Re: [PATCH] ext4: add fallocate mode blocking for debugging purposes

[Eric Sandeen <sandeen@redhat.com>]

On 4/15/14, 1:44 PM, Theodore Ts'o wrote:
> On Tue, Apr 15, 2014 at 11:15:41AM -0500, Eric Sandeen wrote:
>>
>> I tend to agree, better to fix the kernel than to add a knob to turn it
>> off.  And fsx changes can happen a lot quicker than kernel changes.  [1]
>>
>> And if it's really unsafe, and you really want to add a knob, I'd at least
>> default it to off until it's non-corrupting, and add a message that
>> this tunable will go away as soon as it's stable, so you'll have no
>> qualms about quickly deprecating it...
> 
> Yeah, I went back and forth on this.  One of there reasons why I added
> a kernel knob is that *I* can make the kernel change a lot faster than
> it would be to tweak all of the various xfstests program to globally
> disable certain operations in fsx, fstress, etc.
> 
> I also had a sneaking suspicion that we might have a similar issue
> with the INSERT RANGE patches which are coming down the pike, and so
> having a general way of also being able INSERT RANGE if to be able to
> quickly determine whether a potential bug was caused by INSERT RANGE
> or some other pending changes might also be useful.
> 
> I freely admit it is a bit of a hack, though.  Does the hack smell
> less bad if we wrap it in CONFIG_EXT4FS_DEBUG?
> 
>> [1] it'd be nifty to make an env. var in xfstests which can globally
>> disable certain fsx operations across all tests which run fsx...
> 
> Yes, although as I mentioned above, it would be really nice if it
> worked across all of the various tests, and not just be limited to
> fsx, or even just fsx and fstress.

Well, for tests which are specific to collapse range, it'd be trivial
to add a "collapse" group, and exclude it.

For generic stress tests which happen to do collapse range, it'd take
a bit more.  But that'd probably still be the generic solution.

XFS got bitten too, there were collapse range problems.  But the fixes
are already in the pipe AFAIK.

-Eric

> 					- Ted
> 
> 
>