linux-ext4 - Re: Segmentation fault in e4defrag -c

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Date:	Wed, 01 Jul 2009 08:43:14 +0900
From:	Akira Fujita <a-fujita@...jp.nec.com>
To:	Andreas Dilger <adilger@....com>
CC:	"Steinar H. Gunderson" <sgunderson@...foot.com>,
	Kazuya Mio <k-mio@...jp.nec.com>, linux-ext4@...r.kernel.org
Subject: Re: Segmentation fault in e4defrag -c

Hi,
Andreas Dilger wrote:
> On Jun 29, 2009  15:03 +0900, Akira Fujita wrote:
>>>   Size: 4050385   	Blocks: 0          IO Block: 4096   regular file
>>> Device: fd12h/64786d	Inode: 688755      Links: 1
>>> Access: (0644/-rw-r--r--)  Uid: ( 1000/   sesse)   Gid: ( 1000/   sesse)
>>> Access: 2009-05-30 03:08:38.724454316 +0200
>>> Modify: 2008-09-01 20:38:26.135589449 +0200
>>> Change: 2008-09-01 20:38:26.135589449 +0200
>> File size is "4050385" but Blocks is "0"
>> probably means blocks are not allocated yet or file is *corrupted*.
>> Is your mp3 file available?
> 
> Well, this is a sparse file for some reason (e.g. failed mp3 p2p download).
> 

Ah, may be so.

>> Anyway, with this patch, 0 blocks file is skipped,
>> therefore the segmentation fault you had will not happen.
> 
> Is it possible that the code has not been tested with sparse files?
> In that case, the check for size == 0 is only going to catch a single
> case of problem, and not handle general sparse files.
> 

I have tested files that have sparse blocks
(e.g. files that have sparse blocks in its beginning,
middle and those combinations) and got fine results.
Unfortunately, like this case, only 0 blocks file (all sparse blocks)
has not been tested yet.

But the kernel space (EXT4_IOC_MOVE_EXTENT) does not have this kind of issue.
Because there is a check of whether the extents of orig_inode
that ext4_ext_find_extent() gets is NULL.
If extents is NULL or ext4_ext_find_extent() fails,
ext4_move_extents() returns an error value (e.g. EINVAL) to the user space.

Regards,
Akira Fujita


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