On Tue, 15 Oct 2013 12:43:50 +0200 Rodolfo Giometti <giome...@enneenne.com> wrote:
> On Fri, Oct 11, 2013 at 12:47:20PM -0700, Andrew Morton wrote: > > On Fri, 11 Oct 2013 14:40:32 +0200 Paul Chavent <paul.chav...@onera.fr> > > wrote: > > > > > The PPS_FETCH ioctl is blocking still the reception of a PPS > > > event. But, in some case, one may immediately need the last event > > > date. This patch allow to get the result of PPS_FETCH if the device > > > has the O_NONBLOCK flag set. > > > > Are the PPS ioctls actually documented anywhere? > > Documentation/pps/pps.txt is silent. > > > > That's a shame, because it would be nice to have a formal description > > of the the PPS_FETCH semantics which leads to an understanding of why > > things are the way they are, how PPS_FETCH is supposed to be used, etc. > > > > Also, the presence of such documentation would permit me to bug you for > > not having updated it! We need *some* channel for telling people about > > the driver, and updates to it. Maybe linuxpps.org has it somewhere, > > but I couldn't immediately find it. > > Hi Andrew! Actually RFC 2783 doesn't use ioctls to get access to PPS > data but it defines some functions. LinuxPPS, that is the Linux PPS > implementation, uses ioctls to implement these functions. > > If you like having an idea about how these functions are implemented > into LinuxPPS, you can see here: > > > http://www.linuxpps.org/gitweb/?p=pps-tools;a=blob;f=timepps.h;h=d2628d2d061ea2a3623e57990d9ada62623773cf;hb=5980a044bcdb4c1d1a8b1ecff986fa63719519b3 > > > Your implementation requires that the file be opened non-blocking. But > > I'd have thought that adding a new and separate ioctl mode would be a > > cleaner and more flexible implementation - that way an app which wants > > both blocking and non-blocking behaviour doesn't need to open the file > > twice. > > > > Also, this is actually a non-backward-compatible change for any > > application which happened to be opening the file with O_NONBLOCK! > > Hopefully there aren't any such applications... > > The major application that I know using these layer is NTPD... however > all RFC compliant applications should not use ioctls to get access the > PPS data and this patch should be a "special" case. > Thanks, but this doesn't really address my concerns. - Where, if anywhere, is the Linux PPS API documented and how do we communicate changes such as this one to kernel users? - Why require open(O_NONBLOCK) for this instead of adding a separate ioctl? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
