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

To: Josef Bacik <jbacik@xxxxxx>, linux-btrfs@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Subject: Re: [PATCH] xfstests: kill lib/random.c
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Mon, 06 Jan 2014 15:46:58 -0600
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <52CB2336.2060009@xxxxxx>
References: <1389038323-8304-1-git-send-email-jbacik@xxxxxx> <52CB20ED.1010705@xxxxxxxxxx> <52CB2336.2060009@xxxxxx>
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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.

Thanks,
-Eric

> Josef

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