iov: handle EOF in iov_send_recv

Without this patch, iov_send_recv() never returns when do_send_recv()
returns zero.
Signed-off-by: NMORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
(cherry picked from commit 84004290)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

util/iov.c

@@ -202,6 +202,12 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
             return -1;
         }
 
+        if (ret == 0 && !do_send) {
+            /* recv returns 0 when the peer has performed an orderly
+             * shutdown. */
+            break;
+        }
+
         /* Prepare for the next iteration */
         offset += ret;
         total += ret;