Re: Reiser 3.6: Recover partition start position & Journal

[Jeff Mahoney <jeffm@suse.com>]

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On 1/1/15 5:15 AM, Felipe Monteiro de Carvalho wrote:
> On Wed, Dec 31, 2014 at 6:15 PM, Toby Thain
> <toby@telegraphics.com.au> wrote:
>> I've done this for Reiser 3. I blogged about it here: 
>> http://slashdot.org/journal/110587
> 
> Thanks,
> 
> Indeed, supposing that the first found superblock is located at 
> REISERFS_DISK_OFFSET_IN_BYTES (0x10000) is a possibility. I was
> just wondering if there is anything more reliable, but it looks
> like that there isnt. The problem with this approach for an
> automated program is

Yeah, that's really your best bet. Any modern (read: any file system
created since the ~ Linux 2.2 days) reiserfs file system will have the
superblock at that offset.

> that it will fail if the first superblock was overwritten somehow.

Yep. If that's the case, you should be able to find many superblocks
in the journal. From there, you can go backwards until you find the
journal header block which, if internal, usually has a defined
location that starts immediately after the superblock. Then you'll
want to try to figure out which one is the most recent and part of a
complete transaction.

One caveat to all of this, and why newer file systems like btrfs have
self-identifying metadata, is if you encounter a file system image
hosted on the reiserfs file system. Since there's no way to determine
whether the blocks are part of the file or the file system hosting it,
you could get false positives. This is a problem for reiserfsck -S as
well.

- -Jeff

- -- 
Jeff Mahoney
SUSE Labs
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