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Subject: Re: [PATCH] [JFFS2] check xattr data integrity during the scan.
From: Artem Bityutskiy <dedekind1@gmail.com>
To: Jean-Christophe DUBOIS <jcd@tribudubois.net>
Date: Sun, 22 Apr 2012 16:04:32 +0300
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On Wed, 2012-04-11 at 22:23 +0200, Jean-Christophe DUBOIS wrote:
> If the system was powered off while JFFS2 was creating or moving
> (GC) an extended attribute node, it might happen at next reboot
> that the node CRC is OK but the data (name and value) might be
> incomplete and therefore corrupted.
>=20
> During the mount scan we need to check the xattr data integrity to
> weed out bad ones and keep good ones (whith an earlier version).
>=20
> Whitout this check the xattr data integrity problem was detected
> a lot later and was not cured automatically (-EIO was returned).
>=20
> Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
> ---

AFAIR, the whole idea of having 2 CRC checksums in JFFS2 nodes is to
speed up scanning. E.g., if we hit an inode node, we check only
"node_crc" to validate the "metadata", insert the inode to the in-memory
data structures, and read the next node. We do not check the data CRC
(data_crc), otherwise scanning would be much slower. If the data are
corrupted, we notice this later, wen reading it.

The same is done for xattrs - during scanning we do not check the data
payload.

I do not say this is ideal design, but it is how it is. So I do not
think your patch should be merged.

--=20
Best Regards,
Artem Bityutskiy

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