}
> +
> +static bool is_usbdev_in_array(libxl_device_usbdev *usbdevs, int num,
> +                               libxl_device_usbdev *usbdev)
> +{
> +    int i;
> +
> +    for (i = 0; i < num; i++) {
> +        if (usbdevs[i].u.hostdev.hostbus == usbdev->u.hostdev.hostbus &&
> +            usbdevs[i].u.hostdev.hostaddr == usbdev->u.hostdev.hostaddr)
> +            return true;
> +    }
> +
> +    return false;
> +}
> +
> +/* check if USB device type is assignable */
> +static bool is_usbdev_assignable(libxl__gc *gc, libxl_device_usbdev *usbdev)
> +{
> +    int classcode;
> +    char *filename;
> +    void *buf = NULL;
> +    char *busid = NULL;
> +
> +    busid = usbdev_busaddr_to_busid(gc, usbdev->u.hostdev.hostbus,
> +                                    usbdev->u.hostdev.hostaddr);
> +    if (!busid) return false;
> +
> +    filename = GCSPRINTF(SYSFS_USB_DEV "/%s/bDeviceClass", busid);
> +    if (libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
> +        return false;
> +
> +    classcode = atoi(buf);
> +    return classcode != USBHUB_CLASS_CODE;
> +}
> +
> +/* get usb devices under certain usb controller */
> +static int
> +libxl__device_usbdev_list_for_usbctrl(libxl__gc *gc,
> +                                      uint32_t domid,
> +                                      libxl_devid usbctrl,
> +                                      libxl_device_usbdev **usbdevs,
> +                                      int *num)
> +{
> +    const char *fe_path, *be_path, *num_devs;
> +    int n, i, rc;
> +
> +    *usbdevs = NULL;
> +    *num = 0;
> +
> +    fe_path = GCSPRINTF("%s/device/vusb/%d",
> +                        libxl__xs_get_dompath(gc, domid), usbctrl);
> +
> +    be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
> +    if (!be_path) {
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    rc = libxl__xs_read_checked(gc, XBT_NULL,
> +                                GCSPRINTF("%s/num-ports", be_path),
> +                                &num_devs);
> +    if (rc) goto out;
> +
> +    n = num_devs ? atoi(num_devs) : 0;
> +
> +    for (i = 0; i < n; i++) {
> +        const char *busid;
> +        libxl_device_usbdev *usbdev;
> +
> +        rc = libxl__xs_read_checked(gc, XBT_NULL,
> +                                    GCSPRINTF("%s/port/%d", be_path, i + 1),
> +                                    &busid);
> +        if (rc) goto out;
> +
> +        if (busid && strcmp(busid, "")) {
> +            GCREALLOC_ARRAY(*usbdevs, *num + 1);
> +            usbdev = *usbdevs + *num;
> +            (*num)++;
> +            libxl_device_usbdev_init(usbdev);
> +            usbdev->ctrl = usbctrl;
> +            usbdev->port = i + 1;
> +            usbdev->type = LIBXL_USBDEV_TYPE_HOSTDEV;
> +            rc = usbdev_busaddr_from_busid(gc, busid,
> +                                           &usbdev->u.hostdev.hostbus,
> +                                           &usbdev->u.hostdev.hostaddr);
> +            if (rc) goto out;
> +        }
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    return rc;
> +}
> +
> +/* get all usb devices of the domain */
> +libxl_device_usbdev *
> +libxl_device_usbdev_list(libxl_ctx *ctx, uint32_t domid, int *num)
> +{
> +    GC_INIT(ctx);
> +    libxl_device_usbdev *usbdevs = NULL;
> +    const char *path;
> +    char **usbctrls;
> +    unsigned int nc = 0;
> +    int i, j;
> +
> +    *num = 0;
> +
> +    path = GCSPRINTF("%s/device/vusb",
> +                        libxl__xs_get_dompath(gc, domid));
> +    usbctrls = libxl__xs_directory(gc, XBT_NULL, path, &nc);
> +
> +    for (i = 0; i < nc; i++) {
> +        int r, nd = 0;
> +        libxl_device_usbdev *tmp = NULL;
> +
> +        r = libxl__device_usbdev_list_for_usbctrl(gc, domid,
> +                                                  atoi(usbctrls[i]),
> +                                                  &tmp, &nd);
> +        if (!r || !nd) continue;
> +
> +        usbdevs = libxl__realloc(NOGC, usbdevs,
> +                                 sizeof(*usbdevs) * (*num + nd));
> +        for (j = 0; j < nd; j++) {
> +            libxl_device_usbdev_copy(ctx, usbdevs + *num, tmp + j);
> +            (*num)++;
> +        }
> +    }
> +
> +    GC_FREE;
> +    return usbdevs;
> +}
> +
> +/* find first unused controller:port and give that to usb device */
> +static int
> +libxl__device_usbdev_set_default_usbctrl(libxl__gc *gc, uint32_t domid,
> +                                         libxl_device_usbdev *usbdev)
> +{
> +    libxl_device_usbctrl *usbctrls = NULL;
> +    int numctrl = 0;
> +    int i, j, rc;
> +
> +    usbctrls = libxl_device_usbctrl_list(CTX, domid, &numctrl);
> +    if (!numctrl || !usbctrls) {
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    for (i = 0; i < numctrl; i++) {
> +        for (j = 0; j < usbctrls[i].ports; j++) {
> +            const char *path, *tmp;
> +
> +            path = GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
> +                             libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
> +                             domid, usbctrls[i].devid, j + 1);
> +            rc = libxl__xs_read_checked(gc, XBT_NULL, path, &tmp);
> +            if (rc) goto out;
> +
> +            if (tmp && !strcmp(tmp, "")) {
> +                usbdev->ctrl = usbctrls[i].devid;
> +                usbdev->port = j + 1;
> +                rc = 0;
> +                goto out;
> +            }
> +        }
> +    }
> +
> +    /* no available controller:port */
> +    rc = ERROR_FAIL;
> +
> +out:
> +    libxl_device_usbctrl_list_free(usbctrls, numctrl);
> +    return rc;
> +}
> +
> +/* Fill in usb information with default value.
> + *
> + * Generally, it does:
> + * 1) if "controller" is not specified:
> + *    - if "port" is not specified, try to find an available controller:port,
> + *      if found, use that; otherwise, create a new controller, use this
> + *      controller and its first port
> + *    - if "port" is specified, report error.
> + * 2) if "controller" is specified, but port is not specified:
> + *    try to find an available port under this controller, if found, use
> + *    that, otherwise, report error.
> + * 3) if both "controller" and "port" are specified:
> + *    check the controller:port is available, if not, report error.
> + */
> +static int libxl__device_usbdev_setdefault(libxl__gc *gc,
> +                                           uint32_t domid,
> +                                           libxl_device_usbdev *usbdev,
> +                                           bool update_json)
> +{
> +    int rc;
> +
> +    if (!usbdev->type)
> +        usbdev->type = LIBXL_USBDEV_TYPE_HOSTDEV;
> +
> +    if (usbdev->ctrl == -1) {
> +        if (usbdev->port) {
> +            LOG(ERROR, "USB controller must be specified if you specify port");
> +            return ERROR_INVAL;
> +        }
> +
> +        rc = libxl__device_usbdev_set_default_usbctrl(gc, domid, usbdev);
> +        /* If no existing controller to host this usb device, add a new one */
> +        if (rc) {
> +            libxl_device_usbctrl *usbctrl;
> +
> +            GCNEW(usbctrl);
> +            libxl_device_usbctrl_init(usbctrl);
> +            rc = libxl__device_usbctrl_setdefault(gc, domid, usbctrl);
> +            if (rc < 0) goto out;
> +
> +            if (usbctrl->devid == -1) {
> +                usbctrl->devid = libxl__device_nextid(gc, domid, "vusb");
> +                if (usbctrl->devid < 0) {
> +                    rc = ERROR_FAIL;
> +                    goto out;
> +                }
> +            }
> +
> +            rc = libxl__device_usbctrl_add_xenstore(gc, domid, usbctrl,
> +                                                    update_json);
> +            if (rc) goto out;
> +
> +            usbdev->ctrl = usbctrl->devid;
> +            usbdev->port = 1;
> +        }
> +    } else {
> +        /* A controller was specified; look it up */
> +        const char *fe_path, *be_path, *tmp;
> +
> +        fe_path = GCSPRINTF("%s/device/vusb/%d",
> +                            libxl__xs_get_dompath(gc, domid),
> +                            usbdev->ctrl);
> +
> +        be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
> +        if (!be_path) {
> +            rc = ERROR_FAIL;
> +            goto out;
> +        }
> +
> +        if (usbdev->port) {
> +            /* A specific port was requested; see if it's available */
> +            rc = libxl__xs_read_checked(gc, XBT_NULL,
> +                                        GCSPRINTF("%s/port/%d",
> +                                                  be_path, usbdev->port),
> +                                        &tmp);
> +            if (rc) goto out;
> +
> +            if (tmp && strcmp(tmp, "")) {
> +                LOG(ERROR, "The controller port isn't available");
> +                rc = ERROR_FAIL;
> +                goto out;
> +            }
> +        } else {
> +            /* No port was requested. Choose free port. */
> +            int i, ports;
> +
> +            rc = libxl__xs_read_checked(gc, XBT_NULL,
> +                                        GCSPRINTF("%s/num-ports", be_path), &tmp);
> +            if (rc) goto out;
> +
> +            ports = tmp ? atoi(tmp) : 0;
> +
> +            for (i = 0; i < ports; i++) {
> +                rc = libxl__xs_read_checked(gc, XBT_NULL,
> +                                            GCSPRINTF("%s/port/%d", be_path, i + 1),
> +                                            &tmp);
> +                if (rc) goto out;
> +
> +                if (tmp && !strcmp(tmp, "")) {
> +                    usbdev->port = i + 1;
> +                    break;
> +                }
> +            }
> +
> +            if (!usbdev->port) {
> +                LOG(ERROR, "No available port under specified controller");
> +                rc = ERROR_FAIL;
> +                goto out;
> +            }
> +        }
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    return rc;
> +}
> +
> +/* Add usb information to xenstore
> + *
> + * Adding a usb device won't create new 'vusb' device, but only write
> + * the device busid to the controller:port in xenstore.
> + */
> +static int libxl__device_usbdev_add_xenstore(libxl__gc *gc, uint32_t domid,
> +                                             libxl_device_usbdev *usbdev,
> +                                             bool update_json)
> +{
> +    char *be_path, *busid;
> +    int rc;
> +    xs_transaction_t t = XBT_NULL;
> +    libxl_domain_config d_config;
> +    libxl_device_usbdev usbdev_saved;
> +    libxl__domain_userdata_lock *lock = NULL;
> +
> +    libxl_domain_config_init(&d_config);
> +    libxl_device_usbdev_init(&usbdev_saved);
> +    libxl_device_usbdev_copy(CTX, &usbdev_saved, usbdev);
> +
> +    busid = usbdev_busaddr_to_busid(gc, usbdev->u.hostdev.hostbus,
> +                                    usbdev->u.hostdev.hostaddr);
> +    if (!busid) {
> +        LOG(DEBUG, "Fail to get busid of usb device");
> +        goto out;
> +    }
> +
> +    if (update_json) {
> +        lock = libxl__lock_domain_userdata(gc, domid);
> +        if (!lock) {
> +            rc = ERROR_LOCK_FAIL;
> +            goto out;
> +        }
> +
> +        rc = libxl__get_domain_configuration(gc, domid, &d_config);
> +        if (rc) goto out;
> +
> +        DEVICE_ADD(usbdev, usbdevs, domid, &usbdev_saved,
> +                   COMPARE_USB, &d_config);
> +    }
> +
> +    for (;;) {
> +        rc = libxl__xs_transaction_start(gc, &t);
> +        if (rc) goto out;
> +
> +        if (update_json) {
> +            rc = libxl__set_domain_configuration(gc, domid, &d_config);
> +            if (rc) goto out;
> +        }
> +
> +        be_path = GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
> +                            libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
> +                            domid, usbdev->ctrl, usbdev->port);
> +
> +        LOG(DEBUG, "Adding usb device %s to xenstore: controller %d, port %d",
> +            busid, usbdev->ctrl, usbdev->port);
> +
> +        rc = libxl__xs_write_checked(gc, t, be_path, busid);
> +        if (rc) goto out;
> +
> +        rc = libxl__xs_transaction_commit(gc, &t);
> +        if (!rc) break;
> +        if (rc < 0) goto out;
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    if (lock) libxl__unlock_domain_userdata(lock);
> +    libxl_device_usbdev_dispose(&usbdev_saved);
> +    libxl_domain_config_dispose(&d_config);
> +    return rc;
> +}
> +
> +static int libxl__device_usbdev_remove_xenstore(libxl__gc *gc, uint32_t domid,
> +                                                libxl_device_usbdev *usbdev)
> +{
> +    char *be_path;
> +
> +    be_path = GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
> +                        libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
> +                        domid, usbdev->ctrl, usbdev->port);
> +
> +    LOG(DEBUG, "Removing usb device from xenstore: controller %d, port %d",
> +        usbdev->ctrl, usbdev->port);
> +
> +    return libxl__xs_write_checked(gc, XBT_NULL, be_path, "");
> +}
> +
> +static char *usbdev_busid_from_ctrlport(libxl__gc *gc, uint32_t domid,
> +                                        libxl_device_usbdev *usbdev)
> +{
> +    return libxl__xs_read(gc, XBT_NULL,
> +                          GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
> +                              libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
> +                          domid, usbdev->ctrl, usbdev->port));
> +}
> +
> +/* get original driver path of usb interface, stored in @drvpath */
> +static int usbintf_get_drvpath(libxl__gc *gc, const char *intf, char **drvpath)
> +{
> +    char *spath, *dp = NULL;
> +    struct stat st;
> +    int r;
> +
> +    spath = GCSPRINTF(SYSFS_USB_DEV "/%s/driver", intf);
> +
> +    r = lstat(spath, &st);
> +    if (r == 0) {
> +        /* Find the canonical path to the driver. */
> +        dp = libxl__zalloc(gc, PATH_MAX);
> +        dp = realpath(spath, dp);
> +        if (!dp) {
> +            LOGE(ERROR, "get realpath failed: '%s'", spath);
> +            return ERROR_FAIL;
> +        }
> +    } else if (errno == ENOENT) {
> +        /* driver path doesn't exist */
> +        dp = NULL;
> +    } else {
> +        LOGE(ERROR, "lstat failed: '%s'", spath);
> +        return ERROR_FAIL;
> +    }
> +
> +    *drvpath = dp;
> +
> +    return 0;
> +}
> +
> +static int unbind_usbintf(libxl__gc *gc, const char *intf)
> +{
> +    char *path;
> +    int fd = -1;
> +    int rc;
> +
> +    path = GCSPRINTF(SYSFS_USB_DEV "/%s/driver/unbind", intf);
> +
> +    fd = open(path, O_WRONLY);
> +    if (fd < 0) {
> +        LOGE(ERROR, "open file failed: '%s'", path);
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    if (libxl_write_exactly(CTX, fd, intf, sizeof(intf), path, intf)) {
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    if (fd >= 0) close(fd);
> +    return rc;
> +}
> +
> +static int bind_usbintf(libxl__gc *gc, const char *intf, const char *drvpath)
> +{
> +    char *path;
> +    struct stat st;
> +    int fd = -1;
> +    int rc, r;
> +
> +    path = GCSPRINTF("%s/%s", drvpath, intf);
> +
> +    /* check through lstat, if intf already exists under drvpath,
> +     * it's already bound, return directly; if it doesn't exist,
> +     * continue to do bind work; otherwise, return error.
> +     */
> +    r = lstat(path, &st);
> +    if (r == 0)
> +        return 0;
> +    if (r < 0 && errno != ENOENT)
> +        return ERROR_FAIL;
> +
> +    path = GCSPRINTF("%s/bind", drvpath);
> +
> +    fd = open(path, O_WRONLY);
> +    if (fd < 0) {
> +        LOGE(ERROR, "open file failed: '%s'", path);
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    if (libxl_write_exactly(CTX, fd, intf, sizeof(intf), path, intf)) {
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    if (fd >= 0) close(fd);
> +    return rc;
> +}
> +
> +/* Is usb interface bound to usbback? */
> +static int usbintf_is_assigned(libxl__gc *gc, char *intf)
> +{
> +    char *spath;
> +    int r;
> +    struct stat st;
> +
> +    spath = GCSPRINTF(SYSFS_USBBACK_DRIVER "/%s", intf);
> +    r = lstat(spath, &st);
> +
> +    if (r == 0)
> +        return 1;
> +    if (r < 0 && errno == ENOENT)
> +        return 0;
> +    LOGE(ERROR, "Accessing %s", spath);
> +    return -1;
> +}
> +
> +static int usbdev_get_all_interfaces(libxl__gc *gc, const char *busid,
> +                                     char ***intfs, int *num)
> +{
> +    DIR *dir;
> +    char *buf;
> +    struct dirent *de_buf;
> +    struct dirent *de;
> +    int rc;
> +
> +    *intfs = NULL;
> +    *num = 0;
> +
> +    buf = GCSPRINTF("%s:", busid);
> +
> +    dir = opendir(SYSFS_USB_DEV);
> +    if (!dir) {
> +        LOGE(ERROR, "opendir failed: '%s'", SYSFS_USB_DEV);
> +        return ERROR_FAIL;
> +    }
> +
> +    de_buf = zalloc_dirent(gc, SYSFS_USB_DEV);
> +
> +    for (;;) {
> +        int r = readdir_r(dir, de_buf, &de);
> +
> +        if (r) {
> +            LOGE(ERROR, "failed to readdir %s", SYSFS_USB_DEV);
> +            rc = ERROR_FAIL;
> +            goto out;
> +        }
> +        if (!de)
> +            break;
> +
> +        if (!strcmp(de->d_name, ".") ||
> +            !strcmp(de->d_name, ".."))
> +            continue;
> +
> +        if (!strncmp(de->d_name, buf, strlen(buf))) {
> +            GCREALLOC_ARRAY(*intfs, *num + 1);
> +            (*intfs)[*num] = libxl__strdup(gc, de->d_name);
> +            (*num)++;
> +        }
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    closedir(dir);
> +    return rc;
> +}
> +
> +/* Encode usb interface so that it could be written to xenstore as a key.
> + *
> + * Since xenstore key cannot include '.' or ':', we'll change '.' to '_',
> + * change ':' to '@'. For example, 3-1:2.1 will be encoded to 3-1@2_1.
> + * This will be used to save original driver of USB device to xenstore.
> + */
> +static char *usb_interface_xenstore_encode(libxl__gc *gc, const char *busid)
> +{
> +    char *str = libxl__strdup(gc, busid);
> +    int i, len = strlen(str);
> +
> +    for (i = 0; i < len; i++) {
> +        if (str[i] == '.') str[i] = '_';
> +        if (str[i] == ':') str[i] = '@';
> +    }
> +    return str;
> +}
> +
> +/* Unbind USB device from "usbback" driver.
> + *
> + * If there are many interfaces under USB device, check each interface,
> + * unbind from "usbback" driver.
> + */
> +static int usbback_dev_unassign(libxl__gc *gc, const char *busid)
> +{
> +    char **intfs = NULL;
> +    int i, num = 0;
> +    int rc;
> +
> +    rc = usbdev_get_all_interfaces(gc, busid, &intfs, &num);
> +    if (rc) goto out;
> +
> +    for (i = 0; i < num; i++) {
> +        char *intf = intfs[i];
> +
> +        /* check if the USB interface is already bound to "usbback" */
> +        if (usbintf_is_assigned(gc, intf) > 0) {
> +            /* unbind interface from usbback driver */
> +            rc = unbind_usbintf(gc, intf);
> +            if (rc) {
> +                LOGE(ERROR, "Couldn't unbind %s from usbback", intf);
> +                goto out;
> +            }
> +        }
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    return rc;
> +}
> +
> +/* rebind USB device to original driver.
> + *
> + * If there are many interfaces under USB device, for reach interface,
> + * read driver_path from xenstore (if there is) and rebind to its
> + * original driver, then remove driver_path information from xenstore.
> + */
> +static int usbdev_rebind(libxl__gc *gc, const char *busid)
> +{
> +    char **intfs = NULL;
> +    char *usbdev_encode = NULL;
> +    char *path = NULL;
> +    int i, num = 0;
> +    int rc;
> +
> +    rc = usbdev_get_all_interfaces(gc, busid, &intfs, &num);
> +    if (rc) goto out;
> +
> +    usbdev_encode = usb_interface_xenstore_encode(gc, busid);
> +
> +    for (i = 0; i < num; i++) {
> +        char *intf = intfs[i];
> +        char *usbintf_encode = NULL;
> +        const char *drvpath;
> +
> +        /* rebind USB interface to its originial driver */
> +        usbintf_encode = usb_interface_xenstore_encode(gc, intf);
> +        path = GCSPRINTF(USBBACK_INFO_PATH "/%s/%s/driver_path",
> +                         usbdev_encode, usbintf_encode);
> +        rc = libxl__xs_read_checked(gc, XBT_NULL, path, &drvpath);
> +        if (rc) goto out;
> +
> +        if (drvpath) {
> +            rc = bind_usbintf(gc, intf, drvpath);
> +            if (rc) {
> +                LOGE(ERROR, "Couldn't rebind %s to %s", intf, drvpath);
> +                goto out;
> +            }
> +        }
> +    }
> +
> +out:
> +    path = GCSPRINTF(USBBACK_INFO_PATH "/%s", usbdev_encode);
> +    libxl__xs_rm_checked(gc, XBT_NULL, path);
> +    return rc;
> +}
> +
> +
> +/* Bind USB device to "usbback" driver.
> + *
> + * If there are many interfaces under USB device, check each interface,
> + * unbind from original driver and bind to "usbback" driver.
> + */
> +static int usbback_dev_assign(libxl__gc *gc, const char *busid)
> +{
> +    char **intfs = NULL;
> +    int num = 0, i;
> +    int rc;
> +    char *usbdev_encode = NULL;
> +
> +    rc = usbdev_get_all_interfaces(gc, busid, &intfs, &num);
> +    if (rc) return rc;
> +
> +    usbdev_encode = usb_interface_xenstore_encode(gc, busid);
> +
> +    for (i = 0; i < num; i++) {
> +        char *intf = intfs[i];
> +        char *drvpath = NULL;
> +
> +        /* already assigned to usbback */
> +        if (usbintf_is_assigned(gc, intf) > 0)
> +            continue;
> +
> +        rc = usbintf_get_drvpath(gc, intf, &drvpath);
> +        if (rc) goto out;
> +
> +        if (drvpath) {
> +            /* write driver path to xenstore for later rebinding */
> +            char *usbintf_encode = NULL;
> +            char *path;
> +
> +            usbintf_encode = usb_interface_xenstore_encode(gc, intf);
> +            path = GCSPRINTF(USBBACK_INFO_PATH "/%s/%s/driver_path",
> +                             usbdev_encode, usbintf_encode);
> +            rc = libxl__xs_write_checked(gc, XBT_NULL, path, drvpath);
> +            if (rc) goto out;
> +
> +            /* unbind interface from original driver */
> +            rc = unbind_usbintf(gc, intf);
> +            if (rc) goto out;
> +        }
> +
> +        /* bind interface to usbback */
> +        rc = bind_usbintf(gc, intf, SYSFS_USBBACK_DRIVER);
> +        if (rc) {
> +            LOG(ERROR, "Couldn't bind %s to %s", intf, SYSFS_USBBACK_DRIVER);
> +            goto out;
> +        }
> +    }
> +
> +    return 0;
> +
> +out:
> +    /* some interfaces might be bound to usbback, unbind it and
> +     * rebind it to its original driver
> +     */
> +    usbback_dev_unassign(gc, busid);
> +    usbdev_rebind(gc, busid);
> +    return rc;
> +}
> +
> +static int do_usbdev_add(libxl__gc *gc, uint32_t domid,
> +                         libxl_device_usbdev *usbdev,
> +                         bool update_json)
> +{
> +    int rc;
> +    char *busid;
> +    libxl_device_usbctrl usbctrl;
> +    libxl_usbctrlinfo usbctrlinfo;
> +
> +    libxl_device_usbctrl_init(&usbctrl);
> +    libxl_usbctrlinfo_init(&usbctrlinfo);
> +    usbctrl.devid = usbdev->ctrl;
> +
> +    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
> +    if (rc) goto out;
> +
> +    switch (usbctrlinfo.type) {
> +    case LIBXL_USBCTRL_TYPE_PV:
> +        busid = usbdev_busaddr_to_busid(gc, usbdev->u.hostdev.hostbus,
> +                                        usbdev->u.hostdev.hostaddr);
> +        if (!busid) {
> +            rc = ERROR_FAIL;
> +            goto out;
> +        }
> +
> +        rc = libxl__device_usbdev_add_xenstore(gc, domid, usbdev, update_json);
> +        if (rc) goto out;
> +
> +        rc = usbback_dev_assign(gc, busid);
> +        if (rc) {
> +            libxl__device_usbdev_remove_xenstore(gc, domid, usbdev);
> +            goto out;
> +        }
> +        break;
> +    case LIBXL_USBCTRL_TYPE_DEVICEMODEL:
> +    default:
> +        LOG(ERROR, "Unsupported usb controller type");
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    libxl_device_usbctrl_dispose(&usbctrl);
> +    libxl_usbctrlinfo_dispose(&usbctrlinfo);
> +    return rc;
> +}
> +
> +/* AO operation to add a usb device.
> + *
> + * Generally, it does:
> + * 1) check if the usb device type is assignable
> + * 2) check if the usb device is already assigned to a domain
> + * 3) add 'busid' of the usb device to xenstore contoller/port/.
> + *    (PVUSB driver watches the xenstore changes and will detect that.)
> + * 4) unbind usb device from original driver and bind to usbback.
> + *    If usb device has many interfaces, then:
> + *    - unbind each interface from its original driver and bind to usbback.
> + *    - store the original driver to xenstore for later rebinding when
> + *      detaching the device.
> + *
> + * Before calling this function, aodev should be properly filled:
> + * aodev->ao, aodev->callback, aodev->update_json, ...
> + */
> +void libxl__device_usbdev_add(libxl__egc *egc, uint32_t domid,
> +                              libxl_device_usbdev *usbdev,
> +                              libxl__ao_device *aodev)
> +{
> +    STATE_AO_GC(aodev->ao);
> +    int rc;
> +    libxl_device_usbdev *assigned;
> +    int num_assigned;
> +    libxl_device_usbctrl usbctrl;
> +    libxl_usbctrlinfo usbctrlinfo;
> +
> +    libxl_device_usbctrl_init(&usbctrl);
> +    libxl_usbctrlinfo_init(&usbctrlinfo);
> +
> +    /* Currently only support adding USB device from Dom0 backend.
> +     * So, if USB controller is specified, check its backend domain,
> +     * if it's not Dom0, report error.
> +     */
> +    if (usbdev->ctrl != -1) {
> +        usbctrl.devid = usbdev->ctrl;
> +        rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
> +        if (rc) goto out;
> +
> +        if (usbctrlinfo.backend_id != LIBXL_TOOLSTACK_DOMID) {
> +            LOG(ERROR, "Don't support adding USB device from non-Dom0 backend");
> +            rc = ERROR_INVAL;
> +            goto out;
> +        }
> +    }
> +
> +    /* check usb device is assignable type */
> +    if (!is_usbdev_assignable(gc, usbdev)) {
> +        LOG(ERROR, "USB device is not assignable.");
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    /* check usb device is already assigned */
> +    rc = get_assigned_devices(gc, &assigned, &num_assigned);
> +    if (rc) {
> +        LOG(ERROR, "cannot determine if device is assigned,"
> +                   " refusing to continue");
> +        goto out;
> +    }
> +
> +    if (is_usbdev_in_array(assigned, num_assigned, usbdev)) {
> +        LOG(ERROR, "USB device already attached to a domain");
> +        rc = ERROR_INVAL;
> +        goto out;
> +    }
> +
> +    /* fill default values, e.g, if usbdev->ctrl and usbdev->port
> +     * not specified, choose available controller:port and fill in. */
> +    rc = libxl__device_usbdev_setdefault(gc, domid, usbdev,
> +                                         aodev->update_json);
> +    if (rc) goto out;
> +
> +    /* do actual adding usb device operation */
> +    rc = do_usbdev_add(gc, domid, usbdev, aodev->update_json);
> +
> +out:
> +    libxl_device_usbctrl_dispose(&usbctrl);
> +    libxl_usbctrlinfo_dispose(&usbctrlinfo);
> +    aodev->rc = rc;
> +    aodev->callback(egc, aodev);
> +    return;
> +}
> +
> +static int do_usbdev_remove(libxl__gc *gc, uint32_t domid,
> +                            libxl_device_usbdev *usbdev)
> +{
> +    int rc;
> +    char *busid;
> +    libxl_device_usbctrl usbctrl;
> +    libxl_usbctrlinfo usbctrlinfo;
> +
> +    libxl_device_usbctrl_init(&usbctrl);
> +    libxl_usbctrlinfo_init(&usbctrlinfo);
> +    usbctrl.devid = usbdev->ctrl;
> +
> +    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
> +    if (rc) goto out;
> +
> +    switch (usbctrlinfo.type) {
> +    case LIBXL_USBCTRL_TYPE_PV:
> +        busid = usbdev_busid_from_ctrlport(gc, domid, usbdev);
> +        if (!busid) {
> +            rc = ERROR_FAIL;
> +            goto out;
> +        }
> +
> +        /* Things are done in order of:
> +         *   unbind USB device from usbback,
> +         *   remove USB device from xenstore,
> +         *   rebind USB device to original driver.
> +         * It is to balance simplicity with robustness in case of failure:
> +         * - We unbind all interfaces before rebinding any interfaces, so
> +         *   that we never get into a situation where some interfaces are
> +         *   assigned to usbback and some are assigned to the original drivers.
> +         * - We also unbind the interfaces before removing the pvusb xenstore
> +         *   nodes, so that if the unbind fails in the middle, the device still
> +         *   shows up in xl usb-list, and the user can re-try removing it.
> +         */
> +        rc = usbback_dev_unassign(gc, busid);
> +        if (rc) {
> +            LOG(ERROR, "Error removing device from guest."
> +                " Try running usbdev-detach again.");
> +            goto out;
> +        }
> +
> +        rc = libxl__device_usbdev_remove_xenstore(gc, domid, usbdev);
> +        if (rc) {
> +            LOG(ERROR, "Error removing device from guest."
> +                " Try running usbdev-detach again.");
> +            goto out;
> +        }
> +
> +        rc = usbdev_rebind(gc, busid);
> +        if (rc) {
> +            LOG(ERROR, "USB device removed from guest, but couldn't"
> +                " re-bind to domain 0. Try removing and re-inserting"
> +                " the USB device or reloading the driver modules.");
> +            goto out;
> +        }
> +
> +        break;
> +    case LIBXL_USBCTRL_TYPE_DEVICEMODEL:
> +    default:
> +        LOG(ERROR, "Unsupported usb controller type");
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    rc = 0;
> +
> +out:
> +    libxl_device_usbctrl_dispose(&usbctrl);
> +    libxl_usbctrlinfo_dispose(&usbctrlinfo);
> +    return rc;
> +}
> +
> +/* Operation to remove usb device.
> + *
> + * Generally, it does:
> + * 1) check if the usb device is assigned to the domain
> + * 2) remove the usb device from xenstore controller/port.
> + * 3) unbind usb device from usbback and rebind to its original driver.
> + *    If usb device has many interfaces, do it to each interface.
> + */
> +static int libxl__device_usbdev_remove(libxl__gc *gc, uint32_t domid,
> +                                       libxl_device_usbdev *usbdev)
> +{
> +    libxl_usbctrlinfo usbctrlinfo;
> +    libxl_device_usbctrl usbctrl;
> +    int rc;
> +
> +    if (usbdev->ctrl < 0 || usbdev->port < 1) {
> +        LOG(ERROR, "Invalid USB device");
> +        return ERROR_FAIL;
> +    }
> +
> +    libxl_device_usbctrl_init(&usbctrl);
> +    libxl_usbctrlinfo_init(&usbctrlinfo);
> +    usbctrl.devid = usbdev->ctrl;
> +
> +    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
> +    if (rc) goto out;
> +
> +    if (usbctrlinfo.backend_id != LIBXL_TOOLSTACK_DOMID) {
> +        LOG(ERROR, "Don't support removing USB device from non-Dom0 backend");
> +        rc = ERROR_INVAL;
> +        goto out;
> +    }
> +
> +    /* do actual removing usb device operation */
> +    rc = do_usbdev_remove(gc, domid, usbdev);
> +
> +out:
> +    libxl_device_usbctrl_dispose(&usbctrl);
> +    libxl_usbctrlinfo_dispose(&usbctrlinfo);
> +    return rc;
> +}
> +
> +int libxl_device_usbdev_remove(libxl_ctx *ctx, uint32_t domid,
> +                               libxl_device_usbdev *usbdev,
> +                               const libxl_asyncop_how *ao_how)
> +
> +{
> +    AO_CREATE(ctx, domid, ao_how);
> +    int rc;
> +
> +    rc = libxl__device_usbdev_remove(gc, domid, usbdev);
> +
> +    libxl__ao_complete(egc, ao, rc);
> +    return AO_INPROGRESS;
> +}
> +
> +int libxl_ctrlport_to_device_usbdev(libxl_ctx *ctx,
> +                                    uint32_t domid,
> +                                    int ctrl,
> +                                    int port,
> +                                    libxl_device_usbdev *usbdev)
> +{
> +    GC_INIT(ctx);
> +    const char *dompath, *fe_path, *be_path, *busid;
> +    int rc;
> +
> +    dompath = libxl__xs_get_dompath(gc, domid);
> +
> +    fe_path = GCSPRINTF("%s/device/vusb/%d", dompath, ctrl);
> +
> +    be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
> +    if (!be_path) {
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    rc = libxl__xs_read_checked(gc, XBT_NULL,
> +                           GCSPRINTF("%s/port/%d", be_path, port),
> +                           &busid);
> +    if (rc) goto out;
> +
> +    if (!busid || !strcmp(busid, "")) {
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    usbdev->ctrl = ctrl;
> +    usbdev->port = port;
> +    usbdev->type = LIBXL_USBDEV_TYPE_HOSTDEV;
> +    rc = usbdev_busaddr_from_busid(gc, busid,
> +                                   &usbdev->u.hostdev.hostbus,
> +                                   &usbdev->u.hostdev.hostaddr);
> +
> +out:
> +    GC_FREE;
> +    return rc;
> +}
> +/*
> + * Local variables:
> + * mode: C
> + * c-basic-offset: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
> index 632c009..2a99eeb 100644
> --- a/tools/libxl/libxl_types.idl
> +++ b/tools/libxl/libxl_types.idl
> @@ -613,6 +613,35 @@ libxl_device_rdm = Struct("device_rdm", [
>      ("policy", libxl_rdm_reserve_policy),
>      ])
>  
> +libxl_usbctrl_type = Enumeration("usbctrl_type", [
> +    (0, "AUTO"),
> +    (1, "PV"),
> +    (2, "DEVICEMODEL"),
> +    ])
> +
> +libxl_usbdev_type = Enumeration("usbdev_type", [
> +    (1, "hostdev"),
> +    ])
> +
> +libxl_device_usbctrl = Struct("device_usbctrl", [
> +    ("type", libxl_usbctrl_type),
> +    ("devid", libxl_devid),
> +    ("version", integer),
> +    ("ports", integer),
> +    ("backend_domid", libxl_domid),
> +    ("backend_domname", string),
> +   ])
> +
> +libxl_device_usbdev = Struct("device_usbdev", [
> +    ("ctrl", libxl_devid),
> +    ("port", integer),
> +    ("u", KeyedUnion(None, libxl_usbdev_type, "type",
> +           [("hostdev", Struct(None, [
> +                 ("hostbus",   uint8),
> +                 ("hostaddr",  uint8)])),
> +           ])),
> +    ])
> +
>  libxl_device_dtdev = Struct("device_dtdev", [
>      ("path", string),
>      ])
> @@ -651,6 +680,8 @@ libxl_domain_config = Struct("domain_config", [
>      # a channel manifests as a console with a name,
>      # see docs/misc/channels.txt
>      ("channels", Array(libxl_device_channel, "num_channels")),
> +    ("usbctrls", Array(libxl_device_usbctrl, "num_usbctrls")),
> +    ("usbdevs", Array(libxl_device_usbdev, "num_usbdevs")),
>  
>      ("on_poweroff", libxl_action_on_shutdown),
>      ("on_reboot", libxl_action_on_shutdown),
> @@ -694,6 +725,21 @@ libxl_vtpminfo = Struct("vtpminfo", [
>      ("uuid", libxl_uuid),
>      ], dir=DIR_OUT)
>  
> +libxl_usbctrlinfo = Struct("usbctrlinfo", [
> +    ("type", libxl_usbctrl_type),
> +    ("devid", libxl_devid),
> +    ("version", integer),
> +    ("ports", integer),
> +    ("backend", string),
> +    ("backend_id", uint32),
> +    ("frontend", string),
> +    ("frontend_id", uint32),
> +    ("state", integer),
> +    ("evtch", integer),
> +    ("ref_urb", integer),
> +    ("ref_conn", integer),
> +    ], dir=DIR_OUT)
> +
>  libxl_vcpuinfo = Struct("vcpuinfo", [
>      ("vcpuid", uint32),
>      ("cpu", uint32),
> diff --git a/tools/libxl/libxl_types_internal.idl b/tools/libxl/libxl_types_internal.idl
> index 5e55685..696f5f8 100644
> --- a/tools/libxl/libxl_types_internal.idl
> +++ b/tools/libxl/libxl_types_internal.idl
> @@ -22,6 +22,7 @@ libxl__device_kind = Enumeration("device_kind", [
>      (6, "VKBD"),
>      (7, "CONSOLE"),
>      (8, "VTPM"),
> +    (9, "VUSB"),
>      ])
>  
>  libxl__console_backend = Enumeration("console_backend", [
> diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
> index b0cb9e1..ceb8825 100644
> --- a/tools/libxl/libxl_utils.c
> +++ b/tools/libxl/libxl_utils.c
> @@ -1311,6 +1311,24 @@ int libxl__random_bytes(libxl__gc *gc, uint8_t *buf, size_t len)
>      return ret;
>  }
>  
> +void libxl_device_usbctrl_list_free(libxl_device_usbctrl *list, int nr)
> +{
> +   int i;
> +
> +   for (i = 0; i < nr; i++)
> +       libxl_device_usbctrl_dispose(&list[i]);
> +   free(list);
> +}
> +
> +void libxl_device_usbdev_list_free(libxl_device_usbdev *list, int nr)
> +{
> +   int i;
> +
> +   for (i = 0; i < nr; i++)
> +       libxl_device_usbdev_dispose(&list[i]);
> +   free(list);
> +}
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/tools/libxl/libxl_utils.h b/tools/libxl/libxl_utils.h
> index 339ebdf..4495417 100644
> --- a/tools/libxl/libxl_utils.h
> +++ b/tools/libxl/libxl_utils.h
> @@ -76,6 +76,11 @@ int libxl_uuid_to_device_vtpm(libxl_ctx *ctx, uint32_t domid,
>                                 libxl_uuid *uuid, libxl_device_vtpm *vtpm);
>  int libxl_devid_to_device_vtpm(libxl_ctx *ctx, uint32_t domid,
>                                 int devid, libxl_device_vtpm *vtpm);
> +int libxl_devid_to_device_usbctrl(libxl_ctx *ctx, uint32_t domid,
> +                                  int devid, libxl_device_usbctrl *usbctrl);
> +int libxl_ctrlport_to_device_usbdev(libxl_ctx *ctx, uint32_t domid,
> +                                    int ctrl, int port,
> +                                    libxl_device_usbdev *usbdev);
>  
>  int libxl_bitmap_alloc(libxl_ctx *ctx, libxl_bitmap *bitmap, int n_bits);
>      /* Allocated bimap is from malloc, libxl_bitmap_dispose() to be
>

Patch

diff --git a/tools/libxl/Makefile b/tools/libxl/Makefile
index 789a12e..8fa7b87 100644
--- a/tools/libxl/Makefile
+++ b/tools/libxl/Makefile
@@ -105,7 +105,8 @@  LIBXL_OBJS = flexarray.o libxl.o libxl_create.o libxl_dm.o libxl_pci.o \
 			libxl_stream_read.o libxl_stream_write.o \
 			libxl_save_callout.o _libxl_save_msgs_callout.o \
 			libxl_qmp.o libxl_event.o libxl_fork.o \
-			libxl_dom_suspend.o libxl_dom_save.o $(LIBXL_OBJS-y)
+			libxl_dom_suspend.o libxl_dom_save.o libxl_pvusb.o \
+                        $(LIBXL_OBJS-y)
 LIBXL_OBJS += libxl_genid.o
 LIBXL_OBJS += _libxl_types.o libxl_flask.o _libxl_types_internal.o
 
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 2ab5ad3..1e68688 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -4102,6 +4102,8 @@  out:
  * libxl_device_vkb_destroy
  * libxl_device_vfb_remove
  * libxl_device_vfb_destroy
+ * libxl_device_usbctrl_remove
+ * libxl_device_usbctrl_destroy
  */
 #define DEFINE_DEVICE_REMOVE_EXT(type, remtype, removedestroy, f)        \
     int libxl_device_##type##_##removedestroy(libxl_ctx *ctx,           \
@@ -4159,6 +4161,10 @@  DEFINE_DEVICE_REMOVE(vfb, destroy, 1)
 DEFINE_DEVICE_REMOVE(vtpm, remove, 0)
 DEFINE_DEVICE_REMOVE(vtpm, destroy, 1)
 
+/* usbctrl */
+DEFINE_DEVICE_REMOVE_CUSTOM(usbctrl, remove, 0)
+DEFINE_DEVICE_REMOVE_CUSTOM(usbctrl, destroy, 1)
+
 /* channel/console hotunplug is not implemented. There are 2 possibilities:
  * 1. add support for secondary consoles to xenconsoled
  * 2. dynamically add/remove qemu chardevs via qmp messages. */
@@ -4174,6 +4180,8 @@  DEFINE_DEVICE_REMOVE(vtpm, destroy, 1)
  * libxl_device_disk_add
  * libxl_device_nic_add
  * libxl_device_vtpm_add
+ * libxl_device_usbctrl_add
+ * libxl_device_usbdev_add
  */
 
 #define DEFINE_DEVICE_ADD(type)                                         \
@@ -4205,6 +4213,12 @@  DEFINE_DEVICE_ADD(nic)
 /* vtpm */
 DEFINE_DEVICE_ADD(vtpm)
 
+/* usbctrl */
+DEFINE_DEVICE_ADD(usbctrl)
+
+/* usb */
+DEFINE_DEVICE_ADD(usbdev)
+
 #undef DEFINE_DEVICE_ADD
 
 /******************************************************************************/
@@ -6750,6 +6764,10 @@  int libxl_retrieve_domain_configuration(libxl_ctx *ctx, uint32_t domid,
 
     MERGE(pci, pcidevs, COMPARE_PCI, {});
 
+    MERGE(usbctrl, usbctrls, COMPARE_USBCTRL, {});
+
+    MERGE(usbdev, usbdevs, COMPARE_USB, {});
+
     /* Take care of removable device. We maintain invariant in the
      * insert / remove operation so that:
      * 1. if xenstore is "empty" while JSON is not, the result
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 0859383..5cc3ce3 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -123,6 +123,12 @@ 
 #define LIBXL_HAVE_DOMAIN_NODEAFFINITY 1
 
 /*
+ * LIBXL_HAVE_PVUSB indicates functions for plugging in USB devices
+ * through pvusb -- both hotplug and at domain creation time..
+ */
+#define LIBXL_HAVE_PVUSB 1
+
+/*
  * LIBXL_HAVE_BUILDINFO_HVM_VENDOR_DEVICE indicates that the
  * libxl_vendor_device field is present in the hvm sections of
  * libxl_domain_build_info. This field tells libxl which
@@ -1536,6 +1542,77 @@  int libxl_cdrom_insert(libxl_ctx *ctx, uint32_t domid, libxl_device_disk *disk,
                        const libxl_asyncop_how *ao_how)
                        LIBXL_EXTERNAL_CALLERS_ONLY;
 
+/*
+ * USB
+ *
+ * For each device removed or added, one of these protocols is available:
+ * - PV (i.e., PVUSB)
+ * - DEVICEMODEL (i.e, qemu)
+ *
+ * PV is available for either PV or HVM domains.  DEVICEMODEL is only
+ * available for HVM domains.  The caller can additionally specify
+ * "AUTO", in which case the library will try to determine the best
+ * protocol automatically.
+ *
+ * At the moment, the only protocol implemented is PV.
+ *
+ * One can add/remove USB controllers to/from guest, and attach/detach USB
+ * devices to/from USB controllers.
+ *
+ * To add USB controllers and USB devices, one can adding USB controllers
+ * first and then attaching USB devices to some USB controller, or adding
+ * USB devices to guest directly, it will automatically create a USB
+ * controller for USB devices to attach.
+ *
+ * To remove USB controllers or USB devices, one can remove USB devices
+ * under USB controller one by one and then remove USB controller, or
+ * remove USB controller directly, it will remove all USB devices under
+ * it automatically.
+ *
+ */
+/* USB Controllers*/
+int libxl_device_usbctrl_add(libxl_ctx *ctx, uint32_t domid,
+                             libxl_device_usbctrl *usbctrl,
+                             const libxl_asyncop_how *ao_how)
+                             LIBXL_EXTERNAL_CALLERS_ONLY;
+
+int libxl_device_usbctrl_remove(libxl_ctx *ctx, uint32_t domid,
+                                libxl_device_usbctrl *usbctrl,
+                                const libxl_asyncop_how *ao_how)
+                                LIBXL_EXTERNAL_CALLERS_ONLY;
+
+int libxl_device_usbctrl_destroy(libxl_ctx *ctx, uint32_t domid,
+                                 libxl_device_usbctrl *usbctrl,
+                                 const libxl_asyncop_how *ao_how)
+                                 LIBXL_EXTERNAL_CALLERS_ONLY;
+
+libxl_device_usbctrl *libxl_device_usbctrl_list(libxl_ctx *ctx,
+                                                uint32_t domid, int *num);
+
+void libxl_device_usbctrl_list_free(libxl_device_usbctrl *list, int nr);
+
+
+int libxl_device_usbctrl_getinfo(libxl_ctx *ctx, uint32_t domid,
+                                 libxl_device_usbctrl *usbctrl,
+                                 libxl_usbctrlinfo *usbctrlinfo);
+
+/* USB Devices */
+
+int libxl_device_usbdev_add(libxl_ctx *ctx, uint32_t domid,
+                            libxl_device_usbdev *usbdev,
+                            const libxl_asyncop_how *ao_how)
+                            LIBXL_EXTERNAL_CALLERS_ONLY;
+
+int libxl_device_usbdev_remove(libxl_ctx *ctx, uint32_t domid,
+                               libxl_device_usbdev *usbdev,
+                               const libxl_asyncop_how *ao_how)
+                               LIBXL_EXTERNAL_CALLERS_ONLY;
+
+libxl_device_usbdev *
+libxl_device_usbdev_list(libxl_ctx *ctx, uint32_t domid, int *num);
+
+void libxl_device_usbdev_list_free(libxl_device_usbdev *list, int nr);
+
 /* Network Interfaces */
 int libxl_device_nic_add(libxl_ctx *ctx, uint32_t domid, libxl_device_nic *nic,
                          const libxl_asyncop_how *ao_how)
diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index a356e2a..b7a6a13 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -676,7 +676,10 @@  void libxl__devices_destroy(libxl__egc *egc, libxl__devices_remove_state *drs)
                 aodev->action = LIBXL__DEVICE_ACTION_REMOVE;
                 aodev->dev = dev;
                 aodev->force = drs->force;
-                libxl__initiate_device_generic_remove(egc, aodev);
+                if (dev->backend_kind == LIBXL__DEVICE_KIND_VUSB)
+                    libxl__initiate_device_usbctrl_remove(egc, aodev);
+                else
+                    libxl__initiate_device_generic_remove(egc, aodev);
             }
         }
     }
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 082f656..f78cb72 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -2587,6 +2587,14 @@  _hidden void libxl__device_vtpm_add(libxl__egc *egc, uint32_t domid,
                                    libxl_device_vtpm *vtpm,
                                    libxl__ao_device *aodev);
 
+_hidden void libxl__device_usbctrl_add(libxl__egc *egc, uint32_t domid,
+                                       libxl_device_usbctrl *usbctrl,
+                                       libxl__ao_device *aodev);
+
+_hidden void libxl__device_usbdev_add(libxl__egc *egc, uint32_t domid,
+                                      libxl_device_usbdev *usbdev,
+                                      libxl__ao_device *aodev);
+
 /* Internal function to connect a vkb device */
 _hidden int libxl__device_vkb_add(libxl__gc *gc, uint32_t domid,
                                   libxl_device_vkb *vkb);
@@ -2619,6 +2627,13 @@  _hidden void libxl__wait_device_connection(libxl__egc*,
 _hidden void libxl__initiate_device_generic_remove(libxl__egc *egc,
                                                    libxl__ao_device *aodev);
 
+_hidden int libxl__device_from_usbctrl(libxl__gc *gc, uint32_t domid,
+                               libxl_device_usbctrl *usbctrl,
+                               libxl__device *device);
+
+_hidden void libxl__initiate_device_usbctrl_remove(libxl__egc *egc,
+                                                   libxl__ao_device *aodev);
+
 /*
  * libxl__get_hotplug_script_info returns the args and env that should
  * be passed to the hotplug script for the requested device.
@@ -4014,6 +4029,9 @@  static inline void libxl__update_config_vtpm(libxl__gc *gc,
 #define COMPARE_PCI(a, b) ((a)->func == (b)->func &&    \
                            (a)->bus == (b)->bus &&      \
                            (a)->dev == (b)->dev)
+#define COMPARE_USB(a, b) ((a)->ctrl == (b)->ctrl && \
+                           (a)->port == (b)->port)
+#define COMPARE_USBCTRL(a, b) ((a)->devid == (b)->devid)
 
 /* DEVICE_ADD
  *
diff --git a/tools/libxl/libxl_osdeps.h b/tools/libxl/libxl_osdeps.h
index d9661c9..802c762 100644
--- a/tools/libxl/libxl_osdeps.h
+++ b/tools/libxl/libxl_osdeps.h
@@ -24,6 +24,8 @@ 
 #define _GNU_SOURCE
 
 #if defined(__NetBSD__)
+#define SYSFS_USB_DEV          "/sys/bus/usb/devices"
+#define SYSFS_USBBACK_DRIVER   "/kern/xen/usb"
 #define SYSFS_PCI_DEV          "/sys/bus/pci/devices"
 #define SYSFS_PCIBACK_DRIVER   "/kern/xen/pci"
 #define NETBACK_NIC_NAME       "xvif%ui%d"
@@ -31,6 +33,8 @@ 
 #elif defined(__OpenBSD__)
 #include <util.h>
 #elif defined(__linux__)
+#define SYSFS_USB_DEV          "/sys/bus/usb/devices"
+#define SYSFS_USBBACK_DRIVER   "/sys/bus/usb/drivers/usbback"
 #define SYSFS_PCI_DEV          "/sys/bus/pci/devices"
 #define SYSFS_PCIBACK_DRIVER   "/sys/bus/pci/drivers/pciback"
 #define NETBACK_NIC_NAME       "vif%u.%d"
@@ -38,6 +42,8 @@ 
 #elif defined(__sun__)
 #include <stropts.h>
 #elif defined(__FreeBSD__)
+#define SYSFS_USB_DEV          "/dev/null"
+#define SYSFS_USBBACK_DRIVER   "/dev/null"
 #define SYSFS_PCI_DEV          "/dev/null"
 #define SYSFS_PCIBACK_DRIVER   "/dev/null"
 #define NETBACK_NIC_NAME       "xnb%u.%d"
@@ -45,6 +51,13 @@ 
 #include <sys/endian.h>
 #endif
 
+#ifndef SYSFS_USBBACK_DRIVER
+#error define SYSFS_USBBACK_DRIVER for your platform
+#endif
+#ifndef SYSFS_USB_DEV
+#error define SYSFS_USB_DEV for your platform
+#endif
+
 #ifndef SYSFS_PCIBACK_DRIVER
 #error define SYSFS_PCIBACK_DRIVER for your platform
 #endif
diff --git a/tools/libxl/libxl_pvusb.c b/tools/libxl/libxl_pvusb.c
new file mode 100644
index 0000000..5f92628
--- /dev/null
+++ b/tools/libxl/libxl_pvusb.c
@@ -0,0 +1,1620 @@ 
+/*
+ * Copyright (C) 2015 SUSE LINUX Products GmbH, Nuernberg, Germany.
+ * Author Chunyan Liu <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ */
+
+#include "libxl_osdeps.h" /* must come before any other headers */
+
+#include "libxl_internal.h"
+#include <inttypes.h>
+
+#define USBBACK_INFO_PATH "/libxl/usbback"
+
+#define USBHUB_CLASS_CODE 9
+
+static int libxl__device_usbctrl_setdefault(libxl__gc *gc, uint32_t domid,
+                                            libxl_device_usbctrl *usbctrl)
+{
+    int rc;
+    libxl_domain_type domtype = libxl__domain_type(gc, domid);
+
+    if (!usbctrl->version)
+        usbctrl->version = 2;
+
+    if (!usbctrl->ports)
+        usbctrl->ports = 8;
+
+    if (usbctrl->type == LIBXL_USBCTRL_TYPE_AUTO) {
+        if (domtype == LIBXL_DOMAIN_TYPE_PV) {
+            usbctrl->type = LIBXL_USBCTRL_TYPE_PV;
+        } else if (domtype == LIBXL_DOMAIN_TYPE_HVM) {
+            /* FIXME: See if we can detect PV frontend */
+            usbctrl->type = LIBXL_USBCTRL_TYPE_DEVICEMODEL;
+        }
+    }
+
+    rc = libxl__resolve_domid(gc, usbctrl->backend_domname,
+                              &usbctrl->backend_domid);
+    return rc;
+}
+
+int libxl__device_from_usbctrl(libxl__gc *gc, uint32_t domid,
+                               libxl_device_usbctrl *usbctrl,
+                               libxl__device *device)
+{
+    device->backend_devid   = usbctrl->devid;
+    device->backend_domid   = usbctrl->backend_domid;
+    device->backend_kind    = LIBXL__DEVICE_KIND_VUSB;
+    device->devid           = usbctrl->devid;
+    device->domid           = domid;
+    device->kind            = LIBXL__DEVICE_KIND_VUSB;
+
+    return 0;
+}
+
+/* Add usbctrl information to xenstore.
+ *
+ * Adding a usb controller will add a new 'vusb' device in xenstore, and
+ * add corresponding frontend, backend information to it. According to
+ * "update_json", decide wether to update json config file.
+ */
+static int libxl__device_usbctrl_add_xenstore(libxl__gc *gc, uint32_t domid,
+                                              libxl_device_usbctrl *usbctrl,
+                                              bool update_json)
+{
+    libxl__device *device;
+    flexarray_t *front;
+    flexarray_t *back;
+    xs_transaction_t t = XBT_NULL;
+    int i, rc;
+    libxl_domain_config d_config;
+    libxl_device_usbctrl usbctrl_saved;
+    libxl__domain_userdata_lock *lock = NULL;
+
+    libxl_domain_config_init(&d_config);
+    libxl_device_usbctrl_init(&usbctrl_saved);
+    libxl_device_usbctrl_copy(CTX, &usbctrl_saved, usbctrl);
+
+    GCNEW(device);
+    rc = libxl__device_from_usbctrl(gc, domid, usbctrl, device);
+    if (rc) goto out;
+
+    front = flexarray_make(gc, 4, 1);
+    back = flexarray_make(gc, 12, 1);
+
+    flexarray_append_pair(back, "frontend-id", GCSPRINTF("%d", domid));
+    flexarray_append_pair(back, "online", "1");
+    flexarray_append_pair(back, "state",
+                          GCSPRINTF("%d", XenbusStateInitialising));
+    flexarray_append_pair(back, "type",
+                          (char *)libxl_usbctrl_type_to_string(usbctrl->type));
+    flexarray_append_pair(back, "usb-ver", GCSPRINTF("%d", usbctrl->version));
+    flexarray_append_pair(back, "num-ports", GCSPRINTF("%d", usbctrl->ports));
+    flexarray_append_pair(back, "port", "");
+    for (i = 0; i < usbctrl->ports; i++)
+        flexarray_append_pair(back, GCSPRINTF("port/%d", i + 1), "");
+
+    flexarray_append_pair(front, "backend-id",
+                          GCSPRINTF("%d", usbctrl->backend_domid));
+    flexarray_append_pair(front, "state",
+                          GCSPRINTF("%d", XenbusStateInitialising));
+
+    if (update_json) {
+        lock = libxl__lock_domain_userdata(gc, domid);
+        if (!lock) {
+            rc = ERROR_LOCK_FAIL;
+            goto out;
+        }
+
+        rc = libxl__get_domain_configuration(gc, domid, &d_config);
+        if (rc) goto out;
+
+        DEVICE_ADD(usbctrl, usbctrls, domid, &usbctrl_saved,
+                   COMPARE_USBCTRL, &d_config);
+    }
+
+    for (;;) {
+        rc = libxl__xs_transaction_start(gc, &t);
+        if (rc) goto out;
+
+        rc = libxl__device_exists(gc, t, device);
+        if (rc < 0) goto out;
+        if (rc == 1) {
+            /* already exists in xenstore */
+            LOG(ERROR, "device already exists in xenstore");
+            rc = ERROR_DEVICE_EXISTS;
+            goto out;
+        }
+
+        if (update_json) {
+            rc = libxl__set_domain_configuration(gc, domid, &d_config);
+            if (rc) goto out;
+        }
+
+        libxl__device_generic_add(gc, t, device,
+                          libxl__xs_kvs_of_flexarray(gc, back, back->count),
+                          libxl__xs_kvs_of_flexarray(gc, front, front->count),
+                          NULL);
+
+        rc = libxl__xs_transaction_commit(gc, &t);
+        if (!rc) break;
+        if (rc < 0) goto out;
+    }
+
+out:
+    libxl__xs_transaction_abort(gc, &t);
+    if (lock) libxl__unlock_domain_userdata(lock);
+    libxl_device_usbctrl_dispose(&usbctrl_saved);
+    libxl_domain_config_dispose(&d_config);
+    return rc;
+}
+
+/* AO operation to add a usb controller.
+ *
+ * Generally, it does:
+ * 1) fill in necessary usb controler information with default value
+ * 2) write usb controller frontend/backend info to xenstore, update json
+ *    config file if necessary.
+ * 3) wait for device connection. PVUSB frontend and backend driver will
+ *    probe xenstore paths and build connection between frontend and backend.
+ *
+ * Before calling this function, aodev should be properly filled:
+ * aodev->ao, aodev->callback, aodev->update_json, ...
+ */
+void libxl__device_usbctrl_add(libxl__egc *egc, uint32_t domid,
+                               libxl_device_usbctrl *usbctrl,
+                               libxl__ao_device *aodev)
+{
+    STATE_AO_GC(aodev->ao);
+    libxl__device *device;
+    int rc;
+
+    rc = libxl__device_usbctrl_setdefault(gc, domid, usbctrl);
+    if (rc < 0) goto out;
+
+    if (usbctrl->devid == -1) {
+        usbctrl->devid = libxl__device_nextid(gc, domid, "vusb");
+        if (usbctrl->devid < 0) {
+            rc = ERROR_FAIL;
+            goto out;
+        }
+    }
+
+    if (usbctrl->type != LIBXL_USBCTRL_TYPE_PV) {
+        LOG(ERROR, "Unsupported USB controller type");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = libxl__device_usbctrl_add_xenstore(gc, domid, usbctrl,
+                                            aodev->update_json);
+    if (rc) goto out;
+
+    GCNEW(device);
+    rc = libxl__device_from_usbctrl(gc, domid, usbctrl, device);
+    if (rc) goto out;
+
+    aodev->dev = device;
+    aodev->action = LIBXL__DEVICE_ACTION_ADD;
+    libxl__wait_device_connection(egc, aodev);
+    return;
+
+out:
+    aodev->rc = rc;
+    aodev->callback(egc, aodev);
+    return;
+}
+
+static int libxl__device_usbdev_list_for_usbctrl(libxl__gc *gc, uint32_t domid,
+                                                 libxl_devid usbctrl,
+                                                 libxl_device_usbdev **usbdevs,
+                                                 int *num);
+
+static int libxl__device_usbdev_remove(libxl__gc *gc, uint32_t domid,
+                                       libxl_device_usbdev *usbdev);
+
+/* AO function to remove a usb controller.
+ *
+ * Generally, it does:
+ * 1) check if the usb controller exists or not
+ * 2) remove all usb devices under controller
+ * 3) remove usb controller information from xenstore
+ *
+ * Before calling this function, aodev should be properly filled:
+ * aodev->ao, aodev->dev, aodev->callback, ...
+ */
+void libxl__initiate_device_usbctrl_remove(libxl__egc *egc,
+                                           libxl__ao_device *aodev)
+{
+    STATE_AO_GC(aodev->ao);
+    libxl_device_usbdev *usbdevs = NULL;
+    int num_usbdev = 0;
+    int i, rc;
+    uint32_t domid = ao->domid;
+    int usbctrl_devid = aodev->dev->devid;
+    libxl_device_usbctrl usbctrl;
+    libxl_usbctrlinfo usbctrlinfo;
+
+    libxl_device_usbctrl_init(&usbctrl);
+    libxl_usbctrlinfo_init(&usbctrlinfo);
+    usbctrl.devid = usbctrl_devid;
+
+    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
+    if (rc) goto out;
+
+    if (usbctrlinfo.type != LIBXL_USBCTRL_TYPE_PV) {
+        LOG(ERROR, "Unsupported USB controller type");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    /* Remove usb devices first */
+    rc = libxl__device_usbdev_list_for_usbctrl(gc, domid, usbctrl_devid,
+                                               &usbdevs, &num_usbdev);
+    if (rc) goto out;
+
+    for (i = 0; i < num_usbdev; i++) {
+        rc = libxl__device_usbdev_remove(gc, domid, &usbdevs[i]);
+        if (rc) {
+            LOG(ERROR, "libxl__device_usbdev_remove failed: controller %d, "
+                "port %d", usbdevs[i].ctrl, usbdevs[i].port);
+            goto out;
+        }
+    }
+
+    libxl_device_usbctrl_dispose(&usbctrl);
+    libxl_usbctrlinfo_dispose(&usbctrlinfo);
+
+    /* Remove usbctrl */
+    libxl__initiate_device_generic_remove(egc, aodev);
+    return;
+
+out:
+    libxl_device_usbctrl_dispose(&usbctrl);
+    libxl_usbctrlinfo_dispose(&usbctrlinfo);
+    aodev->rc = rc;
+    aodev->callback(egc, aodev);
+    return;
+}
+
+static const char *vusb_be_from_xs_fe(libxl__gc *gc, const char *fe_path,
+                                      uint32_t tgt_domid)
+{
+    const char *be_path;
+    int r;
+    uint32_t be_domid, fe_domid;
+
+    r = libxl__xs_read_checked(gc, XBT_NULL, GCSPRINTF("%s/backend", fe_path),
+                               &be_path);
+    if (r || !be_path) return NULL;
+
+    /* Check to see that it has the proper form, and that fe_domid ==
+     * target domid */
+    r = sscanf(be_path, "/local/domain/%d/backend/vusb/%d",
+               &be_domid, &fe_domid);
+
+    if (r != 2 || fe_domid != tgt_domid) {
+        LOG(ERROR, "Malformed backend, refusing to use");
+        return NULL;
+    }
+
+    return be_path;
+}
+
+libxl_device_usbctrl *
+libxl_device_usbctrl_list(libxl_ctx *ctx, uint32_t domid, int *num)
+{
+    GC_INIT(ctx);
+    libxl_device_usbctrl *usbctrls = NULL;
+    char *path = NULL;
+    char **entry = NULL;
+    unsigned int nentries = 0;
+
+    *num = 0;
+
+    path = GCSPRINTF("%s/device/vusb",
+                     libxl__xs_get_dompath(gc, domid));
+    entry = libxl__xs_directory(gc, XBT_NULL, path, &nentries);
+
+    if (entry && nentries) {
+        usbctrls = libxl__zalloc(NOGC, sizeof(*usbctrls) * nentries);
+        libxl_device_usbctrl *usbctrl;
+        libxl_device_usbctrl *end = usbctrls + nentries;
+        for (usbctrl = usbctrls;
+             usbctrl < end;
+             usbctrl++, entry++, (*num)++) {
+            const char *tmp, *be_path, *fe_path;
+            int ret;
+
+            libxl_device_usbctrl_init(usbctrl);
+            usbctrl->devid = atoi(*entry);
+
+#define READ_SUBPATH(path, subpath) ({                                  \
+        ret = libxl__xs_read_checked(gc, XBT_NULL,                      \
+                                     GCSPRINTF("%s/" subpath, path),    \
+                                     &tmp);                             \
+        if (ret) goto out;                                              \
+        (char *)tmp;                                                    \
+    })
+
+#define READ_SUBPATH_INT(path, subpath) ({                              \
+        ret = libxl__xs_read_checked(gc, XBT_NULL,                      \
+                                     GCSPRINTF("%s/" subpath, path),    \
+                                     &tmp);                             \
+        if (ret) goto out;                                              \
+        tmp ? atoi(tmp) : -1;                                           \
+    })
+
+            fe_path = GCSPRINTF("%s/%s", path, *entry);
+            be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
+            if (!be_path) goto out;
+            usbctrl->backend_domid = READ_SUBPATH_INT(fe_path, "backend-id");
+            usbctrl->version = READ_SUBPATH_INT(be_path, "usb-ver");
+            usbctrl->ports = READ_SUBPATH_INT(be_path, "num-ports");
+            libxl_usbctrl_type_from_string(READ_SUBPATH(be_path, "type"),
+                                           &usbctrl->type);
+
+#undef READ_SUBPATH
+#undef READ_SUBPATH_INT
+       }
+    }
+
+    GC_FREE;
+    return usbctrls;
+
+out:
+    LOG(ERROR, "Unable to list USB Controllers");
+    libxl_device_usbctrl_list_free(usbctrls, *num);
+    GC_FREE;
+    *num = 0;
+    return NULL;
+}
+
+int libxl_device_usbctrl_getinfo(libxl_ctx *ctx, uint32_t domid,
+                                 libxl_device_usbctrl *usbctrl,
+                                 libxl_usbctrlinfo *usbctrlinfo)
+{
+    GC_INIT(ctx);
+    const char *dompath, *fe_path, *be_path, *tmp;
+    int rc;
+
+    usbctrlinfo->devid = usbctrl->devid;
+
+#define READ_SUBPATH(path, subpath) ({                                  \
+        rc = libxl__xs_read_checked(gc, XBT_NULL,                       \
+                                    GCSPRINTF("%s/" subpath, path),     \
+                                    &tmp);                              \
+        if (rc) goto out;                                               \
+        (char *)tmp;                                                    \
+    })
+
+#define READ_SUBPATH_INT(path, subpath) ({                              \
+        rc = libxl__xs_read_checked(gc, XBT_NULL,                       \
+                                    GCSPRINTF("%s/" subpath, path),     \
+                                    &tmp);                              \
+        if (rc) goto out;                                               \
+        tmp ? atoi(tmp) : -1;                                           \
+    })
+
+    dompath = libxl__xs_get_dompath(gc, domid);
+    fe_path = GCSPRINTF("%s/device/vusb/%d", dompath, usbctrl->devid);
+    be_path = READ_SUBPATH(fe_path, "backend");
+    usbctrlinfo->backend = libxl__strdup(NOGC, be_path);
+    usbctrlinfo->backend_id = READ_SUBPATH_INT(fe_path, "backend-id");
+    usbctrlinfo->state = READ_SUBPATH_INT(fe_path, "state");
+    usbctrlinfo->evtch = READ_SUBPATH_INT(fe_path, "event-channel");
+    usbctrlinfo->ref_urb = READ_SUBPATH_INT(fe_path, "urb-ring-ref");
+    usbctrlinfo->ref_conn = READ_SUBPATH_INT(fe_path, "urb-ring-ref");
+    tmp = READ_SUBPATH(be_path, "frontend");
+    usbctrlinfo->frontend = libxl__strdup(NOGC, tmp);
+    usbctrlinfo->frontend_id = READ_SUBPATH_INT(be_path, "frontend-id");
+    usbctrlinfo->ports = READ_SUBPATH_INT(be_path, "num-ports");
+    usbctrlinfo->version = READ_SUBPATH_INT(be_path, "usb-ver");;
+    tmp = READ_SUBPATH(be_path, "type");
+    libxl_usbctrl_type_from_string(tmp, &usbctrlinfo->type);
+
+#undef READ_SUBPATH
+#undef READ_SUBPATH_INT
+
+    rc = 0;
+
+out:
+    GC_FREE;
+    return rc;
+}
+
+int libxl_devid_to_device_usbctrl(libxl_ctx *ctx,
+                                  uint32_t domid,
+                                  int devid,
+                                  libxl_device_usbctrl *usbctrl)
+{
+    libxl_device_usbctrl *usbctrls;
+    int nb = 0;
+    int i, rc;
+
+    usbctrls = libxl_device_usbctrl_list(ctx, domid, &nb);
+    if (!usbctrls) return ERROR_FAIL;
+
+    rc = ERROR_FAIL;
+    for (i = 0; i < nb; i++) {
+        if (devid == usbctrls[i].devid) {
+            libxl_device_usbctrl_copy(ctx, usbctrl, &usbctrls[i]);
+            rc = 0;
+            break;
+        }
+    }
+
+    libxl_device_usbctrl_list_free(usbctrls, nb);
+    return rc;
+}
+
+static void *zalloc_dirent(libxl__gc *gc, const char *dirpath)
+{
+    size_t need = offsetof(struct dirent, d_name) +
+                  pathconf(dirpath, _PC_NAME_MAX) + 1;
+
+    return libxl__zalloc(gc, need);
+}
+
+static char *usbdev_busaddr_to_busid(libxl__gc *gc, int bus, int addr)
+{
+    DIR *dir;
+    char *busid = NULL;
+    struct dirent *de_buf;
+    struct dirent *de;
+
+    /* invalid hostbus or hostaddr */
+    if (bus < 1 || addr < 1)
+        return NULL;
+
+    dir = opendir(SYSFS_USB_DEV);
+    if (!dir) {
+        LOGE(ERROR, "opendir failed: '%s'", SYSFS_USB_DEV);
+        return NULL;
+    }
+
+    de_buf = zalloc_dirent(gc, SYSFS_USB_DEV);
+
+    for (;;) {
+        char *filename;
+        void *buf;
+        int busnum = -1;
+        int devnum = -1;
+
+        int r = readdir_r(dir, de_buf, &de);
+        if (r) {
+            LOGE(ERROR, "failed to readdir %s", SYSFS_USB_DEV);
+            break;
+        }
+        if (!de)
+            break;
+
+        if (!strcmp(de->d_name, ".") ||
+            !strcmp(de->d_name, ".."))
+            continue;
+
+        filename = GCSPRINTF(SYSFS_USB_DEV "/%s/devnum", de->d_name);
+        if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
+            devnum = atoi(buf);
+
+        filename = GCSPRINTF(SYSFS_USB_DEV "/%s/busnum", de->d_name);
+        if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
+            busnum = atoi(buf);
+
+        if (bus == busnum && addr == devnum) {
+            busid = libxl__strdup(gc, de->d_name);
+            break;
+        }
+    }
+
+    closedir(dir);
+    return busid;
+}
+
+static int usbdev_busaddr_from_busid(libxl__gc *gc, const char *busid,
+                                     uint8_t *bus, uint8_t *addr)
+{
+    char *filename;
+    void *buf;
+
+    filename = GCSPRINTF(SYSFS_USB_DEV "/%s/busnum", busid);
+    if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
+        *bus = atoi(buf);
+    else
+        return ERROR_FAIL;
+
+    filename = GCSPRINTF(SYSFS_USB_DEV "/%s/devnum", busid);
+    if (!libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
+        *addr = atoi(buf);
+    else
+        return ERROR_FAIL;
+
+    return 0;
+}
+
+static int get_assigned_devices(libxl__gc *gc,
+                                libxl_device_usbdev **list, int *num)
+{
+    char **domlist;
+    unsigned int ndom = 0;
+    int i, j, k;
+    int rc;
+
+    *list = NULL;
+    *num = 0;
+
+    domlist = libxl__xs_directory(gc, XBT_NULL, "/local/domain", &ndom);
+    for (i = 0; i < ndom; i++) {
+        char *path;
+        char **usbctrls;
+        unsigned int nc = 0;
+        uint32_t domid = atoi(domlist[i]);
+
+        path = GCSPRINTF("%s/device/vusb", libxl__xs_get_dompath(gc, domid));
+        usbctrls = libxl__xs_directory(gc, XBT_NULL, path, &nc);
+
+        for (j = 0; j < nc; j++) {
+            libxl_device_usbdev *tmp = NULL;
+            int nd = 0;
+
+            rc = libxl__device_usbdev_list_for_usbctrl(gc, domid,
+                                                       atoi(usbctrls[j]),
+                                                       &tmp, &nd);
+            if (rc) goto out;
+
+            if (!nd) continue;
+
+            GCREALLOC_ARRAY(*list, *num + nd);
+            for (k = 0; k < nd; k++) {
+                libxl_device_usbdev_copy(CTX, *list + *num, tmp + k);
+                (*num)++;
+            }
+        }
+    }
+
+    return 0;
+
+out:
+    LOG(ERROR, "fail to get assigned devices");
+    return rc;
+}
+
+static bool is_usbdev_in_array(libxl_device_usbdev *usbdevs, int num,
+                               libxl_device_usbdev *usbdev)
+{
+    int i;
+
+    for (i = 0; i < num; i++) {
+        if (usbdevs[i].u.hostdev.hostbus == usbdev->u.hostdev.hostbus &&
+            usbdevs[i].u.hostdev.hostaddr == usbdev->u.hostdev.hostaddr)
+            return true;
+    }
+
+    return false;
+}
+
+/* check if USB device type is assignable */
+static bool is_usbdev_assignable(libxl__gc *gc, libxl_device_usbdev *usbdev)
+{
+    int classcode;
+    char *filename;
+    void *buf = NULL;
+    char *busid = NULL;
+
+    busid = usbdev_busaddr_to_busid(gc, usbdev->u.hostdev.hostbus,
+                                    usbdev->u.hostdev.hostaddr);
+    if (!busid) return false;
+
+    filename = GCSPRINTF(SYSFS_USB_DEV "/%s/bDeviceClass", busid);
+    if (libxl__read_sysfs_file_contents(gc, filename, &buf, NULL))
+        return false;
+
+    classcode = atoi(buf);
+    return classcode != USBHUB_CLASS_CODE;
+}
+
+/* get usb devices under certain usb controller */
+static int
+libxl__device_usbdev_list_for_usbctrl(libxl__gc *gc,
+                                      uint32_t domid,
+                                      libxl_devid usbctrl,
+                                      libxl_device_usbdev **usbdevs,
+                                      int *num)
+{
+    const char *fe_path, *be_path, *num_devs;
+    int n, i, rc;
+
+    *usbdevs = NULL;
+    *num = 0;
+
+    fe_path = GCSPRINTF("%s/device/vusb/%d",
+                        libxl__xs_get_dompath(gc, domid), usbctrl);
+
+    be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
+    if (!be_path) {
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = libxl__xs_read_checked(gc, XBT_NULL,
+                                GCSPRINTF("%s/num-ports", be_path),
+                                &num_devs);
+    if (rc) goto out;
+
+    n = num_devs ? atoi(num_devs) : 0;
+
+    for (i = 0; i < n; i++) {
+        const char *busid;
+        libxl_device_usbdev *usbdev;
+
+        rc = libxl__xs_read_checked(gc, XBT_NULL,
+                                    GCSPRINTF("%s/port/%d", be_path, i + 1),
+                                    &busid);
+        if (rc) goto out;
+
+        if (busid && strcmp(busid, "")) {
+            GCREALLOC_ARRAY(*usbdevs, *num + 1);
+            usbdev = *usbdevs + *num;
+            (*num)++;
+            libxl_device_usbdev_init(usbdev);
+            usbdev->ctrl = usbctrl;
+            usbdev->port = i + 1;
+            usbdev->type = LIBXL_USBDEV_TYPE_HOSTDEV;
+            rc = usbdev_busaddr_from_busid(gc, busid,
+                                           &usbdev->u.hostdev.hostbus,
+                                           &usbdev->u.hostdev.hostaddr);
+            if (rc) goto out;
+        }
+    }
+
+    rc = 0;
+
+out:
+    return rc;
+}
+
+/* get all usb devices of the domain */
+libxl_device_usbdev *
+libxl_device_usbdev_list(libxl_ctx *ctx, uint32_t domid, int *num)
+{
+    GC_INIT(ctx);
+    libxl_device_usbdev *usbdevs = NULL;
+    const char *path;
+    char **usbctrls;
+    unsigned int nc = 0;
+    int i, j;
+
+    *num = 0;
+
+    path = GCSPRINTF("%s/device/vusb",
+                        libxl__xs_get_dompath(gc, domid));
+    usbctrls = libxl__xs_directory(gc, XBT_NULL, path, &nc);
+
+    for (i = 0; i < nc; i++) {
+        int r, nd = 0;
+        libxl_device_usbdev *tmp = NULL;
+
+        r = libxl__device_usbdev_list_for_usbctrl(gc, domid,
+                                                  atoi(usbctrls[i]),
+                                                  &tmp, &nd);
+        if (!r || !nd) continue;
+
+        usbdevs = libxl__realloc(NOGC, usbdevs,
+                                 sizeof(*usbdevs) * (*num + nd));
+        for (j = 0; j < nd; j++) {
+            libxl_device_usbdev_copy(ctx, usbdevs + *num, tmp + j);
+            (*num)++;
+        }
+    }
+
+    GC_FREE;
+    return usbdevs;
+}
+
+/* find first unused controller:port and give that to usb device */
+static int
+libxl__device_usbdev_set_default_usbctrl(libxl__gc *gc, uint32_t domid,
+                                         libxl_device_usbdev *usbdev)
+{
+    libxl_device_usbctrl *usbctrls = NULL;
+    int numctrl = 0;
+    int i, j, rc;
+
+    usbctrls = libxl_device_usbctrl_list(CTX, domid, &numctrl);
+    if (!numctrl || !usbctrls) {
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    for (i = 0; i < numctrl; i++) {
+        for (j = 0; j < usbctrls[i].ports; j++) {
+            const char *path, *tmp;
+
+            path = GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
+                             libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
+                             domid, usbctrls[i].devid, j + 1);
+            rc = libxl__xs_read_checked(gc, XBT_NULL, path, &tmp);
+            if (rc) goto out;
+
+            if (tmp && !strcmp(tmp, "")) {
+                usbdev->ctrl = usbctrls[i].devid;
+                usbdev->port = j + 1;
+                rc = 0;
+                goto out;
+            }
+        }
+    }
+
+    /* no available controller:port */
+    rc = ERROR_FAIL;
+
+out:
+    libxl_device_usbctrl_list_free(usbctrls, numctrl);
+    return rc;
+}
+
+/* Fill in usb information with default value.
+ *
+ * Generally, it does:
+ * 1) if "controller" is not specified:
+ *    - if "port" is not specified, try to find an available controller:port,
+ *      if found, use that; otherwise, create a new controller, use this
+ *      controller and its first port
+ *    - if "port" is specified, report error.
+ * 2) if "controller" is specified, but port is not specified:
+ *    try to find an available port under this controller, if found, use
+ *    that, otherwise, report error.
+ * 3) if both "controller" and "port" are specified:
+ *    check the controller:port is available, if not, report error.
+ */
+static int libxl__device_usbdev_setdefault(libxl__gc *gc,
+                                           uint32_t domid,
+                                           libxl_device_usbdev *usbdev,
+                                           bool update_json)
+{
+    int rc;
+
+    if (!usbdev->type)
+        usbdev->type = LIBXL_USBDEV_TYPE_HOSTDEV;
+
+    if (usbdev->ctrl == -1) {
+        if (usbdev->port) {
+            LOG(ERROR, "USB controller must be specified if you specify port");
+            return ERROR_INVAL;
+        }
+
+        rc = libxl__device_usbdev_set_default_usbctrl(gc, domid, usbdev);
+        /* If no existing controller to host this usb device, add a new one */
+        if (rc) {
+            libxl_device_usbctrl *usbctrl;
+
+            GCNEW(usbctrl);
+            libxl_device_usbctrl_init(usbctrl);
+            rc = libxl__device_usbctrl_setdefault(gc, domid, usbctrl);
+            if (rc < 0) goto out;
+
+            if (usbctrl->devid == -1) {
+                usbctrl->devid = libxl__device_nextid(gc, domid, "vusb");
+                if (usbctrl->devid < 0) {
+                    rc = ERROR_FAIL;
+                    goto out;
+                }
+            }
+
+            rc = libxl__device_usbctrl_add_xenstore(gc, domid, usbctrl,
+                                                    update_json);
+            if (rc) goto out;
+
+            usbdev->ctrl = usbctrl->devid;
+            usbdev->port = 1;
+        }
+    } else {
+        /* A controller was specified; look it up */
+        const char *fe_path, *be_path, *tmp;
+
+        fe_path = GCSPRINTF("%s/device/vusb/%d",
+                            libxl__xs_get_dompath(gc, domid),
+                            usbdev->ctrl);
+
+        be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
+        if (!be_path) {
+            rc = ERROR_FAIL;
+            goto out;
+        }
+
+        if (usbdev->port) {
+            /* A specific port was requested; see if it's available */
+            rc = libxl__xs_read_checked(gc, XBT_NULL,
+                                        GCSPRINTF("%s/port/%d",
+                                                  be_path, usbdev->port),
+                                        &tmp);
+            if (rc) goto out;
+
+            if (tmp && strcmp(tmp, "")) {
+                LOG(ERROR, "The controller port isn't available");
+                rc = ERROR_FAIL;
+                goto out;
+            }
+        } else {
+            /* No port was requested. Choose free port. */
+            int i, ports;
+
+            rc = libxl__xs_read_checked(gc, XBT_NULL,
+                                        GCSPRINTF("%s/num-ports", be_path), &tmp);
+            if (rc) goto out;
+
+            ports = tmp ? atoi(tmp) : 0;
+
+            for (i = 0; i < ports; i++) {
+                rc = libxl__xs_read_checked(gc, XBT_NULL,
+                                            GCSPRINTF("%s/port/%d", be_path, i + 1),
+                                            &tmp);
+                if (rc) goto out;
+
+                if (tmp && !strcmp(tmp, "")) {
+                    usbdev->port = i + 1;
+                    break;
+                }
+            }
+
+            if (!usbdev->port) {
+                LOG(ERROR, "No available port under specified controller");
+                rc = ERROR_FAIL;
+                goto out;
+            }
+        }
+    }
+
+    rc = 0;
+
+out:
+    return rc;
+}
+
+/* Add usb information to xenstore
+ *
+ * Adding a usb device won't create new 'vusb' device, but only write
+ * the device busid to the controller:port in xenstore.
+ */
+static int libxl__device_usbdev_add_xenstore(libxl__gc *gc, uint32_t domid,
+                                             libxl_device_usbdev *usbdev,
+                                             bool update_json)
+{
+    char *be_path, *busid;
+    int rc;
+    xs_transaction_t t = XBT_NULL;
+    libxl_domain_config d_config;
+    libxl_device_usbdev usbdev_saved;
+    libxl__domain_userdata_lock *lock = NULL;
+
+    libxl_domain_config_init(&d_config);
+    libxl_device_usbdev_init(&usbdev_saved);
+    libxl_device_usbdev_copy(CTX, &usbdev_saved, usbdev);
+
+    busid = usbdev_busaddr_to_busid(gc, usbdev->u.hostdev.hostbus,
+                                    usbdev->u.hostdev.hostaddr);
+    if (!busid) {
+        LOG(DEBUG, "Fail to get busid of usb device");
+        goto out;
+    }
+
+    if (update_json) {
+        lock = libxl__lock_domain_userdata(gc, domid);
+        if (!lock) {
+            rc = ERROR_LOCK_FAIL;
+            goto out;
+        }
+
+        rc = libxl__get_domain_configuration(gc, domid, &d_config);
+        if (rc) goto out;
+
+        DEVICE_ADD(usbdev, usbdevs, domid, &usbdev_saved,
+                   COMPARE_USB, &d_config);
+    }
+
+    for (;;) {
+        rc = libxl__xs_transaction_start(gc, &t);
+        if (rc) goto out;
+
+        if (update_json) {
+            rc = libxl__set_domain_configuration(gc, domid, &d_config);
+            if (rc) goto out;
+        }
+
+        be_path = GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
+                            libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
+                            domid, usbdev->ctrl, usbdev->port);
+
+        LOG(DEBUG, "Adding usb device %s to xenstore: controller %d, port %d",
+            busid, usbdev->ctrl, usbdev->port);
+
+        rc = libxl__xs_write_checked(gc, t, be_path, busid);
+        if (rc) goto out;
+
+        rc = libxl__xs_transaction_commit(gc, &t);
+        if (!rc) break;
+        if (rc < 0) goto out;
+    }
+
+    rc = 0;
+
+out:
+    if (lock) libxl__unlock_domain_userdata(lock);
+    libxl_device_usbdev_dispose(&usbdev_saved);
+    libxl_domain_config_dispose(&d_config);
+    return rc;
+}
+
+static int libxl__device_usbdev_remove_xenstore(libxl__gc *gc, uint32_t domid,
+                                                libxl_device_usbdev *usbdev)
+{
+    char *be_path;
+
+    be_path = GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
+                        libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
+                        domid, usbdev->ctrl, usbdev->port);
+
+    LOG(DEBUG, "Removing usb device from xenstore: controller %d, port %d",
+        usbdev->ctrl, usbdev->port);
+
+    return libxl__xs_write_checked(gc, XBT_NULL, be_path, "");
+}
+
+static char *usbdev_busid_from_ctrlport(libxl__gc *gc, uint32_t domid,
+                                        libxl_device_usbdev *usbdev)
+{
+    return libxl__xs_read(gc, XBT_NULL,
+                          GCSPRINTF("%s/backend/vusb/%d/%d/port/%d",
+                              libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID),
+                          domid, usbdev->ctrl, usbdev->port));
+}
+
+/* get original driver path of usb interface, stored in @drvpath */
+static int usbintf_get_drvpath(libxl__gc *gc, const char *intf, char **drvpath)
+{
+    char *spath, *dp = NULL;
+    struct stat st;
+    int r;
+
+    spath = GCSPRINTF(SYSFS_USB_DEV "/%s/driver", intf);
+
+    r = lstat(spath, &st);
+    if (r == 0) {
+        /* Find the canonical path to the driver. */
+        dp = libxl__zalloc(gc, PATH_MAX);
+        dp = realpath(spath, dp);
+        if (!dp) {
+            LOGE(ERROR, "get realpath failed: '%s'", spath);
+            return ERROR_FAIL;
+        }
+    } else if (errno == ENOENT) {
+        /* driver path doesn't exist */
+        dp = NULL;
+    } else {
+        LOGE(ERROR, "lstat failed: '%s'", spath);
+        return ERROR_FAIL;
+    }
+
+    *drvpath = dp;
+
+    return 0;
+}
+
+static int unbind_usbintf(libxl__gc *gc, const char *intf)
+{
+    char *path;
+    int fd = -1;
+    int rc;
+
+    path = GCSPRINTF(SYSFS_USB_DEV "/%s/driver/unbind", intf);
+
+    fd = open(path, O_WRONLY);
+    if (fd < 0) {
+        LOGE(ERROR, "open file failed: '%s'", path);
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    if (libxl_write_exactly(CTX, fd, intf, sizeof(intf), path, intf)) {
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = 0;
+
+out:
+    if (fd >= 0) close(fd);
+    return rc;
+}
+
+static int bind_usbintf(libxl__gc *gc, const char *intf, const char *drvpath)
+{
+    char *path;
+    struct stat st;
+    int fd = -1;
+    int rc, r;
+
+    path = GCSPRINTF("%s/%s", drvpath, intf);
+
+    /* check through lstat, if intf already exists under drvpath,
+     * it's already bound, return directly; if it doesn't exist,
+     * continue to do bind work; otherwise, return error.
+     */
+    r = lstat(path, &st);
+    if (r == 0)
+        return 0;
+    if (r < 0 && errno != ENOENT)
+        return ERROR_FAIL;
+
+    path = GCSPRINTF("%s/bind", drvpath);
+
+    fd = open(path, O_WRONLY);
+    if (fd < 0) {
+        LOGE(ERROR, "open file failed: '%s'", path);
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    if (libxl_write_exactly(CTX, fd, intf, sizeof(intf), path, intf)) {
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = 0;
+
+out:
+    if (fd >= 0) close(fd);
+    return rc;
+}
+
+/* Is usb interface bound to usbback? */
+static int usbintf_is_assigned(libxl__gc *gc, char *intf)
+{
+    char *spath;
+    int r;
+    struct stat st;
+
+    spath = GCSPRINTF(SYSFS_USBBACK_DRIVER "/%s", intf);
+    r = lstat(spath, &st);
+
+    if (r == 0)
+        return 1;
+    if (r < 0 && errno == ENOENT)
+        return 0;
+    LOGE(ERROR, "Accessing %s", spath);
+    return -1;
+}
+
+static int usbdev_get_all_interfaces(libxl__gc *gc, const char *busid,
+                                     char ***intfs, int *num)
+{
+    DIR *dir;
+    char *buf;
+    struct dirent *de_buf;
+    struct dirent *de;
+    int rc;
+
+    *intfs = NULL;
+    *num = 0;
+
+    buf = GCSPRINTF("%s:", busid);
+
+    dir = opendir(SYSFS_USB_DEV);
+    if (!dir) {
+        LOGE(ERROR, "opendir failed: '%s'", SYSFS_USB_DEV);
+        return ERROR_FAIL;
+    }
+
+    de_buf = zalloc_dirent(gc, SYSFS_USB_DEV);
+
+    for (;;) {
+        int r = readdir_r(dir, de_buf, &de);
+
+        if (r) {
+            LOGE(ERROR, "failed to readdir %s", SYSFS_USB_DEV);
+            rc = ERROR_FAIL;
+            goto out;
+        }
+        if (!de)
+            break;
+
+        if (!strcmp(de->d_name, ".") ||
+            !strcmp(de->d_name, ".."))
+            continue;
+
+        if (!strncmp(de->d_name, buf, strlen(buf))) {
+            GCREALLOC_ARRAY(*intfs, *num + 1);
+            (*intfs)[*num] = libxl__strdup(gc, de->d_name);
+            (*num)++;
+        }
+    }
+
+    rc = 0;
+
+out:
+    closedir(dir);
+    return rc;
+}
+
+/* Encode usb interface so that it could be written to xenstore as a key.
+ *
+ * Since xenstore key cannot include '.' or ':', we'll change '.' to '_',
+ * change ':' to '@'. For example, 3-1:2.1 will be encoded to 3-1@2_1.
+ * This will be used to save original driver of USB device to xenstore.
+ */
+static char *usb_interface_xenstore_encode(libxl__gc *gc, const char *busid)
+{
+    char *str = libxl__strdup(gc, busid);
+    int i, len = strlen(str);
+
+    for (i = 0; i < len; i++) {
+        if (str[i] == '.') str[i] = '_';
+        if (str[i] == ':') str[i] = '@';
+    }
+    return str;
+}
+
+/* Unbind USB device from "usbback" driver.
+ *
+ * If there are many interfaces under USB device, check each interface,
+ * unbind from "usbback" driver.
+ */
+static int usbback_dev_unassign(libxl__gc *gc, const char *busid)
+{
+    char **intfs = NULL;
+    int i, num = 0;
+    int rc;
+
+    rc = usbdev_get_all_interfaces(gc, busid, &intfs, &num);
+    if (rc) goto out;
+
+    for (i = 0; i < num; i++) {
+        char *intf = intfs[i];
+
+        /* check if the USB interface is already bound to "usbback" */
+        if (usbintf_is_assigned(gc, intf) > 0) {
+            /* unbind interface from usbback driver */
+            rc = unbind_usbintf(gc, intf);
+            if (rc) {
+                LOGE(ERROR, "Couldn't unbind %s from usbback", intf);
+                goto out;
+            }
+        }
+    }
+
+    rc = 0;
+
+out:
+    return rc;
+}
+
+/* rebind USB device to original driver.
+ *
+ * If there are many interfaces under USB device, for reach interface,
+ * read driver_path from xenstore (if there is) and rebind to its
+ * original driver, then remove driver_path information from xenstore.
+ */
+static int usbdev_rebind(libxl__gc *gc, const char *busid)
+{
+    char **intfs = NULL;
+    char *usbdev_encode = NULL;
+    char *path = NULL;
+    int i, num = 0;
+    int rc;
+
+    rc = usbdev_get_all_interfaces(gc, busid, &intfs, &num);
+    if (rc) goto out;
+
+    usbdev_encode = usb_interface_xenstore_encode(gc, busid);
+
+    for (i = 0; i < num; i++) {
+        char *intf = intfs[i];
+        char *usbintf_encode = NULL;
+        const char *drvpath;
+
+        /* rebind USB interface to its originial driver */
+        usbintf_encode = usb_interface_xenstore_encode(gc, intf);
+        path = GCSPRINTF(USBBACK_INFO_PATH "/%s/%s/driver_path",
+                         usbdev_encode, usbintf_encode);
+        rc = libxl__xs_read_checked(gc, XBT_NULL, path, &drvpath);
+        if (rc) goto out;
+
+        if (drvpath) {
+            rc = bind_usbintf(gc, intf, drvpath);
+            if (rc) {
+                LOGE(ERROR, "Couldn't rebind %s to %s", intf, drvpath);
+                goto out;
+            }
+        }
+    }
+
+out:
+    path = GCSPRINTF(USBBACK_INFO_PATH "/%s", usbdev_encode);
+    libxl__xs_rm_checked(gc, XBT_NULL, path);
+    return rc;
+}
+
+
+/* Bind USB device to "usbback" driver.
+ *
+ * If there are many interfaces under USB device, check each interface,
+ * unbind from original driver and bind to "usbback" driver.
+ */
+static int usbback_dev_assign(libxl__gc *gc, const char *busid)
+{
+    char **intfs = NULL;
+    int num = 0, i;
+    int rc;
+    char *usbdev_encode = NULL;
+
+    rc = usbdev_get_all_interfaces(gc, busid, &intfs, &num);
+    if (rc) return rc;
+
+    usbdev_encode = usb_interface_xenstore_encode(gc, busid);
+
+    for (i = 0; i < num; i++) {
+        char *intf = intfs[i];
+        char *drvpath = NULL;
+
+        /* already assigned to usbback */
+        if (usbintf_is_assigned(gc, intf) > 0)
+            continue;
+
+        rc = usbintf_get_drvpath(gc, intf, &drvpath);
+        if (rc) goto out;
+
+        if (drvpath) {
+            /* write driver path to xenstore for later rebinding */
+            char *usbintf_encode = NULL;
+            char *path;
+
+            usbintf_encode = usb_interface_xenstore_encode(gc, intf);
+            path = GCSPRINTF(USBBACK_INFO_PATH "/%s/%s/driver_path",
+                             usbdev_encode, usbintf_encode);
+            rc = libxl__xs_write_checked(gc, XBT_NULL, path, drvpath);
+            if (rc) goto out;
+
+            /* unbind interface from original driver */
+            rc = unbind_usbintf(gc, intf);
+            if (rc) goto out;
+        }
+
+        /* bind interface to usbback */
+        rc = bind_usbintf(gc, intf, SYSFS_USBBACK_DRIVER);
+        if (rc) {
+            LOG(ERROR, "Couldn't bind %s to %s", intf, SYSFS_USBBACK_DRIVER);
+            goto out;
+        }
+    }
+
+    return 0;
+
+out:
+    /* some interfaces might be bound to usbback, unbind it and
+     * rebind it to its original driver
+     */
+    usbback_dev_unassign(gc, busid);
+    usbdev_rebind(gc, busid);
+    return rc;
+}
+
+static int do_usbdev_add(libxl__gc *gc, uint32_t domid,
+                         libxl_device_usbdev *usbdev,
+                         bool update_json)
+{
+    int rc;
+    char *busid;
+    libxl_device_usbctrl usbctrl;
+    libxl_usbctrlinfo usbctrlinfo;
+
+    libxl_device_usbctrl_init(&usbctrl);
+    libxl_usbctrlinfo_init(&usbctrlinfo);
+    usbctrl.devid = usbdev->ctrl;
+
+    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
+    if (rc) goto out;
+
+    switch (usbctrlinfo.type) {
+    case LIBXL_USBCTRL_TYPE_PV:
+        busid = usbdev_busaddr_to_busid(gc, usbdev->u.hostdev.hostbus,
+                                        usbdev->u.hostdev.hostaddr);
+        if (!busid) {
+            rc = ERROR_FAIL;
+            goto out;
+        }
+
+        rc = libxl__device_usbdev_add_xenstore(gc, domid, usbdev, update_json);
+        if (rc) goto out;
+
+        rc = usbback_dev_assign(gc, busid);
+        if (rc) {
+            libxl__device_usbdev_remove_xenstore(gc, domid, usbdev);
+            goto out;
+        }
+        break;
+    case LIBXL_USBCTRL_TYPE_DEVICEMODEL:
+    default:
+        LOG(ERROR, "Unsupported usb controller type");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = 0;
+
+out:
+    libxl_device_usbctrl_dispose(&usbctrl);
+    libxl_usbctrlinfo_dispose(&usbctrlinfo);
+    return rc;
+}
+
+/* AO operation to add a usb device.
+ *
+ * Generally, it does:
+ * 1) check if the usb device type is assignable
+ * 2) check if the usb device is already assigned to a domain
+ * 3) add 'busid' of the usb device to xenstore contoller/port/.
+ *    (PVUSB driver watches the xenstore changes and will detect that.)
+ * 4) unbind usb device from original driver and bind to usbback.
+ *    If usb device has many interfaces, then:
+ *    - unbind each interface from its original driver and bind to usbback.
+ *    - store the original driver to xenstore for later rebinding when
+ *      detaching the device.
+ *
+ * Before calling this function, aodev should be properly filled:
+ * aodev->ao, aodev->callback, aodev->update_json, ...
+ */
+void libxl__device_usbdev_add(libxl__egc *egc, uint32_t domid,
+                              libxl_device_usbdev *usbdev,
+                              libxl__ao_device *aodev)
+{
+    STATE_AO_GC(aodev->ao);
+    int rc;
+    libxl_device_usbdev *assigned;
+    int num_assigned;
+    libxl_device_usbctrl usbctrl;
+    libxl_usbctrlinfo usbctrlinfo;
+
+    libxl_device_usbctrl_init(&usbctrl);
+    libxl_usbctrlinfo_init(&usbctrlinfo);
+
+    /* Currently only support adding USB device from Dom0 backend.
+     * So, if USB controller is specified, check its backend domain,
+     * if it's not Dom0, report error.
+     */
+    if (usbdev->ctrl != -1) {
+        usbctrl.devid = usbdev->ctrl;
+        rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
+        if (rc) goto out;
+
+        if (usbctrlinfo.backend_id != LIBXL_TOOLSTACK_DOMID) {
+            LOG(ERROR, "Don't support adding USB device from non-Dom0 backend");
+            rc = ERROR_INVAL;
+            goto out;
+        }
+    }
+
+    /* check usb device is assignable type */
+    if (!is_usbdev_assignable(gc, usbdev)) {
+        LOG(ERROR, "USB device is not assignable.");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    /* check usb device is already assigned */
+    rc = get_assigned_devices(gc, &assigned, &num_assigned);
+    if (rc) {
+        LOG(ERROR, "cannot determine if device is assigned,"
+                   " refusing to continue");
+        goto out;
+    }
+
+    if (is_usbdev_in_array(assigned, num_assigned, usbdev)) {
+        LOG(ERROR, "USB device already attached to a domain");
+        rc = ERROR_INVAL;
+        goto out;
+    }
+
+    /* fill default values, e.g, if usbdev->ctrl and usbdev->port
+     * not specified, choose available controller:port and fill in. */
+    rc = libxl__device_usbdev_setdefault(gc, domid, usbdev,
+                                         aodev->update_json);
+    if (rc) goto out;
+
+    /* do actual adding usb device operation */
+    rc = do_usbdev_add(gc, domid, usbdev, aodev->update_json);
+
+out:
+    libxl_device_usbctrl_dispose(&usbctrl);
+    libxl_usbctrlinfo_dispose(&usbctrlinfo);
+    aodev->rc = rc;
+    aodev->callback(egc, aodev);
+    return;
+}
+
+static int do_usbdev_remove(libxl__gc *gc, uint32_t domid,
+                            libxl_device_usbdev *usbdev)
+{
+    int rc;
+    char *busid;
+    libxl_device_usbctrl usbctrl;
+    libxl_usbctrlinfo usbctrlinfo;
+
+    libxl_device_usbctrl_init(&usbctrl);
+    libxl_usbctrlinfo_init(&usbctrlinfo);
+    usbctrl.devid = usbdev->ctrl;
+
+    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
+    if (rc) goto out;
+
+    switch (usbctrlinfo.type) {
+    case LIBXL_USBCTRL_TYPE_PV:
+        busid = usbdev_busid_from_ctrlport(gc, domid, usbdev);
+        if (!busid) {
+            rc = ERROR_FAIL;
+            goto out;
+        }
+
+        /* Things are done in order of:
+         *   unbind USB device from usbback,
+         *   remove USB device from xenstore,
+         *   rebind USB device to original driver.
+         * It is to balance simplicity with robustness in case of failure:
+         * - We unbind all interfaces before rebinding any interfaces, so
+         *   that we never get into a situation where some interfaces are
+         *   assigned to usbback and some are assigned to the original drivers.
+         * - We also unbind the interfaces before removing the pvusb xenstore
+         *   nodes, so that if the unbind fails in the middle, the device still
+         *   shows up in xl usb-list, and the user can re-try removing it.
+         */
+        rc = usbback_dev_unassign(gc, busid);
+        if (rc) {
+            LOG(ERROR, "Error removing device from guest."
+                " Try running usbdev-detach again.");
+            goto out;
+        }
+
+        rc = libxl__device_usbdev_remove_xenstore(gc, domid, usbdev);
+        if (rc) {
+            LOG(ERROR, "Error removing device from guest."
+                " Try running usbdev-detach again.");
+            goto out;
+        }
+
+        rc = usbdev_rebind(gc, busid);
+        if (rc) {
+            LOG(ERROR, "USB device removed from guest, but couldn't"
+                " re-bind to domain 0. Try removing and re-inserting"
+                " the USB device or reloading the driver modules.");
+            goto out;
+        }
+
+        break;
+    case LIBXL_USBCTRL_TYPE_DEVICEMODEL:
+    default:
+        LOG(ERROR, "Unsupported usb controller type");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = 0;
+
+out:
+    libxl_device_usbctrl_dispose(&usbctrl);
+    libxl_usbctrlinfo_dispose(&usbctrlinfo);
+    return rc;
+}
+
+/* Operation to remove usb device.
+ *
+ * Generally, it does:
+ * 1) check if the usb device is assigned to the domain
+ * 2) remove the usb device from xenstore controller/port.
+ * 3) unbind usb device from usbback and rebind to its original driver.
+ *    If usb device has many interfaces, do it to each interface.
+ */
+static int libxl__device_usbdev_remove(libxl__gc *gc, uint32_t domid,
+                                       libxl_device_usbdev *usbdev)
+{
+    libxl_usbctrlinfo usbctrlinfo;
+    libxl_device_usbctrl usbctrl;
+    int rc;
+
+    if (usbdev->ctrl < 0 || usbdev->port < 1) {
+        LOG(ERROR, "Invalid USB device");
+        return ERROR_FAIL;
+    }
+
+    libxl_device_usbctrl_init(&usbctrl);
+    libxl_usbctrlinfo_init(&usbctrlinfo);
+    usbctrl.devid = usbdev->ctrl;
+
+    rc = libxl_device_usbctrl_getinfo(CTX, domid, &usbctrl, &usbctrlinfo);
+    if (rc) goto out;
+
+    if (usbctrlinfo.backend_id != LIBXL_TOOLSTACK_DOMID) {
+        LOG(ERROR, "Don't support removing USB device from non-Dom0 backend");
+        rc = ERROR_INVAL;
+        goto out;
+    }
+
+    /* do actual removing usb device operation */
+    rc = do_usbdev_remove(gc, domid, usbdev);
+
+out:
+    libxl_device_usbctrl_dispose(&usbctrl);
+    libxl_usbctrlinfo_dispose(&usbctrlinfo);
+    return rc;
+}
+
+int libxl_device_usbdev_remove(libxl_ctx *ctx, uint32_t domid,
+                               libxl_device_usbdev *usbdev,
+                               const libxl_asyncop_how *ao_how)
+
+{
+    AO_CREATE(ctx, domid, ao_how);
+    int rc;
+
+    rc = libxl__device_usbdev_remove(gc, domid, usbdev);
+
+    libxl__ao_complete(egc, ao, rc);
+    return AO_INPROGRESS;
+}
+
+int libxl_ctrlport_to_device_usbdev(libxl_ctx *ctx,
+                                    uint32_t domid,
+                                    int ctrl,
+                                    int port,
+                                    libxl_device_usbdev *usbdev)
+{
+    GC_INIT(ctx);
+    const char *dompath, *fe_path, *be_path, *busid;
+    int rc;
+
+    dompath = libxl__xs_get_dompath(gc, domid);
+
+    fe_path = GCSPRINTF("%s/device/vusb/%d", dompath, ctrl);
+
+    be_path = vusb_be_from_xs_fe(gc, fe_path, domid);
+    if (!be_path) {
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    rc = libxl__xs_read_checked(gc, XBT_NULL,
+                           GCSPRINTF("%s/port/%d", be_path, port),
+                           &busid);
+    if (rc) goto out;
+
+    if (!busid || !strcmp(busid, "")) {
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    usbdev->ctrl = ctrl;
+    usbdev->port = port;
+    usbdev->type = LIBXL_USBDEV_TYPE_HOSTDEV;
+    rc = usbdev_busaddr_from_busid(gc, busid,
+                                   &usbdev->u.hostdev.hostbus,
+                                   &usbdev->u.hostdev.hostaddr);
+
+out:
+    GC_FREE;
+    return rc;
+}
+/*
+ * Local variables:
+ * mode: C
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 632c009..2a99eeb 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -613,6 +613,35 @@  libxl_device_rdm = Struct("device_rdm", [
     ("policy", libxl_rdm_reserve_policy),
     ])
 
+libxl_usbctrl_type = Enumeration("usbctrl_type", [
+    (0, "AUTO"),
+    (1, "PV"),
+    (2, "DEVICEMODEL"),
+    ])
+
+libxl_usbdev_type = Enumeration("usbdev_type", [
+    (1, "hostdev"),
+    ])
+
+libxl_device_usbctrl = Struct("device_usbctrl", [
+    ("type", libxl_usbctrl_type),
+    ("devid", libxl_devid),
+    ("version", integer),
+    ("ports", integer),
+    ("backend_domid", libxl_domid),
+    ("backend_domname", string),
+   ])
+
+libxl_device_usbdev = Struct("device_usbdev", [
+    ("ctrl", libxl_devid),
+    ("port", integer),
+    ("u", KeyedUnion(None, libxl_usbdev_type, "type",
+           [("hostdev", Struct(None, [
+                 ("hostbus",   uint8),
+                 ("hostaddr",  uint8)])),
+           ])),
+    ])
+
 libxl_device_dtdev = Struct("device_dtdev", [
     ("path", string),
     ])
@@ -651,6 +680,8 @@  libxl_domain_config = Struct("domain_config", [
     # a channel manifests as a console with a name,
     # see docs/misc/channels.txt
     ("channels", Array(libxl_device_channel, "num_channels")),
+    ("usbctrls", Array(libxl_device_usbctrl, "num_usbctrls")),
+    ("usbdevs", Array(libxl_device_usbdev, "num_usbdevs")),
 
     ("on_poweroff", libxl_action_on_shutdown),
     ("on_reboot", libxl_action_on_shutdown),
@@ -694,6 +725,21 @@  libxl_vtpminfo = Struct("vtpminfo", [
     ("uuid", libxl_uuid),
     ], dir=DIR_OUT)
 
+libxl_usbctrlinfo = Struct("usbctrlinfo", [
+    ("type", libxl_usbctrl_type),
+    ("devid", libxl_devid),
+    ("version", integer),
+    ("ports", integer),
+    ("backend", string),
+    ("backend_id", uint32),
+    ("frontend", string),
+    ("frontend_id", uint32),
+    ("state", integer),
+    ("evtch", integer),
+    ("ref_urb", integer),
+    ("ref_conn", integer),
+    ], dir=DIR_OUT)
+
 libxl_vcpuinfo = Struct("vcpuinfo", [
     ("vcpuid", uint32),
     ("cpu", uint32),
diff --git a/tools/libxl/libxl_types_internal.idl b/tools/libxl/libxl_types_internal.idl
index 5e55685..696f5f8 100644
--- a/tools/libxl/libxl_types_internal.idl
+++ b/tools/libxl/libxl_types_internal.idl
@@ -22,6 +22,7 @@  libxl__device_kind = Enumeration("device_kind", [
     (6, "VKBD"),
     (7, "CONSOLE"),
     (8, "VTPM"),
+    (9, "VUSB"),
     ])
 
 libxl__console_backend = Enumeration("console_backend", [
diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index b0cb9e1..ceb8825 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -1311,6 +1311,24 @@  int libxl__random_bytes(libxl__gc *gc, uint8_t *buf, size_t len)
     return ret;
 }
 
+void libxl_device_usbctrl_list_free(libxl_device_usbctrl *list, int nr)
+{
+   int i;
+
+   for (i = 0; i < nr; i++)
+       libxl_device_usbctrl_dispose(&list[i]);
+   free(list);
+}
+
+void libxl_device_usbdev_list_free(libxl_device_usbdev *list, int nr)
+{
+   int i;
+
+   for (i = 0; i < nr; i++)
+       libxl_device_usbdev_dispose(&list[i]);
+   free(list);
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/tools/libxl/libxl_utils.h b/tools/libxl/libxl_utils.h
index 339ebdf..4495417 100644
--- a/tools/libxl/libxl_utils.h
+++ b/tools/libxl/libxl_utils.h
@@ -76,6 +76,11 @@  int libxl_uuid_to_device_vtpm(libxl_ctx *ctx, uint32_t domid,
                                libxl_uuid *uuid, libxl_device_vtpm *vtpm);
 int libxl_devid_to_device_vtpm(libxl_ctx *ctx, uint32_t domid,
                                int devid, libxl_device_vtpm *vtpm);
+int libxl_devid_to_device_usbctrl(libxl_ctx *ctx, uint32_t domid,
+                                  int devid, libxl_device_usbctrl *usbctrl);
+int libxl_ctrlport_to_device_usbdev(libxl_ctx *ctx, uint32_t domid,
+                                    int ctrl, int port,
+                                    libxl_device_usbdev *usbdev);
 
 int libxl_bitmap_alloc(libxl_ctx *ctx, libxl_bitmap *bitmap, int n_bits);
     /* Allocated bimap is from malloc, libxl_bitmap_dispose() to be