Support parsing /proc/self/mountinfo

[agrover]

/proc/self/mountinfo has been present in Linux since 2.6.26 (2008), is documented (in the kernel's Documentation/filesystems/proc.txt) and has more info than /proc/mounts.

I'd like to add support for parsing it, and was wondering if it would be better to a) implement it as a separate, parallel API to the existing MountIter/MountParam (MountInfoIter/MountInfoParam?) or b) change the existing API to use mountinfo (would lose Freq and PassNo fields) or c) change the existing API to use mountinfo if present but fall back to /proc/mounts (Freq, PassNo, and new mountinfo fields (MountId, ParentId, Major, Minor, Root, Optionals, SuperOptions) would all be Options).

Thanks.

cc @tasleson

[mulkieran]

FYI: blivet uses something like option 3.

[l0kod]

It makes sense to switch to /proc/self/mountinfo (MountEntry, MountIter) while keeping the ability to parse fstab files (copy MountEntry to FstabEntry, with minimum copy-pasted code).

I think the better way to do this would be to have a common (generic) trait for both types, used to implement the get_*mount_from functions.

[tasleson]

Option C looks like a good approach to me, although I'm not sure about needing to expose every individual thing available for each. I suppose supporting a least common denominator wouldn't suffice for a general use API?