Re: [Qemu-devel] [PATCH v4 1/7] qemu-char: Add MSG_CMSG_CLOEXEC flag to recvmsg

Corey Bryant <coreyb@xxxxxxxxxxxxxxxxxx> · Mon, 25 Jun 2012 09:44:09 -0400

On 06/25/2012 05:16 AM, Stefan Hajnoczi wrote:

On Fri, Jun 22, 2012 at 01:31:17PM -0600, Eric Blake wrote:

On 06/22/2012 12:36 PM, Corey Bryant wrote:

This sets the close-on-exec flag for the file descriptor received
via SCM_RIGHTS.

Signed-off-by: Corey Bryant <coreyb@xxxxxxxxxxxxxxxxxx>
---
v4
  -This patch is new in v4 (eblake@xxxxxxxxxx)

  qemu-char.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/qemu-char.c b/qemu-char.c
index c2aaaee..f890113 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2263,7 +2263,7 @@ static ssize_t tcp_chr_recv(CharDriverState *chr, char *buf, size_t len)
      msg.msg_control = &msg_control;
      msg.msg_controllen = sizeof(msg_control);

-    ret = recvmsg(s->fd, &msg, 0);
+    ret = recvmsg(s->fd, &msg, MSG_CMSG_CLOEXEC);


MSG_CMSG_CLOEXEC is not (yet) in POSIX (although it has been proposed
for addition); therefore, at the moment, it only exists on Linux and
Cygwin.  Does this need to have conditional code to allow compilation on
BSD, such as:

#ifndef MSG_CMSG_CLOEXEC
# define MSG_CMSG_CLOEXEC 0
#endif

as well as fallback code that sets FD_CLOEXEC manually via fcntl() when
MSG_CMSG_CLOEXEC is missing?


Good point.  I think the answer is yes.  Just like qemu_open() we can
wrap "recvmsg(2) with fd" so that platforms with MSG_CMSG_CLOEXEC use
that flag and other platforms use qemu_set_cloexec().

Stefan



Thanks for pointing this out.  I'll make the updates in v5.

--
Regards,
Corey


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