Re: CVS commit: src/sys/sys

[Matt Thomas <matt%3am-software.com@localhost>]

On Feb 24, 2013, at 12:37 AM, Iain Hibbert <plunky%ogmig.net@localhost> wrote:

> On Sun, 24 Feb 2013, Matt Thomas wrote:
> 
>> Module Name: src
>> Committed By:        matt
>> Date:                Sun Feb 24 06:20:24 UTC 2013
>> 
>> Modified Files:
>>      src/sys/sys: tty.h
>> 
>> Log Message:
>> Add a t_softc member to struct tty in which a driver can store a pointer
>> to its softc.  (analogous to if_softc in struct ifnet).
> 
> Currently, all the tty drivers use a macro to extract an index to the
> devices private cfdriver array from the dev_t that is formed from the
> major/minor numbers and provided by the framework (and incidentally,
> already stored in the tty structure as t_dev)
> 
> So what is your intention with this change? Are you changing the design
> and if so, has that been discussed on a public list?
> 
> Having written tty drivers in the past, I do think this could do with a
> redesign, but I also feel that all uses should remain consistent..

It's not a radical change.  You can still use device_lookup_private on
tp->t_dev but now there is a cheaper method.  But store the sc pointer
in tp->t_softc after tty_alloc and then use that to retrieve it.

It's simply a little more efficient.  As I indicated, if_softc already
provides this functionality for struct ifnet.