Re: devfs vs udev, thoughts from a devfs user

Helge Hafting
2004-02-14T11:29:29Z

On Sat, Feb 14, 2004 at 10:13:50AM +0100, Christian Borntraeger wrote:
> Mike Bell wrote:
> > On Fri, Feb 13, 2004 at 01:19:20PM -0800, Greg KH wrote:
> > > > That's a pretty minor difference, from the kernel's point of view.
> > > > It's basically putting the same numbers in different fields.
> > >
> > > Heh, that's a HUGE difference!
> >
> > Only from userspace's point of view. To the kernel, it's basically the
> > same thing.
>
> No. Giving a major and minor number is simple.
> Creating a device node means: you have to define a policy. Now the kernel
> has to think about:
> - user id
> - group id
> - access rights
> - naming
>
> These are the reasons why devfsd was/is necessary for devfs.
> A Kernel should only enforce a policy, it should not define it.
>
There is one more security-related point:
We may decide to not make the device node at all, in order
to prevent use of some dangerous/experimental device or driver.
We can't do that if the device is auto-created.

Root is usually capable of running mknod of course,
but it can be prevented. For example with a fs that
starts out rw but is remounted ro with no option for going back.
Or /dev on cdrom . . .

Helge Hafting