[LinuxPPS] multiple access to /dev/ppsN entries

[Bernhard Schiffner]

On Wednesday, 17. March 2010 20:16:52 Miroslav Lichvar wrote:
> On Wed, Mar 17, 2010 at 12:15:59PM -0600, clemens at dwf.com wrote:
> > > Unless they set the PPS parameters differently, the first started
> > > application could be receiving something else than it's expecting.
> > 
> > How so?
> > Seems that they should both be reading the same register.
> 
> I tried opening the same PPS device twice, one for assert events and
> one for clear events, and only the later worked, so I'm assuming the
> setting is per device instead of per open. If both capture same
> events, it works fine.
> 
> On Wed, Mar 17, 2010 at 07:21:09PM +0100, Bernhard Schiffner wrote:
> > because I'am a little bit out of business here: does cat /dev/pps* return
> > nowadays something usefull?
> > IIR it is intended as a container for functioncalls (RCF2783) and does
> > provide -EINVAL to a normal read(2).
> 
> # cat /dev/pps0
> cat: /dev/pps0: Invalid argument
Ok. Nothing changed.

> > I used a patch from George Spelvin and was _very_ happy to have a (multi)
> > readable  /dev/pps*.
> > 
> > It starts with
> > http://ml.enneenne.com/pipermail/linuxpps/2009-February/002831.html
> > 
> > and George sent me (later, PM) his patch-queue against 2.6.32-rc6. If
> > there is interest in, I'll ask him to post this to the list.
> 
> Not sure if this is good enough for your need, but it's possible to
> read the timestamps also directly from /sys/class/pps/pps0/{assert,clear}.
 Yes, I know this.

Again:
1.)  An "Unixer" simply expects something useable from reading a character 
device.
2.) The RFC2783 does neither prohibit nor force a human readable readout of 
/dev/pps.
3.) Mar 2009 were some related discussions about (IIRC) /dev/time(?) | Plan9 | 
BSD etc. There was no conclusion about a standardized format of timestamps. I 
don't know the state of the onion today.
4.) Mar 2009 were other priorities to work on first (inclusion into mainline, 
hick hack about ldisk etc.)
5.) I think it's a good time to discuss this topic again.
6.) This thread is a base to do so.
7.) Last and very least George and me want this feature in one or an other 
form implemented.  A patch exists.

What's your POW?
(Redhat?)

TIA!


Bernhard

@Rodolfo:
Is your opinion about this topic still more or less "indifferent"?
IIRC you "only" don't want to raise or solve interoperabily-issues?