From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay2.corp.sgi.com [137.38.102.29]) by oss.sgi.com (Postfix) with ESMTP id 71FD57F63 for ; Wed, 9 Apr 2014 15:48:12 -0500 (CDT) Message-ID: <5345B209.5040906@sgi.com> Date: Wed, 09 Apr 2014 15:48:09 -0500 From: Mark Tinguely MIME-Version: 1.0 Subject: Re: [PATCH] xfs_io: fix random pread/pwrite to honor offset References: <53459C4E.9030902@sandeen.net> In-Reply-To: <53459C4E.9030902@sandeen.net> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Eric Sandeen Cc: xfs-oss On 04/09/14 14:15, Eric Sandeen wrote: > xfs_io's pread & pwrite claim to support a random IO mode > where it will do random IOs between offset & offset+len. > > However, offset was ignored, and we did the IOs between 0 > and len instead. > > Clang caught this by pointing out that the calculated/normalized > "offset" variable was never read. > > (NB: If the range is larger than RAND_MAX, these functions don't > work, but that's always been true, so I'll leave it for another > day...) > > Signed-off-by: Eric Sandeen > --- > > I haven't tested this w/ xfstests but I don't see anyone who calls > pread/pwrite with "-R" (and it's not documented in the manpage!) > > diff --git a/io/pread.c b/io/pread.c > index a42baed..465c22b 100644 > --- a/io/pread.c > +++ b/io/pread.c > @@ -246,7 +246,7 @@ read_random( offset can be the end of file offset. Do we care that the read (/write) could start or end past the end of file? > > *total = 0; > while (count > 0) { > - off = ((random() % range) / buffersize) * buffersize; > + off = ((offset + (random() % range)) / buffersize) * buffersize; > bytes = do_pread(fd, off, buffersize, buffersize); > if (bytes == 0) > break; Looks like this was introduced in: commit 8fb2237e65555ff540e8b6108ffccfffefe239ac Author: Nathan Scott Date: Fri Nov 11 14:25:18 2005 +0000 Provide further debugging options and tweaks for analysing the read/write paths. Merge of master-melb:xfs-cmds:24372a by kenmcd. --- If it was broken for 8.5 years, I think it could be removed. --Mark. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs