[Bug 1861941] Re: bcache by-uuid links disappear after mounting bcache0

[Rafael David Tinoco]

Alright, summarizing this so far, we have the following fixes landed in
Groovy:

udev (systemd pkg):

- 60-persistent-storage.rules: skip_bcache_fs_type:
  - /dev/disk/by-uuid/_ and /dev/disk/by-label/_ not created for bcache devs

Since it does not make sense to have the caching device symlink like if
it was a regular filesystem disk to be used:

(k)rafaeldtinoco at bcache:~$ ls -lah /dev/disk/by-uuid
total 0
drwxr-xr-x 2 root root 100 Jul 21 18:49 .
drwxr-xr-x 7 root root 140 Jul 21 17:39 ..
lrwxrwxrwx 1 root root  10 Jul 21 17:39 022E-07E1 -> ../../vda1
lrwxrwxrwx 1 root root  13 Jul 21 18:49 50b98f0d-c0e0-49d2-9856-8ac6bc91e232 -> ../../bcache0
lrwxrwxrwx 1 root root  10 Jul 21 17:39 67993d4f-fa55-49b1-886e-c692f88393ba -> ../../vda2

- 69-bcache.rules:
  - if any other driver - than bcache - touches /dev/bcache[0-9]*
    bcache/by-uuid/_ (BCACHE_CACHED_UUID and LABEL) symlinks are
    recreated.

To address the udev event responsible for wiping /dev/bcache/by-uuid,
like:

KERNEL[4175.725930] change   /devices/virtual/block/bcache0 (block)
ACTION=change
DEVPATH=/devices/virtual/block/bcache0
SUBSYSTEM=block
SYNTH_UUID=0
DEVNAME=/dev/bcache0
DEVTYPE=disk
SEQNUM=6746
MAJOR=251
MINOR=0
 
UDEV  [4175.758078] change   /devices/virtual/block/bcache0 (block)
ACTION=change
DEVPATH=/devices/virtual/block/bcache0
SUBSYSTEM=block
SYNTH_UUID=0
DEVNAME=/dev/bcache0
DEVTYPE=disk
SEQNUM=6746
USEC_INITIALIZED=4151438558
ID_FS_UUID=50b98f0d-c0e0-49d2-9856-8ac6bc91e232
ID_FS_UUID_ENC=50b98f0d-c0e0-49d2-9856-8ac6bc91e232
ID_FS_VERSION=1.0
ID_FS_TYPE=ext4
ID_FS_USAGE=filesystem
MAJOR=251
MINOR=0
DEVLINKS=/dev/disk/by-uuid/50b98f0d-c0e0-49d2-9856-8ac6bc91e232
TAGS=:systemd:

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to systemd in Ubuntu.
https://bugs.launchpad.net/bugs/1861941

Title:
  bcache by-uuid links disappear after mounting bcache0

Status in bcache-tools package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in bcache-tools source package in Bionic:
  Triaged
Status in systemd source package in Bionic:
  Triaged
Status in bcache-tools source package in Focal:
  Confirmed
Status in systemd source package in Focal:
  Triaged

Bug description:
  1.
  root at ubuntu:~# lsb_release -rd
  Description:	Ubuntu Focal Fossa (development branch)
  Release:	20.04

  2. 
  root at ubuntu:~# lsb_release -rd
  Description:	Ubuntu Focal Fossa (development branch)
  Release:	20.04
  root at ubuntu:~# apt-cache policy linux-image-virtual 
  linux-image-virtual:
    Installed: 5.4.0.12.15
    Candidate: 5.4.0.12.15
    Version table:
   *** 5.4.0.12.15 500
          500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages
          100 /var/lib/dpkg/status
  root at ubuntu:~# apt-cache policy linux-image-5.4.0-12-generic 
  linux-image-5.4.0-12-generic:
    Installed: 5.4.0-12.15
    Candidate: 5.4.0-12.15
    Version table:
   *** 5.4.0-12.15 500
          500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages
          100 /var/lib/dpkg/status

  3. mount /dev/bcache0 && ls -al /dev/bcache/by-uuid/
  + ls -al /dev/bcache/by-uuid/
  total 0
  drwxr-xr-x 2 root root 60 Feb  4 23:31 .
  drwxr-xr-x 3 root root 60 Feb  4 23:31 ..
  lrwxrwxrwx 1 root root 13 Feb  4 23:31 abdfd1f6-44ce-4266-91db-24667b9ae51a -> ../../bcache0

  4.
  root at ubuntu:~# ls -al /dev/bcache/by-uuid
  ls: cannot access '/dev/bcache/by-uuid': No such file or directory

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: linux-image-5.4.0-12-generic 5.4.0-12.15
  ProcVersionSignature: Ubuntu 5.4.0-12.15-generic 5.4.8
  Uname: Linux 5.4.0-12-generic x86_64
  ApportVersion: 2.20.11-0ubuntu16
  Architecture: amd64
  Date: Tue Feb  4 23:31:52 2020
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   LANG=C.UTF-8
   SHELL=/bin/bash
  SourcePackage: linux-signed-5.4
  UpgradeStatus: No upgrade log present (probably fresh install)

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/bcache-tools/+bug/1861941/+subscriptions