Re: Cloning a Btrfs partition

[Goffredo Baroncelli <kreijack@inwind.it>]

On Monday, 12 December, 2011 15:41:29 you wrote:
> >You can't change the uuid of an existing btrfs partition. Well, you
> >can, but you have to rewrite all the metadata blocks.
> 
> Is there a tool that would allow me to rewrite all the metadata blocks with
> a new UUID?  At this point, it can't possibly take longer than the way I'm
> trying to do it now...
> 
> Someone once said "Resetting the UUID on btrfs isn't a quick-and-easy thing
> - you have to walk the entire tree and change every object. We've got a
> bad-hack in meego that uses btrfs-debug-tree and changes the UUID while it
> runs the entire tree, but it's ugly as hell."

I am looking for that. btrfs-debug-tree is capable to dump every leaf and 
every node logical address.

To change the UUID of a btrfs filesystem

On every leaf/node we should
- update the FSID						(a)
- update the chunk_uuid [*]
- update the checksum

for the "dev_item" items we should update the
- device UUID							(b)
- FSID									(see 'a')

for the "chunk_item" items we should update the
- device UUID of every stripe			(b)

for every superblock (three for device), we should update:
- FSID									(see 'a')
- device uuid							(see 'b')
- for every "system chunk" items contained in the superblock we should update:
	- device UUID of every stripe			(b)
- update the checksum

The most complex part is to map the logical address to the physical device. 

In the next days I will tray (if I had enough time) to make something...




> 
> Ok, I'll take the bad-hack.  How would I actually go about using said
> bad-hack?
> 
> -BJ
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