Hi Tollef Fog Heen, > What does mountinfo look like if you do a bind mount of a subvolume?
Subvolume /@home mounted on /home: # mount --bind /home/lost+found /tmp/h_a # mount --bind /home/niels/.local /tmp/h_b # mount --bind /tmp/h_b/share /tmp/h_c # egrep @home /proc/self/mountinfo 26 20 0:16 /@home /home rw,relatime - btrfs /dev/sdb3 rw,space_cache 34 20 0:16 /@home/lost+found /tmp/h_a rw,relatime - btrfs /dev/sdb3 rw,space_cache 35 20 0:16 /@home/niels/.local /tmp/h_b rw,relatime - btrfs /dev/sdb3 rw,space_cache 36 20 0:16 /@home/niels/.local/share /tmp/h_c rw,relatime - btrfs /dev/sdb3 rw,space_cache For reference, here's also subvolume /@jessie mounted on /: # mount --bind /bin /tmp/j_a # mount --bind /usr/local /tmp/j_b # mount --bind /tmp/j_b/share /tmp/j_c # egrep @jessie /proc/self/mountinfo 20 1 0:16 /@jessie / rw,relatime - btrfs /dev/sdb3 rw,space_cache 31 20 0:16 /@jessie/bin /tmp/j_a rw,relatime - btrfs /dev/sdb3 rw,space_cache 32 20 0:16 /@jessie/usr/local /tmp/j_b rw,relatime - btrfs /dev/sdb3 rw,space_cache 33 20 0:16 /@jessie/usr/local/share /tmp/j_c rw,relatime - btrfs /dev/sdb3 rw,space_cache > And ditto if you do multiple mounts of the same subvolume (to different > locations)? Subvolume /@home mounted at multiple points: # mount -t btrfs -o subvol=/@home /dev/sdb3 /tmp/s_a # mount -t btrfs -o subvol=/@home /dev/sdb3 /tmp/s_b # egrep @home /proc/self/mountinfo 26 20 0:16 /@home /home rw,relatime - btrfs /dev/sdb3 rw,space_cache 31 20 0:16 /@home /tmp/s_a rw,relatime - btrfs /dev/sdb3 rw,space_cache 32 20 0:16 /@home /tmp/s_b rw,relatime - btrfs /dev/sdb3 rw,space_cache Top (sub)volume / mounted at multiple points: # mount -t btrfs -o subvol=/ /dev/sdb3 /mnt/tmp # mount -t btrfs -o subvol=/ /dev/sdb3 /tmp/t_a # mount -t btrfs -o subvol=/ /dev/sdb3 /tmp/t_b # egrep '0:16 / ' /proc/self/mountinfo 33 20 0:16 / /mnt/tmp rw,relatime - btrfs /dev/sdb3 rw,space_cache 34 20 0:16 / /tmp/t_a rw,relatime - btrfs /dev/sdb3 rw,space_cache 35 20 0:16 / /tmp/t_b rw,relatime - btrfs /dev/sdb3 rw,space_cache Essentially, from a VFS user's point of view, btrfs subvolumes look and behave like bind mounts (apart from requiring different mount options) - they create an additional view into the same filesystem, possibly rooted further down the tree. The root (root of the mount within the filesystem) of mountinfo cascades nicely, even if there are bind mounts on subvolumes. The / root of a particular filesystem (partition) is not guaranteed to be mounted even if deeper levels of the hierarchy are. This is more common for btrfs subvolumes, but in fact also possible for bind mounts. Thanks for your work, Niels Boehm -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
