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

[Yongji Xie <xieyongji@bytedance.com>]

On Thu, Apr 8, 2021 at 3:18 PM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2021/3/31 下午4:05, 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>
> > ---
> >   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