David Sterba posted on Mon, 31 Aug 2015 15:45:17 +0200 as excerpted: > On Sun, Aug 30, 2015 at 11:17:44AM -0600, Chris Murphy wrote: >> Does anyone know when this changed? Maybe it's a 4.2 thing... anyway >> it's very much welcome! > > And another "side effect" is that /proc/self/mountinfo will report the > mounted subvolume, even if it was an implicit mount of non-toplevel > subvolume. Another very nice side effect, likely accidental, but still very nice... is how subvol= ends up being reported for bind-mounts. I don't use subvolumes here, but I do use multiple separate btrfs, so subvolid=5, subvol=/ for all of them, would be technically correct, if not particularly useful. But while the subvolid=5 is indeed constant (and actually useful given the following), subvol= turns out to be rather more helpful than the / that would normally be expected. I have a number of bind-mounts. Formerly mount's output for these wasn't particularly helpful, since I ended up with a number of... /dev/sda5 on <mountpoint> ... ... lines (/dev/sda5 being my rootfs), for instance. The mountpoint is listed, but exactly what part of the filesystem is being bind-mounted there isn't (tho /proc/self/mountinfo does contain it). While the filesystem component (/etc/bind, for instance) actually being bind- mounted was generally what I was interested in, it wasn't actually displayed, and could only be indirectly derived from the mountpoint, by looking up the mountpoint in fstab, for instance, or by using /proc/ self/mountinfo instead of the mount output or /proc/mounts. With the new subvolume thing, despite the fact that as I said I don't use subvolumes so subvolume=/ would be technically correct, the subvol= now points at the particular component of the filesystem being bind-mounted at the given mountpoint. So while I still have a bunch of /dev/sda5 on <mountpoint> lines, now the subvolume= bit actually tells me what's bind-mounted there, as in (sda5 is /, sda4 is /var/log)... /dev/sda5 on /mnt/cbind/etc/bind type btrfs (...,subvol=/etc/bind) /dev/sda4 on /mnt/cbind/var/log/named type btrfs (...,subvol=/named) Again, technically the subvol is actually / in both cases, since I don't use subvols. And the subvolid is indeed 5, as expected. But the actually reported subvol=/etc/bind is *so* much more helpful than the subvol=/ that I might have expected. =:^) -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
