From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55495) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xou3p-0001kF-OQ for qemu-devel@nongnu.org; Thu, 13 Nov 2014 08:03:47 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xou3j-0003AV-GJ for qemu-devel@nongnu.org; Thu, 13 Nov 2014 08:03:41 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34435) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xou3j-0003AL-6a for qemu-devel@nongnu.org; Thu, 13 Nov 2014 08:03:35 -0500 Date: Thu, 13 Nov 2014 14:03:27 +0100 From: Kevin Wolf Message-ID: <20141113130327.GD3933@noname.redhat.com> References: <1415873823-13844-1-git-send-email-armbru@redhat.com> <1415873823-13844-4-git-send-email-armbru@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1415873823-13844-4-git-send-email-armbru@redhat.com> Subject: Re: [Qemu-devel] [PATCH v2 3/4] raw-posix: Fix try_seek_hole()'s handling of SEEK_DATA failure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: famz@redhat.com, tony@bakeyournoodle.com, qemu-devel@nongnu.org, stefanha@redhat.com, pbonzini@redhat.com, mreitz@redhat.com Am 13.11.2014 um 11:17 hat Markus Armbruster geschrieben: > When SEEK_HOLE tells us we're in a hole, we try SEEK_DATA to find its > end. When that fails, we pretend the hole extends to the end of file. > Wrong. Wrong only in some cases, see below. > Except when SEEK_END fails, we screw up and claim it extends > to offset -1. More wrong. > > Fortunately, these seeks are very unlikely to fail. Fix it anyway, by > returning failure. The caller will then pretend there are no holes. > Inaccurate, but safe. > > Signed-off-by: Markus Armbruster > --- > block/raw-posix.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/block/raw-posix.c b/block/raw-posix.c > index fd80d84..2a12a50 100644 > --- a/block/raw-posix.c > +++ b/block/raw-posix.c > @@ -1494,8 +1494,9 @@ static int try_seek_hole(BlockDriverState *bs, off_t start, off_t *data, > } else { > /* On a hole. We need another syscall to find its end. */ > *data = lseek(s->fd, start, SEEK_DATA); > - if (*data == -1) { > - *data = lseek(s->fd, 0, SEEK_END); > + if (*data < 0) { > + /* no idea where the hole ends, give up (unlikely to happen) */ Not quite unlikely. If the file ends with a sparse area, we'll get -1/ENXIO here. lseek() with SEEK_DATA starting in a hole when there is no data until EOF is actually the part that isn't documented in the man page, but ENXIO is what I'm seeing here on RHEL 7. > + return -errno; > } > } Kevin