@@ -1,3 +1,3 @@
ifeq ($(CONFIG_VIRTIO), y)
-common-obj-$(CONFIG_VIRTIO_BLK_DATA_PLANE) += hostmem.o vring.o
+common-obj-$(CONFIG_VIRTIO_BLK_DATA_PLANE) += hostmem.o vring.o event-poll.o
endif
new file mode 100644
@@ -0,0 +1,109 @@
+/*
+ * Event loop with file descriptor polling
+ *
+ * Copyright 2012 IBM, Corp.
+ * Copyright 2012 Red Hat, Inc. and/or its affiliates
+ *
+ * Authors:
+ * Stefan Hajnoczi <stefanha@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include <sys/epoll.h>
+#include "hw/dataplane/event-poll.h"
+
+/* Add an event notifier and its callback for polling */
+void event_poll_add(EventPoll *poll, EventHandler *handler,
+ EventNotifier *notifier, EventCallback *callback)
+{
+ struct epoll_event event = {
+ .events = EPOLLIN,
+ .data.ptr = handler,
+ };
+ handler->notifier = notifier;
+ handler->callback = callback;
+ if (epoll_ctl(poll->epoll_fd, EPOLL_CTL_ADD,
+ event_notifier_get_fd(notifier), &event) != 0) {
+ fprintf(stderr, "failed to add event handler to epoll: %m\n");
+ exit(1);
+ }
+}
+
+/* Event callback for stopping the event_poll_run() loop */
+static bool handle_stop(EventHandler *handler)
+{
+ return false; /* stop event loop */
+}
+
+void event_poll_init(EventPoll *poll)
+{
+ /* Create epoll file descriptor */
+ poll->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
+ if (poll->epoll_fd < 0) {
+ fprintf(stderr, "epoll_create1 failed: %m\n");
+ exit(1);
+ }
+
+ /* Set up stop notifier */
+ if (event_notifier_init(&poll->stop_notifier, 0) < 0) {
+ fprintf(stderr, "failed to init stop notifier\n");
+ exit(1);
+ }
+ event_poll_add(poll, &poll->stop_handler,
+ &poll->stop_notifier, handle_stop);
+}
+
+void event_poll_cleanup(EventPoll *poll)
+{
+ event_notifier_cleanup(&poll->stop_notifier);
+ close(poll->epoll_fd);
+ poll->epoll_fd = -1;
+}
+
+/* Block until the next event and invoke its callback
+ *
+ * Signals must be masked, EINTR should never happen. This is true for QEMU
+ * threads.
+ */
+static bool event_poll(EventPoll *poll)
+{
+ EventHandler *handler;
+ struct epoll_event event;
+ int nevents;
+
+ /* Wait for the next event. Only do one event per call to keep the
+ * function simple, this could be changed later. */
+ nevents = epoll_wait(poll->epoll_fd, &event, 1, -1);
+ if (unlikely(nevents != 1)) {
+ fprintf(stderr, "epoll_wait failed: %m\n");
+ exit(1); /* should never happen */
+ }
+
+ /* Find out which event handler has become active */
+ handler = event.data.ptr;
+
+ /* Clear the eventfd */
+ event_notifier_test_and_clear(handler->notifier);
+
+ /* Handle the event */
+ return handler->callback(handler);
+}
+
+void event_poll_run(EventPoll *poll)
+{
+ while (event_poll(poll)) {
+ /* do nothing */
+ }
+}
+
+/* Stop the event_poll_run() loop
+ *
+ * This function can be used from another thread.
+ */
+void event_poll_stop(EventPoll *poll)
+{
+ event_notifier_set(&poll->stop_notifier);
+}
new file mode 100644
@@ -0,0 +1,40 @@
+/*
+ * Event loop with file descriptor polling
+ *
+ * Copyright 2012 IBM, Corp.
+ * Copyright 2012 Red Hat, Inc. and/or its affiliates
+ *
+ * Authors:
+ * Stefan Hajnoczi <stefanha@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef EVENT_POLL_H
+#define EVENT_POLL_H
+
+#include "event_notifier.h"
+
+typedef struct EventHandler EventHandler;
+typedef bool EventCallback(EventHandler *handler);
+struct EventHandler {
+ EventNotifier *notifier; /* eventfd */
+ EventCallback *callback; /* callback function */
+};
+
+typedef struct {
+ int epoll_fd; /* epoll(2) file descriptor */
+ EventNotifier stop_notifier; /* stop poll notifier */
+ EventHandler stop_handler; /* stop poll handler */
+} EventPoll;
+
+void event_poll_add(EventPoll *poll, EventHandler *handler,
+ EventNotifier *notifier, EventCallback *callback);
+void event_poll_init(EventPoll *poll);
+void event_poll_cleanup(EventPoll *poll);
+void event_poll_run(EventPoll *poll);
+void event_poll_stop(EventPoll *poll);
+
+#endif /* EVENT_POLL_H */
Outside the safety of the global mutex we need to poll on file descriptors. I found epoll(2) is a convenient way to do that, although other options could replace this module in the future (such as an AioContext-based loop or glib's GMainLoop). One important feature of this small event loop implementation is that the loop can be terminated in a thread-safe way. This allows QEMU to stop the data plane thread cleanly. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- hw/dataplane/Makefile.objs | 2 +- hw/dataplane/event-poll.c | 109 +++++++++++++++++++++++++++++++++++++++++++++ hw/dataplane/event-poll.h | 40 +++++++++++++++++ 3 files changed, 150 insertions(+), 1 deletion(-) create mode 100644 hw/dataplane/event-poll.c create mode 100644 hw/dataplane/event-poll.h