Rename shared file within read-only external storage fails with error

[MorrisJobke]

Steps to reproduce

1. have userA and userB
2. create an external storage mount that is read-only, does not have any files and is mounted to / for userB
3. as userA create a file foo.txt and share it with userB
4. as userB try to rename the received shared file foo.txt to bar.txt

Expected behaviour

• file should be renamed

Actual behaviour

• there is an error that says "there is not file 'foo.txt'" and the file is removed from the file list
• after a reload the file foo.txt is still there.

cc @icewind1991 @rullzer

[rullzer]

Well. One could argue the share should not be mounted in the first place since it is a mountpoint inside a mountpoint.

This really is abusing the system in a way it was not designed to be used.

[nickvergessen]

I agree, the correct behaviour should be a decent error message and the file should not disappear, if we at all allow this.

[MorrisJobke]

This really is abusing the system in a way it was not designed to be used.

Actually we allowed to mount external storages on /. It's just that it misbehaves somehow weirdly as well. So we need to look into what to fix.

[rullzer]

@MorrisJobke that is not what I'm saying is the abuse. The abuse is that we in all other cases forbid mountpoints in mountpoints. Because it is a weird scenario. And incomming shares are exactly that.

[MorrisJobke]

But then we need to cut the „mount into /„ feature of external storage. Or do you see an other option? What about external storage amount points in each other? Because I think this is possible nowadays

[rullzer]

My point is there is a reason we block this normally. It might work but there might be unexpected side effects. We can look into the reported issue but I guess it is a world of pain to figure out what goes on there.