Qeuestion: Why is make-slave the one-way operation?

Qeuestion: Why is make-slave the one-way operation?

[Etsuji Nakai]

Hi,

I have a question regarding the sharedsubtree operation. 

It looks make-slave is the one-way operation. For example,

# mount --make-shared A
# mount --bind A B
# mount --make-shared B

At this point, B is in the shared peer of A. i.e. B's mnt_share is linked to A's mnt_share.

I'll change B to the slave of A.

# mount --make-slave B

Now, B's mnt_share is detached from the A's mnt_share.

Then, from some reason, I want to change B back to the shared peer of A again.
But there's no way to do so. Don't you think it's reasonable to add an new operation
for that? It may look like:

# mount --make-shared-with A B

By the way, here's the specific reason why I need it:

Bug 1010673 - PrivateTmp keeps the whole filesystem as MS_SLAVE
https://bugzilla.redhat.com/show_bug.cgi?id=1010673

- Etsuji