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Re: [PATCH] xfstests: kill lib/random.c

To: Eric Sandeen <sandeen@xxxxxxxxxxx>, Ben Myers <bpm@xxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH] xfstests: kill lib/random.c
From: Josef Bacik <jbacik@xxxxxx>
Date: Tue, 7 Jan 2014 15:15:14 -0500
Cc: <linux-btrfs@xxxxxxxxxxxxxxx>, <xfs@xxxxxxxxxxx>
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On 01/07/2014 03:10 PM, Eric Sandeen wrote:
On 1/7/14, 2:01 PM, Ben Myers wrote:
Hey Gents,

On Mon, Jan 06, 2014 at 03:46:58PM -0600, Eric Sandeen wrote:
On 1/6/14, 3:42 PM, Josef Bacik wrote:
On 01/06/2014 04:32 PM, Eric Sandeen wrote:
On 1/6/14, 1:58 PM, Josef Bacik wrote:
I was trying to reproduce something with fsx and I noticed that no matter what
seed I set I was getting the same file.  Come to find out we are overloading
random() with our own custom horribleness for some unknown reason.  So nuke the
damn thing from orbit and rely on glibc's random().  With this fix the -S option
actually does something with fsx.  Thanks,
Hm, old comments seem to indicate that this was done <handwave> to make random
behave the same on different architectures (i.e. same result from same seed,
I guess?)  I . . . don't know if that is true of glibc's random(), is it?

I'd like to dig into the history just a bit before we yank this, just to
be sure.
I think that if we need the output to match based on a predictable
random() output then we've lost already. We shouldn't be checking for
specific output (like inode numbers or sizes etc) that are dependant
on random()'s behaviour, and if we are we need to fix those tests. So
even if that is why it was put in place originally I'd say it is high
time we ripped it out and fixed up any tests that rely on this
behaviour. Thanks,
Yeah, you're probably right.  And the ancient xfstests history seems to
be lost in the mists of time, at least as far as I can see.  So I'm ok
with this but let's let Dave & SGI chime in too just to be certain.
I did not have success locating the history prior to what we have posted on
oss.  I agree that it was likely added so that tests that expose output from
random into golden output files will have the same results across arches.
Maybe this is still of concern for folks who use a different c library with the
kernel.

Looks there are quite a few callers.  IMO if we're going to remove this we
should fix the tests first.
Or first, determine if they really need fixing.  Did you find tests which
actually contain the random results in the golden output?


I looked through stuff when I ripped it out and I couldn't find anything that relied on consistent numbers, we tend to filter all that stuff out. I think ripping it out and waiting to see if somebody complains is a good way to figure out if things need fixing, but that may be less than friendly ;). Thanks,

Josef

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