linux-kernel - Re: [patch 4/8] fs, exportfs: Add export_encode_inode

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Message-ID: <20120816150749.GC13382@moon>
Date:	Thu, 16 Aug 2012 19:07:49 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	James Bottomley <jbottomley@...allels.com>,
	Pavel Emelianov <xemul@...allels.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Helsley <matt.helsley@...il.com>
Subject: Re: [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper

On Thu, Aug 16, 2012 at 03:55:27PM +0100, Al Viro wrote:
> On Thu, Aug 16, 2012 at 06:48:35PM +0400, Cyrill Gorcunov wrote:
> 
> > > Good luck doing that with e.g. VFAT...  And then there's such thing
> > > as filesystems that don't have ->encode_fh() for a lot of very good
> > 
> > Wait, Al, it seems I messed up. If some fs has no encode_fh() implemented
> > the default encoding with FILEID_INO32_GEN_PARENT will be used for that.
> 
> ... which doesn't work for a lot of filesystems.  Not if you want to be
> able to decode the result afterwards and get something useful out of
> that.  Trying to implement ->fh_to_dentry(), especially with fhandle
> generated by inode alone is going to be really interesting for a bunch
> of stuff...

hmm, yup (and Bruce just pointed me to exportfs_decode_fh). So, if fs doesn't
provide encode_fh (and decode as well) but the FILEID_INO32_GEN_PARENT used
instead, we will not be able to restore such inotify later. Then I suppose
such application will be unrestorable at least for a while. Would not this
be acceptable trade off?

	Cyrill
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