bcache doesn't register/recognize devices on s390x

[Ryan Harper]

1. # cat /proc/version_signature
Ubuntu 4.4.0-16.32-generic 4.4.6

# no pci on s390x, but none-the-less
2. root@ubuntu:~# sudo lspci -vnvn
root@ubuntu:~#

# lsb_release -rd
Description: Ubuntu Xenial Xerus (development branch)
Release: 16.04

# apt-cache policy linux-image-generic
linux-image-generic:
  Installed: 4.4.0.16.17
  Candidate: 4.4.0.16.17
  Version table:
 *** 4.4.0.16.17 500
        500 http://us.ports.ubuntu.com/ubuntu-ports xenial/main s390x Packages
        100 /var/lib/dpkg/status

3. bcache cache and backing devices auto register when created (or can be registered manually vi /sys/fs/bcache/register

4. what currently happens:

- modprobe bcache
- create a cache device and a backing device

# make-bcache -C /dev/vda1
# make-bcache -B /dev/vda2

on amd64, the cache device is automatically registered, on s390x, there is a kernel error

[ 4127.805719] bcache: register_bcache() error opening /dev/vda1: Not a bcache superblock

But bcache-show-super says it's fine:

# bcache-super-show /dev/vda1
sb.magic ok
sb.first_sector 8 [match]
sb.csum 70C54F690E440FF5 [match]
sb.version 1 [backing device]

dev.label (empty)
dev.uuid 83e7fe43-66d9-4cf1-8050-8469e86ffff9
dev.sectors_per_block 8
dev.sectors_per_bucket 1024
dev.data.first_sector 16
dev.data.cache_mode 0 [writethrough]
dev.data.cache_state 0 [detached]

cset.uuid 72f737d7-0dc6-491a-929c-37a4b3e8d058

echo "/dev/vda1" | sudo tee /sys/fs/bcache/register fails as well, with:

bash: echo: write error: Invalid argument

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-generic 4.4.0.16.17
ProcVersionSignature: Ubuntu 4.4.0-2.16-generic 4.4.0
Uname: Linux 4.4.0-2-generic s390x
AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access '/dev/snd/': No such file or directory
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.20-0ubuntu3
Architecture: s390x
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found.
Date: Fri Apr 1 11:52:00 2016
IwConfig:
 lo no wireless extensions.

 docker0 no wireless extensions.

 eth0 no wireless extensions.
Lspci:

Lsusb: Error: command ['lsusb'] failed with exit code 1:
PciMultimedia:

ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=C
 SHELL=/bin/bash
ProcFB: Error: [Errno 2] No such file or directory: '/proc/fb'
ProcKernelCmdLine: root=UUID=2a60026a-b696-4b21-88df-e7fc236f4472
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-2-generic N/A
 linux-backports-modules-4.4.0-2-generic N/A
 linux-firmware 1.157
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)

[Brad Figg (brad-figg)]

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

apport-collect 1565029

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Ryan Harper (raharper)]

This still fails on s390x. I've an LPAR with 18.04 and kernel 4.15.0-39-generic.