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

[Chris Mason <clm@fb.com>]

On Tue, 2014-01-07 at 16:17 -0500, Josef Bacik wrote:
> On 01/07/2014 03:40 PM, Ben Myers wrote:
> > On Tue, Jan 07, 2014 at 02:10:15PM -0600, 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?
> > At one point random.c was modified because it was returning different test
> > results on i386 and ia64 with test 007.  Looks like nametest.c is a good
> > candidate.
> >
> 
> Ugh you're right.  Just ignore this patch for now, I'll be in the corner 
> banging my head against the wall.  Thanks,

For now we can just use srandom?

-chris