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[Qemu-devel] [PATCH 8/9] iov_send_recv(): Handle zero bytes case even if

From: Stefan Hajnoczi
Subject: [Qemu-devel] [PATCH 8/9] iov_send_recv(): Handle zero bytes case even if OS does not
Date: Wed, 15 Aug 2012 16:09:03 +0100

From: Peter Maydell <address@hidden>

POSIX allows sendmsg() and recvmsg() to fail EMSGSIZE if passed a zero
msg.msg_iovlen (in particular the MacOS X implementation will do this).
Handle the case where iov_send_recv() is passed a zero byte count
explicitly, to avoid accidentally depending on the OS to treat zero
msg_iovlen as a no-op.

Signed-off-by: Peter Maydell <address@hidden>
Acked-by: Michael Tokarev <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
 iov.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/iov.c b/iov.c
index b333061..60705c7 100644
--- a/iov.c
+++ b/iov.c
@@ -146,6 +146,13 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, 
unsigned iov_cnt,
     ssize_t ret;
     unsigned si, ei;            /* start and end indexes */
+    if (bytes == 0) {
+        /* Catch the do-nothing case early, as otherwise we will pass an
+         * empty iovec to sendmsg/recvmsg(), and not all implementations
+         * accept this.
+         */
+        return 0;
+    }
     /* Find the start position, skipping `offset' bytes:
      * first, skip all full-sized vector elements, */

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