tevent: Add in the new implementation of "standard" tevent backend.

Falls back cleanly from epoll -> poll, or uses poll if
epoll not available.

Signed-off-by: Jeremy Allison <jra@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

lib/tevent/tevent_standard.c

@@ -2,7 +2,8 @@
    Unix SMB/CIFS implementation.
    main select loop and event handling
    Copyright (C) Andrew Tridgell	2003-2005
-   Copyright (C) Stefan Metzmacher	2005-2009
+   Copyright (C) Stefan Metzmacher      2005-2013
+   Copyright (C) Jeremy Allison         2013
 
      ** NOTE! The following LGPL license applies to the tevent
      ** library. This does NOT imply that all of Samba is released
@@ -26,18 +27,17 @@
   This is SAMBA's default event loop code
 
   - we try to use epoll if configure detected support for it
-    otherwise we use select()
+    otherwise we use poll()
   - if epoll is broken on the system or the kernel doesn't support it
-    at runtime we fallback to select()
+    at runtime we fallback to poll()
 */
 
 #include "replace.h"
-#include "system/filesys.h"
-#include "system/select.h"
 #include "tevent.h"
 #include "tevent_util.h"
 #include "tevent_internal.h"
 
+#if 0
 struct std_event_context {
 	/* a pointer back to the generic event_context */
 	struct tevent_context *ev;
@@ -589,10 +589,184 @@ static const struct tevent_ops std_event_ops = {
 	.loop_once		= std_event_loop_once,
 	.loop_wait		= tevent_common_loop_wait,
 };
+#endif
 
+struct std_event_glue {
+	const struct tevent_ops *epoll_ops;
+	const struct tevent_ops *poll_ops;
+	struct tevent_ops *glue_ops;
+	bool fallback_replay;
+};
+
+static int std_event_context_init(struct tevent_context *ev);
+
+static const struct tevent_ops std_event_ops = {
+	.context_init           = std_event_context_init,
+};
+
+/*
+  If this function gets called. epoll failed at runtime.
+  Move us to using poll instead. If we return false here,
+  caller should abort().
+*/
+static bool std_fallback_to_poll(struct tevent_context *ev, bool replay)
+{
+	void *glue_ptr = talloc_parent(ev->ops);
+	struct std_event_glue *glue =
+		talloc_get_type_abort(glue_ptr,
+		struct std_event_glue);
+	int ret;
+	struct tevent_fd *fde;
+	struct tevent_fd *fde_next;
+
+	glue->fallback_replay = replay;
+
+	/* First switch all the ops to poll. */
+	glue->epoll_ops = NULL;
+	TALLOC_FREE(ev->additional_data);
+
+	/*
+	 * Set custom_ops the same as poll.
+	 */
+	*glue->glue_ops = *glue->poll_ops;
+	glue->glue_ops->context_init = std_event_context_init;
+
+	/* Next initialize the poll backend. */
+	ret = glue->poll_ops->context_init(ev);
+	if (ret != 0) {
+		return false;
+	}
+
+	/*
+	 * Now we have to change all the existing file descriptor
+	 * events from the epoll backend to the poll backend.
+	 */
+	for (fde = ev->fd_events; fde; fde = fde_next) {
+		/*
+		 * We must remove this fde off the ev->fd_events list.
+		 */
+		fde_next = fde->next;
+
+		/* Remove from the ev->fd_events list. */
+		DLIST_REMOVE(ev->fd_events, fde);
+
+		/* Re-add this event as a poll backend event. */
+		tevent_poll_event_add_fd_internal(ev, fde);
+	}
+
+	return true;
+}
+
+static int std_event_loop_once(struct tevent_context *ev, const char *location)
+{
+	void *glue_ptr = talloc_parent(ev->ops);
+	struct std_event_glue *glue =
+		talloc_get_type_abort(glue_ptr,
+		struct std_event_glue);
+	int ret;
+
+	ret = glue->epoll_ops->loop_once(ev, location);
+	if (glue->epoll_ops != NULL) {
+		/* No fallback */
+		return ret;
+	}
+
+	if (!glue->fallback_replay) {
+		/*
+		 * The problem happened while modifying an event.
+		 * An event handler was triggered in this case
+		 * and there is no need to call loop_once() again.
+		 */
+		return ret;
+	}
+
+	return glue->poll_ops->loop_once(ev, location);
+}
+
+/*
+  Initialize the epoll backend and allow it to call a
+  switch function if epoll fails at runtime.
+*/
+static int std_event_context_init(struct tevent_context *ev)
+{
+	struct std_event_glue *glue;
+	int ret;
+
+	/*
+	 * If this is the first initialization
+	 * we need to set up the allocated ops
+	 * pointers.
+	 */
+
+	if (ev->ops == &std_event_ops) {
+		glue = talloc_zero(ev, struct std_event_glue);
+		if (glue == NULL) {
+			return -1;
+		}
+
+		glue->epoll_ops = tevent_find_ops_byname("epoll");
+
+		glue->poll_ops = tevent_find_ops_byname("poll");
+		if (glue->poll_ops == NULL) {
+			return -1;
+		}
+
+		/*
+		 * Allocate space for our custom ops.
+		 * Allocate as a child of our epoll_ops pointer
+		 * so we can easily get to it using talloc_parent.
+		 */
+		glue->glue_ops = talloc_zero(glue, struct tevent_ops);
+		if (glue->glue_ops == NULL) {
+			talloc_free(glue);
+			return -1;
+		}
+
+		ev->ops = glue->glue_ops;
+	} else {
+		void *glue_ptr = talloc_parent(ev->ops);
+		glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
+	}
+
+	if (glue->epoll_ops != NULL) {
+		/*
+		 * Set custom_ops the same as epoll,
+		 * except re-init using std_event_context_init()
+		 * and use std_event_loop_once() to add the
+		 * ability to fallback to a poll backend on
+		 * epoll runtime error.
+		 */
+		*glue->glue_ops = *glue->epoll_ops;
+		glue->glue_ops->context_init = std_event_context_init;
+		glue->glue_ops->loop_once = std_event_loop_once;
+
+		ret = glue->epoll_ops->context_init(ev);
+		if (ret == -1) {
+			goto fallback;
+		}
+#ifdef HAVE_EPOLL
+		if (!tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll)) {
+			TALLOC_FREE(ev->additional_data);
+			goto fallback;
+		}
+#endif
+
+		return ret;
+	}
+
+fallback:
+	glue->epoll_ops = NULL;
+
+	/*
+	 * Set custom_ops the same as poll.
+	 */
+	*glue->glue_ops = *glue->poll_ops;
+	glue->glue_ops->context_init = std_event_context_init;
+
+	return glue->poll_ops->context_init(ev);
+}
 
 _PRIVATE_ bool tevent_standard_init(void)
 {
 	return tevent_register_backend("standard", &std_event_ops);
 }
-