[Libguestfs] Patchable build problems on OS X 10.10

[Richard W.M. Jones]

On Mon, Feb 09, 2015 at 10:56:54AM +0100, Pino Toscano wrote:
> On Friday 06 February 2015 10:03:37 Richard W.M. Jones wrote:
> > On Thu, Feb 05, 2015 at 10:53:06PM +0000, Margaret Lewicka wrote:
> > > +/* Fixes for Mac OS X */
> > > +#if defined __APPLE__ && defined __MACH__
> > > +#include <sys/un.h>
> > > +#endif
> > > +#ifndef SOCK_CLOEXEC
> > > +# define SOCK_CLOEXEC O_CLOEXEC
> > > +#endif
> > > +#ifndef SOCK_NONBLOCK
> > > +# define SOCK_NONBLOCK O_NONBLOCK
> > > +#endif
> > > +/* End of fixes for Mac OS X */
> > > +
> > >  /* Check minimum required version of libvirt.  The libvirt backend
> > >   * is new and not the default, so we can get away with forcing
> > >   * people who want to try it to have a reasonably new version of
> 
> This IMHO is clearly wrong: the O_* constants are for open() & friends,
> not for socket & socket4.

I checked this out before committing it, and I accepted it because on
Linux/glibc, SOCK_CLOEXEC == O_CLOEXEC and SOCK_NONBLOCK == O_NONBLOCK
(see the definitions in bits/socket.h and bits/socket_type.h on a
Linux system).

Of course this is not a law of nature and there could be systems where
this is not true.

The macros as defined only affect systems that don't define SOCK_* at
all.

> Theoretically, we could switch the socket() usages in launch-libvirt.c
> to socket4(), which can be replaced by gnulib if missing (we already
> use the "accept4" gnulib module). On the other hand, it seems that
> such gnulib emulation does not provide SOCK_NONBLOCK, so either
> a) fix that in gnulib
> b) use the "nonblocking" gnulib module, using set_nonblocking_flag()
>    instead of SOCK_NONBLOCK

(b) would not be atomic.  I'm not certain if there's a case where that
matters for O_NONBLOCK.  (Of course it definitely matters for
O_CLOEXEC and we've have bugs caused by that in the past)

> Also, sys/un.h is POSIX [1], so it can be included unconditionally.

Agreed.

Rich.

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