[included linux-fsdevel in CC]
> So, from what I can see, the lookup will result in finding the existing
> inode pointer. Is there a need to invalidate the previous directory alias?
>
> How could I create a directory loop now?
You can create a loop with the rename() system call by moving a
directory into a subdirectory of itself.
Normally this is prohibited by the VFS, but once you have directory
aliases, you can do a rename that does not look like it would create a
loop.
For example if "b/a" and "c/a" are aliases of the same directory, then
doing rename("b/a", "c/a/d/a") would create a loop.
You can also create a loop with with lookup:
Local: cd a/b
Remote: mv a/b b
Remote: mv a b/a
Local: ls a
Now locally "a" and "a/b/a" are aliases which means you have a loop.
The problem with directory loops is that locking rules are no longer
enforced, and two parallel operations may deadlock.
All this is very unlikely to happen accidentaly, but even so
filesystem deadlocks are not nice.
Miklos
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