ivshmem: add check on protocol version in QEMU

Send a protocol version as the first message from server, clients must
close communication if they don't support this protocol version.  Older
QEMUs should be fine with this change in the protocol since they
overrides their own vm_id on reception of an id associated to no
eventfd.

Signed-off-by: David Marchand <david.marchand@6wind.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[use fifo_update_and_get()]
Reviewed-by: Claudio Fontana <claudio.fontana@huawei.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/contrib/ivshmem-client/ivshmem-client.c b/contrib/ivshmem-client/ivshmem-client.c
index bfaf584ba7..076e3ec31c 100644
--- a/contrib/ivshmem-client/ivshmem-client.c
+++ b/contrib/ivshmem-client/ivshmem-client.c
@@ -206,10 +206,17 @@ ivshmem_client_connect(IvshmemClient *client)
         goto err_close;
     }
 
-    /* first, we expect our index + a fd == -1 */
+    /* first, we expect a protocol version */
+    if (ivshmem_client_read_one_msg(client, &tmp, &fd) < 0 ||
+        (tmp != IVSHMEM_PROTOCOL_VERSION) || fd != -1) {
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server\n");
+        goto err_close;
+    }
+
+    /* then, we expect our index + a fd == -1 */
     if (ivshmem_client_read_one_msg(client, &client->local.id, &fd) < 0 ||
         client->local.id < 0 || fd != -1) {
-        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server\n");
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (2)\n");
         goto err_close;
     }
     IVSHMEM_CLIENT_DEBUG(client, "our_id=%ld\n", client->local.id);
@@ -221,7 +228,7 @@ ivshmem_client_connect(IvshmemClient *client)
         if (fd >= 0) {
             close(fd);
         }
-        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (2)\n");
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (3)\n");
         goto err_close;
     }
     client->shm_fd = fd;