required/suggested devfs userland tool functionality

[Alex]

Hi,

as I soon want to start with the userland tool for devfs, I would like
to hear some thoughts on what userland functionality is needed for
devfs.

While my original intentions were to also replace the current devd, I
don't see the need for it, neither do I think it's appropriate as it
for example can execute commands for devices that nobody ( as in: no
driver ) attached to, which is something devfs won't be able to do.

So what is left for devfs userland tool to do is to apply certain
permissions/rules to devices that are created. I currently see two
solutions to this:

1) notify the userland tool of every single device attach/detach and
give it some time to answer with a set of permissions for the newly
created device. This approach requires running the devfs userland tool
as a daemon, with one instance per devfs mount point. This has the
advantage that rules could be kept in userspace.

2) let the userland tool load a whole set of rules (for each devfs
mount point) into the kernel. In turn the kernel applies the set of
rules every time a device is attached. This has several advantages:
- userland wouldn't have to be asked for every device attach
- rules would continue to be applied even if the userland tool isn't running
- for that same reason, userland tool wouldn't have to be a daemon.

While I prefer the second approach, I would like to hear your thoughts
about this before making a final decision on which one to use. I'd
also welcome suggestions of other things you think the userland devfs
tool should be able to do.


Cheers,
Alex Hornung