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On 2013-07-08T14:48:43+00:00 Jussi Pakkanen wrote:

Created attachment 82191
Source code to demonstrate the issue

Sorry if this bug is filed in the wrong place. Information on GUdev is
sparse and as far as I can tell, systemd is the upstream.

Anyway, the g_udev_client_query_by_device_number function fails on
directories that are in subvolumes. An example is a btrfs file system
with two subvolumes, @ (mounted as root) and @home (mounted as /home).
This also happens when using encrypted home directories.

Having a subvolume might not be the real reason it fails, but that is
what seems to be triggering the issue.

To replicate, download the attached source code. Compile it with "gcc
-Wall -o idnum idnum.c `pkg-config --cflags --libs glib-2.0 gio-2.0
gudev-1.0`".

When run on a plain ext4 volume, the output is this:

./idnum
Device id is 2065.

Whereas on btrfs the output is this:

./idnum
Device id is 25.
Could not get device from num.

Originally filed here:
https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1197796

Reply at:
https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1197796/comments/3

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On 2013-07-08T20:48:00+00:00 Kay Sievers wrote:

Btrfs volumes are like NFS or tmpfs, a superblock without any associated
device. The behavior is expected and intentional.

Btrfs volumes might be constructed of many volumes, there cannot be the
concept of *that* device, like the "dumb" filesystems use.

There is no way for the udev API to find out which device is behind
a btrfs volume. Btrfs specific command need to be used to determine that,
no generic interface exists for that task.

Reply at:
https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1197796/comments/4

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On 2013-07-09T07:28:01+00:00 Jussi Pakkanen wrote:

Would it be possible for you to add a comment to the reference
documentation about this so other people don't have to spend time with
this issue? The page on GUdevClient does not mention subvolumes.

Reply at:
https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1197796/comments/6


** Changed in: systemd
       Status: Unknown => Invalid

** Changed in: systemd
   Importance: Unknown => Medium

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https://bugs.launchpad.net/bugs/1197796

Title:
  g_udev_client_query_by_device_number fails on btrfs disks

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