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

[Janne Savikko]

For me Alan's workaround didn't work. But I found an another one that
worked for me for sending @ and @home subvolumes (kernel bug tracker,
comment 1 [0]):

1. Make directory for snapshots: "mkdir /.snapshots"
2. Take snapshot of subvolume, eg. @home: "btrfs subvolume snapshot -r /home /.snapshots/$(date -Is -u)@home"
3. Mount partition (not subvolume) with the btrfs FS: "mount /dev/sda1 /mnt/btrfs-data"
4. Send btrfs snapshot: "btrfs send /mnt/btrfs-data/.snapshots/2015-08-28T10:07:22+0000 at home | btrfs receive /some-directory/"


Based on the comments of the above mentioned kernel bug tracker, this problem should have been fixed in btrfs-progs commit 8d68cb2bad0e8e7951811e0641188c447165141f [1].


References:
[0] https://bugzilla.kernel.org/show_bug.cgi?id=69401#c1
[1] http://git.kernel.org/cgit/linux/kernel/git/kdave/btrfs-progs.git/commit/?id=8d68cb2bad0e8e7951811e0641188c447165141f

** Bug watch added: Linux Kernel Bug Tracker #69401
   http://bugzilla.kernel.org/show_bug.cgi?id=69401

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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:
  Confirmed

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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