vhost-user-bridge: fix iov_restore_front() warning

  CC      tests/vhost-user-bridge.o
/home/dgilbert/git/qemu-world3/tests/vhost-user-bridge.c:228:23: warning: variables 'front' and 'iov' used in loop condition not modified in loop body [-Wfor-loop-analysis]
    for (cur = front; front != iov; cur++) {
                      ^~~~~    ~~~
1 warning generated.

Fix the loop, document the function, and fix some related assert().

In practice, the loop bug was harmless because the front sg buffer is
enough to discard/restore the header size.

Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-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>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: Jens Freimann <jfreiman@redhat.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/tests/vhost-user-bridge.c b/tests/vhost-user-bridge.c
index 8618c20..1e5b5ca 100644
--- a/tests/vhost-user-bridge.c
+++ b/tests/vhost-user-bridge.c
@@ -220,12 +220,18 @@ vubr_handle_tx(VuDev *dev, int qidx)
     free(elem);
 }
 
+
+/* this function reverse the effect of iov_discard_front() it must be
+ * called with 'front' being the original struct iovec and 'bytes'
+ * being the number of bytes you shaved off
+ */
 static void
 iov_restore_front(struct iovec *front, struct iovec *iov, size_t bytes)
 {
     struct iovec *cur;
 
-    for (cur = front; front != iov; cur++) {
+    for (cur = front; cur != iov; cur++) {
+        assert(bytes >= cur->iov_len);
         bytes -= cur->iov_len;
     }
 
@@ -302,7 +308,8 @@ vubr_backend_recv_cb(int sock, void *ctx)
             }
             iov_from_buf(sg, elem->in_num, 0, &hdr, sizeof hdr);
             total += hdrlen;
-            assert(iov_discard_front(&sg, &num, hdrlen) == hdrlen);
+            ret = iov_discard_front(&sg, &num, hdrlen);
+            assert(ret == hdrlen);
         }
 
         struct msghdr msg = {