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

To: Ben Myers <bpm@xxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>, Josef Bacik <jbacik@xxxxxx>
Subject: Re: [PATCH] xfstests: kill lib/random.c
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Tue, 07 Jan 2014 14:10:15 -0600
Cc: linux-btrfs@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140107200135.GD1935@xxxxxxx>
References: <1389038323-8304-1-git-send-email-jbacik@xxxxxx> <52CB20ED.1010705@xxxxxxxxxx> <52CB2336.2060009@xxxxxx> <52CB2452.70507@xxxxxxxxxx> <20140107200135.GD1935@xxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.2.0
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?

-Eric

> -Ben
> 
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