From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: Buffer state bits
Date: Thu, 27 Aug 2009 18:03:18 +0530
Message-ID: <20090827123318.GA19422@skywalker.linux.vnet.ibm.com>
References: <20090826200021.GA5716@duck.novell.com>
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Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
To: Jan Kara <jack@suse.cz>
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> 
> BH_Mapped
> - Buffer has a physical block backing it stored in b_bdev + b_blocknr. This bit
>   is set by filesystem's get_block() function (or by VFS itself for block device
>   mappings).
> 
>   XXX: Some filesystems set BH_Mapped even for buffers that do no really
>   have the backing block (like buffers for delayed allocation). I think
>   we should get rid of it...
> 

Also we don't want get_block to be called multiple times for the same file offset.
__block_prepare_write does get_block looking at the BH_Mapped flag. ie one of reason
delay and unwritten buffer_heads are also marked mapped.


-aneesh