Control: retitle -1 lsof does not work correctly with btrfs subvolumes
So it turned out the whole thing is about btrfs subvolumes. When a btrfs filesystem is mounted with default subvol=/, lsof works as expected, the same way it works for, say, ext4 or xfs. But when non-root subvolume is mounted, eg subvol=@rootfs, lsof does not find any files on the filesystem anymore: lsof /btrfs/file lsof /btrfs both list nothing, while lsof | grep /btrfs/file lsof | grep /btrfs does. It is somehting about the matching of files/inodes in lsof which gets confused about btrfs subvolume mounts. /mjt
