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

Tue Jul 21 20:02:54 UTC 2020

Status from old attempts to solve same nature issues:

----

Older (2018) merge request from @raharper:

https://github.com/koverstreet/bcache-tools/pull/1

addressing the fact that kernel uevents would not always emit 
CACHED_UUID parameters, making udev to delete (whenever that happens) 
/dev/bcache/{by-uuid,by-label} symlinks.

This last MR pointed to previous related bugs:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=890446
https://bugs.launchpad.net/curtin/+bug/1728742

And to an upstream kernel patch:

https://lore.kernel.org/patchwork/patch/921298/

to

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1729145

that wasn't accepted upstream.

Even not being accepted upstream, the SRU was attempted:

LP: #1729145

https://lists.ubuntu.com/archives/kernel-team/2017-December/088680.html
https://lists.ubuntu.com/archives/kernel-team/2017-December/088679.html

Both were NACKED.

Attempted again:

https://lists.ubuntu.com/archives/kernel-team/2017-December/088682.html
https://lists.ubuntu.com/archives/kernel-team/2017-December/088683.html

NACKED again.

And a v2 was sent:

https://lists.ubuntu.com/archives/kernel-team/2017-December/088751.html
https://lists.ubuntu.com/archives/kernel-team/2017-December/088750.html
https://lists.ubuntu.com/archives/kernel-team/2017-December/088749.html

and acked in January 2018 by Coling:

https://lists.ubuntu.com/archives/kernel-team/2018-January/089492.html

but not upstreamed.

BIONIC contains the fix:

commit ed9333e1b583
Author: Ryan Harper <ryan.harper at canonical.com>
Date:   Mon Dec 11 12:12:01 2017

    UBUNTU: SAUCE: (no-up) bcache: decouple emitting a cached_dev CHANGE uevent

    BugLink: http://bugs.launchpad.net/bugs/1729145

    - decouple emitting a cached_dev CHANGE uevent which includes dev.uuid
      and dev.label from bch_cached_dev_run() which only happens when a
      bcacheX device is bound to the actual backing block device (bcache0 -> vdb)

    - update bch_cached_dev_run() to invoke bch_cached_dev_emit_change() as
      needed; no functional code path changes here

    - Modify register_bcache to detect a re-registering of a bcache
      cached_dev, and in that case call bcache_cached_dev_emit_change() to

    Signed-off-by: Ryan Harper <ryan.harper at canonical.com>
    Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
    Acked-by: Colin Ian King <colin.king at canonical.com>
    Acked-by: Stefan Bader <stefan.bader at canonical.com>
    Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
    [ saf: fix incorrect indentation ]
    Signed-off-by: Seth Forshee <seth.forshee at canonical.com>

FOCAL contains the fix:

commit 67553dcd7905
Author: Ryan Harper <ryan.harper at canonical.com>
Date:   Mon Dec 11 12:12:01 2017

    UBUNTU: SAUCE: (no-up) bcache: decouple emitting a cached_dev CHANGE
uevent

GROOVY contains the fix:

commit 67553dcd7905
Author: Ryan Harper <ryan.harper at canonical.com>
Date:   Mon Dec 11 12:12:01 2017

    UBUNTU: SAUCE: (no-up) bcache: decouple emitting a cached_dev CHANGE
uevent

----

So, the kernel patch wasn't accepted, nor bcache-tools patch by 
@raharper, the bcache-export-cached.

----

New Upstream summary from @raharper:

https://github.com/systemd/systemd/pull/16317#issuecomment-655647313

in the upstream merge request made by @rbalint.

** Bug watch added: Debian Bug tracker #890446
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=890446

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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)

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