> > When a non-directory object is accessed without a trailing slash, then
> > path resolution returns the object itself as usual.
> >
> > If a non-directory object is accessed with a trailing slash, then the
> > filesystem may opt to let the file be accessed as a directory. In
> > this case "something" (as supplied by the filesystem) is mounted on
> > top of the non-directory object.
> >
> > This mount will have special properties:
> >
> > - If there's no trailing slash is after the file name, the mount
> > won't be followed, even if the path resolution would otherwise
> > follow mounts.
> >
> > - The mount only stays there while it is referenced by some external
> > object, like a pwd or an open file. When it is no longer
> > referenced, it is automatically unmounted.
> >
> > - Unlike "real" mounts, this won't block unlink(2) or rename(2) on
> > the underlying object.
>
> Interesting... How do you deal with mount propagation and things like
> mount --move?
Moving (or doing other mount operations on) an ancestor shouldn't be a
problem. Moving this mount itself is not allowed, and neither is
doing bind or pivot_root. Maybe bind could be allowed...
When doing recursive bind on ancestor, these mounts are skipped.
> As for unlink... How do you deal with having that thing
> mounted, mounting something _under_ it (so that vfsmount would be kept
> busy) and then unlinking that sucker?
Yeah, that's a good point. Current patch doesn't deal with that.
Simplest solution could be to disallow submounting these. Don't think
it makes much sense anyway.
> I'll look through the patch tonight; it sounds interesting, assuming that
> we don't run into serious crap with locking and <shudder> revalidation
> logics.
Revalidation shouln't be a problem. We'll just end up with an
unhashed dentry with a mount over it, which will be detached when the
vfsmount ref is dropped.
Miklos
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