[Bug 1735046] Re: mkfs.btrfs error checking mount status of loop device backing_file

[Mathew Hodson]

** Changed in: btrfs-tools (Ubuntu)
   Importance: Undecided => Medium

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Title:
  mkfs.btrfs error checking mount status of loop device backing_file

Status in btrfs-tools package in Ubuntu:
  New

Bug description:
  # lsb_release -rd
  Description:    Ubuntu 14.04.5 LTS
  Release:        14.04

  # apt-cache policy btrfs-tools
  btrfs-tools:
    Installed: 3.12-1ubuntu0.1
    Candidate: 3.12-1ubuntu0.1
    Version table:
   *** 3.12-1ubuntu0.1 0
          500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       3.12-1 0
          500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

  # mkfs.btrfs --force /dev/vdd   succeeds

  # # mkfs.btrfs --force /dev/vdd 
  Error: error checking /dev/vdd mount status

  # strace -f mkfs.btrfs --force /dev/vdd
  <snip>
  stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
  lstat("/dev", {st_mode=S_IFDIR|0755, st_size=4180, ...}) = 0
  lstat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
  open("/sys/block//loop0/loop/backing_file", O_RDONLY) = 5
  fstat(5, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
  mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe8bd73c000
  read(5, "/root.tmp.img (deleted)\n", 4096) = 24
  close(5)                                = 0
  munmap(0x7fe8bd73c000, 4096)            = 0
  lstat("/dev", {st_mode=S_IFDIR|0755, st_size=4180, ...}) = 0
  lstat("/dev/vdd", {st_mode=S_IFBLK|0660, st_rdev=makedev(253, 48), ...}) = 0
  lstat("/root.tmp.img (deleted)", 0x7ffeaa3f0bf0) = -1 ENOENT (No such file or directory)
  close(4)                                = 0
  munmap(0x7fe8bd73d000, 4096)            = 0
  close(3)                                = 0
  write(2, "Error: error checking /dev/vdd m"..., 44Error: error checking /dev/vdd mount status
  ) = 44
  exit_group(1)                           = ?
  +++ exited with 1 +++

  It appears that mkfs.btrfs doesn't like the loop device, /dev/loop0
  which has a deleted backing file.

  root at ubuntu:~# cat /sys/block/loop0/loop/backing_file 
  /root.tmp.img (deleted)
  root at ubuntu:~# ls -al /root.tmp.img
  ls: cannot access /root.tmp.img: No such file or directory

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: btrfs-tools 3.12-1ubuntu0.1
  ProcVersionSignature: Ubuntu 3.13.0-135.184-generic 3.13.11-ckt39
  Uname: Linux 3.13.0-135-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.27
  Architecture: amd64
  Date: Wed Nov 29 02:58:04 2017
  ProcEnviron:
   TERM=vt102
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: btrfs-tools
  UpgradeStatus: No upgrade log present (probably fresh install)

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