`incus top` doesn't properly report disk usage on BTRFS backends

[phol]

I'm using Incus with a BTRFS backend. When I run the new incus top command on Incus 6.0.1. LTS, disk usage for all containers is reported to be the same, except for my Docker container, which uses a separate storage pool. Having this report properly would be very useful, especially given the fact that du isn't reliable with BTRFS.

Additionally, but that would be more of a feature request rather than a bug report, it would be nice to have both a 'physical size' as well as `uncompressed / deduplicated size' column.

[stgraber]

What does incus list -cnD show you?

[phol]

incus list -cnD
+--------+------------+
|  NAME  | DISK USAGE |
+--------+------------+
| av     |            |
+--------+------------+
| dns    |            |
+--------+------------+
| docker |            |
+--------+------------+
| hbp    |            |
+--------+------------+
| mdb    |            |
+--------+------------+
| pg     |            |
+--------+------------+
| runner |            |
+--------+------------+
| turn   |            |
+--------+------------+

[phol]

BTW, I just realised I opened this issue in zabbly/incus instead of lxc/incus. If this is the wrong location, I'll gladly reopen it over there.

[stgraber]

It's the wrong location but that's not really a problem, I look at both :)

Okay, so Incus has no idea what the disk usage is. Does df -h / show you the container-specific usage inside the container?

If not, then there's nothing we can do. incus top hits every single instance every 5s so we definitely can't run something heavy weight like du :)

[stgraber]

What we should do though is not show a usage value when we can't figure it out.

[stgraber]

Ah but that's because we can't quite figure it out as all we're told by the kernel is:

• Total space
• Free space
• Available space (basically free - some reserved stuff)

So it's not something we can do from the incus top side of things. But we may be able to make incus just not return the metric at all in environments where there is no such thing as a container-specific value.