diff options
| -rw-r--r-- | docs/interop/vhost-user.rst | 77 |
1 files changed, 73 insertions, 4 deletions
diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst index 768fb5c..9202b16 100644 --- a/docs/interop/vhost-user.rst +++ b/docs/interop/vhost-user.rst @@ -108,6 +108,43 @@ A vring state description :num: a 32-bit number +A vring descriptor index for split virtqueues +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + ++-------------+---------------------+ +| vring index | index in avail ring | ++-------------+---------------------+ + +:vring index: 32-bit index of the respective virtqueue + +:index in avail ring: 32-bit value, of which currently only the lower 16 + bits are used: + + - Bits 0–15: Index of the next *Available Ring* descriptor that the + back-end will process. This is a free-running index that is not + wrapped by the ring size. + - Bits 16–31: Reserved (set to zero) + +Vring descriptor indices for packed virtqueues +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + ++-------------+--------------------+ +| vring index | descriptor indices | ++-------------+--------------------+ + +:vring index: 32-bit index of the respective virtqueue + +:descriptor indices: 32-bit value: + + - Bits 0–14: Index of the next *Available Ring* descriptor that the + back-end will process. This is a free-running index that is not + wrapped by the ring size. + - Bit 15: Driver (Available) Ring Wrap Counter + - Bits 16–30: Index of the entry in the *Used Ring* where the back-end + will place the next descriptor. This is a free-running index that + is not wrapped by the ring size. + - Bit 31: Device (Used) Ring Wrap Counter + A vring address description ^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -1042,18 +1079,50 @@ Front-end message types ``VHOST_USER_SET_VRING_BASE`` :id: 10 :equivalent ioctl: ``VHOST_SET_VRING_BASE`` - :request payload: vring state description + :request payload: vring descriptor index/indices :reply payload: N/A - Sets the base offset in the available vring. + Sets the next index to use for descriptors in this vring: + + * For a split virtqueue, sets only the next descriptor index to + process in the *Available Ring*. The device is supposed to read the + next index in the *Used Ring* from the respective vring structure in + guest memory. + + * For a packed virtqueue, both indices are supplied, as they are not + explicitly available in memory. + + Consequently, the payload type is specific to the type of virt queue + (*a vring descriptor index for split virtqueues* vs. *vring descriptor + indices for packed virtqueues*). ``VHOST_USER_GET_VRING_BASE`` :id: 11 :equivalent ioctl: ``VHOST_USER_GET_VRING_BASE`` :request payload: vring state description - :reply payload: vring state description + :reply payload: vring descriptor index/indices + + Stops the vring and returns the current descriptor index or indices: + + * For a split virtqueue, returns only the 16-bit next descriptor + index to process in the *Available Ring*. Note that this may + differ from the available ring index in the vring structure in + memory, which points to where the driver will put new available + descriptors. For the *Used Ring*, the device only needs the next + descriptor index at which to put new descriptors, which is the + value in the vring structure in memory, so this value is not + covered by this message. + + * For a packed virtqueue, neither index is explicitly available to + read from memory, so both indices (as maintained by the device) are + returned. + + Consequently, the payload type is specific to the type of virt queue + (*a vring descriptor index for split virtqueues* vs. *vring descriptor + indices for packed virtqueues*). - Get the available vring base offset. + The request payload’s *num* field is currently reserved and must be + set to 0. ``VHOST_USER_SET_VRING_KICK`` :id: 12 |