Hello,

Please note that my experience with btrfs is both recent and, above all, very small. However, I've been wondering about the same issue for a different purpose and your question intrigues me.

However, and I may be off-base here, I think that wouldn't be trivial to achieve. 

Even if one would be able to differ the metadata changes between both snapshots, the problem would still be present regarding finding the changed data. It would be possible to check for changed extents, at least by comparing extent checksums, but I don't think it would be trivial to discover where (exactly) the extent was modified.

I would recommend using the generation fields, whenever applicable, but I believe these are private to each subvolume/snapshot.


Anyway, I wonder if keeping a data structure (I would go with a tree) containing metadata regarding the changed files, within the file system, could be a plausible solution, but I'm in no condition (btrfs-knowledge-wise) to make such statement.


Cheers.

---
João Eduardo Luís
gpg key: 477C26E5 from pool.keyserver.eu 





On Feb 25, 2011, at 9:59 AM, Arvin Schnell wrote:

Hi,

for a backup program I have to find all differing files
(including metadata) in two snapshots taken from the same
subvolume.

Having looked at the find-new command I thought about this
process:

1. Get the two transids when the two snapshots were created.

2. Query modifications to the original subvolume between the two
  transids.

Is the general process corrent or have I overseen something?

AFAIS the btrfs tool does not provide the required
information/commands. Would it be possible to add those?

Thanks in advance,
 Arvin

-- 
Arvin Schnell, [off-list ref]
Senior Software Engineer, Research & Development
SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
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