Date: Mon, 14 May 2001 04:10:05 -0700 (PDT) From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/27287: poll(2) returns 0 when POLLIN-ing ordinary files Message-ID: <200105141110.f4EBA5708618@freefall.freebsd.org>
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The following reply was made to PR kern/27287; it has been noted by GNATS.
From: Bruce Evans <bde@zeta.org.au>
To: clemensF <rabat@web.de>
Cc: Jonathan Lemon <jlemon@flugsvamp.com>,
freebsd-gnats-submit@FreeBSD.ORG, Bruce Guenter <bruceg@em.ca>
Subject: Re: kern/27287: poll(2) returns 0 when POLLIN-ing ordinary files
Date: Mon, 14 May 2001 21:08:01 +1000 (EST)
On Mon, 14 May 2001, clemensF wrote:
> > Jonathan Lemon:
>
> > > x.fd = open("trypoll.c",O_RDONLY);
> > > if (x.fd == -1) _exit(111);
> > > x.events = POLLIN;
> > > if (poll(&x,1,10) == -1) _exit(1);
> > > if (x.revents != POLLIN) _exit(1);
> >
> >
> > If you change "POLLIN" to "POLLRDNORM", then this will work as
> > you expect. Hoever, it's fairly pointless to poll() on a file,
> > since it will always return true, no matter what, so the code
> > above is fairly pointless.
> >
> > If you really want to poll a file for readability, use kqueue.
>
> the code snippet is part of "trypoll.c", which tests for a working poll(2) to
> autoconfigure a software-package. and it doesn't seem that pointless,
> because, as stated in the original PR, freebsd's poll(2) *does not* return
> true on an existing (local) file; it returns zero both as it's return- value
> and in x.revents, which is *wrong*.
>
> said package recognizes the deficiency, throws in it's workaround and
> proceeds (cvm-0.6). note that i'm not the author, which is bruce guenter
> <bruceg@em.ca>, but he build the programs on a linux system. i was the one
> who discovered the bug within freebsd 4.
Untested fix for -current, including style fixes.
Index: vfs_default.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/vfs_default.c,v
retrieving revision 1.50
diff -c -2 -r1.50 vfs_default.c
*** vfs_default.c 2001/05/06 17:40:22 1.50
--- vfs_default.c 2001/05/12 18:46:44
***************
*** 331,337 ****
} */ *ap;
{
! if ((ap->a_events & ~POLLSTANDARD) == 0)
! return (ap->a_events & (POLLRDNORM|POLLWRNORM));
! return (vn_pollrecord(ap->a_vp, ap->a_p, ap->a_events));
}
--- 331,339 ----
} */ *ap;
{
!
! if (ap->a_events & ~POLLSTANDARD)
! return (vn_pollrecord(ap->a_vp, ap->a_p, ap->a_events));
! /* PR27287: */
! return (ap->a_events & (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM));
}
Bruce
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