The client sends a MStatfs to the mon to get the info for a statfs system call. Currently the mon gives it the global usage information of the cluster.
If a filesystem has exactly one on data pool, it should be straightforward to modify this to pass a pool ID and respond to statfs with pool-specific stats instead.
In the case of filesystems with multiple data pools, we need to fall back to the global stats. Doing a sum of the per-pool stats would probably not make sense because the pools could use overlapping sets of OSDs and we wouldn't want to double-report space.
This would require updates to the mon, fuse client, and kernel client.
Opened from: https://bugzilla.redhat.com/show_bug.cgi?id=1427512