On 1/12/26 23:08, Stefan Hajnoczi wrote:
On Mon, Jan 12, 2026 at 04:45:00PM +0500, Alexandr Moshkov wrote:
Add vhost-user protocol feature
VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT
Now on GET_VRING_BASE this feature can control whether to wait for
in-flight requests to complete or not.
It will be helpfull in future for in-flight requests migration in
vhost-user devices.
Signed-off-by: Alexandr Moshkov<[email protected]>
---
docs/interop/vhost-user.rst | 52 ++++++++++++++++++----------------
include/hw/virtio/vhost-user.h | 1 +
2 files changed, 29 insertions(+), 24 deletions(-)
diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 02908b48fa..80c80aada5 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -1033,26 +1033,27 @@ Protocol features
.. code:: c
- #define VHOST_USER_PROTOCOL_F_MQ 0
- #define VHOST_USER_PROTOCOL_F_LOG_SHMFD 1
- #define VHOST_USER_PROTOCOL_F_RARP 2
- #define VHOST_USER_PROTOCOL_F_REPLY_ACK 3
- #define VHOST_USER_PROTOCOL_F_MTU 4
- #define VHOST_USER_PROTOCOL_F_BACKEND_REQ 5
- #define VHOST_USER_PROTOCOL_F_CROSS_ENDIAN 6
- #define VHOST_USER_PROTOCOL_F_CRYPTO_SESSION 7
- #define VHOST_USER_PROTOCOL_F_PAGEFAULT 8
- #define VHOST_USER_PROTOCOL_F_CONFIG 9
- #define VHOST_USER_PROTOCOL_F_BACKEND_SEND_FD 10
- #define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER 11
- #define VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD 12
- #define VHOST_USER_PROTOCOL_F_RESET_DEVICE 13
- #define VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS 14
- #define VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS 15
- #define VHOST_USER_PROTOCOL_F_STATUS 16
- #define VHOST_USER_PROTOCOL_F_XEN_MMAP 17
- #define VHOST_USER_PROTOCOL_F_SHARED_OBJECT 18
- #define VHOST_USER_PROTOCOL_F_DEVICE_STATE 19
+ #define VHOST_USER_PROTOCOL_F_MQ 0
+ #define VHOST_USER_PROTOCOL_F_LOG_SHMFD 1
+ #define VHOST_USER_PROTOCOL_F_RARP 2
+ #define VHOST_USER_PROTOCOL_F_REPLY_ACK 3
+ #define VHOST_USER_PROTOCOL_F_MTU 4
+ #define VHOST_USER_PROTOCOL_F_BACKEND_REQ 5
+ #define VHOST_USER_PROTOCOL_F_CROSS_ENDIAN 6
+ #define VHOST_USER_PROTOCOL_F_CRYPTO_SESSION 7
+ #define VHOST_USER_PROTOCOL_F_PAGEFAULT 8
+ #define VHOST_USER_PROTOCOL_F_CONFIG 9
+ #define VHOST_USER_PROTOCOL_F_BACKEND_SEND_FD 10
+ #define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER 11
+ #define VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD 12
+ #define VHOST_USER_PROTOCOL_F_RESET_DEVICE 13
+ #define VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS 14
+ #define VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS 15
+ #define VHOST_USER_PROTOCOL_F_STATUS 16
+ #define VHOST_USER_PROTOCOL_F_XEN_MMAP 17
+ #define VHOST_USER_PROTOCOL_F_SHARED_OBJECT 18
+ #define VHOST_USER_PROTOCOL_F_DEVICE_STATE 19
+ #define VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT 20
Front-end message types
-----------------------
@@ -1243,11 +1244,14 @@ Front-end message types
When and as long as all of a device's vrings are stopped, it is
*suspended*, see :ref:`Suspended device state
- <suspended_device_state>`. The back-end must complete all inflight I/O
- requests for the specified vring before stopping it.
+ <suspended_device_state>`.
- The request payload's *num* field is currently reserved and must be
- set to 0.
+ By default, the back-end must complete all inflight I/O requests for the
+ specified vring before stopping it.
+
+ If the ``VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT`` protocol feature
+ has been negotiated, the back-end may stop the vring immediately without
+ waiting for inflight I/O requests to complete.
This paragraph is not specific enough. It gives the impression that I/O
requests can be left running, but that's not the case. They need to be
quiesced and recorded in the Inflight I/O Tracking
(VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD) shared memory data structure.
I suggest rewording it as follows:
If the ``VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT`` protocol
feature has been negotiated, the back-end may suspend in-flight I/O
requests and record them as described in :ref:`inflight-io-tracking`
instead of completing them before stopping the vring. How to suspend
an in-flight request depends on the implementation of the back-end but
it typically can be done by aborting or cancelling the underlying I/O
request. The ``VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT``
protocol feature must only be neogotiated if
``VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD`` is also negotiated.
(A _inflight-io-tracking label needs to be added in order to reference
the "Inflight I/O tracking" section.)
I'll fix that, thanks!
