[Bug 1861941] Re: bcache by-uuid links disappear after mounting bcache0
Rafael David Tinoco
1861941 at bugs.launchpad.net
Fri Aug 21 14:05:16 UTC 2020
Bionic verification:
$ apt changelog bcache-tools | head -10
bcache-tools (1.0.8-2ubuntu0.18.04.1) bionic; urgency=medium
[ Ryan Harper ]
* Add helper script to read bcache devs superblock (LP: #1861941)
-- Rafael David Tinoco <rafaeldtinoco at ubuntu.com> Wed, 05 Aug 2020
17:44:05 -0300
bcache-tools (1.0.8-2build1) artful; urgency=medium
----
$ dpkg-query -f '${Package}###${Version}\n' -W 'bcache-tools'
bcache-tools###1.0.8-2ubuntu0.18.04.1
----
$ sudo ./test-bcache.sh
/mnt is a mountpoint
/dev/bcache0: 2 bytes were erased at offset 0x00000438 (ext4): 53 ef
writing 1 to /sys/class/block/bcache0/bcache/stop
writing 1 to /sys/fs/bcache/60412675-9103-47b0-9794-91fcfb12d50d/stop
/dev/vdc: 16 bytes were erased at offset 0x00001018 (bcache): c6 85 73 f6 4e 1a 45 ca 82 65 f5 7f 48 ba 6d 81
10+0 records in
10+0 records out
10485760 bytes (10 MB, 10 MiB) copied, 0.0173157 s, 606 MB/s
/dev/vdb: 16 bytes were erased at offset 0x00001018 (bcache): c6 85 73 f6 4e 1a 45 ca 82 65 f5 7f 48 ba 6d 81
10+0 records in
10+0 records out
10485760 bytes (10 MB, 10 MiB) copied, 0.00634546 s, 1.7 GB/s
UUID: c3758ea3-0e2c-42e3-bb77-da27292d2476
Set UUID: b2b21f55-3599-461a-b162-8377d85fbc34
version: 0
nbuckets: 2048
block_size: 1
bucket_size: 1024
nr_in_set: 1
nr_this_dev: 0
first_bucket: 1
UUID: f4001b7e-386e-4ca3-a5e0-d53f100d156f
Set UUID: b2b21f55-3599-461a-b162-8377d85fbc34
version: 1
block_size: 1
data_offset: 16
/dev/vdc
tee: /sys/fs/bcache/register: Invalid argument
/dev/vdb
tee: /sys/fs/bcache/register: Invalid argument
total 0
drwxr-xr-x 2 root root 60 Aug 21 14:03 .
drwxr-xr-x 3 root root 60 Aug 21 14:03 ..
lrwxrwxrwx 1 root root 13 Aug 21 14:03 f4001b7e-386e-4ca3-a5e0-d53f100d156f -> ../../bcache0
Creating filesystems on bcache0
mke2fs 1.44.1 (24-Mar-2018)
Discarding device blocks: done
Creating filesystem with 262142 4k blocks and 65536 inodes
Filesystem UUID: 4ade91a9-6176-4a93-a34f-158fa08d0091
Superblock backups stored on blocks:
32768, 98304, 163840, 229376
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
mounting bcache0 to /mnt
total 0
drwxr-xr-x 2 root root 60 Aug 21 14:03 .
drwxr-xr-x 3 root root 60 Aug 21 14:03 ..
lrwxrwxrwx 1 root root 13 Aug 21 14:03 f4001b7e-386e-4ca3-a5e0-d53f100d156f -> ../../bcache0
Everything OK
----
** Tags removed: verification-needed verification-needed-bionic
** Tags added: verification-done verification-done-bionic
--
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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 linux package in Ubuntu:
Fix Committed
Status in systemd package in Ubuntu:
Fix Released
Status in bcache-tools source package in Bionic:
Fix Committed
Status in systemd source package in Bionic:
Won't Fix
Status in bcache-tools source package in Focal:
Fix Released
Status in systemd source package in Focal:
In Progress
Bug description:
SRU TEAM: The last 2 commits show a summary for the merges/changes
I added some specific (to Bionic) notes in the template.
Thanks!
[Impact]
* bcache-tools udev created symlinks might disappear when other udev
events are processed for the same devices.
* after mkfs.XXX in /dev/bcacheY you might face a condition where
/dev/bcache/by-{uuid,label}/zzz symlinks are gone.
* /dev/bcache/by-{uuid,label}/ symlinks are important so bcache
devices can be addressed by their UUIDs and not the ordering they were
assembled (MAAS depends on this feature, for example).
* it was also discussed in this bug that systemd-udev should *not*
populate /dev/disk/by-uuid/ with symlinks of disks that were bcache
backing devices. this was turned into a discussion whether blkid
should report those or not, and this discussion "died" after sometime.
This last item is what the systemd update is all about: to disallow
/dev/disk/by-XXX/yyyy creation for bcache backing devices (a simple
change that will reduce end users confusion).
[Test Case]
* The reproducer script is here:
https://paste.ubuntu.com/p/37KGy2Smnp/
* Bionic can't reproduce the issue with the 18.04 kernel, nor with
the HWE kernel. Nevertheless, it is preferable that Bionic also do the
same thing: to read bcache superblock and feed environment for
/dev/bcache/by-{uuid,label} symlinks creation.
[Regression Potential]
* We are not depending on bcache device udev events any more when
creating the /dev/bcache/by-{uuid,label}/ symlinks. Instead, we are
depending on a wrapper script that heads bcache device superblock. If
there is a bug in this wrapper the symlinks wouldn't work.
* Previously we were thinking in asking the kernel team to remove the
bcache udev event delta script they've done for previous case (LP:
#1729145). It creates the udev events that were being read and filling
the symlinks. We decided not to remove those (just from Groovy and on)
so we don't need to worry on Breaks/Conflicts in between the kernel
package and bcache-tools (and udev)).
* Long story short: kernel will continue to emit bcache udev events
as it did previously but now those events won't be used by anything -
after installing this SRU - because udev wrapper script is doing this
job (and doing it properly)
[Other Info]
- Original 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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