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[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu Zesty)
       Status: In Progress => Won't Fix

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https://bugs.launchpad.net/bugs/1729145

Title:
  /dev/bcache/by-uuid links not created after reboot

Status in linux package in Ubuntu:
  In Progress
Status in systemd package in Ubuntu:
  Incomplete
Status in linux source package in Xenial:
  In Progress
Status in systemd source package in Xenial:
  Won't Fix
Status in linux source package in Zesty:
  Won't Fix
Status in systemd source package in Zesty:
  Won't Fix
Status in linux source package in Artful:
  In Progress
Status in systemd source package in Artful:
  Won't Fix
Status in linux source package in Bionic:
  In Progress
Status in systemd source package in Bionic:
  Won't Fix

Bug description:
  1. $ lsb_release -rd
  Description:	Ubuntu 17.10
  Release:	17.10

  2. $ apt-cache policy linux-image-`uname -r`
  linux-image-4.13.0-16-generic:
    Installed: 4.13.0-16.19
    Candidate: 4.13.0-16.19
    Version table:
   *** 4.13.0-16.19 500
          500 http://nova.clouds.archive.ubuntu.com/ubuntu artful/main amd64 Packages
          100 /var/lib/dpkg/status

  3. After creating some bcache devices and rebooting /dev/bcache/by-uuid/<UUID> -> ../../bcacheN
  symlinks point to the current bcache device which is caching the dev.uuid found after creating a backing device.

  4. /dev/bcache/by-uuid does not exist and there are not symlinks
  underneath

  
  It appears that since the initramfs loads the bcache module which probes and finds all of the cache devices and backing devices then once the rootfs is mounted and udev gets to run, the bcache kernel module does not emit the CACHED_UUID value into the environment if the underlying devices are already registered.

  In dmesg, one can see that prior to mounting the rootfs, we see bcache
  register events:

  [    5.333973] bcache: register_bdev() registered backing device vdb2
  [    5.354138] bcache: register_bdev() registered backing device vdb4
  [    5.365665] bcache: register_bdev() registered backing device vdb3
  [    5.397720] bcache: bch_journal_replay() journal replay done, 0 keys in 1 entries, seq 1
  [    5.428683] bcache: register_cache() registered cache device vdb1

  then rootfs ismounted and systemd starts systemd-udev

  [    9.350889] systemd[1]: Listening on udev Kernel Socket.

  And then the coldplug replay of kernel events triggers /lib/udev/rules.d/69-bcache.rules
  which invokes /lib/udev/bcache-register which writes the device name (/dev/vdb1 or /dev/bcache0) into /sys/fs/bcache/register and results is the bcache kernel driver attempting to register the block device.  However, there is already a bcache device associated already and registration fails

  [   11.173141] bcache: register_bcache() error opening /dev/vdb2: device already registered
  [   11.184617] bcache: register_bcache() error opening /dev/vdb3: device already registered
  [   11.199130] bcache: register_bcache() error opening /dev/vdb1: device already registered
  [   11.271694] bcache: register_bcache() error opening /dev/vdb4: device already registered

  The problem then is that only a kernel call to bch_cached_dev_run()
  which happens like this:

  bcache_register()
    register_bdev()
      bch_cached_dev_run()
        kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
        
  where env includes: 
      "DRIVER=bcache",
          kasprintf(GFP_KERNEL, "CACHED_UUID=%pU", dc->sb.uuid),
          NULL,
          NULL,
      };

  Since that event is not emitted for any previously registered device,
  then the symlink will not be created.

  ProblemType: Bug
  DistroRelease: Ubuntu 17.10
  Package: linux-image-4.13.0-16-generic 4.13.0-16.19
  ProcVersionSignature: User Name 4.13.0-16.19-generic 4.13.4
  Uname: Linux 4.13.0-16-generic x86_64
  AlsaDevices:
   total 0
   crw-rw---- 1 root audio 116,  1 Oct 31 22:09 seq
   crw-rw---- 1 root audio 116, 33 Oct 31 22:09 timer
  AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
  ApportVersion: 2.20.7-0ubuntu3.1
  Architecture: amd64
  ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 'arecord'
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  CRDA: N/A
  Date: Wed Nov  1 01:39:01 2017
  Ec2AMI: ami-0000030b
  Ec2AMIManifest: FIXME
  Ec2AvailabilityZone: nova
  Ec2InstanceType: m1.small
  Ec2Kernel: unavailable
  Ec2Ramdisk: unavailable
  IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
  Lsusb:
   Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd 
   Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
  MachineType: OpenStack Foundation OpenStack Nova
  PciMultimedia:
   
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=C.UTF-8
   SHELL=/bin/bash
  ProcFB:
   
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.13.0-16-generic root=LABEL=cloudimg-rootfs ro console=tty1 console=ttyS0
  RelatedPackageVersions:
   linux-restricted-modules-4.13.0-16-generic N/A
   linux-backports-modules-4.13.0-16-generic  N/A
   linux-firmware                             N/A
  RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 04/01/2014
  dmi.bios.vendor: SeaBIOS
  dmi.bios.version: 1.10.1-1ubuntu1~cloud0
  dmi.chassis.type: 1
  dmi.chassis.vendor: QEMU
  dmi.chassis.version: pc-i440fx-zesty
  dmi.modalias: dmi:bvnSeaBIOS:bvr1.10.1-1ubuntu1~cloud0:bd04/01/2014:svnOpenStackFoundation:pnOpenStackNova:pvr15.0.7:cvnQEMU:ct1:cvrpc-i440fx-zesty:
  dmi.product.family: Virtual Machine
  dmi.product.name: OpenStack Nova
  dmi.product.version: 15.0.7
  dmi.sys.vendor: OpenStack Foundation

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