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Subject: [PATCH v3 1/3] spec/vhost-user: extend vhost-user to support the vhost-pci based inter-vm communiaction

The protocol feature, VHOST_USER_PROTOCOL_F_VHOST_PCI, indicates the
support of vhost-pci. The vhost-pci extension requires the master side
implementation to support an asynchronous socket read method. This is
used when the slave side vhost-pci device and driver finishes the
feature bits negotiation. The negotiated feature bits are sent to the
master. If the feature bits sent by the slave are a subset of the ones
that were sent by the master, the master should perform a reset of the
master device (e.g. virtio_net), to re-negotiate the feature bits using
the ones sent by the slave.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
 docs/specs/vhost-user.txt | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
index d70bd83..18e49d0 100644
--- a/docs/specs/vhost-user.txt
+++ b/docs/specs/vhost-user.txt
@@ -17,12 +17,15 @@ The protocol defines 2 sides of the communication, master and slave. Master is
 the application that shares its virtqueues, in our case QEMU. Slave is the
 consumer of the virtqueues.
-In the current implementation QEMU is the Master, and the Slave is intended to
+In the traditional implementation QEMU is the master, and the slave is intended to
 be a software Ethernet switch running in user space, such as Snabbswitch.
 Master and slave can be either a client (i.e. connecting) or server (listening)
 in the socket communication.
+The current vhost-user protocol is extended to support the vhost-pci based inter-VM
+communication. In this case, both the slave and master are QEMU instances.
 Message Specification
@@ -36,7 +39,7 @@ consists of 3 header fields and a payload:
  * Request: 32-bit type of the request
  * Flags: 32-bit bit field:
    - Lower 2 bits are the version (currently 0x01)
-   - Bit 2 is the reply flag - needs to be sent on each reply from the slave
+   - Bit 2 is the reply flag - needs to be sent on each reply
    - Bit 3 is the need_reply flag - see VHOST_USER_PROTOCOL_F_REPLY_ACK for
  * Size - 32-bit size of the payload
@@ -119,9 +122,9 @@ The protocol for vhost-user is based on the existing implementation of vhost
 for the Linux Kernel. Most messages that can be sent via the Unix domain socket
 implementing vhost-user have an equivalent ioctl to the kernel implementation.
-The communication consists of master sending message requests and slave sending
-message replies. Most of the requests don't require replies. Here is a list of
-the ones that do:
+Traditionally, the communication consists of master sending message requests and
+slave sending message replies. Most of the requests don't require replies. Here
+is a list of the ones that do:
@@ -130,6 +133,10 @@ the ones that do:
 [ Also see the section on REPLY_ACK protocol extension. ]
+Currently, the communication also supports the slave actively sending messages
+to the master. Here is a list of them:
 There are several messages that the master sends with file descriptors passed
 in the ancillary data:
@@ -259,6 +266,7 @@ Protocol features
 #define VHOST_USER_PROTOCOL_F_RARP           2
 Message types
@@ -279,8 +287,9 @@ Message types
       Id: 2
       Master payload: u64
+      Slave payload: u64
-      Enable features in the underlying vhost implementation using a bitmask.
+      Feature bits negotiation between the master and slave using a bitmask.
       Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for

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