In message <[EMAIL PROTECTED]>, Alexander
Viro writes:
[...]
> So what about the following trick: let's allow vfsmounts without
> associated superblock and allow to "mount" them even on the negative
> dentries? Notice that the latter will not break walk_name() - checks for
> dentry being negative are done after we try to follow mounts.
> Notice also that once we mount something atop of such vfsmount it
> becomes completely invisible - it's wedged between two real objects and
> following mounts will walk through it without stopping.
> So the only case when these beasts count is when they are
> "mounted", but nothing is mounted atop of them. But that's precisely the
> class of situations we are interested in. In case of autofs we want
> follow_down() into such animal to trigger mounting, in case of portalfs -
> passing the rest of pathname to daemon, in case of devfs-with-automount
> we want to kick devfsd. So let them have a method that would be called
> upon such follow_down() (i.e. one when we have nothing mounted atop of
> us). And that's it.
> These objects are not filesystems - they rather look like a traps
> set in the unified tree. Notice that they do not waste anon device like
> "one node autofs" would do.
> That way if autofs daemon mounted /mnt/net/foo it would not follow
> up with /mnt/net/foo/bar - it would just set the trap in /mnt/net/foo/bar
> and let the actual lookups trigger further mounts.
[...]
This sounds almost identical to what Sun did to solve similar problems in
their first version of autofs. There's a paper in LISA '99 describing their
enhancements to the original autofs. Your proposal, however, is better b/c
it generalizes to more than autofs.
Erez.
