linux-ext4 - Re: [PATCH v2 3/5] ext4: fix wrong m_len value after unwritten extent conversion

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Date:	Sun, 10 Mar 2013 21:07:18 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Zheng Liu <gnehzuil.liu@...il.com>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>,
	Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: Re: [PATCH v2 3/5] ext4: fix wrong m_len value after unwritten
 extent conversion

On Wed, Mar 06, 2013 at 10:17:13PM +0800, Zheng Liu wrote:
> From: Zheng Liu <wenqing.lz@...bao.com>
> 
> We always assume that the return value of ext4_ext_map_blocks is equal
> to map->m_len

Note that in general, this is _never_ safe to assume.  There are a
number of times when the number of blocks mapped is less than what the
caller originally requested, both when allocating blocks (and there
isn't the requestd number of contiguous blocks available), and when
EXT4_GET_BLOCKS_CREATE is not set.

					- Ted
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