linux-kernel - Re: [PATCH 02/11] vfs: Add better VFS support for page

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Date:	Fri, 26 Jun 2009 10:42:25 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 02/11] vfs: Add better VFS support for page_mkwrite when blocksize < pagesize

On Thu, Jun 25, 2009 at 01:47:55PM -0400, Christoph Hellwig wrote:
> On Thu, Jun 25, 2009 at 06:17:53PM +0200, Nick Piggin wrote:
> > Basically the problems is that i_op->truncate a) cannot return an error
> > (which is causing problems missing -EIO today anyway), and b) is called
> > after i_size update which makes it not possible to error-out without
> > races anyway, and c) does not get the old i_size so you can't unmap the
> > last partial page with it.
> > 
> > My patch is basically moving ->truncate call into setattr, and have
> > the filesystem call vmtruncate. I've jt to clean up loose ends.
> 
> We absolutely need to get rid of ->truncate.  Due to the above issues
> XFS already does the majority of the truncate work from setattr, and it
> works pretty well.

Yes well we could get rid of ->truncate and have filesystems do it
themselves in setattr, but I figure that moving truncate into
generic setattr is helpful (makes conversions a bit easier too).
Did you see my patch? What do you think of that basic approach?


>  The only problem is the generic aops calling
> vmtruncate directly.

What should be done is require that filesystems trim blocks past
i_size in case of any errors. I actually need to fix up a few
existing bugs in this area too, so I'll look at this..

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