linux-ext4 - Re: [PATCH 1/2] ext4: be more strict when migrating to non-extent based file

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Date:	Sat, 4 Jul 2015 00:04:50 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Eryu Guan <guaneryu@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/2] ext4: be more strict when migrating to non-extent
 based file

On Sat, Jul 04, 2015 at 12:51:50AM +0800, Eryu Guan wrote:
> Currently the check in ext4_ind_migrate() is not enough before doing the
> real conversion:
> 
> a) delayed allocated extents could bypass the check on eh->eh_entries
>    and eh->eh_depth
> 
> This can be demonstrated by this script
> 
>   xfs_io -fc "pwrite 0 4k" -c "pwrite 8k 4k" /mnt/ext4/testfile
>   chattr -e /mnt/ext4/testfile
> 
> where testfile has two extents but still be converted to non-extent
> based file format.
> 
> b) only extent length is checked but not the offset, which would result
>    in data lose (delalloc) or fs corruption (nodelalloc), because
>    non-extent based file only supports at most (12 + 2^10 + 2^20 + 2^30)
>    blocks
>
> ...

Thanks for the really great commit description!  I've applied this to
the ext4 git tree.

					- Ted
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