linux-ext4 - Re: [PATCH 2/8] vfs: Protect write paths by sb_start_write

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Message-ID: <20120124082119.GO15102@dastard>
Date:	Tue, 24 Jan 2012 19:21:19 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-fsdevel@...r.kernel.org, Eric Sandeen <sandeen@...deen.net>,
	Dave Chinner <dchinner@...hat.com>,
	Surbhi Palande <csurbhi@...il.com>,
	Kamal Mostafa <kamal@...onical.com>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, xfs@....sgi.com,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/8] vfs: Protect write paths by sb_start_write -
 sb_end_write

On Fri, Jan 20, 2012 at 09:34:40PM +0100, Jan Kara wrote:
> There are three entry points which dirty pages in a filesystem.  mmap (handled
> by block_page_mkwrite()), buffered write (handled by
> __generic_file_aio_write()), and truncate (it can dirty last partial page -
> handled inside each filesystem separately). Protect these places with
> sb_start_write() and sb_end_write().

fallocate can also dirty pages, either during preallocation or hole
punching.  Hence if you are going to promote truncate to
SB_FREEZE_WRITE protection then you need to promote everything else
that can zero partial blocks as well.

That also means that anything the has implemented XFS_IOC_ ioctl
interfaces for prellocation and hole punching (xfs, ocfs2 and gfs2
IIRC) also needs to be protected in the same way.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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