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Re: [PATCH] xfs: xfs_bmap_add_attrfork_local is too generic

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: xfs_bmap_add_attrfork_local is too generic
From: Ben Myers <bpm@xxxxxxx>
Date: Thu, 28 Feb 2013 09:26:59 -0600
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130228001034.GI5551@dastard>
References: <1360558693-20354-1-git-send-email-david@xxxxxxxxxxxxx> <20130214234244.GM22182@xxxxxxx> <20130228001034.GI5551@dastard>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu, Feb 28, 2013 at 11:10:34AM +1100, Dave Chinner wrote:
> On Thu, Feb 14, 2013 at 05:42:44PM -0600, Ben Myers wrote:
> > On Mon, Feb 11, 2013 at 03:58:13PM +1100, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > > 
> > > When we are converting local data to an extent format as a result of
> > > adding an attribute, the type of data contained in the local fork
> > > determines the behaviour that needs to occur.
> > > 
> > > xfs_bmap_add_attrfork_local() already handles the directory data
> > > case specially by using S_ISDIR() and calling out to
> > > xfs_dir2_sf_to_block(), but with verifiers we now need to handle
> > > each different type of metadata specially and different metadata
> > > formats require different verifiers (and eventually block header
> > > initialisation).
> > > 
> > > There is only a single place that we add and attribute fork to
> > > the inode, but that is in the attribute code and it knows nothing
> > > about the specific contents of the data fork. It is only the case of
> > > local data that is the issue here, so adding code to hadnle this
> > > case in the attribute specific code is wrong. Hence we are really
> > > stuck trying to detect the data fork contents in
> > > xfs_bmap_add_attrfork_local() and performing the correct callout
> > > there.
> > > 
> > > Luckily the current cases can be determined by S_IS* macros, and we
> > > can push the work off to data specific callouts, but each of those
> > > callouts does a lot of work in common with
> > > xfs_bmap_local_to_extents(). The only reason that this fails for
> > > symlinks right now is is that xfs_bmap_local_to_extents() assumes
> > > the data fork contains extent data, and so attaches a a bmap extent
> > > data verifier to the buffer and simply copies the data fork
> > > information straight into it.
> > > 
> > > To fix this, allow us to pass a "formatting" callback into
> > > xfs_bmap_local_to_extents() which is responsible for setting the
> > > buffer type, initialising it and copying the data fork contents over
> > > to the new buffer. This allows callers to specify how they want to
> > > format the new buffer (which is necessary for the upcoming CRC
> > > enabled metadata blocks) and hence make xfs_bmap_local_to_extents()
> > > useful for any type of data fork content.
> > > 
> > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> > Applied.  We'd like this one in 3.8, one way or the other.
> 
> Ben, seeing as this missed the 3.8 release, can you push it back to
> the 3.8.y stable series? It's already been hit out in the wild, so
> it needs fixing....

Sure.  Thanks for the reminder.

-Ben

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