linux-ext4 - Re: [PATCH 2/3] ext4: Clear the unwritten buffer

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Message-ID: <20090512030856.GI21518@mit.edu>
Date:	Mon, 11 May 2009 23:08:56 -0400
From:	Theodore Tso <tytso@....edu>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	cmm@...ibm.com, sandeen@...hat.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/3] ext4: Clear the unwritten buffer_head flag properly

On Thu, May 07, 2009 at 04:09:29PM +0530, Aneesh Kumar K.V wrote:
> ext4_get_blocks_wrap does a block lookup requesting to
> allocate new blocks. A lookup of blocks in prealloc area
> result in setting the unwritten flag in buffer_head. So
> a write to an unwritten extent will cause the buffer_head
> to have unwritten and mapped flag set. Clear hte unwritten
> buffer_head flag before requesting to allocate blocks.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

I've rewritten the commit changelog to this, which I believe more
accurately describes the patch.  Comments, please?

ext4: Clear the unwritten buffer_head flag after the extent is initialized

From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>

The BH_Unwritten flag indicates that the buffer is allocated on disk
but has not been written; that is, the disk was part of a persistent
preallocation area.  That flag should only be set when a get_blocks()
function is looking up a inode's logical to physical block mapping.

When ext4_get_blocks_wrap() is called with create=1, the uninitialized
extent is converted into an initialized one, so the BH_Unwritten flag
is no longer appropriate.  Hence, we need to make sure the
BH_Unwritten is not left set, to avoid the ensuing confusion and
hilarty.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>

							- Ted
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