linux-ext4 - Re: possible dev branch regression

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Message-ID: <20130319020056.GC4660@thunk.org>
Date:	Mon, 18 Mar 2013 22:00:56 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Dave Chinner <david@...morbit.com>
Cc:	Ben Myers <bpm@....com>, Eric Sandeen <sandeen@...hat.com>,
	xfs-oss <xfs@....sgi.com>, linux-ext4@...r.kernel.org,
	Eric Whitney <enwlinux@...il.com>
Subject: Re: possible dev branch regression - xfstest 285/1k

On Tue, Mar 19, 2013 at 12:47:18PM +1100, Dave Chinner wrote:
> Sorry about this - I've mixed up my threads about ext4 having
> problems with zero-out being re-enabled. I thought this was a
> cross-post of the 218 issue....
> 
> However, the same reasoning can be applied to 285 - the file sizes,
> the size of the holes and the size of the data is all completely
> arbitrary. If we make the holes in the files larger, then the
> zero-out problem simply goes away.

Right.  That was my observation.  We can either make the holes larger,
by changing:

   pwrite(fd, buf, bufsize, bufsize*10);

to

   pwrite(fd, buf, bufsize, bufsize*42);

... and then changing the expected values returned by
SEEK_HOLE/SEEK_DATA.  (By the way; this only matters when we are
testing 1k blocks; if we are using a 4k block size in ext4, the test
currently passes.)

Or we could set some ext4-specific tuning parameters into the #218
shell script, if the file system in question was ext4.

I had assumed that folks would prefer making the holes larger, but
Eric seemed to prefer the second choice as a better one.

Hmm....  Another possibility is to define a directory structure where
each test would look for the existence of some file such as
fscust/<fs>/<test>, and so if fscust/ext4/218 exists, it would get
sourced, and this would define potential hook functions that would get
called after the file system is mounted.  This way, the file system
specific stuff is kept out of the way of the test script.  Would that
make adding fs-specific tuning/setup for tests more palatable?

Regards,

					- Ted
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