diff mbox series

[v11,12/12] Documentation: Add documentation for VDUSE

Message ID 20210818120642.165-13-xieyongji@bytedance.com (mailing list archive)
State Superseded
Headers show
Series Introduce VDUSE - vDPA Device in Userspace | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Yongji Xie Aug. 18, 2021, 12:06 p.m. UTC 
VDUSE (vDPA Device in Userspace) is a framework to support
implementing software-emulated vDPA devices in userspace. This
document is intended to clarify the VDUSE design and usage.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
---
 Documentation/userspace-api/index.rst |   1 +
 Documentation/userspace-api/vduse.rst | 233 ++++++++++++++++++++++++++++++++++
 2 files changed, 234 insertions(+)
 create mode 100644 Documentation/userspace-api/vduse.rst

Comments

Jason Wang Aug. 23, 2021, 6:57 a.m. UTC | #1 
在 2021/8/18 下午8:06, Xie Yongji 写道:
> VDUSE (vDPA Device in Userspace) is a framework to support
> implementing software-emulated vDPA devices in userspace. This
> document is intended to clarify the VDUSE design and usage.
>
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>


Acked-by: Jason Wang <jasowang@redhat.com>


> ---
>   Documentation/userspace-api/index.rst |   1 +
>   Documentation/userspace-api/vduse.rst | 233 ++++++++++++++++++++++++++++++++++
>   2 files changed, 234 insertions(+)
>   create mode 100644 Documentation/userspace-api/vduse.rst
>
> diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
> index 0b5eefed027e..c432be070f67 100644
> --- a/Documentation/userspace-api/index.rst
> +++ b/Documentation/userspace-api/index.rst
> @@ -27,6 +27,7 @@ place where this information is gathered.
>      iommu
>      media/index
>      sysfs-platform_profile
> +   vduse
>   
>   .. only::  subproject and html
>   
> diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst
> new file mode 100644
> index 000000000000..42ef59ea5314
> --- /dev/null
> +++ b/Documentation/userspace-api/vduse.rst
> @@ -0,0 +1,233 @@
> +==================================
> +VDUSE - "vDPA Device in Userspace"
> +==================================
> +
> +vDPA (virtio data path acceleration) device is a device that uses a
> +datapath which complies with the virtio specifications with vendor
> +specific control path. vDPA devices can be both physically located on
> +the hardware or emulated by software. VDUSE is a framework that makes it
> +possible to implement software-emulated vDPA devices in userspace. And
> +to make the device emulation more secure, the emulated vDPA device's
> +control path is handled in the kernel and only the data path is
> +implemented in the userspace.
> +
> +Note that only virtio block device is supported by VDUSE framework now,
> +which can reduce security risks when the userspace process that implements
> +the data path is run by an unprivileged user. The support for other device
> +types can be added after the security issue of corresponding device driver
> +is clarified or fixed in the future.
> +
> +Create/Destroy VDUSE devices
> +------------------------
> +
> +VDUSE devices are created as follows:
> +
> +1. Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on
> +   /dev/vduse/control.
> +
> +2. Setup each virtqueue with ioctl(VDUSE_VQ_SETUP) on /dev/vduse/$NAME.
> +
> +3. Begin processing VDUSE messages from /dev/vduse/$NAME. The first
> +   messages will arrive while attaching the VDUSE instance to vDPA bus.
> +
> +4. Send the VDPA_CMD_DEV_NEW netlink message to attach the VDUSE
> +   instance to vDPA bus.
> +
> +VDUSE devices are destroyed as follows:
> +
> +1. Send the VDPA_CMD_DEV_DEL netlink message to detach the VDUSE
> +   instance from vDPA bus.
> +
> +2. Close the file descriptor referring to /dev/vduse/$NAME.
> +
> +3. Destroy the VDUSE instance with ioctl(VDUSE_DESTROY_DEV) on
> +   /dev/vduse/control.
> +
> +The netlink messages can be sent via vdpa tool in iproute2 or use the
> +below sample codes:
> +
> +.. code-block:: c
> +
> +	static int netlink_add_vduse(const char *name, enum vdpa_command cmd)
> +	{
> +		struct nl_sock *nlsock;
> +		struct nl_msg *msg;
> +		int famid;
> +
> +		nlsock = nl_socket_alloc();
> +		if (!nlsock)
> +			return -ENOMEM;
> +
> +		if (genl_connect(nlsock))
> +			goto free_sock;
> +
> +		famid = genl_ctrl_resolve(nlsock, VDPA_GENL_NAME);
> +		if (famid < 0)
> +			goto close_sock;
> +
> +		msg = nlmsg_alloc();
> +		if (!msg)
> +			goto close_sock;
> +
> +		if (!genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, famid, 0, 0, cmd, 0))
> +			goto nla_put_failure;
> +
> +		NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name);
> +		if (cmd == VDPA_CMD_DEV_NEW)
> +			NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse");
> +
> +		if (nl_send_sync(nlsock, msg))
> +			goto close_sock;
> +
> +		nl_close(nlsock);
> +		nl_socket_free(nlsock);
> +
> +		return 0;
> +	nla_put_failure:
> +		nlmsg_free(msg);
> +	close_sock:
> +		nl_close(nlsock);
> +	free_sock:
> +		nl_socket_free(nlsock);
> +		return -1;
> +	}
> +
> +How VDUSE works
> +---------------
> +
> +As mentioned above, a VDUSE device is created by ioctl(VDUSE_CREATE_DEV) on
> +/dev/vduse/control. With this ioctl, userspace can specify some basic configuration
> +such as device name (uniquely identify a VDUSE device), virtio features, virtio
> +configuration space, the number of virtqueues and so on for this emulated device.
> +Then a char device interface (/dev/vduse/$NAME) is exported to userspace for device
> +emulation. Userspace can use the VDUSE_VQ_SETUP ioctl on /dev/vduse/$NAME to
> +add per-virtqueue configuration such as the max size of virtqueue to the device.
> +
> +After the initialization, the VDUSE device can be attached to vDPA bus via
> +the VDPA_CMD_DEV_NEW netlink message. Userspace needs to read()/write() on
> +/dev/vduse/$NAME to receive/reply some control messages from/to VDUSE kernel
> +module as follows:
> +
> +.. code-block:: c
> +
> +	static int vduse_message_handler(int dev_fd)
> +	{
> +		int len;
> +		struct vduse_dev_request req;
> +		struct vduse_dev_response resp;
> +
> +		len = read(dev_fd, &req, sizeof(req));
> +		if (len != sizeof(req))
> +			return -1;
> +
> +		resp.request_id = req.request_id;
> +
> +		switch (req.type) {
> +
> +		/* handle different types of messages */
> +
> +		}
> +
> +		len = write(dev_fd, &resp, sizeof(resp));
> +		if (len != sizeof(resp))
> +			return -1;
> +
> +		return 0;
> +	}
> +
> +There are now three types of messages introduced by VDUSE framework:
> +
> +- VDUSE_GET_VQ_STATE: Get the state for virtqueue, userspace should return
> +  avail index for split virtqueue or the device/driver ring wrap counters and
> +  the avail and used index for packed virtqueue.
> +
> +- VDUSE_SET_STATUS: Set the device status, userspace should follow
> +  the virtio spec: https://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.html
> +  to process this message. For example, fail to set the FEATURES_OK device
> +  status bit if the device can not accept the negotiated virtio features
> +  get from the VDUSE_DEV_GET_FEATURES ioctl.
> +
> +- VDUSE_UPDATE_IOTLB: Notify userspace to update the memory mapping for specified
> +  IOVA range, userspace should firstly remove the old mapping, then setup the new
> +  mapping via the VDUSE_IOTLB_GET_FD ioctl.
> +
> +After DRIVER_OK status bit is set via the VDUSE_SET_STATUS message, userspace is
> +able to start the dataplane processing as follows:
> +
> +1. Get the specified virtqueue's information with the VDUSE_VQ_GET_INFO ioctl,
> +   including the size, the IOVAs of descriptor table, available ring and used ring,
> +   the state and the ready status.
> +
> +2. Pass the above IOVAs to the VDUSE_IOTLB_GET_FD ioctl so that those IOVA regions
> +   can be mapped into userspace. Some sample codes is shown below:
> +
> +.. code-block:: c
> +
> +	static int perm_to_prot(uint8_t perm)
> +	{
> +		int prot = 0;
> +
> +		switch (perm) {
> +		case VDUSE_ACCESS_WO:
> +			prot |= PROT_WRITE;
> +			break;
> +		case VDUSE_ACCESS_RO:
> +			prot |= PROT_READ;
> +			break;
> +		case VDUSE_ACCESS_RW:
> +			prot |= PROT_READ | PROT_WRITE;
> +			break;
> +		}
> +
> +		return prot;
> +	}
> +
> +	static void *iova_to_va(int dev_fd, uint64_t iova, uint64_t *len)
> +	{
> +		int fd;
> +		void *addr;
> +		size_t size;
> +		struct vduse_iotlb_entry entry;
> +
> +		entry.start = iova;
> +		entry.last = iova;
> +
> +		/*
> +		 * Find the first IOVA region that overlaps with the specified
> +		 * range [start, last] and return the corresponding file descriptor.
> +		 */
> +		fd = ioctl(dev_fd, VDUSE_IOTLB_GET_FD, &entry);
> +		if (fd < 0)
> +			return NULL;
> +
> +		size = entry.last - entry.start + 1;
> +		*len = entry.last - iova + 1;
> +		addr = mmap(0, size, perm_to_prot(entry.perm), MAP_SHARED,
> +			    fd, entry.offset);
> +		close(fd);
> +		if (addr == MAP_FAILED)
> +			return NULL;
> +
> +		/*
> +		 * Using some data structures such as linked list to store
> +		 * the iotlb mapping. The munmap(2) should be called for the
> +		 * cached mapping when the corresponding VDUSE_UPDATE_IOTLB
> +		 * message is received or the device is reset.
> +		 */
> +
> +		return addr + iova - entry.start;
> +	}
> +
> +3. Setup the kick eventfd for the specified virtqueues with the VDUSE_VQ_SETUP_KICKFD
> +   ioctl. The kick eventfd is used by VDUSE kernel module to notify userspace to
> +   consume the available ring. This is optional since userspace can choose to poll the
> +   available ring instead.
> +
> +4. Listen to the kick eventfd (optional) and consume the available ring. The buffer
> +   described by the descriptors in the descriptor table should be also mapped into
> +   userspace via the VDUSE_IOTLB_GET_FD ioctl before accessing.
> +
> +5. Inject an interrupt for specific virtqueue with the VDUSE_INJECT_VQ_IRQ ioctl
> +   after the used ring is filled.
> +
> +For more details on the uAPI, please see include/uapi/linux/vduse.h.
Jason Wang Aug. 23, 2021, 7:54 a.m. UTC | #2 
在 2021/8/18 下午8:06, Xie Yongji 写道:
> VDUSE (vDPA Device in Userspace) is a framework to support
> implementing software-emulated vDPA devices in userspace. This
> document is intended to clarify the VDUSE design and usage.
>
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>


Acked-by: Jason Wang <jasowang@redhat.com>


> ---
>   Documentation/userspace-api/index.rst |   1 +
>   Documentation/userspace-api/vduse.rst | 233 ++++++++++++++++++++++++++++++++++
>   2 files changed, 234 insertions(+)
>   create mode 100644 Documentation/userspace-api/vduse.rst
>
> diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
> index 0b5eefed027e..c432be070f67 100644
> --- a/Documentation/userspace-api/index.rst
> +++ b/Documentation/userspace-api/index.rst
> @@ -27,6 +27,7 @@ place where this information is gathered.
>      iommu
>      media/index
>      sysfs-platform_profile
> +   vduse
>   
>   .. only::  subproject and html
>   
> diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst
> new file mode 100644
> index 000000000000..42ef59ea5314
> --- /dev/null
> +++ b/Documentation/userspace-api/vduse.rst
> @@ -0,0 +1,233 @@
> +==================================
> +VDUSE - "vDPA Device in Userspace"
> +==================================
> +
> +vDPA (virtio data path acceleration) device is a device that uses a
> +datapath which complies with the virtio specifications with vendor
> +specific control path. vDPA devices can be both physically located on
> +the hardware or emulated by software. VDUSE is a framework that makes it
> +possible to implement software-emulated vDPA devices in userspace. And
> +to make the device emulation more secure, the emulated vDPA device's
> +control path is handled in the kernel and only the data path is
> +implemented in the userspace.
> +
> +Note that only virtio block device is supported by VDUSE framework now,
> +which can reduce security risks when the userspace process that implements
> +the data path is run by an unprivileged user. The support for other device
> +types can be added after the security issue of corresponding device driver
> +is clarified or fixed in the future.
> +
> +Create/Destroy VDUSE devices
> +------------------------
> +
> +VDUSE devices are created as follows:
> +
> +1. Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on
> +   /dev/vduse/control.
> +
> +2. Setup each virtqueue with ioctl(VDUSE_VQ_SETUP) on /dev/vduse/$NAME.
> +
> +3. Begin processing VDUSE messages from /dev/vduse/$NAME. The first
> +   messages will arrive while attaching the VDUSE instance to vDPA bus.
> +
> +4. Send the VDPA_CMD_DEV_NEW netlink message to attach the VDUSE
> +   instance to vDPA bus.
> +
> +VDUSE devices are destroyed as follows:
> +
> +1. Send the VDPA_CMD_DEV_DEL netlink message to detach the VDUSE
> +   instance from vDPA bus.
> +
> +2. Close the file descriptor referring to /dev/vduse/$NAME.
> +
> +3. Destroy the VDUSE instance with ioctl(VDUSE_DESTROY_DEV) on
> +   /dev/vduse/control.
> +
> +The netlink messages can be sent via vdpa tool in iproute2 or use the
> +below sample codes:
> +
> +.. code-block:: c
> +
> +	static int netlink_add_vduse(const char *name, enum vdpa_command cmd)
> +	{
> +		struct nl_sock *nlsock;
> +		struct nl_msg *msg;
> +		int famid;
> +
> +		nlsock = nl_socket_alloc();
> +		if (!nlsock)
> +			return -ENOMEM;
> +
> +		if (genl_connect(nlsock))
> +			goto free_sock;
> +
> +		famid = genl_ctrl_resolve(nlsock, VDPA_GENL_NAME);
> +		if (famid < 0)
> +			goto close_sock;
> +
> +		msg = nlmsg_alloc();
> +		if (!msg)
> +			goto close_sock;
> +
> +		if (!genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, famid, 0, 0, cmd, 0))
> +			goto nla_put_failure;
> +
> +		NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name);
> +		if (cmd == VDPA_CMD_DEV_NEW)
> +			NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse");
> +
> +		if (nl_send_sync(nlsock, msg))
> +			goto close_sock;
> +
> +		nl_close(nlsock);
> +		nl_socket_free(nlsock);
> +
> +		return 0;
> +	nla_put_failure:
> +		nlmsg_free(msg);
> +	close_sock:
> +		nl_close(nlsock);
> +	free_sock:
> +		nl_socket_free(nlsock);
> +		return -1;
> +	}
> +
> +How VDUSE works
> +---------------
> +
> +As mentioned above, a VDUSE device is created by ioctl(VDUSE_CREATE_DEV) on
> +/dev/vduse/control. With this ioctl, userspace can specify some basic configuration
> +such as device name (uniquely identify a VDUSE device), virtio features, virtio
> +configuration space, the number of virtqueues and so on for this emulated device.
> +Then a char device interface (/dev/vduse/$NAME) is exported to userspace for device
> +emulation. Userspace can use the VDUSE_VQ_SETUP ioctl on /dev/vduse/$NAME to
> +add per-virtqueue configuration such as the max size of virtqueue to the device.
> +
> +After the initialization, the VDUSE device can be attached to vDPA bus via
> +the VDPA_CMD_DEV_NEW netlink message. Userspace needs to read()/write() on
> +/dev/vduse/$NAME to receive/reply some control messages from/to VDUSE kernel
> +module as follows:
> +
> +.. code-block:: c
> +
> +	static int vduse_message_handler(int dev_fd)
> +	{
> +		int len;
> +		struct vduse_dev_request req;
> +		struct vduse_dev_response resp;
> +
> +		len = read(dev_fd, &req, sizeof(req));
> +		if (len != sizeof(req))
> +			return -1;
> +
> +		resp.request_id = req.request_id;
> +
> +		switch (req.type) {
> +
> +		/* handle different types of messages */
> +
> +		}
> +
> +		len = write(dev_fd, &resp, sizeof(resp));
> +		if (len != sizeof(resp))
> +			return -1;
> +
> +		return 0;
> +	}
> +
> +There are now three types of messages introduced by VDUSE framework:
> +
> +- VDUSE_GET_VQ_STATE: Get the state for virtqueue, userspace should return
> +  avail index for split virtqueue or the device/driver ring wrap counters and
> +  the avail and used index for packed virtqueue.
> +
> +- VDUSE_SET_STATUS: Set the device status, userspace should follow
> +  the virtio spec: https://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.html
> +  to process this message. For example, fail to set the FEATURES_OK device
> +  status bit if the device can not accept the negotiated virtio features
> +  get from the VDUSE_DEV_GET_FEATURES ioctl.
> +
> +- VDUSE_UPDATE_IOTLB: Notify userspace to update the memory mapping for specified
> +  IOVA range, userspace should firstly remove the old mapping, then setup the new
> +  mapping via the VDUSE_IOTLB_GET_FD ioctl.
> +
> +After DRIVER_OK status bit is set via the VDUSE_SET_STATUS message, userspace is
> +able to start the dataplane processing as follows:
> +
> +1. Get the specified virtqueue's information with the VDUSE_VQ_GET_INFO ioctl,
> +   including the size, the IOVAs of descriptor table, available ring and used ring,
> +   the state and the ready status.
> +
> +2. Pass the above IOVAs to the VDUSE_IOTLB_GET_FD ioctl so that those IOVA regions
> +   can be mapped into userspace. Some sample codes is shown below:
> +
> +.. code-block:: c
> +
> +	static int perm_to_prot(uint8_t perm)
> +	{
> +		int prot = 0;
> +
> +		switch (perm) {
> +		case VDUSE_ACCESS_WO:
> +			prot |= PROT_WRITE;
> +			break;
> +		case VDUSE_ACCESS_RO:
> +			prot |= PROT_READ;
> +			break;
> +		case VDUSE_ACCESS_RW:
> +			prot |= PROT_READ | PROT_WRITE;
> +			break;
> +		}
> +
> +		return prot;
> +	}
> +
> +	static void *iova_to_va(int dev_fd, uint64_t iova, uint64_t *len)
> +	{
> +		int fd;
> +		void *addr;
> +		size_t size;
> +		struct vduse_iotlb_entry entry;
> +
> +		entry.start = iova;
> +		entry.last = iova;
> +
> +		/*
> +		 * Find the first IOVA region that overlaps with the specified
> +		 * range [start, last] and return the corresponding file descriptor.
> +		 */
> +		fd = ioctl(dev_fd, VDUSE_IOTLB_GET_FD, &entry);
> +		if (fd < 0)
> +			return NULL;
> +
> +		size = entry.last - entry.start + 1;
> +		*len = entry.last - iova + 1;
> +		addr = mmap(0, size, perm_to_prot(entry.perm), MAP_SHARED,
> +			    fd, entry.offset);
> +		close(fd);
> +		if (addr == MAP_FAILED)
> +			return NULL;
> +
> +		/*
> +		 * Using some data structures such as linked list to store
> +		 * the iotlb mapping. The munmap(2) should be called for the
> +		 * cached mapping when the corresponding VDUSE_UPDATE_IOTLB
> +		 * message is received or the device is reset.
> +		 */
> +
> +		return addr + iova - entry.start;
> +	}
> +
> +3. Setup the kick eventfd for the specified virtqueues with the VDUSE_VQ_SETUP_KICKFD
> +   ioctl. The kick eventfd is used by VDUSE kernel module to notify userspace to
> +   consume the available ring. This is optional since userspace can choose to poll the
> +   available ring instead.
> +
> +4. Listen to the kick eventfd (optional) and consume the available ring. The buffer
> +   described by the descriptors in the descriptor table should be also mapped into
> +   userspace via the VDUSE_IOTLB_GET_FD ioctl before accessing.
> +
> +5. Inject an interrupt for specific virtqueue with the VDUSE_INJECT_VQ_IRQ ioctl
> +   after the used ring is filled.
> +
> +For more details on the uAPI, please see include/uapi/linux/vduse.h.
diff mbox series

Patch

diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index 0b5eefed027e..c432be070f67 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -27,6 +27,7 @@  place where this information is gathered.
    iommu
    media/index
    sysfs-platform_profile
+   vduse
 
 .. only::  subproject and html
 
diff --git a/Documentation/userspace-api/vduse.rst b/Documentation/userspace-api/vduse.rst
new file mode 100644
index 000000000000..42ef59ea5314
--- /dev/null
+++ b/Documentation/userspace-api/vduse.rst
@@ -0,0 +1,233 @@ 
+==================================
+VDUSE - "vDPA Device in Userspace"
+==================================
+
+vDPA (virtio data path acceleration) device is a device that uses a
+datapath which complies with the virtio specifications with vendor
+specific control path. vDPA devices can be both physically located on
+the hardware or emulated by software. VDUSE is a framework that makes it
+possible to implement software-emulated vDPA devices in userspace. And
+to make the device emulation more secure, the emulated vDPA device's
+control path is handled in the kernel and only the data path is
+implemented in the userspace.
+
+Note that only virtio block device is supported by VDUSE framework now,
+which can reduce security risks when the userspace process that implements
+the data path is run by an unprivileged user. The support for other device
+types can be added after the security issue of corresponding device driver
+is clarified or fixed in the future.
+
+Create/Destroy VDUSE devices
+------------------------
+
+VDUSE devices are created as follows:
+
+1. Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on
+   /dev/vduse/control.
+
+2. Setup each virtqueue with ioctl(VDUSE_VQ_SETUP) on /dev/vduse/$NAME.
+
+3. Begin processing VDUSE messages from /dev/vduse/$NAME. The first
+   messages will arrive while attaching the VDUSE instance to vDPA bus.
+
+4. Send the VDPA_CMD_DEV_NEW netlink message to attach the VDUSE
+   instance to vDPA bus.
+
+VDUSE devices are destroyed as follows:
+
+1. Send the VDPA_CMD_DEV_DEL netlink message to detach the VDUSE
+   instance from vDPA bus.
+
+2. Close the file descriptor referring to /dev/vduse/$NAME.
+
+3. Destroy the VDUSE instance with ioctl(VDUSE_DESTROY_DEV) on
+   /dev/vduse/control.
+
+The netlink messages can be sent via vdpa tool in iproute2 or use the
+below sample codes:
+
+.. code-block:: c
+
+	static int netlink_add_vduse(const char *name, enum vdpa_command cmd)
+	{
+		struct nl_sock *nlsock;
+		struct nl_msg *msg;
+		int famid;
+
+		nlsock = nl_socket_alloc();
+		if (!nlsock)
+			return -ENOMEM;
+
+		if (genl_connect(nlsock))
+			goto free_sock;
+
+		famid = genl_ctrl_resolve(nlsock, VDPA_GENL_NAME);
+		if (famid < 0)
+			goto close_sock;
+
+		msg = nlmsg_alloc();
+		if (!msg)
+			goto close_sock;
+
+		if (!genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, famid, 0, 0, cmd, 0))
+			goto nla_put_failure;
+
+		NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name);
+		if (cmd == VDPA_CMD_DEV_NEW)
+			NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse");
+
+		if (nl_send_sync(nlsock, msg))
+			goto close_sock;
+
+		nl_close(nlsock);
+		nl_socket_free(nlsock);
+
+		return 0;
+	nla_put_failure:
+		nlmsg_free(msg);
+	close_sock:
+		nl_close(nlsock);
+	free_sock:
+		nl_socket_free(nlsock);
+		return -1;
+	}
+
+How VDUSE works
+---------------
+
+As mentioned above, a VDUSE device is created by ioctl(VDUSE_CREATE_DEV) on
+/dev/vduse/control. With this ioctl, userspace can specify some basic configuration
+such as device name (uniquely identify a VDUSE device), virtio features, virtio
+configuration space, the number of virtqueues and so on for this emulated device.
+Then a char device interface (/dev/vduse/$NAME) is exported to userspace for device
+emulation. Userspace can use the VDUSE_VQ_SETUP ioctl on /dev/vduse/$NAME to
+add per-virtqueue configuration such as the max size of virtqueue to the device.
+
+After the initialization, the VDUSE device can be attached to vDPA bus via
+the VDPA_CMD_DEV_NEW netlink message. Userspace needs to read()/write() on
+/dev/vduse/$NAME to receive/reply some control messages from/to VDUSE kernel
+module as follows:
+
+.. code-block:: c
+
+	static int vduse_message_handler(int dev_fd)
+	{
+		int len;
+		struct vduse_dev_request req;
+		struct vduse_dev_response resp;
+
+		len = read(dev_fd, &req, sizeof(req));
+		if (len != sizeof(req))
+			return -1;
+
+		resp.request_id = req.request_id;
+
+		switch (req.type) {
+
+		/* handle different types of messages */
+
+		}
+
+		len = write(dev_fd, &resp, sizeof(resp));
+		if (len != sizeof(resp))
+			return -1;
+
+		return 0;
+	}
+
+There are now three types of messages introduced by VDUSE framework:
+
+- VDUSE_GET_VQ_STATE: Get the state for virtqueue, userspace should return
+  avail index for split virtqueue or the device/driver ring wrap counters and
+  the avail and used index for packed virtqueue.
+
+- VDUSE_SET_STATUS: Set the device status, userspace should follow
+  the virtio spec: https://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.html
+  to process this message. For example, fail to set the FEATURES_OK device
+  status bit if the device can not accept the negotiated virtio features
+  get from the VDUSE_DEV_GET_FEATURES ioctl.
+
+- VDUSE_UPDATE_IOTLB: Notify userspace to update the memory mapping for specified
+  IOVA range, userspace should firstly remove the old mapping, then setup the new
+  mapping via the VDUSE_IOTLB_GET_FD ioctl.
+
+After DRIVER_OK status bit is set via the VDUSE_SET_STATUS message, userspace is
+able to start the dataplane processing as follows:
+
+1. Get the specified virtqueue's information with the VDUSE_VQ_GET_INFO ioctl,
+   including the size, the IOVAs of descriptor table, available ring and used ring,
+   the state and the ready status.
+
+2. Pass the above IOVAs to the VDUSE_IOTLB_GET_FD ioctl so that those IOVA regions
+   can be mapped into userspace. Some sample codes is shown below:
+
+.. code-block:: c
+
+	static int perm_to_prot(uint8_t perm)
+	{
+		int prot = 0;
+
+		switch (perm) {
+		case VDUSE_ACCESS_WO:
+			prot |= PROT_WRITE;
+			break;
+		case VDUSE_ACCESS_RO:
+			prot |= PROT_READ;
+			break;
+		case VDUSE_ACCESS_RW:
+			prot |= PROT_READ | PROT_WRITE;
+			break;
+		}
+
+		return prot;
+	}
+
+	static void *iova_to_va(int dev_fd, uint64_t iova, uint64_t *len)
+	{
+		int fd;
+		void *addr;
+		size_t size;
+		struct vduse_iotlb_entry entry;
+
+		entry.start = iova;
+		entry.last = iova;
+
+		/*
+		 * Find the first IOVA region that overlaps with the specified
+		 * range [start, last] and return the corresponding file descriptor.
+		 */
+		fd = ioctl(dev_fd, VDUSE_IOTLB_GET_FD, &entry);
+		if (fd < 0)
+			return NULL;
+
+		size = entry.last - entry.start + 1;
+		*len = entry.last - iova + 1;
+		addr = mmap(0, size, perm_to_prot(entry.perm), MAP_SHARED,
+			    fd, entry.offset);
+		close(fd);
+		if (addr == MAP_FAILED)
+			return NULL;
+
+		/*
+		 * Using some data structures such as linked list to store
+		 * the iotlb mapping. The munmap(2) should be called for the
+		 * cached mapping when the corresponding VDUSE_UPDATE_IOTLB
+		 * message is received or the device is reset.
+		 */
+
+		return addr + iova - entry.start;
+	}
+
+3. Setup the kick eventfd for the specified virtqueues with the VDUSE_VQ_SETUP_KICKFD
+   ioctl. The kick eventfd is used by VDUSE kernel module to notify userspace to
+   consume the available ring. This is optional since userspace can choose to poll the
+   available ring instead.
+
+4. Listen to the kick eventfd (optional) and consume the available ring. The buffer
+   described by the descriptors in the descriptor table should be also mapped into
+   userspace via the VDUSE_IOTLB_GET_FD ioctl before accessing.
+
+5. Inject an interrupt for specific virtqueue with the VDUSE_INJECT_VQ_IRQ ioctl
+   after the used ring is filled.
+
+For more details on the uAPI, please see include/uapi/linux/vduse.h.