Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.

On Fri, Aug 27, 2010 at 18:30, John Stultz [off-list ref] wrote:

On one side, there is the view that the kernel should abstract and hide
the hardware details to increase app portability. And the other is that
the raw hardware details should be exposed, so the OS stays out of the
way.

Neither of these views are always right. Ideally we can come up with a
abstracted way to provide the hardware data needed that's generic enough
that applications don't have to be changed when moving between hardware
or configurations.

The posix clock id interface is frustrating because the flat static
enumeration is really limiting.

I wonder if a dynamic enumeration for posix clocks would be possibly a
way to go?

Well how about something much more straightforward:

#define CLOCK_FD 0x80000000
fd = open("/dev/clocks/some_clock_name", O_RDONLY);
clock_gettime(CLOCK_FD | fd, &ts);

This would provide all of the standard character-device semantics that
everyone is accustomed to, and furthermore you could allow non-root
users to manage specific clocks using just DAC permission bits.

You'd still probably need to add a clock_adjtimex() syscall, but it
could easily fail with EINVAL for software or per-thread clocks, but
that seems like it would nicely abstract the hardware without forcing
a numeric address space.

Cheers,
Kyle Moffett