Following up my question;  we should see both events in all kernels.

The first event is when the /dev/bcache0 is joined with a cache device,
and emitts the CACHED_UUID value in the uevent; the UUID is the *backing
device bcache metadata UUID* it is not related to the content contained
within the backing device; this CACHED_UUID is symlinked at /dev/bcache
/by-uuid

Once /dev/bcache0 is created, blkid will scan the contents of
/dev/bcache0 which contains an ext4 filesystem and the FS_UUID is
symlinked at /dev/disk/by-uuid.

CACHED_UUID != FS_UUID
/dev/bcache/by-uuid != /dev/disk/by-uuid

I speculate that udev has a bug where it's only looking at the basename
of the symlink target and removing any other 'by-uuid' link against the
device when it needs to account for the full path of the symlink since
the bcache/by-uuid is different than the disk/by-uuid.

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

Title:
  bcache by-uuid links disappear after mounting bcache0

Status in linux package in Ubuntu:
  Incomplete
Status in linux-signed-5.4 package in Ubuntu:
  New
Status in udev package in Ubuntu:
  New

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

  2. 
  root@ubuntu:~# lsb_release -rd
  Description:  Ubuntu Focal Fossa (development branch)
  Release:      20.04
  root@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@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@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/linux/+bug/1861941/+subscriptions

-- 
Mailing list: https://launchpad.net/~kernel-packages
Post to     : kernel-packages@lists.launchpad.net
Unsubscribe : https://launchpad.net/~kernel-packages
More help   : https://help.launchpad.net/ListHelp

Reply via email to