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-rw-r--r--docs/interop/vhost-user.txt21
1 files changed, 12 insertions, 9 deletions
diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
index c058c407df..534caab18a 100644
--- a/docs/interop/vhost-user.txt
+++ b/docs/interop/vhost-user.txt
@@ -379,6 +379,7 @@ Protocol features
 #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
 
 Master message types
 --------------------
@@ -664,7 +665,8 @@ Master message types
       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
+      When VHOST_USER_PROTOCOL_F_CONFIG is negotiated, this message is
+      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
@@ -677,7 +679,8 @@ Master message types
       Master payload: virtio device config space
       Slave payload: N/A
 
-      Submitted by the vhost-user master when the Guest changes the virtio
+      When VHOST_USER_PROTOCOL_F_CONFIG is negotiated, this message is
+      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
@@ -766,13 +769,13 @@ Slave message types
      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.
+     When VHOST_USER_PROTOCOL_F_CONFIG is negotiated, 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:
 -------------------------------