linux-kernel - Re: [PATCH v2 1/5] fat: allocate persistent inode numbers

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Message-ID: <87r4q7f8fw.fsf@devron.myhome.or.jp>
Date:	Thu, 13 Sep 2012 02:38:11 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Namjae Jeon <linkinjeon@...il.com>,
	"Steven J. Magnani" <steve@...idescorp.com>,
	Al Viro <viro@...iv.linux.org.uk>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Ravishankar N <ravi.n1@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH v2 1/5] fat: allocate persistent inode numbers

"J. Bruce Fields" <bfields@...ldses.org> writes:

>> On other view (as server side solution), we are thinking there is
>> possible to make the stable filehandle on FAT if we disabled some
>> operations (e.g. rename(), unlink()) which change inode location in FAT.
>> 
>> Yes, it would be stable, but supporting limited operations.
>> 
>> This is server side solution, and we comparing it with client solution.
>
> Is that useful to anyone?

Good question. I'm not sure though, Namjae is asking. And I was asked
about stable read-only export in past.

>> >> LOOKUP return NFS FH->[inode number changed at NFS Server] ->
>> >> But we still use old NFS FH returned from LOOKUP for any file
>> >> operation(write,read,etc..)
>> >> -> ESTALE will be returned.
>> 
>> Yes.  And I'm expecting as client side solution,
>> 
>> -> ESTALE will be returned -> discard old FH -> restart from LOOKUP ->
>> make cached inode -> use returned new FH.
>> 
>> Yeah, I know this is unstable (there is no perfect solution for now),
>
> You may end up with a totally different file, of course:
>
> 	client:			server:
>
> 	open "/foo/bar"
> 				rename "/foo/baz"->"/foo/bar"
> 	write to file
>
> And now we're writing to the file that was originally named /foo/baz
> when we should have gotten ESTALE.

I see. So, client can't solve the ESTALE if inode cache was evicted,
right? (without application changes)
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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