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?
--
error compiling committee.c: too many arguments to function
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