Paolo Bonzini <pbonz...@redhat.com> writes: > 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.
Double-checking: can i rely on ivshmem_io_write() getting called on a write of a non-matching value?
