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From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Eric Sandeen <sandeen@sandeen.net>
Cc: Carlos Maiolino <cmaiolino@redhat.com>,
	linux-fsdevel@vger.kernel.org, david@fromorbit.com,
	hch@infradead.org
Subject: Re: Ext4 fiemap implementation
Date: Sat, 2 Jun 2018 23:28:53 -0400	[thread overview]
Message-ID: <20180603032853.GA3585@thunk.org> (raw)
In-Reply-To: <f63d1a08-1b6a-d2ad-48af-d8b08e1a4e26@sandeen.net>

On Fri, Jun 01, 2018 at 10:01:54AM -0500, Eric Sandeen wrote:
> > Ted, is there any restriction why ext4_fiemap isn't using iomap_fiemap()? Or any
> > reason why ext4 fiemap always returns the offset from the beginning of the
> > extent? Would you oppose to have it updated to return the offset initially
> > requested? Or maybe, change ext4_fiemap() to use iomap_fiemap()?

ext4_fiemap() predates iomap_fiemap().  In fact, it used to be that
all of the file systems had their own fiemap() implementation.   

> > I read the fiemap documentation, but I didn't get a clear understanding if
> > fiemap should be returning the beginning of the extent, the offset initially
> > requested, or if it depends on FS implementation.
> 
> I think the fiemap docs[1] explicitly state that ext4's behavior is valid:
> 
> > Extents returned mirror
> > those on disk - that is, the logical offset of the 1st returned extent
> > may start before fm_start, and the range covered by the last returned
> > extent may end after fm_length.

Actually, I read, "Extents returned mirror those on disk" as meaning
that the ext4 behavior is *mandated* by the docs.  It would be
interesting to see what XFS did before the iomap_fiemap() conversion.
Or it could have been that the docs were inconsistent with what XFS
was doing and then when when ext4_fiemap() was implemented, we
followed the docs.  Some software archeology would be required to know
for sure.

						- Ted

  reply	other threads:[~2018-06-03  3:29 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-01 12:36 Carlos Maiolino
2018-06-01 15:01 ` Eric Sandeen
2018-06-03  3:28   ` Theodore Y. Ts'o [this message]
2018-06-04 16:43     ` Darrick J. Wong
2018-06-06 13:13       ` Carlos Maiolino
2018-06-06 14:40         ` Darrick J. Wong
2018-06-07  8:31           ` Carlos Maiolino
2018-06-07 16:25             ` Darrick J. Wong
2018-06-08  8:18               ` Carlos Maiolino
2018-06-08 22:41       ` Mark Fasheh
2018-06-11  7:28         ` Carlos Maiolino
2018-06-12 23:52           ` Mark Fasheh
2018-06-13  3:06             ` Theodore Y. Ts'o
2018-06-13  3:32               ` Dave Chinner
2018-06-13  5:04                 ` Theodore Y. Ts'o
2018-06-13  7:41                   ` Dave Chinner
2018-06-13 12:09                     ` Christoph Hellwig
2018-06-14  8:14                       ` Carlos Maiolino
2018-06-01 18:57 ` Andreas Dilger

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