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Message-ID: <20070803180916.GT6142@schatzie.adilger.int>
Date:	Fri, 3 Aug 2007 12:09:16 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	Yan Zheng <yanzheng@...n.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: How to insure ext4_alloc_blocks always returns blocks below 0xffffffff when using indirect index.

On Aug 03, 2007  10:22 +0800, Yan Zheng wrote:
> Druing reading the source codes of indirect index,  there is a doubt
> in my mind. When using indirect index, physical block number must not
> exceed 0xffffffff, but I cann' t find any clue  about how
> ext4_alloc_blocks insure that.  Codes that check 64bit_feature is only
> in ext4_fill_super and they do nothing affects block allocation
> algorithm.  Maybe ext4_alloc_blocks should  check whether inode has
> EXT4_EXTENTS_FL flags and only search block groups that have blocks
> below 0xffffffff when not.
> 
> The source codes I read is 2.6.22.

Good question.  It is intended that extents be used for filesystems
larger than 2^32 blocks, but there is no guarantee that existing
block-mapped files will not still exist.

I think the check you propose makes sense.  The code should return
EFBIG or maybe EOVERFLOW in this case (not ENOSPC I think).

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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