Re: UUIDs (and devfs and major/minor numbers)

Mark H. Wood (mwood@iupui.edu)
Sat, 19 Jun 1999 08:59:07 -0500 (EST)


On Thu, 17 Jun 1999, Nathan Hand wrote:
> On Wed, Jun 16, 1999 at 11:15:43PM -0500, Edward S. Marshall wrote:
> > On Thu, 17 Jun 1999 tytso@mit.edu wrote:
> > > the names in /dev *are* policy, and kernel should not be dictating
> > > policy. Therefore, the kernel should not be deciding what names appear
> > > in /dev. Q.E.D.
> >
> > Like it or not, the names in /proc *are* policy, and kernel should not be
> > dictating policy. Therefore, the kernel should not be deciding what names
> > appear in /proc. Q.E.D.
>
> Oh don't worry, a lot of people agree with this and think that the
> move away from sysctl was a big mistake.

That just moves the supposed problem: now the kernel is dictating "names"
passed to sysctl(). The argument doesn't seem to be over names so much as
it is over the *structure* imposed on the names.

The real question is whether there is any alternative to the kernel
dictating these so-called policies. The kernel and userspace have to
agree on a minimum set of "names" or the kernel is not usable. You can't
decide to use your own arrangement of syscall number bindings; you have to
use the same ones that the kernel recognizes. For a given syscall, you
can't give the arguments in any order you like; you have to give what the
kernel expects to get if you want the results *you* expect.

In the case of sysctl() the user and the kernel must agree on which names
are passed because there is no mapping interposed. But things are
different with /dev, because there is a mapping (major, minor) <-
/dev/{name} . We can't take the sysctl() name policy away from the kernel
because there is no other way for the user and the kernel to understand
each other. We *can* take away the /dev name policy if we agree on the
(major, minor) name policy, because of the mapping. Therefor I conclude
that it is reasonable for the kernel to dictate sysctl() names but it is
reasonable to refuse to have it dictate /dev names.

-- 
Mark H. Wood, Lead System Programmer   mwood@IUPUI.Edu
Specializing in unusual perspectives for more than twenty years.

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