From: Christoph Hellwig <hch@infradead.org>
Date: Tue, 7 Jan 2014 07:52:15 -0800
Subject: [Cluster-devel] [GFS2 PATCH] GFS2: Increase i_writecount during
 gfs2_setattr_chown
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On Mon, Jan 06, 2014 at 05:16:01PM -0500, Bob Peterson wrote:
> Hi,
> 
> This patch calls get_write_access in function gfs2_setattr_chown,
> which merely increases inode->i_writecount for the duration of the
> function. That will ensure that any file closes won't delete the
> inode's multi-block reservation while the function is running.
> It also ensures that a multi-block reservation exists when needed
> for quota change operations during the chown.

Can you explain how gfs2 (ab-)uses i_writecount in the allocator?
i_writecunt has very complicated semantics including negative values
to deal with mappings for executables, and I can't really see how these
high-level semantics interact well with a block allocator.