[Bug 1640823] Re: [trusty] limited to 8 loop devices

[Martin Pitt]

** Description changed:

  trusty has a very old util-linux which does not yet know about /dev
  /loop-control to create arbitrarily many loop devices. This feature was
  introduced in Linux 3.1 already (i. e. before precise even). This is a
  showstopper for backporting snappy as that needs a lot of loop mounts.
  
  Support for loop-control got introduced in
  http://git.kernel.org/cgit/utils/util-linux/util-
  linux.git/commit/?id=0b14bf7a
  
  SRU TEST CASE:
- $ for i in `seq 20`; do echo $i; sudo losetup --find --show /etc/issue; done
+ First, use up all default 8 loop devices:
+ $ for i in `seq 8`; do echo $i; sudo losetup --find /etc/issue; done
  
- With current trusty's util-linux this will only work for 8 loop devices
- and then start failing:
+ Now try to use a 9th:
+ $ sudo mount -o loop /etc/issue /mnt
  
- 8
- /dev/loop7
- 9
- losetup: could not find any free loop device
- [...]
- 
- With the proposed version, they should all work.
+ With current trusty's util-linux this will fail with "could not find any
+ free loop device". With the proposed version, this should "only" fail
+ with "you must specify the filesystem type" (or try it on an actual file
+ system image).
  
  REGRESSION POTENTIAL: /dev/loop-control and the corresponding util-linux
  support has exited for a long time without known/major issues, so this
  should be fairly safe. Also, the patch falls back to the previous
  "iterate over loop0 to loop7" behaviour if loop-control is not
  available.

** Summary changed:

- [trusty] limited to 8 loop devices
+ [trusty] mount -o loop is limited to 8 loop devices

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https://bugs.launchpad.net/bugs/1640823

Title:
  [trusty] mount -o loop is limited to 8 loop devices

Status in util-linux package in Ubuntu:
  Fix Released
Status in util-linux source package in Trusty:
  Triaged

Bug description:
  trusty has a very old util-linux which does not yet know about /dev
  /loop-control to create arbitrarily many loop devices. This feature
  was introduced in Linux 3.1 already (i. e. before precise even). This
  is a showstopper for backporting snappy as that needs a lot of loop
  mounts.

  Support for loop-control got introduced in
  http://git.kernel.org/cgit/utils/util-linux/util-
  linux.git/commit/?id=0b14bf7a

  SRU TEST CASE:
  First, use up all default 8 loop devices:
  $ for i in `seq 8`; do echo $i; sudo losetup --find /etc/issue; done

  Now try to use a 9th:
  $ sudo mount -o loop /etc/issue /mnt

  With current trusty's util-linux this will fail with "could not find
  any free loop device". With the proposed version, this should "only"
  fail with "you must specify the filesystem type" (or try it on an
  actual file system image).

  REGRESSION POTENTIAL: /dev/loop-control and the corresponding util-
  linux support has exited for a long time without known/major issues,
  so this should be fairly safe. Also, the patch falls back to the
  previous "iterate over loop0 to loop7" behaviour if loop-control is
  not available.

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