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Reviewed:  https://review.openstack.org/277402
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=33749d2875b4e63ad8f663a734cd087980489b6e
Submitter: Jenkins
Branch:    master

commit 33749d2875b4e63ad8f663a734cd087980489b6e
Author: Matthew Booth <mbooth@xxxxxxxxxx>
Date:   Mon Feb 8 12:41:06 2016 +0000

    Fix fallocate test on newer util-linux
    
    Newer util-linux raises an error when calling fallocate with the -n
    option if the target file does not already exist. This is because the
    -n option directs it to retain the file's existing size. A
    non-existent file does not have an existing size. fallocate in older
    releases of util-linux creates a zero-sized file in this case. This
    results in _can_fallocate() always returning false, and therefore
    never preallocating.
    
    While this may reasonably be argued to be a regression in util-linux,
    the -n option doesn't make sense here anyway, so we remove it.
    
    Closes-Bug: #1543181
    
    Change-Id: Ie96fa71e7d2641d30572b8eda5609dd3ca5b6708


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1543181

Title:
  Raw and qcow2 disks are never preallocated on systems with newer util-
  linux

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  imagebackend.Image._can_fallocate tests if fallocate works by running
  the following command:

    fallocate -n -l 1 <image path>.fallocate_test

  where <image path> exists, but <image path>.fallocate_test does not.
  This command line is copied from the code which actually fallocates a
  disk. However, while this works on systems with an older version of
  util-linux, such as RHEL 7, it does not work on systems with a newer
  version of util-linux, such as Fedora 23. The result of this is that
  this test will always fail, and preallocation with fallocate will be
  erroneously disabled.

  On RHEL 7, which has util-linux-2.23.2-26.el7.x86_64 on my system:

  $ fallocate -n -l 1 foo
  $ ls -lh foo
  -rw-r--r--. 1 mbooth mbooth 0 Feb  8 15:33 foo
  $ du -sh foo
  4.0K	foo

  On Fedora 23, which has util-linux-2.27.1-2.fc23.x86_64 on my system:

  $ fallocate -n -l 1 foo
  fallocate: cannot open foo: No such file or directory

  The F23 behaviour actually makes sense. From the fallocate man page:

        -n, --keep-size
                Do  not modify the apparent length of the file.

  This doesn't make any sense if the file doesn't exist. That is, the -n
  option makes sense when preallocating an existing disk image, but not
  when testing if fallocate works on a given filesystem and the test
  file doesn't already exist.

  You could also reasonably argue that util-linux probably should be
  breaking an interface like this, even when misused. However, that's a
  separate discussion. We shouldn't be misusing it.

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