> step 1: mount --bind /mnt /mnt > a new mount 'A' is created at /mnt > > step 2: mount --make-shared /mnt > mounts under 'A' are made shared. But in this case > there are no other mounts. So only 'A' will be made shared. > > > step 3: mkdir -p /mnt/1 /mnt/2 > nothing special here > > step 4: mount --bind /usr /mnt/1 > a new mount 'B' is created at /mnt/1 which is > 'shared;. > > > step 5: mount --bind /mnt /mnt/2 > > a new mount 'C' is created at /mnt/2 > and propogation is set between 'A' and 'C'. > note: 'C' is made shared. > > > > lets say, at this point I try > mount --bind /var /mnt/1 > > this is going to mount 'D' on top of mount 'B'. However > there is no other mount to which 'B' propogates to. So that is > it. the contents of /var is only visible at /mnt/1 and it > propogates no where else. > > but lets say, we tried mount --bind /var /mnt/2/1 > /mnt/2/1 belongs to mount 'C'. And mounts under 'C' propogates to 'A' > too. So in this case a new mount 'E' is created at mnt/1/2
You mean /mnt/2/1 > i.e on top of 'C' at dentry '2' On dentry '1' > and due to propogation a new mount 'F' is created at /mnt/1 i.e on > top of mount 'A' at dentry '1' But note: /mnt/1 already has a mount > 'B' on top of it. The new mount 'F' as per the 'most-current mount > rule' obscures 'B' even though the mount is on top of 'A'. As a > result the contents of /var are now visible both at /mnt/2/1 and > /mnt/1 True. > Ok the net effect is, mount at /mnt/1 is visible only under /mnt/1 > but mount at /mnt/2/1 is visible at mount /mnt/2/1 and /mnt/1 > This makes it confusing. But this asymmetry is caused by the fact that mounts from /mnt/1 (B) don't propagate, while mounts from /mnt/2/1 (C) do. And not because of the mount lookup semantics you want to change. That change in fact would only _hide_ the asymmetry and not fix it: there would be propagation in one case and no propagation in the other. If you did before step 4 in another shell 'cd /mnt/1', then after step 5 you did 'mount --bind /var .', that would have had the same symmetric effect as the 'mount --bind /var /mnt/2/1'. > So the point I am driving at is, is there any special reason > for having 'most-recent mount visible rule' instead of 'top-most mount > visible rule'? I don't think, that 'topmost mount is visible' is any more logical than 'latest mount is visible'. The fact that the later has been in the kernel for a long time means, that there may be systems relying on this behavior, and changing it would break them. Miklos - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
