Hi,

On Sat, Dec 29, 2012 at 12:42 AM,  [off-list ref] wrote:

Hi everyone!

(I use kernel 3.7.1 and mason/btrfs-progs.git head + the receive
lchown patch [1]. Is there a more up to date btrfs-progs repo for
send/receive enthusiasts?)

There is no special repo, but you may want, in addition to the patch
you mentioned, apply this one as well:
https://patchwork.kernel.org/patch/1604391/
Whether you need it or not depends on how your subvolumes are
organized in a file tree.

What I'm trying is basically:

# Transfer a snapshot of my old system from a backup to the new system
btrfs send /mnt/bak/.snap | btrfs receive /                 # OK

# Merge the old system's files with the new system's files
btrfs subvolume snapshot /.snap /.snap-merge                # OK
mkdir /.snap-merge/.old                                     # OK
mv /.snap-merge/* /.snap-merge/.old                         # OK
cp -a --reflink /* /.snap-merge                             # OK
btrfs subvolume snapshot -r /.snap-merge /.snap-merge-done  # OK

# Incrementally transfer the merged files back to the backup drive
btrfs send -p /.snap /.snap-merge-done | btrfs receive -p /mnt/bak

The last step fails due to the changed direction of the transfer.
"ERROR: could not find parent subvolume". It seems like btrfs receive
cannot find the parent/clone source because it is searching for its UUID
only by looking through the /mnt/bak snapshots' received_uuid fields.

Is there a way for me to directly change the received_uuid of
/mnt/bak/.snap to make it identical to the UUID of /.snap? This looks
like the easiest way if I only need to do it once.

There is no implemented way, but since you debugged this far, you can
put up some code that sends BTRFS_IOC_SET_RECEIVED_SUBVOL, which is
the one setting the received_uuid (and some other small stuff, please
check the kernel code for it).

Thanks,
Alex.

[1] https://patchwork.kernel.org/patch/1606091/
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