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

[Josef Bacik <jbacik@fb.com>]

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