[Parted-maintainers] Bug#577927: parted fails without superuser privileges when dealing with a user-writable device from devmapper

[Daniel Kahn Gillmor]

Package: parted
Version: 2.2-5
Severity: normal

i've got a logical volume exported by the device mapper which happens
to be readable by a regular user.  It's used as a block device for a
VM, so it's got a partition table on it.  I'd like to be able to
modify that partition table without needing superuser privileges.

However, parted appears to refuse to do it, even though the user is
capable of reading and writing every block on the disk.  The program
itself even seems to think that this is a bug:

bar at foo:~$ ls -la /dev/mapper/vg_foo0-bar 
brw-rw---- 1 root bar 253, 8 2010-04-15 04:42 /dev/mapper/vg_foo0-bar
bar at foo:~$ /sbin/parted /dev/mapper/vg_foo0-bar 
WARNING: You are not superuser.  Watch out for permissions.
/dev/mapper/control: open failed: Permission denied
Failure to communicate with kernel device-mapper driver.
                                                                          

You found a bug in GNU Parted! Here's what you have to do:

Don't panic! The bug has most likely not affected any of your data.
Help us to fix this bug by doing the following:

Check whether the bug has already been fixed by checking
the last version of GNU Parted that you can find at:

    http://ftp.gnu.org/gnu/parted/

Please check this version prior to bug reporting.

If this has not been fixed yet or if you don't know how to check,
please visit the GNU Parted website:

       http://www.gnu.org/software/parted

for further information.

Your report should contain the version of this release (2.2)
along with the error message below, the output of

      parted DEVICE unit co print unit s print

and the following history of commands you entered.
Also include any additional information about your setup you
consider important.

Unable to determine the dm type of /dev/mapper/vg_foo0-bar.

bar at foo:~$ 

Thanks for maintaining parted!

       --dkg

-- System Information:
Debian Release: squeeze/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.32-3-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages parted depends on:
ii  libc6                     2.10.2-6       Embedded GNU C Library: Shared lib
ii  libncurses5               5.7+20100313-2 shared libraries for terminal hand
ii  libparted0debian1         2.2-5          The GNU Parted disk partitioning s
ii  libreadline6              6.1-1          GNU readline and history libraries

parted recommends no packages.

Versions of packages parted suggests:
pn  parted-doc                    <none>     (no description available)

-- no debconf information