[1/3] virtio: Basic implementation of virtio pstore driver

Commit Message

Namhyung Kim July 18, 2016, 4:37 a.m. UTC

The virtio pstore driver provides interface to the pstore subsystem so
that the guest kernel's log/dump message can be saved on the host
machine.  Users can access the log file directly on the host, or on the
guest at the next boot using pstore filesystem.  It currently deals with
kernel log (printk) buffer only, but we can extend it to have other
information (like ftrace dump) later.

It supports legacy PCI device using single order-2 page buffer.  As all
operation of pstore is synchronous, it would be fine IMHO.  However I
don't know how to make write operation synchronous since it's called
with a spinlock held (from any context including NMI).

Cc: Paolo Bonzini <[e-mail]>
Cc: Radim Krčmář <[e-mail]>
Cc: "Michael S. Tsirkin" <[e-mail]>
Cc: Anthony Liguori <[e-mail]>
Cc: Anton Vorontsov <[e-mail]>
Cc: Colin Cross <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Tony Luck <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>
---
 drivers/virtio/Kconfig             |  10 ++
 drivers/virtio/Makefile            |   1 +
 drivers/virtio/virtio_pstore.c     | 317 +++++++++++++++++++++++++++++++++++++
 include/uapi/linux/Kbuild          |   1 +
 include/uapi/linux/virtio_ids.h    |   1 +
 include/uapi/linux/virtio_pstore.h |  53 +++++++
 6 files changed, 383 insertions(+)
 create mode 100644 drivers/virtio/virtio_pstore.c
 create mode 100644 include/uapi/linux/virtio_pstore.h

Comments

Kees Cook July 18, 2016, 5:12 a.m. UTC | #1

On Sun, Jul 17, 2016 at 9:37 PM, Namhyung Kim <[e-mail]> wrote:
> The virtio pstore driver provides interface to the pstore subsystem so
> that the guest kernel's log/dump message can be saved on the host
> machine.  Users can access the log file directly on the host, or on the
> guest at the next boot using pstore filesystem.  It currently deals with
> kernel log (printk) buffer only, but we can extend it to have other
> information (like ftrace dump) later.
>
> It supports legacy PCI device using single order-2 page buffer.  As all
> operation of pstore is synchronous, it would be fine IMHO.  However I
> don't know how to make write operation synchronous since it's called
> with a spinlock held (from any context including NMI).
>
> Cc: Paolo Bonzini <[e-mail]>
> Cc: Radim Krčmář <[e-mail]>
> Cc: "Michael S. Tsirkin" <[e-mail]>
> Cc: Anthony Liguori <[e-mail]>
> Cc: Anton Vorontsov <[e-mail]>
> Cc: Colin Cross <[e-mail]>
> Cc: Kees Cook <[e-mail]>
> Cc: Tony Luck <[e-mail]>
> Cc: Steven Rostedt <[e-mail]>
> Cc: Ingo Molnar <[e-mail]>
> Cc: Minchan Kim <[e-mail]>
> Cc: [e-mail]
> Cc: [e-mail]
> Cc: [e-mail]
> Signed-off-by: Namhyung Kim <[e-mail]>

This looks great to me! I'd love to use this in qemu. (Right now I go
through hoops to use the ramoops backend for testing.)

Reviewed-by: Kees Cook <[e-mail]>

Notes below...

> ---
>  drivers/virtio/Kconfig             |  10 ++
>  drivers/virtio/Makefile            |   1 +
>  drivers/virtio/virtio_pstore.c     | 317 +++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/Kbuild          |   1 +
>  include/uapi/linux/virtio_ids.h    |   1 +
>  include/uapi/linux/virtio_pstore.h |  53 +++++++
>  6 files changed, 383 insertions(+)
>  create mode 100644 drivers/virtio/virtio_pstore.c
>  create mode 100644 include/uapi/linux/virtio_pstore.h
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 77590320d44c..8f0e6c796c12 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -58,6 +58,16 @@ config VIRTIO_INPUT
>
>          If unsure, say M.
>
> +config VIRTIO_PSTORE
> +       tristate "Virtio pstore driver"
> +       depends on VIRTIO
> +       depends on PSTORE
> +       ---help---
> +        This driver supports virtio pstore devices to save/restore
> +        panic and oops messages on the host.
> +
> +        If unsure, say M.
> +
>   config VIRTIO_MMIO
>         tristate "Platform bus driver for memory mapped virtio devices"
>         depends on HAS_IOMEM && HAS_DMA
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 41e30e3dc842..bee68cb26d48 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -5,3 +5,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
>  virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
>  obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
>  obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
> +obj-$(CONFIG_VIRTIO_PSTORE) += virtio_pstore.o
> diff --git a/drivers/virtio/virtio_pstore.c b/drivers/virtio/virtio_pstore.c
> new file mode 100644
> index 000000000000..6fe62c0f1508
> --- /dev/null
> +++ b/drivers/virtio/virtio_pstore.c
> @@ -0,0 +1,317 @@
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/pstore.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <uapi/linux/virtio_ids.h>
> +#include <uapi/linux/virtio_pstore.h>
> +
> +#define VIRT_PSTORE_ORDER    2
> +#define VIRT_PSTORE_BUFSIZE  (4096 << VIRT_PSTORE_ORDER)
> +
> +struct virtio_pstore {
> +       struct virtio_device    *vdev;
> +       struct virtqueue        *vq;
> +       struct pstore_info       pstore;
> +       struct virtio_pstore_hdr hdr;
> +       size_t                   buflen;
> +       u64                      id;
> +
> +       /* Waiting for host to ack */
> +       wait_queue_head_t       acked;
> +};
> +
> +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
> +{
> +       u16 ret;
> +
> +       switch (type) {
> +       case PSTORE_TYPE_DMESG:
> +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_DMESG);
> +               break;
> +       default:
> +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
> +               break;
> +       }

I would love to see this support PSTORE_TYPE_CONSOLE too. It should be
relatively easy to add: I think it'd just be another virtio command?

> +
> +       return ret;
> +}
> +
> +static enum pstore_type_id from_virtio_type(struct virtio_pstore *vps, u16 type)
> +{
> +       enum pstore_type_id ret;
> +
> +       switch (virtio16_to_cpu(vps->vdev, type)) {
> +       case VIRTIO_PSTORE_TYPE_DMESG:
> +               ret = PSTORE_TYPE_DMESG;
> +               break;
> +       default:
> +               ret = PSTORE_TYPE_UNKNOWN;
> +               break;
> +       }
> +
> +       return ret;
> +}
> +
> +static void virtpstore_ack(struct virtqueue *vq)
> +{
> +       struct virtio_pstore *vps = vq->vdev->priv;
> +
> +       wake_up(&vps->acked);
> +}
> +
> +static int virt_pstore_open(struct pstore_info *psi)
> +{
> +       struct virtio_pstore *vps = psi->data;
> +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> +       struct scatterlist sg[1];
> +       unsigned int len;
> +
> +       hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_OPEN);
> +
> +       sg_init_one(sg, hdr, sizeof(*hdr));
> +       virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
> +       virtqueue_kick(vps->vq);
> +
> +       wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
> +       return 0;
> +}
> +
> +static int virt_pstore_close(struct pstore_info *psi)
> +{
> +       struct virtio_pstore *vps = psi->data;
> +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> +       struct scatterlist sg[1];
> +       unsigned int len;
> +
> +       hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_CLOSE);
> +
> +       sg_init_one(sg, hdr, sizeof(*hdr));
> +       virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
> +       virtqueue_kick(vps->vq);
> +
> +       wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
> +       return 0;
> +}
> +
> +static ssize_t virt_pstore_read(u64 *id, enum pstore_type_id *type,
> +                               int *count, struct timespec *time,
> +                               char **buf, bool *compressed,
> +                               struct pstore_info *psi)
> +{
> +       struct virtio_pstore *vps = psi->data;
> +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> +       struct scatterlist sgi[1], sgo[1];
> +       struct scatterlist *sgs[2] = { sgo, sgi };
> +       unsigned int len;
> +       unsigned int flags;
> +       void *bf;
> +
> +       hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_READ);
> +
> +       sg_init_one(sgo, hdr, sizeof(*hdr));
> +       sg_init_one(sgi, psi->buf, psi->bufsize);
> +       virtqueue_add_sgs(vps->vq, sgs, 1, 1, vps, GFP_KERNEL);
> +       virtqueue_kick(vps->vq);
> +
> +       wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
> +       if (len == 0)
> +               return 0;
> +
> +       bf = kmalloc(len, GFP_KERNEL);
> +       if (bf == NULL)
> +               return -ENOMEM;
> +
> +       *id = virtio64_to_cpu(vps->vdev, hdr->id);
> +       *type = from_virtio_type(vps, hdr->type);
> +
> +       flags = virtio32_to_cpu(vps->vdev, hdr->flags);
> +       *compressed = flags & VIRTIO_PSTORE_FL_COMPRESSED;
> +       *count = 1;
> +
> +       time->tv_sec  = virtio64_to_cpu(vps->vdev, hdr->time_sec);
> +       time->tv_nsec = virtio32_to_cpu(vps->vdev, hdr->time_nsec);
> +
> +       memcpy(bf, psi->buf, len);
> +       *buf = bf;
> +
> +       return len;
> +}
> +
> +static int notrace virt_pstore_write(enum pstore_type_id type,
> +                                    enum kmsg_dump_reason reason,
> +                                    u64 *id, unsigned int part, int count,
> +                                    bool compressed, size_t size,
> +                                    struct pstore_info *psi)
> +{
> +       struct virtio_pstore *vps = psi->data;
> +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> +       struct scatterlist sg[2];
> +       unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
> +
> +       *id = vps->id++;
> +
> +       hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
> +       hdr->id    = cpu_to_virtio64(vps->vdev, *id);
> +       hdr->flags = cpu_to_virtio32(vps->vdev, flags);
> +       hdr->type  = to_virtio_type(vps, type);
> +
> +       sg_init_table(sg, 2);
> +       sg_set_buf(&sg[0], hdr, sizeof(*hdr));
> +       sg_set_buf(&sg[1], psi->buf, size);
> +       virtqueue_add_outbuf(vps->vq, sg, 2, vps, GFP_ATOMIC);
> +       virtqueue_kick(vps->vq);
> +
> +       /* TODO: make it synchronous */
> +       return 0;

The down side to this being asynchronous is the lack of error
reporting. Perhaps this could check hdr->type before queuing and error
for any VIRTIO_PSTORE_TYPE_UNKNOWN message instead of trying to send
it?

> +}
> +
> +static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
> +                            struct timespec time, struct pstore_info *psi)
> +{
> +       struct virtio_pstore *vps = psi->data;
> +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> +       struct scatterlist sg[1];
> +       unsigned int len;
> +
> +       hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
> +       hdr->id    = cpu_to_virtio64(vps->vdev, id);
> +       hdr->type  = to_virtio_type(vps, type);
> +
> +       sg_init_one(sg, hdr, sizeof(*hdr));
> +       virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
> +       virtqueue_kick(vps->vq);
> +
> +       wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
> +       return 0;
> +}
> +
> +static int virt_pstore_init(struct virtio_pstore *vps)
> +{
> +       struct pstore_info *psinfo = &vps->pstore;
> +       int err;
> +
> +       vps->id = 0;
> +       vps->buflen = 0;
> +       psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
> +       psinfo->buf = (void *)__get_free_pages(GFP_KERNEL, VIRT_PSTORE_ORDER);
> +       if (!psinfo->buf) {
> +               pr_err("cannot allocate pstore buffer\n");
> +               return -ENOMEM;
> +       }
> +
> +       psinfo->owner = THIS_MODULE;
> +       psinfo->name  = "virtio";
> +       psinfo->open  = virt_pstore_open;
> +       psinfo->close = virt_pstore_close;
> +       psinfo->read  = virt_pstore_read;
> +       psinfo->erase = virt_pstore_erase;
> +       psinfo->write = virt_pstore_write;
> +       psinfo->flags = PSTORE_FLAGS_FRAGILE;

For console support, this flag would need to be dropped -- though I
suspect you know that already.:)

> +       psinfo->data  = vps;
> +       spin_lock_init(&psinfo->buf_lock);
> +
> +       err = pstore_register(psinfo);
> +       if (err)
> +               kfree(psinfo->buf);
> +
> +       return err;
> +}
> +
> +static int virt_pstore_exit(struct virtio_pstore *vps)
> +{
> +       struct pstore_info *psinfo = &vps->pstore;
> +
> +       pstore_unregister(psinfo);
> +
> +       free_pages((unsigned long)psinfo->buf, VIRT_PSTORE_ORDER);
> +       psinfo->bufsize = 0;
> +
> +       return 0;
> +}
> +
> +static int virtpstore_probe(struct virtio_device *vdev)
> +{
> +       struct virtio_pstore *vps;
> +       int err;
> +
> +       if (!vdev->config->get) {
> +               dev_err(&vdev->dev, "%s failure: config access disabled\n",
> +                       __func__);
> +               return -EINVAL;
> +       }
> +
> +       vdev->priv = vps = kmalloc(sizeof(*vps), GFP_KERNEL);
> +       if (!vps) {
> +               err = -ENOMEM;
> +               goto out;
> +       }
> +
> +       vps->vdev = vdev;
> +
> +       vps->vq = virtio_find_single_vq(vdev, virtpstore_ack, "pstore");
> +       if (IS_ERR(vps->vq)) {
> +               err = PTR_ERR(vps->vq);
> +               goto out_free;
> +       }
> +
> +       err = virt_pstore_init(vps);
> +       if (err)
> +               goto out_del_vq;
> +
> +       init_waitqueue_head(&vps->acked);
> +
> +       virtio_device_ready(vdev);
> +       dev_info(&vdev->dev, "virtio pstore driver init: ok\n");
> +
> +       return 0;
> +
> +out_del_vq:
> +       vdev->config->del_vqs(vdev);
> +out_free:
> +       kfree(vps);
> +out:
> +       dev_err(&vdev->dev, "virtio pstore driver init: failed with %d\n", err);
> +       return err;
> +}
> +
> +static void virtpstore_remove(struct virtio_device *vdev)
> +{
> +       struct virtio_pstore *vps = vdev->priv;
> +
> +       virt_pstore_exit(vps);
> +
> +       /* Now we reset the device so we can clean up the queues. */
> +       vdev->config->reset(vdev);
> +
> +       vdev->config->del_vqs(vdev);
> +
> +       kfree(vps);
> +}
> +
> +static unsigned int features[] = {
> +};
> +
> +static struct virtio_device_id id_table[] = {
> +       { VIRTIO_ID_PSTORE, VIRTIO_DEV_ANY_ID },
> +       { 0 },
> +};
> +
> +static struct virtio_driver virtio_pstore_driver = {
> +       .driver.name         = KBUILD_MODNAME,
> +       .driver.owner        = THIS_MODULE,
> +       .feature_table       = features,
> +       .feature_table_size  = ARRAY_SIZE(features),
> +       .id_table            = id_table,
> +       .probe               = virtpstore_probe,
> +       .remove              = virtpstore_remove,
> +};
> +
> +module_virtio_driver(virtio_pstore_driver);
> +MODULE_DEVICE_TABLE(virtio, id_table);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Namhyung Kim <[e-mail]>");
> +MODULE_DESCRIPTION("Virtio pstore driver");
> diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
> index 8bdae34d1f9a..57b0d08db322 100644
> --- a/include/uapi/linux/Kbuild
> +++ b/include/uapi/linux/Kbuild
> @@ -448,6 +448,7 @@ header-y += virtio_ids.h
>  header-y += virtio_input.h
>  header-y += virtio_net.h
>  header-y += virtio_pci.h
> +header-y += virtio_pstore.h
>  header-y += virtio_ring.h
>  header-y += virtio_rng.h
>  header-y += virtio_scsi.h
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index 77925f587b15..cba63225d85a 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -41,5 +41,6 @@
>  #define VIRTIO_ID_CAIF        12 /* Virtio caif */
>  #define VIRTIO_ID_GPU          16 /* virtio GPU */
>  #define VIRTIO_ID_INPUT        18 /* virtio input */
> +#define VIRTIO_ID_PSTORE       19 /* virtio pstore */
>
>  #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/include/uapi/linux/virtio_pstore.h b/include/uapi/linux/virtio_pstore.h
> new file mode 100644
> index 000000000000..0aa1575ee35f
> --- /dev/null
> +++ b/include/uapi/linux/virtio_pstore.h
> @@ -0,0 +1,53 @@
> +#ifndef _LINUX_VIRTIO_PSTORE_H
> +#define _LINUX_VIRTIO_PSTORE_H
> +/* This header is BSD licensed so anyone can use the definitions to implement
> + * compatible drivers/servers.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + * 3. Neither the name of IBM nor the names of its contributors
> + *    may be used to endorse or promote products derived from this software
> + *    without specific prior written permission.
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
> + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
> + * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
> + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
> + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
> + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
> + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
> + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
> + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE. */
> +#include <linux/types.h>
> +#include <linux/virtio_types.h>
> +
> +#define VIRTIO_PSTORE_CMD_NULL   0
> +#define VIRTIO_PSTORE_CMD_OPEN   1
> +#define VIRTIO_PSTORE_CMD_READ   2
> +#define VIRTIO_PSTORE_CMD_WRITE  3
> +#define VIRTIO_PSTORE_CMD_ERASE  4
> +#define VIRTIO_PSTORE_CMD_CLOSE  5
> +
> +#define VIRTIO_PSTORE_TYPE_UNKNOWN  0
> +#define VIRTIO_PSTORE_TYPE_DMESG    1
> +
> +#define VIRTIO_PSTORE_FL_COMPRESSED  1
> +
> +struct virtio_pstore_hdr {
> +       __virtio64              id;
> +       __virtio32              flags;
> +       __virtio16              cmd;
> +       __virtio16              type;
> +       __virtio64              time_sec;
> +       __virtio32              time_nsec;
> +       __virtio32              unused;
> +};
> +
> +#endif /* _LINUX_VIRTIO_PSTORE_H */
> --
> 2.8.0
>

Awesome! Can't wait to use it. :)

-Kees

Namhyung Kim July 18, 2016, 5:50 a.m. UTC | #2

Hello,

On Sun, Jul 17, 2016 at 10:12:26PM -0700, Kees Cook wrote:
> On Sun, Jul 17, 2016 at 9:37 PM, Namhyung Kim <[e-mail]> wrote:
> > The virtio pstore driver provides interface to the pstore subsystem so
> > that the guest kernel's log/dump message can be saved on the host
> > machine.  Users can access the log file directly on the host, or on the
> > guest at the next boot using pstore filesystem.  It currently deals with
> > kernel log (printk) buffer only, but we can extend it to have other
> > information (like ftrace dump) later.
> >
> > It supports legacy PCI device using single order-2 page buffer.  As all
> > operation of pstore is synchronous, it would be fine IMHO.  However I
> > don't know how to make write operation synchronous since it's called
> > with a spinlock held (from any context including NMI).
> >
> > Cc: Paolo Bonzini <[e-mail]>
> > Cc: Radim Kr??m???? <[e-mail]>
> > Cc: "Michael S. Tsirkin" <[e-mail]>
> > Cc: Anthony Liguori <[e-mail]>
> > Cc: Anton Vorontsov <[e-mail]>
> > Cc: Colin Cross <[e-mail]>
> > Cc: Kees Cook <[e-mail]>
> > Cc: Tony Luck <[e-mail]>
> > Cc: Steven Rostedt <[e-mail]>
> > Cc: Ingo Molnar <[e-mail]>
> > Cc: Minchan Kim <[e-mail]>
> > Cc: [e-mail]
> > Cc: [e-mail]
> > Cc: [e-mail]
> > Signed-off-by: Namhyung Kim <[e-mail]>
> 
> This looks great to me! I'd love to use this in qemu. (Right now I go
> through hoops to use the ramoops backend for testing.)
> 
> Reviewed-by: Kees Cook <[e-mail]>

Thank you!

> 
> Notes below...
>

[SNIP]
> > +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
> > +{
> > +       u16 ret;
> > +
> > +       switch (type) {
> > +       case PSTORE_TYPE_DMESG:
> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_DMESG);
> > +               break;
> > +       default:
> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
> > +               break;
> > +       }
> 
> I would love to see this support PSTORE_TYPE_CONSOLE too. It should be
> relatively easy to add: I think it'd just be another virtio command?

Do you want to append the data to the host file as guest does
printk()?  I think it needs some kind of buffer management, but it's
not hard to add IMHO.


> 
> > +
> > +       return ret;
> > +}
> > +

[SNIP]
> > +static int notrace virt_pstore_write(enum pstore_type_id type,
> > +                                    enum kmsg_dump_reason reason,
> > +                                    u64 *id, unsigned int part, int count,
> > +                                    bool compressed, size_t size,
> > +                                    struct pstore_info *psi)
> > +{
> > +       struct virtio_pstore *vps = psi->data;
> > +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> > +       struct scatterlist sg[2];
> > +       unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
> > +
> > +       *id = vps->id++;
> > +
> > +       hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
> > +       hdr->id    = cpu_to_virtio64(vps->vdev, *id);
> > +       hdr->flags = cpu_to_virtio32(vps->vdev, flags);
> > +       hdr->type  = to_virtio_type(vps, type);
> > +
> > +       sg_init_table(sg, 2);
> > +       sg_set_buf(&sg[0], hdr, sizeof(*hdr));
> > +       sg_set_buf(&sg[1], psi->buf, size);
> > +       virtqueue_add_outbuf(vps->vq, sg, 2, vps, GFP_ATOMIC);
> > +       virtqueue_kick(vps->vq);
> > +
> > +       /* TODO: make it synchronous */
> > +       return 0;
> 
> The down side to this being asynchronous is the lack of error
> reporting. Perhaps this could check hdr->type before queuing and error
> for any VIRTIO_PSTORE_TYPE_UNKNOWN message instead of trying to send
> it?

I cannot follow, sorry.  Could you please elaborate it more?


> 
> > +}
> > +
> > +static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
> > +                            struct timespec time, struct pstore_info *psi)
> > +{
> > +       struct virtio_pstore *vps = psi->data;
> > +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> > +       struct scatterlist sg[1];
> > +       unsigned int len;
> > +
> > +       hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
> > +       hdr->id    = cpu_to_virtio64(vps->vdev, id);
> > +       hdr->type  = to_virtio_type(vps, type);
> > +
> > +       sg_init_one(sg, hdr, sizeof(*hdr));
> > +       virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
> > +       virtqueue_kick(vps->vq);
> > +
> > +       wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
> > +       return 0;
> > +}
> > +
> > +static int virt_pstore_init(struct virtio_pstore *vps)
> > +{
> > +       struct pstore_info *psinfo = &vps->pstore;
> > +       int err;
> > +
> > +       vps->id = 0;
> > +       vps->buflen = 0;
> > +       psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
> > +       psinfo->buf = (void *)__get_free_pages(GFP_KERNEL, VIRT_PSTORE_ORDER);
> > +       if (!psinfo->buf) {
> > +               pr_err("cannot allocate pstore buffer\n");
> > +               return -ENOMEM;
> > +       }
> > +
> > +       psinfo->owner = THIS_MODULE;
> > +       psinfo->name  = "virtio";
> > +       psinfo->open  = virt_pstore_open;
> > +       psinfo->close = virt_pstore_close;
> > +       psinfo->read  = virt_pstore_read;
> > +       psinfo->erase = virt_pstore_erase;
> > +       psinfo->write = virt_pstore_write;
> > +       psinfo->flags = PSTORE_FLAGS_FRAGILE;
> 
> For console support, this flag would need to be dropped -- though I
> suspect you know that already.:)

Yep, I intentionally support DMESG type only in this patchset for
simplicity.  Others could be added later. :)


> 
> > +       psinfo->data  = vps;
> > +       spin_lock_init(&psinfo->buf_lock);
> > +
> > +       err = pstore_register(psinfo);
> > +       if (err)
> > +               kfree(psinfo->buf);
> > +
> > +       return err;
> > +}

[SNIP]
> 
> Awesome! Can't wait to use it. :)

Thanks for your review! :)

Thanks,
Namhyung

> 
> -Kees
> 
> -- 
> Kees Cook
> Chrome OS & Brillo Security
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Cornelia Huck July 18, 2016, 7:54 a.m. UTC | #3

On Mon, 18 Jul 2016 13:37:39 +0900
Namhyung Kim <[e-mail]> wrote:

> The virtio pstore driver provides interface to the pstore subsystem so
> that the guest kernel's log/dump message can be saved on the host
> machine.  Users can access the log file directly on the host, or on the
> guest at the next boot using pstore filesystem.  It currently deals with
> kernel log (printk) buffer only, but we can extend it to have other
> information (like ftrace dump) later.

Like the idea.

> 
> It supports legacy PCI device using single order-2 page buffer.  As all

There should not be anything in there that limits this to pci, no?

> operation of pstore is synchronous, it would be fine IMHO.  However I
> don't know how to make write operation synchronous since it's called
> with a spinlock held (from any context including NMI).
> 
> Cc: Paolo Bonzini <[e-mail]>
> Cc: Radim Krčmář <[e-mail]>
> Cc: "Michael S. Tsirkin" <[e-mail]>
> Cc: Anthony Liguori <[e-mail]>
> Cc: Anton Vorontsov <[e-mail]>
> Cc: Colin Cross <[e-mail]>
> Cc: Kees Cook <[e-mail]>
> Cc: Tony Luck <[e-mail]>
> Cc: Steven Rostedt <[e-mail]>
> Cc: Ingo Molnar <[e-mail]>
> Cc: Minchan Kim <[e-mail]>
> Cc: [e-mail]
> Cc: [e-mail]
> Cc: [e-mail]
> Signed-off-by: Namhyung Kim <[e-mail]>
> ---
>  drivers/virtio/Kconfig             |  10 ++
>  drivers/virtio/Makefile            |   1 +
>  drivers/virtio/virtio_pstore.c     | 317 +++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/Kbuild          |   1 +
>  include/uapi/linux/virtio_ids.h    |   1 +
>  include/uapi/linux/virtio_pstore.h |  53 +++++++
>  6 files changed, 383 insertions(+)
>  create mode 100644 drivers/virtio/virtio_pstore.c
>  create mode 100644 include/uapi/linux/virtio_pstore.h
> 

(...)

> diff --git a/drivers/virtio/virtio_pstore.c b/drivers/virtio/virtio_pstore.c
> new file mode 100644
> index 000000000000..6fe62c0f1508
> --- /dev/null
> +++ b/drivers/virtio/virtio_pstore.c
> @@ -0,0 +1,317 @@
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/pstore.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <uapi/linux/virtio_ids.h>
> +#include <uapi/linux/virtio_pstore.h>
> +
> +#define VIRT_PSTORE_ORDER    2
> +#define VIRT_PSTORE_BUFSIZE  (4096 << VIRT_PSTORE_ORDER)

It may make sense to make the size of the buffer configurable through
the config space.

(...)

> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index 77925f587b15..cba63225d85a 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -41,5 +41,6 @@
>  #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
>  #define VIRTIO_ID_GPU          16 /* virtio GPU */
>  #define VIRTIO_ID_INPUT        18 /* virtio input */
> +#define VIRTIO_ID_PSTORE       19 /* virtio pstore */

This id is already used by one of the new device types queued but not
yet in the standard. IIRC, 22 is the next free one.

Speaking of the standard: I think it makes sense to at least reserve a
device id for pstore, as the idea is sound. Maybe prepare a patch to
the standard as well if you have time?

>  
>  #endif /* _LINUX_VIRTIO_IDS_H */

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Namhyung Kim July 18, 2016, 8:29 a.m. UTC | #4

Hello,

On Mon, Jul 18, 2016 at 09:54:39AM +0200, Cornelia Huck wrote:
> On Mon, 18 Jul 2016 13:37:39 +0900
> Namhyung Kim <[e-mail]> wrote:
> 
> > The virtio pstore driver provides interface to the pstore subsystem so
> > that the guest kernel's log/dump message can be saved on the host
> > machine.  Users can access the log file directly on the host, or on the
> > guest at the next boot using pstore filesystem.  It currently deals with
> > kernel log (printk) buffer only, but we can extend it to have other
> > information (like ftrace dump) later.
> 
> Like the idea.

Thanks!

> 
> > 
> > It supports legacy PCI device using single order-2 page buffer.  As all
> 
> There should not be anything in there that limits this to pci, no?

Yep, there's no restriction AFAIK.  I just choose it to implement the poc
code quickly.

> 
> > operation of pstore is synchronous, it would be fine IMHO.  However I
> > don't know how to make write operation synchronous since it's called
> > with a spinlock held (from any context including NMI).
> > 
> > Cc: Paolo Bonzini <[e-mail]>
> > Cc: Radim Kr??m???? <[e-mail]>
> > Cc: "Michael S. Tsirkin" <[e-mail]>
> > Cc: Anthony Liguori <[e-mail]>
> > Cc: Anton Vorontsov <[e-mail]>
> > Cc: Colin Cross <[e-mail]>
> > Cc: Kees Cook <[e-mail]>
> > Cc: Tony Luck <[e-mail]>
> > Cc: Steven Rostedt <[e-mail]>
> > Cc: Ingo Molnar <[e-mail]>
> > Cc: Minchan Kim <[e-mail]>
> > Cc: [e-mail]
> > Cc: [e-mail]
> > Cc: [e-mail]
> > Signed-off-by: Namhyung Kim <[e-mail]>
> > ---
> >  drivers/virtio/Kconfig             |  10 ++
> >  drivers/virtio/Makefile            |   1 +
> >  drivers/virtio/virtio_pstore.c     | 317 +++++++++++++++++++++++++++++++++++++
> >  include/uapi/linux/Kbuild          |   1 +
> >  include/uapi/linux/virtio_ids.h    |   1 +
> >  include/uapi/linux/virtio_pstore.h |  53 +++++++
> >  6 files changed, 383 insertions(+)
> >  create mode 100644 drivers/virtio/virtio_pstore.c
> >  create mode 100644 include/uapi/linux/virtio_pstore.h
> > 
> 
> (...)
> 
> > diff --git a/drivers/virtio/virtio_pstore.c b/drivers/virtio/virtio_pstore.c
> > new file mode 100644
> > index 000000000000..6fe62c0f1508
> > --- /dev/null
> > +++ b/drivers/virtio/virtio_pstore.c
> > @@ -0,0 +1,317 @@
> > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/pstore.h>
> > +#include <linux/virtio.h>
> > +#include <linux/virtio_config.h>
> > +#include <uapi/linux/virtio_ids.h>
> > +#include <uapi/linux/virtio_pstore.h>
> > +
> > +#define VIRT_PSTORE_ORDER    2
> > +#define VIRT_PSTORE_BUFSIZE  (4096 << VIRT_PSTORE_ORDER)
> 
> It may make sense to make the size of the buffer configurable through
> the config space.

Right.  I'm considering it too, but it needs a buffer larger than
kmsg_bytes (= 10K) to work properly in the current implementation.  As
this version is just to verify the idea is sane and useful, I used a
fixed size buffer.  Will change in the next version.

> 
> (...)
> 
> > diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> > index 77925f587b15..cba63225d85a 100644
> > --- a/include/uapi/linux/virtio_ids.h
> > +++ b/include/uapi/linux/virtio_ids.h
> > @@ -41,5 +41,6 @@
> >  #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
> >  #define VIRTIO_ID_GPU          16 /* virtio GPU */
> >  #define VIRTIO_ID_INPUT        18 /* virtio input */
> > +#define VIRTIO_ID_PSTORE       19 /* virtio pstore */
> 
> This id is already used by one of the new device types queued but not
> yet in the standard. IIRC, 22 is the next free one.

Ok, will update.

> 
> Speaking of the standard: I think it makes sense to at least reserve a
> device id for pstore, as the idea is sound. Maybe prepare a patch to
> the standard as well if you have time?

I'd love to.  As I mentioned earlier, I don't have enough knowledge in
this area.  Could you please provide some links about how can I do that?

Thanks,
Namhyung
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Cornelia Huck July 18, 2016, 9:02 a.m. UTC | #5

On Mon, 18 Jul 2016 17:29:55 +0900
Namhyung Kim <[e-mail]> wrote:

> On Mon, Jul 18, 2016 at 09:54:39AM +0200, Cornelia Huck wrote:
> > On Mon, 18 Jul 2016 13:37:39 +0900
> > Namhyung Kim <[e-mail]> wrote:

> > > +#define VIRT_PSTORE_ORDER    2
> > > +#define VIRT_PSTORE_BUFSIZE  (4096 << VIRT_PSTORE_ORDER)
> > 
> > It may make sense to make the size of the buffer configurable through
> > the config space.
> 
> Right.  I'm considering it too, but it needs a buffer larger than
> kmsg_bytes (= 10K) to work properly in the current implementation.  As
> this version is just to verify the idea is sane and useful, I used a
> fixed size buffer.  Will change in the next version.

Sure, that makes sense for a prototype. We can guard any config space
entry with a feature bit, but this one makes sense to add from the
beginning.

> > Speaking of the standard: I think it makes sense to at least reserve a
> > device id for pstore, as the idea is sound. Maybe prepare a patch to
> > the standard as well if you have time?
> 
> I'd love to.  As I mentioned earlier, I don't have enough knowledge in
> this area.  Could you please provide some links about how can I do that?

See the virtio page at OASIS
(https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio)
for a link to our subversion (yes...) repository. Just do two patches:
one to reserve a device id, and one that specifies how device and
driver work. (For examples, look at the proposed device types that have
been posted to the virtualization lists, e.g. virtio-crypto or
virtio-sdm). You just need to be patient, we're currently a bit
stalled...

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Kees Cook July 18, 2016, 5:50 p.m. UTC | #6

On Sun, Jul 17, 2016 at 10:50 PM, Namhyung Kim <[e-mail]> wrote:
> Hello,
>
> On Sun, Jul 17, 2016 at 10:12:26PM -0700, Kees Cook wrote:
>> On Sun, Jul 17, 2016 at 9:37 PM, Namhyung Kim <[e-mail]> wrote:
>> > The virtio pstore driver provides interface to the pstore subsystem so
>> > that the guest kernel's log/dump message can be saved on the host
>> > machine.  Users can access the log file directly on the host, or on the
>> > guest at the next boot using pstore filesystem.  It currently deals with
>> > kernel log (printk) buffer only, but we can extend it to have other
>> > information (like ftrace dump) later.
>> >
>> > It supports legacy PCI device using single order-2 page buffer.  As all
>> > operation of pstore is synchronous, it would be fine IMHO.  However I
>> > don't know how to make write operation synchronous since it's called
>> > with a spinlock held (from any context including NMI).
>> >
>> > Cc: Paolo Bonzini <[e-mail]>
>> > Cc: Radim Kr??m???? <[e-mail]>
>> > Cc: "Michael S. Tsirkin" <[e-mail]>
>> > Cc: Anthony Liguori <[e-mail]>
>> > Cc: Anton Vorontsov <[e-mail]>
>> > Cc: Colin Cross <[e-mail]>
>> > Cc: Kees Cook <[e-mail]>
>> > Cc: Tony Luck <[e-mail]>
>> > Cc: Steven Rostedt <[e-mail]>
>> > Cc: Ingo Molnar <[e-mail]>
>> > Cc: Minchan Kim <[e-mail]>
>> > Cc: [e-mail]
>> > Cc: [e-mail]
>> > Cc: [e-mail]
>> > Signed-off-by: Namhyung Kim <[e-mail]>
>>
>> This looks great to me! I'd love to use this in qemu. (Right now I go
>> through hoops to use the ramoops backend for testing.)
>>
>> Reviewed-by: Kees Cook <[e-mail]>
>
> Thank you!
>
>>
>> Notes below...
>>
>
> [SNIP]
>> > +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
>> > +{
>> > +       u16 ret;
>> > +
>> > +       switch (type) {
>> > +       case PSTORE_TYPE_DMESG:
>> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_DMESG);
>> > +               break;
>> > +       default:
>> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
>> > +               break;
>> > +       }
>>
>> I would love to see this support PSTORE_TYPE_CONSOLE too. It should be
>> relatively easy to add: I think it'd just be another virtio command?
>
> Do you want to append the data to the host file as guest does
> printk()?  I think it needs some kind of buffer management, but it's
> not hard to add IMHO.

Well, with most pstore backends, the buffer size is limited, so it
tends to be a circular buffer of some sort. I think whatever you
choose to do is fine (I saw the various mentions of resource limits in
the qemu part of this thread), as long as the last N bytes of console
can be seen on the host side, where N is some portion of the memory
set aside for the log. (I don't mind the idea of an unlimited console
log either, but I suspect that will not be accepted on the qemu
side...)

> [SNIP]
>> > +static int notrace virt_pstore_write(enum pstore_type_id type,
>> > +                                    enum kmsg_dump_reason reason,
>> > +                                    u64 *id, unsigned int part, int count,
>> > +                                    bool compressed, size_t size,
>> > +                                    struct pstore_info *psi)
>> > +{
>> > +       struct virtio_pstore *vps = psi->data;
>> > +       struct virtio_pstore_hdr *hdr = &vps->hdr;
>> > +       struct scatterlist sg[2];
>> > +       unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
>> > +
>> > +       *id = vps->id++;
>> > +
>> > +       hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
>> > +       hdr->id    = cpu_to_virtio64(vps->vdev, *id);
>> > +       hdr->flags = cpu_to_virtio32(vps->vdev, flags);
>> > +       hdr->type  = to_virtio_type(vps, type);
>> > +
>> > +       sg_init_table(sg, 2);
>> > +       sg_set_buf(&sg[0], hdr, sizeof(*hdr));
>> > +       sg_set_buf(&sg[1], psi->buf, size);
>> > +       virtqueue_add_outbuf(vps->vq, sg, 2, vps, GFP_ATOMIC);
>> > +       virtqueue_kick(vps->vq);
>> > +
>> > +       /* TODO: make it synchronous */
>> > +       return 0;
>>
>> The down side to this being asynchronous is the lack of error
>> reporting. Perhaps this could check hdr->type before queuing and error
>> for any VIRTIO_PSTORE_TYPE_UNKNOWN message instead of trying to send
>> it?
>
> I cannot follow, sorry.  Could you please elaborate it more?

The mention you have here of "TODO: make it synchronous" made me think
about what effects that could have. If a pstore_write() were issued
for a type other than DMESG, the above code would send it through
virtio anyway. No error reporting is possible unless this is
synchronous, but the only error here would simply be "I don't know
what anything except DMESG is", so maybe this code could refuse to
forward anything with type UNKNOWN in the first place. (Just an idea:
I don't think there's anything very wrong here. It just seemed like a
potential improvement.)

>> > +}
>> > +
>> > +static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
>> > +                            struct timespec time, struct pstore_info *psi)
>> > +{
>> > +       struct virtio_pstore *vps = psi->data;
>> > +       struct virtio_pstore_hdr *hdr = &vps->hdr;
>> > +       struct scatterlist sg[1];
>> > +       unsigned int len;
>> > +
>> > +       hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
>> > +       hdr->id    = cpu_to_virtio64(vps->vdev, id);
>> > +       hdr->type  = to_virtio_type(vps, type);
>> > +
>> > +       sg_init_one(sg, hdr, sizeof(*hdr));
>> > +       virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
>> > +       virtqueue_kick(vps->vq);
>> > +
>> > +       wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
>> > +       return 0;
>> > +}
>> > +
>> > +static int virt_pstore_init(struct virtio_pstore *vps)
>> > +{
>> > +       struct pstore_info *psinfo = &vps->pstore;
>> > +       int err;
>> > +
>> > +       vps->id = 0;
>> > +       vps->buflen = 0;
>> > +       psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
>> > +       psinfo->buf = (void *)__get_free_pages(GFP_KERNEL, VIRT_PSTORE_ORDER);
>> > +       if (!psinfo->buf) {
>> > +               pr_err("cannot allocate pstore buffer\n");
>> > +               return -ENOMEM;
>> > +       }
>> > +
>> > +       psinfo->owner = THIS_MODULE;
>> > +       psinfo->name  = "virtio";
>> > +       psinfo->open  = virt_pstore_open;
>> > +       psinfo->close = virt_pstore_close;
>> > +       psinfo->read  = virt_pstore_read;
>> > +       psinfo->erase = virt_pstore_erase;
>> > +       psinfo->write = virt_pstore_write;
>> > +       psinfo->flags = PSTORE_FLAGS_FRAGILE;
>>
>> For console support, this flag would need to be dropped -- though I
>> suspect you know that already.:)
>
> Yep, I intentionally support DMESG type only in this patchset for
> simplicity.  Others could be added later. :)

Cool by me. :)

>
>
>>
>> > +       psinfo->data  = vps;
>> > +       spin_lock_init(&psinfo->buf_lock);
>> > +
>> > +       err = pstore_register(psinfo);
>> > +       if (err)
>> > +               kfree(psinfo->buf);
>> > +
>> > +       return err;
>> > +}
>
> [SNIP]
>>
>> Awesome! Can't wait to use it. :)
>
> Thanks for your review! :)

You're welcome! :)

-Kees

Namhyung Kim July 19, 2016, 1:43 p.m. UTC | #7

Hi Kees,

On Mon, Jul 18, 2016 at 10:50:06AM -0700, Kees Cook wrote:
> On Sun, Jul 17, 2016 at 10:50 PM, Namhyung Kim <[e-mail]> wrote:
> > Hello,
> >
> > On Sun, Jul 17, 2016 at 10:12:26PM -0700, Kees Cook wrote:
> >> On Sun, Jul 17, 2016 at 9:37 PM, Namhyung Kim <[e-mail]> wrote:
> > [SNIP]
> >> > +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
> >> > +{
> >> > +       u16 ret;
> >> > +
> >> > +       switch (type) {
> >> > +       case PSTORE_TYPE_DMESG:
> >> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_DMESG);
> >> > +               break;
> >> > +       default:
> >> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
> >> > +               break;
> >> > +       }
> >>
> >> I would love to see this support PSTORE_TYPE_CONSOLE too. It should be
> >> relatively easy to add: I think it'd just be another virtio command?
> >
> > Do you want to append the data to the host file as guest does
> > printk()?  I think it needs some kind of buffer management, but it's
> > not hard to add IMHO.
> 
> Well, with most pstore backends, the buffer size is limited, so it
> tends to be a circular buffer of some sort. I think whatever you
> choose to do is fine (I saw the various mentions of resource limits in
> the qemu part of this thread), as long as the last N bytes of console
> can be seen on the host side, where N is some portion of the memory
> set aside for the log. (I don't mind the idea of an unlimited console
> log either, but I suspect that will not be accepted on the qemu
> side...)

I think it needs two kinds of buffer management.

The first one is the psinfo->buf (or something similar).  IIUC the
PSTORE_TYPE_CONSOLE is different than PSTORE_TYPE_DMESG as it is
emitted every time printk() sends messages to console.  So I think the
it should remain in async mode due to performance reason.  To do that,
the message should be copied to psinfo->buf and then sent via virtio.
Then it needs to keep track of the available buffer position IMHO.

The other one is the file management on the host side.  I am thinking
of a simple way that the log file is splitted when it exceeds the half
of the allowed max size.  It would be configurable and might allow
unlimited logs if user requests it explicitly (if qemu guys say ok)..

Maybe we need to use 'part' or 'count' for filenames to identify
the splitted files.

> 
> > [SNIP]
> >> > +static int notrace virt_pstore_write(enum pstore_type_id type,
> >> > +                                    enum kmsg_dump_reason reason,
> >> > +                                    u64 *id, unsigned int part, int count,
> >> > +                                    bool compressed, size_t size,
> >> > +                                    struct pstore_info *psi)
> >> > +{
> >> > +       struct virtio_pstore *vps = psi->data;
> >> > +       struct virtio_pstore_hdr *hdr = &vps->hdr;
> >> > +       struct scatterlist sg[2];
> >> > +       unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
> >> > +
> >> > +       *id = vps->id++;
> >> > +
> >> > +       hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
> >> > +       hdr->id    = cpu_to_virtio64(vps->vdev, *id);
> >> > +       hdr->flags = cpu_to_virtio32(vps->vdev, flags);
> >> > +       hdr->type  = to_virtio_type(vps, type);
> >> > +
> >> > +       sg_init_table(sg, 2);
> >> > +       sg_set_buf(&sg[0], hdr, sizeof(*hdr));
> >> > +       sg_set_buf(&sg[1], psi->buf, size);
> >> > +       virtqueue_add_outbuf(vps->vq, sg, 2, vps, GFP_ATOMIC);
> >> > +       virtqueue_kick(vps->vq);
> >> > +
> >> > +       /* TODO: make it synchronous */
> >> > +       return 0;
> >>
> >> The down side to this being asynchronous is the lack of error
> >> reporting. Perhaps this could check hdr->type before queuing and error
> >> for any VIRTIO_PSTORE_TYPE_UNKNOWN message instead of trying to send
> >> it?
> >
> > I cannot follow, sorry.  Could you please elaborate it more?
> 
> The mention you have here of "TODO: make it synchronous" made me think
> about what effects that could have. If a pstore_write() were issued
> for a type other than DMESG, the above code would send it through
> virtio anyway. No error reporting is possible unless this is
> synchronous, but the only error here would simply be "I don't know
> what anything except DMESG is", so maybe this code could refuse to
> forward anything with type UNKNOWN in the first place. (Just an idea:
> I don't think there's anything very wrong here. It just seemed like a
> potential improvement.)

Yep, that kind of error handling should be easy.  My concern is when
write operation is failed on the host side.  We need a way to report
it back to the guest and might disallow further writes at least for
the same type.

Thanks,
Namhyung
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Namhyung Kim July 19, 2016, 3:32 p.m. UTC | #8

On Tue, Jul 19, 2016 at 10:43 PM, Namhyung Kim <[e-mail]> wrote:
> Hi Kees,
>
> On Mon, Jul 18, 2016 at 10:50:06AM -0700, Kees Cook wrote:
>> On Sun, Jul 17, 2016 at 10:50 PM, Namhyung Kim <[e-mail]> wrote:
>> > Hello,
>> >
>> > On Sun, Jul 17, 2016 at 10:12:26PM -0700, Kees Cook wrote:
>> >> On Sun, Jul 17, 2016 at 9:37 PM, Namhyung Kim <[e-mail]> wrote:
>> > [SNIP]
>> >> > +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
>> >> > +{
>> >> > +       u16 ret;
>> >> > +
>> >> > +       switch (type) {
>> >> > +       case PSTORE_TYPE_DMESG:
>> >> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_DMESG);
>> >> > +               break;
>> >> > +       default:
>> >> > +               ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
>> >> > +               break;
>> >> > +       }
>> >>
>> >> I would love to see this support PSTORE_TYPE_CONSOLE too. It should be
>> >> relatively easy to add: I think it'd just be another virtio command?
>> >
>> > Do you want to append the data to the host file as guest does
>> > printk()?  I think it needs some kind of buffer management, but it's
>> > not hard to add IMHO.
>>
>> Well, with most pstore backends, the buffer size is limited, so it
>> tends to be a circular buffer of some sort. I think whatever you
>> choose to do is fine (I saw the various mentions of resource limits in
>> the qemu part of this thread), as long as the last N bytes of console
>> can be seen on the host side, where N is some portion of the memory
>> set aside for the log. (I don't mind the idea of an unlimited console
>> log either, but I suspect that will not be accepted on the qemu
>> side...)
>
> I think it needs two kinds of buffer management.
>
> The first one is the psinfo->buf (or something similar).  IIUC the
> PSTORE_TYPE_CONSOLE is different than PSTORE_TYPE_DMESG as it is
> emitted every time printk() sends messages to console.  So I think the
> it should remain in async mode due to performance reason.  To do that,
> the message should be copied to psinfo->buf and then sent via virtio.
> Then it needs to keep track of the available buffer position IMHO.

Looking at the code, I found myself confused with the PSTORE_TYPE_FTRACE
and PSTORE_TYPE_CONSOLE.  It seems that handling of
PSTORE_TYPE_CONSOLE is basically same as PSTORE_TYPE_DMESG..

Thanks,
Namhyung
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Namhyung Kim July 20, 2016, 12:56 p.m. UTC | #9

On Tue, Jul 19, 2016 at 10:43 PM, Namhyung Kim <[e-mail]> wrote:
> The other one is the file management on the host side.  I am thinking
> of a simple way that the log file is splitted when it exceeds the half
> of the allowed max size.  It would be configurable and might allow
> unlimited logs if user requests it explicitly (if qemu guys say ok)..

On a second thought, I think that size of log file should not exceed
the pstore buffer size in order to be read back later.  When total size
of log files becomes larger then the limit, the oldest file of same
type can be deleted. This way looks simpler to manage IMHO.

Also I think the pstore id should be managed by host device rather
than guest driver to handle splitted files properly.

Thanks,
Namhyung
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Patch

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 77590320d44c..8f0e6c796c12 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -58,6 +58,16 @@  config VIRTIO_INPUT
 
 	 If unsure, say M.
 
+config VIRTIO_PSTORE
+	tristate "Virtio pstore driver"
+	depends on VIRTIO
+	depends on PSTORE
+	---help---
+	 This driver supports virtio pstore devices to save/restore
+	 panic and oops messages on the host.
+
+	 If unsure, say M.
+
  config VIRTIO_MMIO
 	tristate "Platform bus driver for memory mapped virtio devices"
 	depends on HAS_IOMEM && HAS_DMA
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 41e30e3dc842..bee68cb26d48 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -5,3 +5,4 @@  virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
 virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
 obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
 obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
+obj-$(CONFIG_VIRTIO_PSTORE) += virtio_pstore.o
diff --git a/drivers/virtio/virtio_pstore.c b/drivers/virtio/virtio_pstore.c
new file mode 100644
index 000000000000..6fe62c0f1508
--- /dev/null
+++ b/drivers/virtio/virtio_pstore.c
@@ -0,0 +1,317 @@ 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/pstore.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_pstore.h>
+
+#define VIRT_PSTORE_ORDER    2
+#define VIRT_PSTORE_BUFSIZE  (4096 << VIRT_PSTORE_ORDER)
+
+struct virtio_pstore {
+	struct virtio_device	*vdev;
+	struct virtqueue	*vq;
+	struct pstore_info	 pstore;
+	struct virtio_pstore_hdr hdr;
+	size_t			 buflen;
+	u64			 id;
+
+	/* Waiting for host to ack */
+	wait_queue_head_t	acked;
+};
+
+static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
+{
+	u16 ret;
+
+	switch (type) {
+	case PSTORE_TYPE_DMESG:
+		ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_DMESG);
+		break;
+	default:
+		ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
+		break;
+	}
+
+	return ret;
+}
+
+static enum pstore_type_id from_virtio_type(struct virtio_pstore *vps, u16 type)
+{
+	enum pstore_type_id ret;
+
+	switch (virtio16_to_cpu(vps->vdev, type)) {
+	case VIRTIO_PSTORE_TYPE_DMESG:
+		ret = PSTORE_TYPE_DMESG;
+		break;
+	default:
+		ret = PSTORE_TYPE_UNKNOWN;
+		break;
+	}
+
+	return ret;
+}
+
+static void virtpstore_ack(struct virtqueue *vq)
+{
+	struct virtio_pstore *vps = vq->vdev->priv;
+
+	wake_up(&vps->acked);
+}
+
+static int virt_pstore_open(struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_hdr *hdr = &vps->hdr;
+	struct scatterlist sg[1];
+	unsigned int len;
+
+	hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_OPEN);
+
+	sg_init_one(sg, hdr, sizeof(*hdr));
+	virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
+	return 0;
+}
+
+static int virt_pstore_close(struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_hdr *hdr = &vps->hdr;
+	struct scatterlist sg[1];
+	unsigned int len;
+
+	hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_CLOSE);
+
+	sg_init_one(sg, hdr, sizeof(*hdr));
+	virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
+	return 0;
+}
+
+static ssize_t virt_pstore_read(u64 *id, enum pstore_type_id *type,
+				int *count, struct timespec *time,
+				char **buf, bool *compressed,
+				struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_hdr *hdr = &vps->hdr;
+	struct scatterlist sgi[1], sgo[1];
+	struct scatterlist *sgs[2] = { sgo, sgi };
+	unsigned int len;
+	unsigned int flags;
+	void *bf;
+
+	hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_READ);
+
+	sg_init_one(sgo, hdr, sizeof(*hdr));
+	sg_init_one(sgi, psi->buf, psi->bufsize);
+	virtqueue_add_sgs(vps->vq, sgs, 1, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
+	if (len == 0)
+		return 0;
+
+	bf = kmalloc(len, GFP_KERNEL);
+	if (bf == NULL)
+		return -ENOMEM;
+
+	*id = virtio64_to_cpu(vps->vdev, hdr->id);
+	*type = from_virtio_type(vps, hdr->type);
+
+	flags = virtio32_to_cpu(vps->vdev, hdr->flags);
+	*compressed = flags & VIRTIO_PSTORE_FL_COMPRESSED;
+	*count = 1;
+
+	time->tv_sec  = virtio64_to_cpu(vps->vdev, hdr->time_sec);
+	time->tv_nsec = virtio32_to_cpu(vps->vdev, hdr->time_nsec);
+
+	memcpy(bf, psi->buf, len);
+	*buf = bf;
+
+	return len;
+}
+
+static int notrace virt_pstore_write(enum pstore_type_id type,
+				     enum kmsg_dump_reason reason,
+				     u64 *id, unsigned int part, int count,
+				     bool compressed, size_t size,
+				     struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_hdr *hdr = &vps->hdr;
+	struct scatterlist sg[2];
+	unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
+
+	*id = vps->id++;
+
+	hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
+	hdr->id	   = cpu_to_virtio64(vps->vdev, *id);
+	hdr->flags = cpu_to_virtio32(vps->vdev, flags);
+	hdr->type  = to_virtio_type(vps, type);
+
+	sg_init_table(sg, 2);
+	sg_set_buf(&sg[0], hdr, sizeof(*hdr));
+	sg_set_buf(&sg[1], psi->buf, size);
+	virtqueue_add_outbuf(vps->vq, sg, 2, vps, GFP_ATOMIC);
+	virtqueue_kick(vps->vq);
+
+	/* TODO: make it synchronous */
+	return 0;
+}
+
+static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
+			     struct timespec time, struct pstore_info *psi)
+{
+	struct virtio_pstore *vps = psi->data;
+	struct virtio_pstore_hdr *hdr = &vps->hdr;
+	struct scatterlist sg[1];
+	unsigned int len;
+
+	hdr->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
+	hdr->id	   = cpu_to_virtio64(vps->vdev, id);
+	hdr->type  = to_virtio_type(vps, type);
+
+	sg_init_one(sg, hdr, sizeof(*hdr));
+	virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
+	virtqueue_kick(vps->vq);
+
+	wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
+	return 0;
+}
+
+static int virt_pstore_init(struct virtio_pstore *vps)
+{
+	struct pstore_info *psinfo = &vps->pstore;
+	int err;
+
+	vps->id = 0;
+	vps->buflen = 0;
+	psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
+	psinfo->buf = (void *)__get_free_pages(GFP_KERNEL, VIRT_PSTORE_ORDER);
+	if (!psinfo->buf) {
+		pr_err("cannot allocate pstore buffer\n");
+		return -ENOMEM;
+	}
+
+	psinfo->owner = THIS_MODULE;
+	psinfo->name  = "virtio";
+	psinfo->open  = virt_pstore_open;
+	psinfo->close = virt_pstore_close;
+	psinfo->read  = virt_pstore_read;
+	psinfo->erase = virt_pstore_erase;
+	psinfo->write = virt_pstore_write;
+	psinfo->flags = PSTORE_FLAGS_FRAGILE;
+	psinfo->data  = vps;
+	spin_lock_init(&psinfo->buf_lock);
+
+	err = pstore_register(psinfo);
+	if (err)
+		kfree(psinfo->buf);
+
+	return err;
+}
+
+static int virt_pstore_exit(struct virtio_pstore *vps)
+{
+	struct pstore_info *psinfo = &vps->pstore;
+
+	pstore_unregister(psinfo);
+
+	free_pages((unsigned long)psinfo->buf, VIRT_PSTORE_ORDER);
+	psinfo->bufsize = 0;
+
+	return 0;
+}
+
+static int virtpstore_probe(struct virtio_device *vdev)
+{
+	struct virtio_pstore *vps;
+	int err;
+
+	if (!vdev->config->get) {
+		dev_err(&vdev->dev, "%s failure: config access disabled\n",
+			__func__);
+		return -EINVAL;
+	}
+
+	vdev->priv = vps = kmalloc(sizeof(*vps), GFP_KERNEL);
+	if (!vps) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	vps->vdev = vdev;
+
+	vps->vq = virtio_find_single_vq(vdev, virtpstore_ack, "pstore");
+	if (IS_ERR(vps->vq)) {
+		err = PTR_ERR(vps->vq);
+		goto out_free;
+	}
+
+	err = virt_pstore_init(vps);
+	if (err)
+		goto out_del_vq;
+
+	init_waitqueue_head(&vps->acked);
+
+	virtio_device_ready(vdev);
+	dev_info(&vdev->dev, "virtio pstore driver init: ok\n");
+
+	return 0;
+
+out_del_vq:
+	vdev->config->del_vqs(vdev);
+out_free:
+	kfree(vps);
+out:
+	dev_err(&vdev->dev, "virtio pstore driver init: failed with %d\n", err);
+	return err;
+}
+
+static void virtpstore_remove(struct virtio_device *vdev)
+{
+	struct virtio_pstore *vps = vdev->priv;
+
+	virt_pstore_exit(vps);
+
+	/* Now we reset the device so we can clean up the queues. */
+	vdev->config->reset(vdev);
+
+	vdev->config->del_vqs(vdev);
+
+	kfree(vps);
+}
+
+static unsigned int features[] = {
+};
+
+static struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_PSTORE, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+static struct virtio_driver virtio_pstore_driver = {
+	.driver.name         = KBUILD_MODNAME,
+	.driver.owner        = THIS_MODULE,
+	.feature_table       = features,
+	.feature_table_size  = ARRAY_SIZE(features),
+	.id_table            = id_table,
+	.probe               = virtpstore_probe,
+	.remove              = virtpstore_remove,
+};
+
+module_virtio_driver(virtio_pstore_driver);
+MODULE_DEVICE_TABLE(virtio, id_table);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Namhyung Kim <[e-mail]>");
+MODULE_DESCRIPTION("Virtio pstore driver");
diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
index 8bdae34d1f9a..57b0d08db322 100644
--- a/include/uapi/linux/Kbuild
+++ b/include/uapi/linux/Kbuild
@@ -448,6 +448,7 @@  header-y += virtio_ids.h
 header-y += virtio_input.h
 header-y += virtio_net.h
 header-y += virtio_pci.h
+header-y += virtio_pstore.h
 header-y += virtio_ring.h
 header-y += virtio_rng.h
 header-y += virtio_scsi.h
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index 77925f587b15..cba63225d85a 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -41,5 +41,6 @@ 
 #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
 #define VIRTIO_ID_GPU          16 /* virtio GPU */
 #define VIRTIO_ID_INPUT        18 /* virtio input */
+#define VIRTIO_ID_PSTORE       19 /* virtio pstore */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
diff --git a/include/uapi/linux/virtio_pstore.h b/include/uapi/linux/virtio_pstore.h
new file mode 100644
index 000000000000..0aa1575ee35f
--- /dev/null
+++ b/include/uapi/linux/virtio_pstore.h
@@ -0,0 +1,53 @@ 
+#ifndef _LINUX_VIRTIO_PSTORE_H
+#define _LINUX_VIRTIO_PSTORE_H
+/* This header is BSD licensed so anyone can use the definitions to implement
+ * compatible drivers/servers.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of IBM nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE. */
+#include <linux/types.h>
+#include <linux/virtio_types.h>
+
+#define VIRTIO_PSTORE_CMD_NULL   0
+#define VIRTIO_PSTORE_CMD_OPEN   1
+#define VIRTIO_PSTORE_CMD_READ   2
+#define VIRTIO_PSTORE_CMD_WRITE  3
+#define VIRTIO_PSTORE_CMD_ERASE  4
+#define VIRTIO_PSTORE_CMD_CLOSE  5
+
+#define VIRTIO_PSTORE_TYPE_UNKNOWN  0
+#define VIRTIO_PSTORE_TYPE_DMESG    1
+
+#define VIRTIO_PSTORE_FL_COMPRESSED  1
+
+struct virtio_pstore_hdr {
+	__virtio64		id;
+	__virtio32		flags;
+	__virtio16		cmd;
+	__virtio16		type;
+	__virtio64		time_sec;
+	__virtio32		time_nsec;
+	__virtio32		unused;
+};
+
+#endif /* _LINUX_VIRTIO_PSTORE_H */