From: Alexandr Moshkov <dtalexundeer@yandex-team.ru>

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.
Also we have to validate that this feature will be enabled only when
qemu and back-end supports in-flight buffer and in-flight migration

It will be helpfull in future for in-flight requests migration in
vhost-user devices.

Update docs, add ref to label for inflight-io-tracking

Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20260115081103.655749-3-dtalexundeer@yandex-team.ru>
---
 docs/interop/vhost-user.rst    | 59 +++++++++++++++++++++-------------
 hw/virtio/vhost-user.c         |  7 ++++
 include/hw/virtio/vhost-user.h |  2 ++
 3 files changed, 46 insertions(+), 22 deletions(-)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 505f8d3a33..137c9f3669 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -743,6 +743,8 @@ negotiated, back-end can send file descriptors (at most 8 descriptors in
 each message) to front-end via ancillary data using this fd communication
 channel.
 
+.. _inflight_io_tracking:
+
 Inflight I/O tracking
 ---------------------
 
@@ -1040,26 +1042,27 @@ 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
 -----------------------
@@ -1250,12 +1253,24 @@ 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 suspend in-flight I/O
+  requests and record them as described in :ref:`Inflight I/O tracking
+  <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.
+
 ``VHOST_USER_SET_VRING_KICK``
   :id: 12
   :equivalent ioctl: ``VHOST_SET_VRING_KICK``
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 63fa9a1b4b..bb8f8eab77 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -2225,6 +2225,13 @@ static int vhost_user_backend_init(struct vhost_dev *dev, void *opaque,
             }
         }
 
+        if (!u->user->supports_inflight_migration ||
+            !virtio_has_feature(protocol_features,
+                                VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)) {
+            protocol_features &= ~(1ULL <<
+                               VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT);
+        }
+
         /* final set of protocol features */
         dev->protocol_features = protocol_features;
         err = vhost_user_set_protocol_features(dev, dev->protocol_features);
diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
index 55d5725ef8..53fe996686 100644
--- a/include/hw/virtio/vhost-user.h
+++ b/include/hw/virtio/vhost-user.h
@@ -32,6 +32,7 @@ enum VhostUserProtocolFeature {
     /* Feature 17 reserved for VHOST_USER_PROTOCOL_F_XEN_MMAP. */
     VHOST_USER_PROTOCOL_F_SHARED_OBJECT = 18,
     VHOST_USER_PROTOCOL_F_DEVICE_STATE = 19,
+    VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT = 20,
     VHOST_USER_PROTOCOL_F_MAX
 };
 
@@ -68,6 +69,7 @@ typedef struct VhostUserState {
     GPtrArray *notifiers;
     int memory_slots;
     bool supports_config;
+    bool supports_inflight_migration;
 } VhostUserState;
 
 /**
-- 
MST