linux-kernel - Re: [PATCH] fsstack: fsstack_copy_inode

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Message-Id: <200807020000.m62009ug014713@agora.fsl.cs.sunysb.edu>
Date:	Tue, 1 Jul 2008 20:00:09 -0400
From:	Erez Zadok <ezk@...sunysb.edu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Michael Halcrow <mhalcrow@...ibm.com>,
	Erez Zadok <ezk@...sunysb.edu>,
	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	hooanon05@...oo.co.jp, viro@...iv.linux.org.uk,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fsstack: fsstack_copy_inode_size locking 

In message <20080701070350.GA22914@...radead.org>, Christoph Hellwig writes:
> On Mon, Jun 30, 2008 at 04:49:01PM -0500, Michael Halcrow wrote:
> > eCryptfs depends on the results of i_size_read() on the lower inode
> > when it needs to interpolate the filesize when the metadata is stored
> > in the lower file's xattr region.
> 
> please use vfs_getattr to get the size in thst case.

So, Christoph, is using vfs_getattr() the preferred choice for stackable
file systems in general to get the lower inode size?

If so, the Hugh's fsstack_copy_inode_size patch will have to be updated: and
we'll probably have to change the names of the src/dst parameters to
lower/upper, possibly watch out for whether "src" was the lower or upper
inode, and be careful about locking semantics when calling vfs_getattr.

Who'd have thought that a concept as simple as
      dst->i_size = src->i_size
could turn out to be so hairy... 1/2 a :-)

Thanks,
Erez.
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