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

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Date:	Tue, 15 Apr 2014 17:32:43 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	Lukáš Czerner <lczerner@...hat.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Namjae Jeon <linkinjeon@...il.com>
Subject: Re: [PATCH] ext4: add fallocate mode blocking for debugging purposes

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.

Also: I'd humbly suggest just not merging those until they pass stringent
tests like fsx & fsstress...

Adding a pre-emptive knob to turn them off post-merge when they turn
out to be broken sounds backwards to me...

-Eric
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