On 26/02/2016 08:51, Markus Armbruster wrote: > /** > * memory_region_add_eventfd: Request an eventfd to be triggered when a word > * is written to a location. > * > * Marks a word in an IO region (initialized with memory_region_init_io()) > * as a trigger for an eventfd event. The I/O callback will not be called. > * The caller must be prepared to handle failure (that is, take the required > * action if the callback _is_ called). > * > * @mr: the memory region being updated. > * @addr: the address within @mr that is to be monitored > * @size: the size of the access to trigger the eventfd > * @match_data: whether to match against @data, instead of just @addr > * @data: the data to match against the guest write > * @fd: the eventfd to be triggered when @addr, @size, and @data all match. > **/ > void memory_region_add_eventfd(MemoryRegion *mr, > hwaddr addr, > unsigned size, > bool match_data, > uint64_t data, > EventNotifier *e); > > What exactly does "The caller must be prepared to handle failure" mean? > What are the failure modes?
I think it simply meant that the caller should be ready for the case where ioeventfd is _not_ implemented (e.g. when running on TCG) and the MMIO callback is invoked anyway. memory.c now implements a generic fallback in memory_region_dispatch_write_eventfds, so that should not be necessary anymore. I cannot think of other meanings of "failure mode". In any case, ivshmem_io_write helpfully does the required event_notifier_set, so you're good. > Does "value written doesn't match" count as failure in the sense of this > clause? Rephrasing my question: what happens when the guest writes a > value to the Doorbell register that does not match any of the values > registered with memory_region_add_eventfd()? Is the I/O callback > called exactly as if ioeventfd was not in use? Yes, the latter. Paolo
