Btrfs statistics input plugin

Feature Request

Opening a feature request kicks off a discussion.

Proposal:

A btrfs input plugin offering btrfs-specific information about allocations and error rates. This information is available per-mount in /sys/fs/btrfs/...

Use case:

Btrfs provides more information than other filesystems and a lot of it doesn't generalise well enough to include it in the disk plugin. Zfs is in a similar situation where it gets its dedicated plugin.