On Fri, Apr 05, 2013 at 07:16:53PM +0100, Pawel Moll wrote: > Ok, so how about the code below? Disclaimer: this is just a proposal. > I'm not sure how welcomed would be an extra field in struct file, but > this makes the clocks ultimately flexible - one can "attach" the clock > to any arbitrary struct file. Alternatively we could mark a "clocked" > file with a special flag in f_mode and have some kind of lookup.
Only a tiny minority of file instances will want to be clocks. Therefore I think adding the extra field will be a hard sell. The flag idea sounds harmless, but how do you perform the lookup? > Also, I can't stop thinking that the posix-clock.c shouldn't actually do > anything about the character device... The PTP core (as the model of > using character device seems to me just one of possible choices) could > do this on its own and have simple open/release attaching/detaching the > clock. This would remove a lot of "generic dev" code in the > posix-clock.c and all the optional cdev methods in struct posix_clock. > It's just a thought, though... Right, the chardev could be pushed into the PHC layer. The original idea of chardev clocks did have precedents, though, like hpet and rtc. > And a couple of questions to Richard... Isn't the kref_put() in > posix_clock_unregister() a bug? I'm not 100% but it looks like a simple > register->unregister sequence was making the ref count == -1, so the > delete_clock() won't be called. Well, posix_clock_register() -> kref_init() -> atomic_set(&kref->refcount, 1); So refcount is now 1 ... posix_clock_unregister() -> kref_put() -> kref_sub(count=1) -> atomic_sub_and_test((int) count, &kref->refcount) and refcount is now 0. Can't see how you would get -1 here. > And was there any particular reason that the ops in struct > posix_clock are *not* a pointer? One less run time indirection maybe? I don't really remember why or how we arrived at this. The whole PHC review took a year, with something like fifteen revisions. Thanks, Richard -- 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/