vhost-user: add new vhost user messages to support virtio config space

Add VHOST_USER_GET_CONFIG/VHOST_USER_SET_CONFIG messages which can be
used for live migration of vhost user devices, also vhost user devices
can benefit from the messages to get/set virtio config space from/to the
I/O target. For the purpose to support virtio config space change,
VHOST_USER_SLAVE_CONFIG_CHANGE_MSG message is added as the event notifier
in case virtio config space change in the slave I/O target.

Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
index d49444e..0875ef4 100644
--- a/docs/interop/vhost-user.txt
+++ b/docs/interop/vhost-user.txt
@@ -119,6 +119,19 @@ Depending on the request type, payload can be:
     - 3: IOTLB invalidate
     - 4: IOTLB access fail
 
+ * Virtio device config space
+   -----------------------------------
+   | offset | size | flags | payload |
+   -----------------------------------
+
+   Offset: a 32-bit offset of virtio device's configuration space
+   Size: a 32-bit configuration space access size in bytes
+   Flags: a 32-bit value:
+    - 0: Vhost master messages used for writeable fields
+    - 1: Vhost master messages used for live migration
+   Payload: Size bytes array holding the contents of the virtio
+       device's configuration space
+
 In QEMU the vhost-user message is implemented with the following struct:
 
 typedef struct VhostUserMsg {
@@ -132,6 +145,7 @@ typedef struct VhostUserMsg {
         VhostUserMemory memory;
         VhostUserLog log;
         struct vhost_iotlb_msg iotlb;
+        VhostUserConfig config;
     };
 } QEMU_PACKED VhostUserMsg;
 
@@ -623,6 +637,32 @@ Master message types
       and expect this message once (per VQ) during device configuration
       (ie. before the master starts the VQ).
 
+ * VHOST_USER_GET_CONFIG
+
+      Id: 24
+      Equivalent ioctl: N/A
+      Master payload: virtio device config space
+      Slave payload: virtio device config space
+
+      Submitted by the vhost-user master to fetch the contents of the virtio
+      device configuration space, vhost-user slave's payload size MUST match
+      master's request, vhost-user slave uses zero length of payload to
+      indicate an error to vhost-user master. The vhost-user master may
+      cache the contents to avoid repeated VHOST_USER_GET_CONFIG calls.
+
+* VHOST_USER_SET_CONFIG
+
+      Id: 25
+      Equivalent ioctl: N/A
+      Master payload: virtio device config space
+      Slave payload: N/A
+
+      Submitted by the vhost-user master when the Guest changes the virtio
+      device configuration space and also can be used for live migration
+      on the destination host. The vhost-user slave must check the flags
+      field, and slaves MUST NOT accept SET_CONFIG for read-only
+      configuration space fields unless the live migration bit is set.
+
 Slave message types
 -------------------
 
@@ -641,6 +681,21 @@ Slave message types
       This request should be send only when VIRTIO_F_IOMMU_PLATFORM feature
       has been successfully negotiated.
 
+* VHOST_USER_SLAVE_CONFIG_CHANGE_MSG
+
+     Id: 2
+     Equivalent ioctl: N/A
+     Slave payload: N/A
+     Master payload: N/A
+
+     Vhost-user slave sends such messages to notify that the virtio device's
+     configuration space has changed, for those host devices which can support
+     such feature, host driver can send VHOST_USER_GET_CONFIG message to slave
+     to get the latest content. If VHOST_USER_PROTOCOL_F_REPLY_ACK is
+     negotiated, and slave set the VHOST_USER_NEED_REPLY flag, master must
+     respond with zero when operation is successfully completed, or non-zero
+     otherwise.
+
 VHOST_USER_PROTOCOL_F_REPLY_ACK:
 -------------------------------
 The original vhost-user specification only demands replies for certain