From: Mark Tinguely <tinguely@sgi.com>
To: Eric Sandeen <sandeen@sandeen.net>
Cc: xfs-oss <xfs@oss.sgi.com>
Subject: Re: [PATCH] xfs_io: fix random pread/pwrite to honor offset
Date: Wed, 09 Apr 2014 15:48:09 -0500 [thread overview]
Message-ID: <5345B209.5040906@sgi.com> (raw)
In-Reply-To: <53459C4E.9030902@sandeen.net>
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<sandeen@redhat.com>
> ---
>
> 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 <nathans@sgi.com>
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.
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next prev parent reply other threads:[~2014-04-09 20:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-09 19:15 [PATCH] xfs_io: fix random pread/pwrite to honor offset Eric Sandeen
2014-04-09 20:48 ` Mark Tinguely [this message]
2014-04-09 20:55 ` Eric Sandeen
2014-04-11 4:48 ` Dave Chinner
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