[Bug 1326110] Re: losetup silently fails to attach small files

[Phillip Susi]

** Changed in: util-linux (Ubuntu)
       Status: New => Triaged

** Changed in: util-linux (Ubuntu)
   Importance: Undecided => Low

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Title:
  losetup silently fails to attach small files

Status in “util-linux” package in Ubuntu:
  Triaged

Bug description:
  1) # lsb_release -rd
  Description:    Ubuntu 12.04.4 LTS
  Release:        12.04

  2) # apt-cache policy util-linux
  util-linux:
    Installed: 2.20.1-1ubuntu3
    Candidate: 2.20.1-1ubuntu3
    Version table:
   *** 2.20.1-1ubuntu3 0
          500 http://archive.ubuntu.com//ubuntu/ precise/main amd64 Packages
          100 /var/lib/dpkg/status

  3) losetup -f /srv/swift.img
  attach the file to a free loop device

  4) losetup -f /srv/swift.img returned 0, but did not attach the file
  to a loop device.

  Specifically, the target file was very small, 20 bytes.  The following
  sequence was run:

  truncate --size 20 /srv/swift.img
  stat /srv/swift.img
  losetup -f /srv/swift.img
  losetup -a

  When the file is small (20 bytes) losetup returns zero, but does not
  setup the file.  Through some investigation, it appears any file of
  size < 512 will fail in this way:

  root at hayward-42:~# truncate --size 511 /srv/swift.img 
  root at hayward-42:~# stat /srv/swift.img 
    File: `/srv/swift.img'
    Size: 511             Blocks: 0          IO Block: 4096   regular file
  Device: 801h/2049d      Inode: 5767170     Links: 1
  Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
  Access: 2014-06-03 19:24:58.213512482 +0000
  Modify: 2014-06-03 19:26:52.593509603 +0000
  Change: 2014-06-03 19:26:52.593509603 +0000
   Birth: -
  root at hayward-42:~# losetup --find /srv/swift.img 
  root at hayward-42:~# echo $?
  0
  root at hayward-42:~# losetup -a

  
  Here is a successful sequence with size=512:

  root at hayward-42:~# truncate --size 512 /srv/swift.img 
  root at hayward-42:~# stat /srv/swift.img 
    File: `/srv/swift.img'
    Size: 512             Blocks: 0          IO Block: 4096   regular file
  Device: 801h/2049d      Inode: 5767170     Links: 1
  Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
  Access: 2014-06-03 19:24:58.213512482 +0000
  Modify: 2014-06-03 19:27:33.029508499 +0000
  Change: 2014-06-03 19:27:33.029508499 +0000
   Birth: -
  root at hayward-42:~# losetup --find /srv/swift.img 
  root at hayward-42:~# echo $?
  0
  root at hayward-42:~# losetup -a
  /dev/loop7: [0801]:5767170 (/srv/swift.img)

  ProblemType: Bug
  DistroRelease: Ubuntu 12.04
  Package: mount 2.20.1-1ubuntu3
  ProcVersionSignature: Ubuntu 3.2.0-60.91-generic 3.2.55
  Uname: Linux 3.2.0-60-generic x86_64
  ApportVersion: 2.0.1-0ubuntu17.6
  Architecture: amd64
  Date: Tue Jun  3 19:16:57 2014
  MarkForUpload: True
  ProcEnviron:
   TERM=screen
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: util-linux
  UpgradeStatus: No upgrade log present (probably fresh install)

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