linux-kernel - Re: lz4hc compression in UBIFS?

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Date:	Wed, 23 Oct 2013 07:49:24 -0500
From:	Brent Taylor <motobud@...il.com>
To:	Konstantin Tokarev <annulen@...dex.ru>
Cc:	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Artem Bityutskiy <dedekind1@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: lz4hc compression in UBIFS?

On Wed, Oct 23, 2013 at 2:40 AM, Konstantin Tokarev <annulen@...dex.ru> wrote:
>
>
> 23.10.2013, 09:26, "Brent Taylor" <motobud@...il.com>:
>> Konstantin,
>>    I did my testing with data from /dev/urandom (which I now realize
>> wasn't the best choice of data source), but if I use /dev/zero (which
>> actually causes data compression to occur), the decompressor fails.  I
>> don't know the internal workings of the lz4hc compressor or the lz4
>> decompressor.  I couldn't find any examples of any code in the kernel
>> actually using the compressor.  I've cc'ed the maintainers of the
>> lz4hc_compress.c to see if they my have some more insight to the
>> issue.
>
> Does decompressor fail for you with the same error messages?
>
> Have you tried to copy my file to the volume? It looks like minimal test case
> for my board, if I remove any line decompressor works fine.
>
> --
> Regards,
> Konstantin

Yes, I get the same error, here's a dump from UBIFS when I cat a file
filled with data from /dev/zero:

UBIFS error (pid 4288): ubifs_decompress: cannot decompress 12 bytes,
compressor lz4hc, error -22
UBIFS error (pid 4288): read_block: bad data node (block 0, inode 71)
        magic          0x6101831
        crc            0xff61a078
        node_type      1 (data node)
        group_type     0 (no node group)
        sqnum          2700
        len            60
        key            (71, data, 0)
        size           512
        compr_typ      3
        data size      12
        data:
        00000000: 1f 00 01 00 ff e8 50 00 00 00 00 00
UBIFS error (pid 4288): do_readpage: cannot read page 0 of inode 71, error -22
cat: /opt/data/zero.bin: Input/output error

Steps to reproduce are:
1.  Create a file with all zeros: dd if=/dev/zero bs=512 count=1
of=/opt/data/zero.bin
2.  Unmount ubifs and detach ubi partition
3.  attach ubi partition and mount ubifs
4. cat /opt/data/zero.bin
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