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

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Date:	Wed, 7 Jul 2010 01:40:53 -0600
From:	Andreas Dilger <andreas.dilger@...cle.com>
To:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>, hch@...radead.org,
	viro@...iv.linux.org.uk, adilger@....com, corbet@....net,
	serue@...ibm.com, hooanon05@...oo.co.jp,
	linux-fsdevel@...r.kernel.org, sfrench@...ibm.com,
	philippe.deniel@....FR, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V14 0/11] Generic name to handle and open by handle syscalls

On 2010-07-06, at 11:09, Aneesh Kumar K. V wrote:
> On Tue, 6 Jul 2010 12:10:02 -0400, "J. Bruce Fields" <bfields@...ldses.org> wrote:
>> ... I don't understand why both need to come in the same system call.
>> Is it purely an efficiency question?  If so, why do you expect this to
>> be significant?
> 
> Since we know that system wide file handle should include a file system
> identifier and a file identifier my plan was to retrieve both in the
> same syscall.

Won't having it be in a separate system call be racy w.r.t. doing the pathname lookup twice?

>> A filesystem uuid seems like a generally useful thing (maybe more so
>> than a filehandle), so it'd seem worth figuring out how to export that
>> separately.
>> 
> 
> I can add a new syscall that returns 
> 
> struct fs_uuid {
>       u8 fs_uuid[16];  
> };
> 
> long sys_get_fs_uuid(int dfd, char *name, struct fs_uuid *fsid, int flag);

While this might be useful, I think the file handle should identify the filesystem itself.

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

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