btrfs snapshot support

[jelly]

Page: Storage

As a user I want to:

• See what subvolumes are snapshots
• Make a snapshot (optionally read only)
• Delete a snapshot

To implemen this, modify our existing btrfs subvolume list and add the -u (uuid) and -q (parent_uuid) flags. An empty parent_uuid means that this is not a snapshot, if there is a uuid this is what I took the snapshot of. Of course you can take a snapshot of a snapshot...

btrfs subvolume list -apuq /

[garrett]

Do we even want to show snapshots as subvolumes? Cockpit Storage is for showing the storage of a system. Subvolumes included.

But snapshots aren't really subvolumes; they're usually frozen, read-only copies used as "backup" (real backup would not be on the same storage device), not really storage locations. Some people have a lot of snapshots, and it's kind of weird for us to show them, especially by default.

We probably need to not show it by default, and have a way to change filters. Then we could deal with snapshots more clearly.

Most people probably either don't use snapshots or they use them a lot (like a new snapshot per day), possibly even with a program that does this for them (like snapper). I suspect most people are probably not too much in the middle?

[jelly]

Made a draft PR here, with the goal to hide the snapshots on the over view and show them under a subvolume of which it is a snapshot:

#20234