On Mon, Aug 03, 2009 at 06:09:38PM +0300, Avi Kivity wrote: > On 07/28/2009 08:55 PM, Michael S. Tsirkin wrote: >> This implements a new EFD_STATE flag for eventfd. >> When set, this flag changes eventfd behaviour in the following way: >> - write simply stores the value written, and is always non-blocking >> - read unblocks when the value written changes, and >> returns the value written >> >> Motivation: we'd like to use eventfd in qemu to pass interrupts from >> (emulated or assigned) devices to guest. For level interrupts, the >> counter supported currently by eventfd is not a good match: we really >> need to set interrupt to a level, typically 0 or 1, and give the guest >> ability to see the last value written. >> >> >> @@ -31,37 +31,59 @@ struct eventfd_ctx { >> * issue a wakeup. >> */ >> __u64 count; >> + /* >> + * When EF_STATE flag is set, eventfd behaves differently: >> + * value written gets stored in "count", read will copy >> + * "count" to "state". >> + */ >> + __u64 state; >> unsigned int flags; >> }; >> > > Why not write the new value into ->count directly? That's what it says. state is ther to detect that value was changed after last read. Makes sense? > -- > error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html