Subject: Re: 32 bit dev_t, Revision 3
To: Chris G. Demetriou <cgd@pa.dec.com>
From: Jason Thorpe <thorpej@nas.nasa.gov>
List: tech-kern
Date: 01/13/1998 18:16:12
On Tue, 13 Jan 98 15:01:47 -0800
"Chris G. Demetriou" <cgd@pa.dec.com> wrote:
> This is a reasonable way to tell, yes. "no need for flags, then." 8-)
>
>
> > - 32-bit dev_t split up as {
> > 12 bits major
> > 20 bits minor {
> > 10 bits "unit"
> > 10 bits "subunit"
> > }
> > }
> > (interpretation of minor is left to the device itself; disks and
> > tapes use the subunit while ttys are generally just sequential);
> > ls -l shows <major,unit,subunit> (even on ttys).
>
> What is the definition of 'unit'? For example, take SCSI. Does
> device,LUN -> unit and partition number -> subunit, or does device ->
> unit and LUN fit into subunit (with other information, e.g. partition
> number)? Looking at the list Paul Vixie posted, it looks like the
> former.
Um ... if you're assigning numbers the way our (Torek's :-) autoconfiguration
does, unit doesn't necessarily map to device,lun ... I would take this
as "unit as far as autoconfiguration is concerned" in all cases.
> How about multi-port TTY devices (e.g. cyclom boards, etc.?) In that
> case, does 'unit' correspond to driver unit, and 'subunit' correspond
> to the individual ttys, or do the ttys all get their own individual
> 'unit' numbers? (I can see logic for either, though probably more
> justification for the former. Paul didn't provide much tty
> information.)
..subunit might also correspond to "mode" ... i.e. "dialout" devices, etc.
Jason R. Thorpe thorpej@nas.nasa.gov
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