linux-ext4 - Re: [PATCH 6/8] fs: always maintain i_dio

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Date:	Mon, 20 Jun 2011 14:29:24 -0700
From:	Joel Becker <jlbec@...lplan.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	viro@...iv.linux.org.uk, tglx@...utronix.de,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org, hirofumi@...l.parknet.co.jp,
	mfasheh@...e.com
Subject: Re: [PATCH 6/8] fs: always maintain i_dio_count

On Mon, Jun 20, 2011 at 04:15:39PM -0400, Christoph Hellwig wrote:
> Maintain i_dio_count for all filesystems, not just those using DIO_LOCKING.
> This these filesystems to also protect truncate against direct I/O requests
> by using common code.  Right now the only non-DIO_LOCKING filesystem that
> appears to do so is XFS, which uses an opencoded variant of the i_dio_count
> scheme.
> 
> Behaviour doesn't change for filesystems never calling inode_dio_wait,
> which are all that never use DIO_LOCKING.
> 
> For ext4 behaviour changes with the dioread_nonlock option, which previous
> was missing any protection between truncate and direct I/O reads.
> 
> For ocfs2 that handcrafted i_dio_count manipulations are replaced with
> the common code noew available.

	Oh god you're making the world scary.  Are you guaranteeing that
all allocation changes are locked out by the time we get into
file_aio_write() and file_aio_read()?  This is not obvious to me.

Joel

-- 

"Glory is fleeting, but obscurity is forever."  
         - Napoleon Bonaparte

			http://www.jlbec.org/
			jlbec@...lplan.org
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