svn commit: r268493 - head/lib/libfetch

[Baptiste Daroussin]

On Thu, Jul 10, 2014 at 07:08:07PM +0300, Konstantin Belousov wrote:
> On Thu, Jul 10, 2014 at 03:52:53PM +0200, Baptiste Daroussin wrote:
> > On Thu, Jul 10, 2014 at 04:28:13PM +0300, Konstantin Belousov wrote:
> > > On Thu, Jul 10, 2014 at 01:04:53PM +0000, Baptiste Daroussin wrote:
> > > > Author: bapt
> > > > Date: Thu Jul 10 13:04:52 2014
> > > > New Revision: 268493
> > > > URL: http://svnweb.freebsd.org/changeset/base/268493
> > > > 
> > > > Log:
> > > >   Support EAGAIN in fetch_writev
> > > >   
> > > >   Reviewed by:	des
> > > >   Approved by:	des
> > > > 
> > > > Modified:
> > > >   head/lib/libfetch/common.c
> > > > 
> > > > Modified: head/lib/libfetch/common.c
> > > > ==============================================================================
> > > > --- head/lib/libfetch/common.c	Thu Jul 10 12:41:58 2014	(r268492)
> > > > +++ head/lib/libfetch/common.c	Thu Jul 10 13:04:52 2014	(r268493)
> > > > @@ -1110,6 +1110,8 @@ fetch_writev(conn_t *conn, struct iovec 
> > > >  			errno = 0;
> > > >  			pfd.revents = 0;
> > > >  			if (poll(&pfd, 1, deltams) < 0) {
> > > > +				if (errno == EAGAIN)
> > > > +					continue;
> > > >  				if (errno == EINTR && fetchRestartCalls)
> > > >  					continue;
> > > >  				return (-1);
> > > 
> > > How is this error possible ? poll(2) converts EAGAIN from seltdwait(9)
> > > to no error.
> > 
> > For posix compliance, libfetch is not only used on FreeBSD, reading at:
> > http://pubs.opengroup.org/onlinepubs/009695399/functions/poll.html I can read:
> > 
> > [EAGAIN]
> >     The allocation of internal data structures failed but a subsequent request
> >     may succeed.
> > 
> > Am I missing something?
> 
> At least for me, it was very surprising.  I accustomed to the facts that
> poll(2) is never restarted after signal, and that you only should test
> for EINTR as the error condition.
> 
> Apparently, the behaviour of converting EAGAIN to no error can be tracked
> back to at least 4.4 lite.  On the other hand, just looking into the man
> page for poll(2) on STREAMS-based systems indeed mention EAGAIN.
> 
> My suggestion is to add a comment, noting that FreeBSD does not return
> EAGAIN from poll(2), but SUSv4 allows it.  This way, the addition would
> be not removed in some code cleanup.  Does it sound reasonable ?

More that reasonable (I was thinking something like this as well) I will do it
tomorrow.

regards,
Bapt
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