Re: USB device allocation
Marcin Dalecki (dalecki@dacotec.net)
Wed, 06 Oct 1999 13:28:46 +0200
Nathan Hand wrote:
>
> On Tue, Oct 05, 1999 at 04:03:34PM -0700, H. Peter Anvin wrote:
> > David Weinehall wrote:
> > >
> > > > That is one way of doing it; IMO a very good way because it lets you
> > > > have policy in user space.
> > >
> > > Oh? And what kind of image of how devfs does things do you have then?
> > >
> > > This is how devfs works. The kernel part of devfs informs devfsd of the
> > > changes (what devices need to be created/removed), and devfsd nicely
> > > carries out its chores. User-space policy and persistent access-rights are
> > > there for you.
> > >
> >
> > ... in which case you don't need devfs at all.
> >
> > -hpa
>
> Agreed. Getting rid of devfs (the dynamic filesystem) makes devfs (the
> concept of dynamic /dev) more acceptable to more punters, and honestly
> doesn't lose all that much functionality. Modules contact devfsd when
> they need a node. The daemon creates/deletes nodes as needed on a real
> filesystem using the policy laid out via /etc/devfsd.conf.
>
> - The /dev directory is updated in user space, not kernel space.
>
> - You can just turn off the daemon, old behaviour is restored.
>
> - Kernel modifications are minimal (changes to init/cleanup_module).
>
> - Major/minors can be assigned dynamically by drivers, avoids GUID.
>
> - Topology rules for USB can be over-engineered totally in user space.
>
> - The policy for naming nodes moves to user space, hpa is happy.
>
> - Persistence of nodes is maintained by the filesystem, tso is happy.
>
> - Devfs gets into the kernel, everyone else in the world is happy.
>
> You lose the ability to run a Linux system without a filesystem which
> knows about major/minor numbers. Only a tiny number of people are going
> to complain about this (David?).
What about just passing something along the lines of request_module("/dev/sdd4")
to the kernel module loader instead of the request_module("k-major-2")
or for example request_module("net_alias-2").
Or even better just provice a request_device("sdd", 'c', major_nr, minor_nr)
istead
and let the modprobe do anything appriopriate about it? This would be the way
as it should had been done since even the beginning of modularization...
--Marcin
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