On Wednesday 09 March 2011 15:36:51 Alexander Shishkin wrote: > This is another attempt to approach notifying userspace about system > clock changes. The other one is using an eventfd and a syscall [1]. In > the course of discussing the necessity of a syscall for this kind of > notifications, it was suggested that this functionality can be achieved > via timers [2] (and timerfd in particular [3]). This idea got quite > some support [4], [5], [6] and some vague criticism [7], so I decided > to try and go a bit further with it. I don't understand from your description or from the patch how user space gets notified. From your description, I would have expected to see a change to the timerfd_poll() function to check if the clock has changed, possibly returning POLLPRI, but the only such change I can see is in the timerfd_read() function. Don't you need to change poll() so that a task knows when to call read()? > +/* TFD_NOTIFY_CLOCK_SET timers go here */ > +static DEFINE_SPINLOCK(notifiers_lock); > +static LIST_HEAD(notifiers_list); Maybe I was the only one to be confused by this, but I think t he naming is slightly misleading, because it's easy to confuse with a struct notifier_block. You could of course use the notifier API instead of building your own, but if you don't, I'd recommend coming up with a different name. I also think that a mutex would be better here than a spinlock. It's unlikely to be under heavy contention, but if you have a lot of threads, it could be held for a significant amount of time. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
