vhost-user: Introduce a new protocol feature REPLY_ACK.

This introduces the VHOST_USER_PROTOCOL_F_REPLY_ACK.

If negotiated, client applications should send a u64 payload in
response to any message that contains the "need_reply" bit set
on the message flags. Setting the payload to "zero" indicates the
command finished successfully. Likewise, setting it to "non-zero"
indicates an error.

Currently implemented only for SET_MEM_TABLE.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Prerna Saxena <prerna.saxena@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 1995fd20bd..b57454a4b7 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -31,6 +31,7 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_MQ = 0,
     VHOST_USER_PROTOCOL_F_LOG_SHMFD = 1,
     VHOST_USER_PROTOCOL_F_RARP = 2,
+    VHOST_USER_PROTOCOL_F_REPLY_ACK = 3,
 
     VHOST_USER_PROTOCOL_F_MAX
 };
@@ -84,6 +85,7 @@ typedef struct VhostUserMsg {
 
 #define VHOST_USER_VERSION_MASK     (0x3)
 #define VHOST_USER_REPLY_MASK       (0x1<<2)
+#define VHOST_USER_NEED_REPLY_MASK  (0x1 << 3)
     uint32_t flags;
     uint32_t size; /* the following payload size */
     union {
@@ -158,6 +160,25 @@ fail:
     return -1;
 }
 
+static int process_message_reply(struct vhost_dev *dev,
+                                 VhostUserRequest request)
+{
+    VhostUserMsg msg;
+
+    if (vhost_user_read(dev, &msg) < 0) {
+        return -1;
+    }
+
+    if (msg.request != request) {
+        error_report("Received unexpected msg type."
+                     "Expected %d received %d",
+                     request, msg.request);
+        return -1;
+    }
+
+    return msg.payload.u64 ? -1 : 0;
+}
+
 static bool vhost_user_one_time_request(VhostUserRequest request)
 {
     switch (request) {
@@ -248,11 +269,18 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
     int fds[VHOST_MEMORY_MAX_NREGIONS];
     int i, fd;
     size_t fd_num = 0;
+    bool reply_supported = virtio_has_feature(dev->protocol_features,
+                                              VHOST_USER_PROTOCOL_F_REPLY_ACK);
+
     VhostUserMsg msg = {
         .request = VHOST_USER_SET_MEM_TABLE,
         .flags = VHOST_USER_VERSION,
     };
 
+    if (reply_supported) {
+        msg.flags |= VHOST_USER_NEED_REPLY_MASK;
+    }
+
     for (i = 0; i < dev->mem->nregions; ++i) {
         struct vhost_memory_region *reg = dev->mem->regions + i;
         ram_addr_t offset;
@@ -288,6 +316,10 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
         return -1;
     }
 
+    if (reply_supported) {
+        return process_message_reply(dev, msg.request);
+    }
+
     return 0;
 }