Re: Re: [PATCH v6 10/10] Documentation: Add documentation for VDUSE

On Thu, Apr 8, 2021 at 3:18 PM Jason Wang [off-list ref] wrote:

在 2021/3/31 下午4:05, Xie Yongji 写道:

quoted

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 <redacted>
---
  Documentation/userspace-api/index.rst |   1 +
  Documentation/userspace-api/vduse.rst | 212 ++++++++++++++++++++++++++++++++++
  2 files changed, 213 insertions(+)
  create mode 100644 Documentation/userspace-api/vduse.rst

diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index acd2cc2a538d..f63119130898 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst

@@ -24,6 +24,7 @@ place where this information is gathered.
     ioctl/index
     iommu
     media/index
+   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..8c4e2b2df8bb
--- /dev/null
+++ b/Documentation/userspace-api/vduse.rst

@@ -0,0 +1,212 @@
+==================================
+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.
+
+How VDUSE works
+------------
+Each userspace vDPA device is created by the VDUSE_CREATE_DEV ioctl on
+the character device (/dev/vduse/control). Then a device file with the
+specified name (/dev/vduse/$NAME) will appear, which can be used to
+implement the userspace vDPA device's control path and data path.
+
+To implement control path, a message-based communication protocol and some
+types of control messages are introduced in the VDUSE framework:
+
+- VDUSE_SET_VQ_ADDR: Set the vring address of virtqueue.
+
+- VDUSE_SET_VQ_NUM: Set the size of virtqueue
+
+- VDUSE_SET_VQ_READY: Set ready status of virtqueue
+
+- VDUSE_GET_VQ_READY: Get ready status of virtqueue
+
+- VDUSE_SET_VQ_STATE: Set the state for virtqueue
+
+- VDUSE_GET_VQ_STATE: Get the state for virtqueue
+
+- VDUSE_SET_FEATURES: Set virtio features supported by the driver
+
+- VDUSE_GET_FEATURES: Get virtio features supported by the device
+
+- VDUSE_SET_STATUS: Set the device status
+
+- VDUSE_GET_STATUS: Get the device status
+
+- VDUSE_SET_CONFIG: Write to device specific configuration space
+
+- VDUSE_GET_CONFIG: Read from device specific configuration space
+
+- VDUSE_UPDATE_IOTLB: Notify userspace to update the memory mapping in device IOTLB
+
+Those control messages are mostly based on the vdpa_config_ops in
+include/linux/vdpa.h which defines a unified interface to control
+different types of vdpa device. Userspace needs to read()/write()
+on the VDUSE device file to receive/reply those 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 message */
+
+             }
+
+             len = write(dev_fd, &resp, sizeof(resp));
+             if (len != sizeof(resp))
+                     return -1;
+
+             return 0;
+     }
+
+In the data path, vDPA device's iova regions will be mapped into userspace
+with the help of VDUSE_IOTLB_GET_FD ioctl on the VDUSE device file:
+
+- VDUSE_IOTLB_GET_FD: get the file descriptor to the first overlapped iova region.
+  Userspace can access this iova region by passing fd and corresponding size, offset,
+  perm to mmap(). For example:
+
+.. 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 + 1;
+             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;
+
+             /* do something to cache this iova region */
+
+             return addr + iova - entry.start;
+     }
+
+Besides, the following ioctls on the VDUSE device file are provided to support
+interrupt injection and setting up eventfd for virtqueue kicks:
+
+- VDUSE_VQ_SETUP_KICKFD: set the kickfd for virtqueue, this eventfd is used
+  by VDUSE kernel module to notify userspace to consume the vring.
+
+- VDUSE_INJECT_VQ_IRQ: inject an interrupt for specific virtqueue
+
+- VDUSE_INJECT_CONFIG_IRQ: inject a config interrupt
+
+Register VDUSE device on vDPA bus
+---------------------------------
+In order to make the VDUSE device work, administrator needs to use the management
+API (netlink) to register it on vDPA bus. Some sample codes are show below:
+
+.. code-block:: c
+
+     static int netlink_add_vduse(const char *name, int device_id)
+     {
+             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,
+                 VDPA_CMD_DEV_NEW, 0))
+                     goto nla_put_failure;
+
+             NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name);
+             NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse");
+             NLA_PUT_U32(msg, VDPA_ATTR_DEV_ID, device_id);
+
+             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;
+     }

Let's also explain this can be done via vdpa tool in iproute2 as well.

Sure.

Thanks,
Yongji