Comment # 8 on bug 997757 from Jan Kara

Jeff, my original question has been whether there is some easy way for
userspace (util-linux in this case) to tell that all those different entries in
/proc/mounts for btrfs are actually the same filesystem. That way fstrim can
avoid calling FITRIM several times for the same filesystem.

Since I last asked in September, I have actually learned the util-linux already
has some support for demangling btrfs subvolume mess used e.g. by lsblk command
so maybe fstrim could use it as well and thus avoid calling FITRIM repeatedly
for all subvolumes? Standa?