From: "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Neil Brown <neilb@suse.de>, hch@infradead.org, viro@zeniv.linux.org.uk,
       adilger@sun.com, corbet@lwn.net, serue@us.ibm.com,
       hooanon05@yahoo.co.jp, linux-fsdevel@vger.kernel.org,
       sfrench@us.ibm.com, philippe.deniel@CEA.FR,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH -V14 0/11] Generic name to handle and open by handle syscalls
In-Reply-To: <20100706161002.GD7387@fieldses.org>
References: <1276621981-2774-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <871vbn2mk9.fsf@linux.vnet.ibm.com> <20100702064108.64034561@notabene.brown> <87iq4y29a6.fsf@linux.vnet.ibm.com> <20100706161002.GD7387@fieldses.org>
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Date: Tue, 06 Jul 2010 22:39:56 +0530
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On Tue, 6 Jul 2010 12:10:02 -0400, "J. Bruce Fields" <bfields@fieldses.org> wrote:
> On Fri, Jul 02, 2010 at 02:45:45AM +0530, Aneesh Kumar K. V wrote:
> > One use case i had was that if the userspace file server can directly
> > work with the returned file system UUID,
> 
> I agree that the uuid should be split out from the rest of the
> filehandle, but ...
> 
> > the it can build the file
> > handle for client in a single call.
> 
> ... 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.


> 
> (I would have thought that the system call overhead is so small, and so
> many calls will already be required to perform the typical rpc, that
> this would be insignificant.)
> 
> 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);

-aneesh
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