[Bug 1348430] Re: btrfs send does not work for snapshots in subvolumes

[KlausHoller]

Current workaround until upstream bug is fixed (works for me):
 If you mount the btrfs root (without specifying subvol=@...) to e.g. /mnt then you can use  btrfs send successfully 
e.g. 
btrfs subvolume snapshot -r /mnt/@ /mnt/snapshots/YYYYMMDD-HHMMSS-@
btrfs send /mnt/snapshots/YYYYMMDD-HHMMSS-@ | btrfs receive /backup
(/backup being the 2nd btrfs volume to which the snapshot shall be sent to)

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https://bugs.launchpad.net/bugs/1348430

Title:
  btrfs send does not work for snapshots in subvolumes

Status in “btrfs-tools” package in Ubuntu:
  New

Bug description:
  If I create a snapshot, of a subvolume and try to use btrfs send it
  fails with "No such file or directory"

  # sudo btrfs sub create /testvol
  Create subvolume '//testvol'
  # sudo btrfs
  btrfs               btrfsck             btrfs-debug-tree    btrfs-image         btrfs-select-super  btrfstune           
  btrfs-calc-size     btrfs-convert       btrfs-find-root     btrfs-map-logical   btrfs-show-super    btrfs-zero-log      
  # sudo btrfs sub list /
  ID 257 gen 16298 top level 5 path @
  ID 276 gen 16298 top level 257 path testvol
  # sudo btrfs sub snap -r /t
  testvol/ tmp/     
  # sudo btrfs sub snap -r /testvol/ /test-snap
  Create a readonly snapshot of '/testvol/' in '//test-snap'
  # sudo btrfs sub list /
  ID 257 gen 16299 top level 5 path @
  ID 276 gen 16299 top level 257 path testvol
  ID 277 gen 16299 top level 257 path test-snap
  # sudo btrfs send /test-snap/ > /dev/null
  At subvol /test-snap/
  ERROR: open @/test-snap failed. No such file or directory

  This error has been reported upstream:
  https://bugzilla.kernel.org/show_bug.cgi?id=69401

  Because ubuntu creates /home and / on subvolumes this currently
  prevents backup solutions based on btrfs send.

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