[Bug 1469143] Re: kpartx -d fails with image paths longer than 63 characters

[Simo Punnonen]

I can't seem to be able to change the state of the bug myself to
'tested' in any way. Everything's grayed out.

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https://bugs.launchpad.net/bugs/1469143

Title:
  kpartx -d fails with image paths longer than 63 characters

Status in multipath-tools package in Ubuntu:
  Fix Released
Status in multipath-tools source package in Precise:
  In Progress
Status in multipath-tools source package in Trusty:
  In Progress
Status in multipath-tools source package in Utopic:
  Won't Fix
Status in multipath-tools source package in Vivid:
  Won't Fix

Bug description:
  [Impact]
  Users of kpartx to load disk images, possibly multiple images with the same file name (but in different paths).

  [Test case]
  See below, also see https://bugs.launchpad.net/ubuntu/+source/multipath-tools/+bug/1469143/comments/3

  [Regression potential]
  This changes makes the matching for loaded images more robust, and so has a very limited risk of regression. Since there is a call to stat() introduced, one may notice a slowdown if the stat() call blocks for a reason, and the operation will fail if the stat() call fails for any reason, since the device and inode are now required.

  ---

  $ apt-show-versions multipath-tools
  multipath-tools:amd64/vivid 0.4.9-3ubuntu12 uptodate

  Reproduce:
  Mount an image from a path longer than 63 chars succeeds:
  $ sudo kpartx -av asfd1asdf2asdf3asdf4asdf5asdf6asfd7asdf8asdf9asf10asdf11asdf12asdf13/disk.img
  add map loop0p1 (252:0): 0 409600 linear /dev/loop0 2048
  add map loop0p2 (252:1): 0 2 linear /dev/loop0 411648
  add map loop0p5 : 0 819200 linear /dev/loop0 413696
  add map loop0p6 : 0 819200 linear /dev/loop0 1234944
  add map loop0p7 : 0 819200 linear /dev/loop0 2056192
  add map loop0p8 : 0 1316864 linear /dev/loop0 2877440

  but dismounting fails:
  $ sudo kpartx -dv asfd1asdf2asdf3asdf4asdf5asdf6asfd7asdf8asdf9asf10asdf11asdf12asdf13/disk.img

  strace shows that the parameter on the dismount appears to get cut at 63 chars:
  ioctl(3, DM_LIST_VERSIONS, 0x15b89b0)   = 0
  stat("asfd1asdf2asdf3asdf4asdf5asdf6asfd7asdf8asdf9asf10asdf11asdf12asdf13/disk.img", {st_mode=S_IFREG|0644, st_size=2147483648, ...}) = 0
  stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
  open("/dev/loop0", O_RDONLY)            = 4
  ioctl(4, LOOP_GET_STATUS, {number=0, offset=0, flags=0, name="asfd1asdf2asdf3asdf4asdf5asdf6asfd7asdf8asdf9asf10asdf11asdf12a", ...}) = 0
  close(4)                                = 0
  stat("/dev/loop1", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 1), ...}) = 0
  open("/dev/loop1", O_RDONLY)            = 4
  ioctl(4, LOOP_GET_STATUS, {number=0, offset=0, flags=0, name="asfd1asdf2asdf3asdf4asdf5asdf6asfd7asdf8asdf9asf10asdf11asdf12a", ...}) = -1 ENXIO (No such device or address)

  if the path is 63 chars or less, the dismount also succeeds.

  This is quickly becomes an issue if you want to use full disk paths in
  your shell scripts.

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