Highlight btrfs subvolumes and mount points; output mount point info

[daviessm]

Ref: #434

I don't expect you to pull this straight in; I'm not a Rust developer so a lot of this code probably isn't very Rust-y and will need error handling and fixups.

That said, I've tested locally and it does what I think it should: identifies btrfs subvolumes and highlights them with the ^ character in the first column (list view) and funky colouring. Mount points are also underlined in all views and in list view include an arrow -> pointing to the device name and filesystem type. That would probably be better as an option, of course.

The code for looking up mount points was borrowed from https://github.com/acdha/mountstatus/tree/master/src/get_mounts and expanded to get the fs type and device name. It would be nice to also get the mount options because the mount point alone isn't very useful for btrfs at least. Also, I don't have a non-Linux system to test on so bsd.rs is almost certainly broken.

There's also the case that a directory could be both a mount point and a subvolume - i.e. a btrfs subvolume is mounted at that point. I'd like to highlight that in the colouring somehow but couldn't think of a good way to do it (background and underline maybe). Likewise, first character in list view would be nice to have different for mount points. Perhaps it would be possible to do something funky with colours.

Comments welcome.

[ariasuni]

I was almost sure I left a comment here a few weeks/months ago, but apparently not… Would you be able to update your code so that it can be merged? That sounds like an interesting feature to have, especially since Btrfs is used a lot nowadays.

[daviessm]

Yeah, I've been meaning to do this for ages! I'll send a new PR when I've rebased it (or rewritten it with my improved Rust knowledge).

[daviessm]

Superseded by #941