ERROR: unable to resolve -c

[NicoHood]

[arch@arch ~]$ sudo snap-sync -n
[sudo] password for arch: 
Select a mounted BTRFS device to backup to.
   1) c91384af-f210-48f5-ba19-d6415a1bb447 (/)
   2) c91384af-f210-48f5-ba19-d6415a1bb447 (/hackallthethings)
   3) c91384af-f210-48f5-ba19-d6415a1bb447 (/var/tmp)
   4) c91384af-f210-48f5-ba19-d6415a1bb447 (/data)
   5) c91384af-f210-48f5-ba19-d6415a1bb447 (/var/abs)
   6) c91384af-f210-48f5-ba19-d6415a1bb447 (/var/log)
   7) c91384af-f210-48f5-ba19-d6415a1bb447 (/var/cache/pacman/pkg)
   8) c91384af-f210-48f5-ba19-d6415a1bb447 (/home)
   9) c91384af-f210-48f5-ba19-d6415a1bb447 (/.snapshots)
  10) c91384af-f210-48f5-ba19-d6415a1bb447 (/srv)
  11) c91384af-f210-48f5-ba19-d6415a1bb447 (/home/arch/hackallthethings)
  12) c91384af-f210-48f5-ba19-d6415a1bb447 (/home/arch/.local/share/Steam)
  13) e5b8a2d6-85a1-4640-a659-acb8d6922bd6 (/run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6)
   0) Exit
Enter a number: 13

You selected the disk with UUID e5b8a2d6-85a1-4640-a659-acb8d6922bd6.
The disk is mounted at /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6.

Creating new snapshot for root...
Will backup //.snapshots/4641/snapshot to /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6/backup/E744/root/4641//snapshot
Sending incremental snapshot for root...
ERROR: unable to resolve -c

No idea why this happens..

Without -n:

Creating new snapshot for root...
Will backup //.snapshots/4642/snapshot to /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6/backup/E744/root/4642//snapshot
Continue with backup [Y/n]? y
Sending incremental snapshot for root...
ERROR: unable to resolve -c

[arch@arch ~]$ snapper list | grep -e snap -e backup
single | 4465 |       | Fri 12 May 2017 01:48:56 PM CEST | root |          | latest incremental backup                           | backupdir=Backup/E744, uuid=d2133005-da15-484f-9dbc-3352e6af0529
single | 4514 |       | Sun 14 May 2017 07:19:17 PM CEST | root |          | latest incremental backup                           | backupdir=backup/E744, uuid=e5b8a2d6-85a1-4640-a659-acb8d6922bd6
single | 4641 |       | Tue 23 May 2017 07:20:10 PM CEST | root |          | snap-sync backup in progress                        |                                                                 
single | 4642 |       | Tue 23 May 2017 07:21:08 PM CEST | root |          | snap-sync backup in progress                        |      

+ printf 'Will backup %s to %s\n' //.snapshots/4644/snapshot /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6/backup/E744/root/4644//snapshot
+ tee /tmp/tmp.V6AaRo9lXE/snap-sync.out
Will backup //.snapshots/4644/snapshot to /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6/backup/E744/root/4644//snapshot
+ cont_backup=K
+ [[ no == \y\e\s ]]
+ [[ -n K ]]
+ [[ K != [Yy]\e\s ]]
+ [[ K != [Yy] ]]
+ [[ K != [Nn]\o ]]
+ [[ K != [Nn] ]]
+ read -r -p 'Continue with backup [Y/n]? ' cont_backup
Continue with backup [Y/n]? 
+ [[ -n '' ]]
+ [[ -n '' ]]
+ [[ '' != [Yy]\e\s ]]
+ [[ '' != [Yy] ]]
+ [[ -n '' ]]
+ mkdir -p /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6/backup/E744/root/4644/
+ [[ -z 4514 ]]
+ tee /tmp/tmp.V6AaRo9lXE/snap-sync.out
+ printf 'Sending incremental snapshot for %s...\n' root
Sending incremental snapshot for root...
+ btrfs send //.snapshots/4644/snapshot -c //.snapshots/4514/snapshot
+ btrfs receive /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6/backup/E744/root/4644/
ERROR: unable to resolve -c

[arch@arch ~]$ sudo btrfs subvolume list / | grep 4514
ID 11975 gen 352561 top level 259 path @snapshots/4514/snapshot
[arch@arch ~]$ ls //.snapshots/4514/snapshot
bin  boot  data  dev  etc  hackallthethings  home  hostrun  lib  lib64  lost+found  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

[arch@arch ~]$ sudo btrfs sub list -auR / | grep 4514
ID 11975 gen 352561 top level 259 received_uuid - uuid d22e8c45-76cd-1e4f-bb1c-5dc37a51e313 path <FS_TREE>/@snapshots/4514/snapshot
ID 12054 gen 354514 top level 259 received_uuid - uuid 56fc424b-5d24-0c4c-8e51-c8467c4aaebf path <FS_TREE>/@snapshots/4548/snapshot
[arch@arch ~]$ sudo btrfs sub list -auR /run/media/arch/e5b8a2d6-85a1-4640-a659-acb8d6922bd6/ | grep 4514
ID 1557 gen 687 top level 5 received_uuid d22e8c45-76cd-1e4f-bb1c-5dc37a51e313 uuid 4904aefc-6884-e242-90c5-f70eb3b70f49 path backup/E744/root/4514/snapshot

18 commits to master since the last release. Maybe this fixed it already?

[NicoHood]

Looks like a btrfs bug!? The subvolume seems to be available to me. Also your script always worked before.
https://git.archlinux.org/svntogit/packages.git/log/trunk?h=packages/btrfs-progs

[kalbasit]

I'm also having the same issue, it used to work before as well.

[kalbasit]

I deleted the latest incremental snapshot, and that forced a new sync, it worked. After the first sync, I tried again and it failed with the same message. I revert btrfs-progs to 4.10.2-1 and now I am getting:

sudo snap-sync -c @root -u e6437994-dced-4441-a3af-344694bb7f37

You selected the disk with UUID e6437994-dced-4441-a3af-344694bb7f37.
The disk is mounted at /mnt/Madea.

Initial configuration...

NOTE: Previous failed snap-sync backup snapshots found for '@root'.

Creating new snapshot for @root...
Will backup //.snapshots/715/snapshot to /mnt/Madea/snap-sync/cratos/@root/715//snapshot
Continue with backup [Y/n]? y

Performing backups...

Sending incremental snapshot for @root...
At subvol //.snapshots/715/snapshot
At snapshot snapshot
ERROR: cannot find parent subvolume
==> ERROR: 
Deleting old snapshot for @root...
Tagging new snapshot as latest backup for @root...

Done!

[kalbasit]

With btrfs-progs 4.10 installed, I deleted the snapshots as previously mentioned, started a new snapshot and now it works again.

[NicoHood]

@kalbasit I assume you also use ArchLinux? I will ask if we should open a bug at kernel.org or only for arch.

Edit: Which kernel do you use? I am using 4.11. Can you try the lts kernel? I currently have no hardware to test.

Edit2: I spoke with the archlinux TUs and they suggested me to report the issue upstream. Ref Signed-off-by: David Sterba <dsterba@suse.com> as he released the last btrfs-progs. Can someone do this please? I currently have no time over the weekend.

[kalbasit]

@NicoHood yes I use ArchLinux and I do use linux-lts as my kernel. We should report it upstream. I checked the ChangeLog and there is some work for btrfs send and btrfs recieve, see https://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git/log/

Did you file upstream or should I?

[NicoHood]

@kalbasit Alright, please file a bug and also refer to this topic. I am using linux-zen (4.11) and also have the issue.

[kalbasit]

@NicoHood I sent an email to the mailing list for now, you can find it here. Let's wait to hear from them.