linux-kernel - Re: [PATCH -V14 0/11] Generic name to handle and open by handle syscalls

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Message-Id: <A55CC567-FA15-48B5-9274-181CC3462D91@oracle.com>
Date:	Wed, 7 Jul 2010 17:54:23 -0600
From:	Andreas Dilger <andreas.dilger@...cle.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Neil Brown <neilb@...e.de>,
	Christoph Hellwig <hch@...radead.org>,
	"viro@...iv.linux.org.uk Viro" <viro@...iv.linux.org.uk>,
	"corbet@....net Corbet" <corbet@....net>,
	"hooanon05@...oo.co.jp Okajima" <hooanon05@...oo.co.jp>,
	linux-fsdevel@...r.kernel.org,
	"sfrench@...ibm.com French" <sfrench@...ibm.com>,
	"philippe.deniel@....FR Deniel" <philippe.deniel@....FR>,
	"linux-kernel@...r.kernel.org Mailinglist" 
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -V14 0/11] Generic name to handle and open by handle syscalls

On 2010-07-07, at 14:39, Alan Cox wrote:
>> I think you are assuming too much about the use of the file handle.  What I'm interested in is not a userspace file server, but rather a more efficient way to have 10000's to millions of clients to be able to open the same regular file, without having to do full path traversal for each one.
> 
> The unix security model requires the traversal. In that respect it
> differs significantly from some other OS's that did have handle based
> direct opens and treat directories as a lookup and translation index only.

There IS full path traversal at the time the file handle is generated, so it meets these requirements.  This isn't really conceptually any different than fd passing over a unix socket on a local system, but passing the fd between user processes (via an out-of-band communication method, likely an MPI broadcast message) that are running on different nodes all accessing the same distributed filesystem.

Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.

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