RE: poll() emulation in git

From: Joachim Schmitz <jojo@schmitz-digital.de>
Date: Sep 5, 2012, 13:36 UTC
Message-ID: <00d801cd8b6b$844bbcd0$8ce33670$@schmitz-digital.de>
In-Reply-To: <50474001.5030407@gnu.org>

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> From: Joachim Schmitz [mailto:jojo@schmitz-digital.de]
> Sent: Wednesday, September 05, 2012 2:58 PM
> To: 'Paolo Bonzini'
> Cc: 'Junio C Hamano'; 'git@vger.kernel.org'; 'Erik Faye-Lund'; 'bug-gnulib@gnu.org'
> Subject: RE: poll() emulation in git
> 
> > From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo Bonzini
> > Sent: Wednesday, September 05, 2012 2:05 PM
> > To: Joachim Schmitz
> > Cc: 'Junio C Hamano'; git@vger.kernel.org; 'Erik Faye-Lund'; bug-gnulib@gnu.org
> > Subject: Re: poll() emulation in git
> >
> > Il 05/09/2012 13:24, Joachim Schmitz ha scritto:
> > > However: this poll implementation, while compiling OK, doesn't work properly.
> > > Because it uses recv(...,MSG_PEEK), it works on sockets only (returns ENOTSOCK on anything else), while the real poll() works

on all

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> > > kind if file descriptors, at least that is my understanding.
> >
> > Actually recv(...,MSG_PEEK) on most Unix variants works on non-sockets
> > too.  The trick is taken from GNU Pth in turn.
> >
> > > Here on HP NonStop, when being connected via an non-interactive SSH, we get a set of pipes (stdin, stdout, stderr) instead of

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> > > socket to talk to, so the poll() just hangs/loops.
> >
> > Does your system have a working FIONREAD ioctl for pipes?
> 
> It does have FIONREAD ioctl. Whether it works properly is to be determined...
> I'll test if you could show me how?

Oh, now I see what you aimed at, but no, that Mac OS X method doesn't work for me, I tried (at least I think I did).

And <sys/ioctl.h> has
/*
 * Normal IOCTL's supported by the socket interface
 */
#define FIONREAD        _IOR(0, 8, _ioctl_int)       /* Num of bytes to read */
#define FIONBIO         _IOW(0, 9, _ioctl_int)       /* Non-blocking I/O     */

So these seem to be supported on sockets only, I guess. And indeed the man pages for ioctl confirms:

          Valid values for the request parameter for AF_INET or
          AF_INET6 sockets are:

          FIONREAD  Gets the number of bytes available for reading and
                    stores it at the int pointed at by arg.

So not even AF_UNIX sockets, not to mention pipes...

Bye, Jojo