[Bug 1640823] Re: [trusty] mount -o loop is limited to 8 loop devices

[Martin Pitt]

Hello Martin, or anyone else affected,

Accepted util-linux into trusty-proposed. The package will build now and
be available at https://launchpad.net/ubuntu/+source/util-
linux/2.20.1-5.1ubuntu20.8 in a few hours, and then in the -proposed
repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, and change the tag
from verification-needed to verification-done. If it does not fix the
bug for you, please add a comment stating that, and change the tag to
verification-failed.  In either case, details of your testing will help
us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

** Changed in: util-linux (Ubuntu Trusty)
       Status: Triaged => Fix Committed

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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:
  Fix Committed

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 later util-linux versions, but
  backporting full support for it (for losetup) is too intrusive. We
  only need a partial backport for "mount -o loop".

  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:
  $ dd if=/dev/zero of=/tmp/img bs=1M count=50
  $ mkfs.ext2 -F /tmp/img
  $ sudo mount -o loop /tmp/img /mnt

  With current trusty's "mount" package this will fail with "could not
  find any free loop device". With the proposed version, this should
  succeed, and "sudo losetup -a" should show "/dev/loop8: ...
  (/tmp/img)".

  Now, reboot, disable loop-control with

    sudo mv /dev/loop-control{,.disabled}

  and run the test case again. Now "mount -o loop" should fail with
  "could not find any free loop device" (as before). Ensure that there
  are no hangs, infinite loops, etc.

  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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