linux-kernel - Re: [patch 3/7] fs, notify: Add file handle entry into inotify_inode

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Date:	Wed, 14 Nov 2012 07:45:49 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	James Bottomley <jbottomley@...allels.com>,
	Matthew Helsley <matt.helsley@...il.com>,
	aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [patch 3/7] fs, notify: Add file handle entry into
 inotify_inode_mark

On Wed, Nov 14, 2012 at 02:46:42PM +0400, Pavel Emelyanov wrote:
> Well, the MAX_HANDLE_SZ is taken from NFSv4 and is 128 bytes which is quite
> big for inotify extension indeed. The good news is that this amount of bytes
> seem to be required for the most descriptive fhandle

That 128-byte constant is just the protocol-defined maximum.

In practice my memory is that no existing filesystems require NFSv4 for
exports, so they all fit in the NFSv3 64-byte limit.  (But I seem to
recall the NFSv2 32-byte limit being too small in some cases.)

> -- with info about parent, etc. We don't need such, we can live with
> shorter handle, people said that 40 bytes was enough for that.
> 
> However, your idea about determining the handle size dynamically seems
> promising.  As far as I can see from the code we can call for
> encode_fh with size equals zero and filesystem would report back the
> amount of bytes it requires for a handle.
> 
> We can try going this route, what do you think?

I still don't understand why you need a dentry to get the filehandle.
The current api may ask for one, but it shouldn't really be necessary
(assuming you don't want parent directory information encoded in the
filehandle, which I hope you don't).

--b.
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