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

[Stefan Hajnoczi]

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 <address@hidden>
> > ---
> > v4
> >  -This patch is new in v4 (address@hidden)
> > 
> >  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