Re: LinuxPPS & spinlocks

Christopher Hoover
2007-08-01T22:35:37Z

Satyam Sharma <satyam <at> infradead.org> writes:
> On Mon, 30 Jul 2007, Rodolfo Giometti wrote:
>
> > On Mon, Jul 30, 2007 at 10:33:35AM +0530, Satyam Sharma wrote:
> > Currently the RFC says to you that you should open the serial port:
> >
> > fd = open("/dev/ttyS0", ...);
>
> No, it does *NOT*. All it says is:
>
> The time_pps_create() is used to convert an already-open UNIX file
> descriptor, for an appropriate special file, into a PPS handle.
>
> See? What I said is precisely the implementation the RFC envisages
> (and the only sane way to implement it too).

If we were totally rigurous about representing each device as a device node,
your solution would be fine. But we don't.

The clocksource model (/sys/devices/system/clocksource) is a better way to
go. One sysfs file is used to enumerate the possible sources and another is
used to read or set the current source. No new system calls; no new ioctls.

-ch

ch (at) murgatroid (dot) com
ch (at) hpl (dot) hp (dot) com