linux-ext4 - Re: Buffer state bits

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Message-ID: <20090827123318.GA19422@skywalker.linux.vnet.ibm.com>
Date:	Thu, 27 Aug 2009 18:03:18 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Buffer state bits

> 
> 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
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