Re: config(5) break down

[David Young <dyoung%pobox.com@localhost>]

On Sat, Mar 20, 2010 at 09:43:21AM -0700, Matt Thomas wrote:
> 
> On Mar 20, 2010, at 9:06 AM, Masao Uebayashi wrote:
> 
> > On Sun, Mar 21, 2010 at 1:01 AM, Matt Thomas 
> > <matt%3am-software.com@localhost> wrote:
> >> I'm talking about <maj, min> to device.  How, as a user, do I know what 
> >> actual tty does /dev/ttyXX open?
> > 
> > If we make tty(4) a device, we can lookup its parent by drvctl(8)
> > (extend it to return dv_parent).
> 
> That is user unfriendly.  The name in /dev should tell me enough to
> know what it is.  I should not have to invoke another command to
> figure that out.

When you say "what it is," it's not clear whether you mean "what kind"
or "what instance".  I have a machine with eleven "dial-out" /dev/
nodes:

crw-rw----  1 uucp  dialer  8, 524288 Mar 20 13:35 /dev/dty00
crw-rw----  1 uucp  dialer  8, 524289 Mar 20 13:35 /dev/dty01
crw-rw----  1 uucp  dialer  8, 524290 Nov  9  2003 /dev/dty02
crw-rw----  1 uucp  dialer  8, 524291 Mar 10 18:48 /dev/dty03
crw-rw----  1 uucp  dialer  8, 524292 Mar 10 18:48 /dev/dty04
crw-rw----  1 uucp  dialer  8, 524293 Mar 10 18:48 /dev/dty05
crw-rw----  1 uucp  dialer  8, 524294 Mar 18 19:57 /dev/dty06
crw-rw----  1 uucp  dialer  8, 524295 Mar 10 18:47 /dev/dty07
crw-rw----  1 uucp  dialer  8, 524296 Mar 20 13:34 /dev/dty08
crw-rw----  1 uucp  dialer  8, 524297 Mar 10 18:46 /dev/dty09
crw-rw----  1 uucp  dialer  8, 524298 Mar 19 23:58 /dev/dty10

It's handy that I can type 'man dty' to see what kind they are, but
beyond that, the listing is not user-friendly: apart from the stand-out
modification time, nothing distinguishes /dev/dty02, the only node that
has no hardware backing, from the rest.  Nothing distinguishes dty00 -
dty01, which are built into the motherboard, from dty03 - dty10, which
reside on a puc(4).  Luckily, dty03 - dty10 correspond directly to
tentacles 1 - 8 of the puc(8).

I think that your concern may be that a /dev/ node's name, major,
and minor will change if we have, say, ttyP at comQ at pucR.  It
needn't be so---and, I say, it shouldn't.  Let the (hypothetical)
tty_attach_args convey either the "type" of ("com", "pty") and/or a
minor/major (hmm...).

I have to say that I really like the idea of splitting com from tty,
with com providing a "raw" interface for changing (e.g.) RS-232
parameters, for reading, and for writing, and with tty providing the
traditional TTY interface.

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933