On 22:09 10/02, Graham Cobb wrote: > On 10/02/2022 22:03, Graham Cobb wrote: > > On 10/02/2022 21:30, Goldwyn Rodrigues wrote: > >> On 19:54 10/02, Graham Cobb wrote: > >>> On 10/02/2022 16:51, Goldwyn Rodrigues wrote: > >>>> If a read-write root mount is remounted as read-only, the subvolume > >>>> is also set to read-only. > >>> > >>> Errrr... Isn't that exactly what I want? > >>> > >>> If I have a btrfs filesystem with hundreds of subvols, some of which may > >>> be mounted into various places in my filesystem, I would expect that if > >>> I remount the main mountpoint as RO, that all the subvols become RO as > >>> well. I actually don't mind if the behaviour went further and remounting > >>> ANY of the mount points as RO would make them all RO. > >>> > >>> My mental model is that mounting a subvol somewhere is rather like a > >>> bind mount. And a bind mount goes RO if the underlying fs goes RO - > >>> doesn't it? > >>> > >> > >> If we want bind mount, we would use bind mount. subvolume mounts and bind > >> mounts are different and should be treated as different features. > > > > Yes that's a good point. However, I am still not convinced that this is > > a change in behaviour that is obvious enough to justify the risk of > > disruption to existing systems, admin scripts or system managers. > > > >> > >>> Or am I just confused about what this patch is discussing? > >> > >> Root can also be considered as a unique subvolume with a unique > >> subvolume id and a unique name=/ > > > > But with an important special property that is different from all other > > subvolumes: all other subvolumes are reachable from it. Not quite. You can mount a subvolume directly without mounting the root: mount -o subvol=<subvolname> <device> <mountpoint> > > I should be a bit clearer. Imagine you create a filesystem and then > create two subvolumes within it: a and a/b. You are suggesting that the > result of remounting the top level of the filesystem as RO causes > different effect on whether subvolume b goes RO depending on whether > subvolume a has also been mounted somewhere? I did not understand the question, too many "whether"s. :) Check the test case. If you mount a root subvolume (/) and a root's subvolume (/a or /a/b in your case). You remount root as ro, the subvolume a or a/b mounts also become read-only. On the other hand, if you mount a or a/b (RW) _after_ root is remounted RO, the subvolume mounts are RW. -- Goldwyn
