/* 
   Unix SMB/CIFS implementation.
   main select loop and event handling
   Copyright (C) Andrew Tridgell	2003-2005
   Copyright (C) Stefan Metzmacher	2005-2009

     ** NOTE! The following LGPL license applies to the tevent
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/

/*
  This is SAMBA's default event loop code

  - we try to use epoll if configure detected support for it
    otherwise we use select()
  - if epoll is broken on the system or the kernel doesn't support it
    at runtime we fallback to select()
*/

#include "replace.h"
#include "system/filesys.h"
#include "system/select.h"
#include "tevent.h"
#include "tevent_util.h"
#include "tevent_internal.h"

struct std_event_context {
	/* a pointer back to the generic event_context */
	struct tevent_context *ev;

	/* the maximum file descriptor number in fd_events */
	int maxfd;

	/* information for exiting from the event loop */
	int exit_code;

	/* this is changed by the destructors for the fd event
	   type. It is used to detect event destruction by event
	   handlers, which means the code that is calling the event
	   handler needs to assume that the linked list is no longer
	   valid
	*/
	uint32_t destruction_count;

	/* when using epoll this is the handle from epoll_create */
	int epoll_fd;

	/* our pid at the time the epoll_fd was created */
	pid_t pid;
};

/* use epoll if it is available */
#if HAVE_EPOLL
/*
  called when a epoll call fails, and we should fallback
  to using select
*/
static void epoll_fallback_to_select(struct std_event_context *std_ev, const char *reason)
{
	tevent_debug(std_ev->ev, TEVENT_DEBUG_FATAL,
		     "%s (%s) - falling back to select()\n",
		     reason, strerror(errno));
	close(std_ev->epoll_fd);
	std_ev->epoll_fd = -1;
	talloc_set_destructor(std_ev, NULL);
}

/*
  map from TEVENT_FD_* to EPOLLIN/EPOLLOUT
*/
static uint32_t epoll_map_flags(uint16_t flags)
{
	uint32_t ret = 0;
	if (flags & TEVENT_FD_READ) ret |= (EPOLLIN | EPOLLERR | EPOLLHUP);
	if (flags & TEVENT_FD_WRITE) ret |= (EPOLLOUT | EPOLLERR | EPOLLHUP);
	return ret;
}

/*
 free the epoll fd
*/
static int epoll_ctx_destructor(struct std_event_context *std_ev)
{
	if (std_ev->epoll_fd != -1) {
		close(std_ev->epoll_fd);
	}
	std_ev->epoll_fd = -1;
	return 0;
}

/*
 init the epoll fd
*/
static void epoll_init_ctx(struct std_event_context *std_ev)
{
	std_ev->epoll_fd = epoll_create(64);
	std_ev->pid = getpid();
	talloc_set_destructor(std_ev, epoll_ctx_destructor);
}

static void epoll_add_event(struct std_event_context *std_ev, struct tevent_fd *fde);

/*
  reopen the epoll handle when our pid changes
  see http://junkcode.samba.org/ftp/unpacked/junkcode/epoll_fork.c for an 
  demonstration of why this is needed
 */
static void epoll_check_reopen(struct std_event_context *std_ev)
{
	struct tevent_fd *fde;

	if (std_ev->pid == getpid()) {
		return;
	}

	close(std_ev->epoll_fd);
	std_ev->epoll_fd = epoll_create(64);
	if (std_ev->epoll_fd == -1) {
		tevent_debug(std_ev->ev, TEVENT_DEBUG_FATAL,
			     "Failed to recreate epoll handle after fork\n");
		return;
	}
	std_ev->pid = getpid();
	for (fde=std_ev->ev->fd_events;fde;fde=fde->next) {
		epoll_add_event(std_ev, fde);
	}
}

#define EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT	(1<<0)
#define EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR	(1<<1)
#define EPOLL_ADDITIONAL_FD_FLAG_GOT_ERROR	(1<<2)

/*
 add the epoll event to the given fd_event
*/
static void epoll_add_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
	struct epoll_event event;
	if (std_ev->epoll_fd == -1) return;

	fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

	/* if we don't want events yet, don't add an epoll_event */
	if (fde->flags == 0) return;

	ZERO_STRUCT(event);
	event.events = epoll_map_flags(fde->flags);
	event.data.ptr = fde;
	if (epoll_ctl(std_ev->epoll_fd, EPOLL_CTL_ADD, fde->fd, &event) != 0) {
		epoll_fallback_to_select(std_ev, "EPOLL_CTL_ADD failed");
	}
	fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT;

	/* only if we want to read we want to tell the event handler about errors */
	if (fde->flags & TEVENT_FD_READ) {
		fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;
	}
}

/*
 delete the epoll event for given fd_event
*/
static void epoll_del_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
	struct epoll_event event;
	if (std_ev->epoll_fd == -1) return;

	fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

	/* if there's no epoll_event, we don't need to delete it */
	if (!(fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT)) return;

	ZERO_STRUCT(event);
	event.events = epoll_map_flags(fde->flags);
	event.data.ptr = fde;
	epoll_ctl(std_ev->epoll_fd, EPOLL_CTL_DEL, fde->fd, &event);
	fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT;
}

/*
 change the epoll event to the given fd_event
*/
static void epoll_mod_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
	struct epoll_event event;
	if (std_ev->epoll_fd == -1) return;

	fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

	ZERO_STRUCT(event);
	event.events = epoll_map_flags(fde->flags);
	event.data.ptr = fde;
	if (epoll_ctl(std_ev->epoll_fd, EPOLL_CTL_MOD, fde->fd, &event) != 0) {
		epoll_fallback_to_select(std_ev, "EPOLL_CTL_MOD failed");
	}

	/* only if we want to read we want to tell the event handler about errors */
	if (fde->flags & TEVENT_FD_READ) {
		fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;
	}
}

static void epoll_change_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
	bool got_error = (fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_GOT_ERROR);
	bool want_read = (fde->flags & TEVENT_FD_READ);
	bool want_write= (fde->flags & TEVENT_FD_WRITE);

	if (std_ev->epoll_fd == -1) return;

	fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

	/* there's already an event */
	if (fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT) {
		if (want_read || (want_write && !got_error)) {
			epoll_mod_event(std_ev, fde);
			return;
		}
		/* 
		 * if we want to match the select behavior, we need to remove the epoll_event
		 * when the caller isn't interested in events.
		 *
		 * this is because epoll reports EPOLLERR and EPOLLHUP, even without asking for them
		 */
		epoll_del_event(std_ev, fde);
		return;
	}

	/* there's no epoll_event attached to the fde */
	if (want_read || (want_write && !got_error)) {
		epoll_add_event(std_ev, fde);
		return;
	}
}

/*
  event loop handling using epoll
*/
static int epoll_event_loop(struct std_event_context *std_ev, struct timeval *tvalp)
{
	int ret, i;
#define MAXEVENTS 8
	struct epoll_event events[MAXEVENTS];
	uint32_t destruction_count = ++std_ev->destruction_count;
	int timeout = -1;

	if (std_ev->epoll_fd == -1) return -1;

	if (tvalp) {
		/* it's better to trigger timed events a bit later than to early */
		timeout = ((tvalp->tv_usec+999) / 1000) + (tvalp->tv_sec*1000);
	}

	if (std_ev->ev->signal_events &&
	    tevent_common_check_signal(std_ev->ev)) {
		return 0;
	}

	ret = epoll_wait(std_ev->epoll_fd, events, MAXEVENTS, timeout);

	if (ret == -1 && errno == EINTR && std_ev->ev->signal_events) {
		if (tevent_common_check_signal(std_ev->ev)) {
			return 0;
		}
	}

	if (ret == -1 && errno != EINTR) {
		epoll_fallback_to_select(std_ev, "epoll_wait() failed");
		return -1;
	}

	if (ret == 0 && tvalp) {
		/* we don't care about a possible delay here */
		tevent_common_loop_timer_delay(std_ev->ev);
		return 0;
	}

	for (i=0;i<ret;i++) {
		struct tevent_fd *fde = talloc_get_type(events[i].data.ptr, 
						       struct tevent_fd);
		uint16_t flags = 0;

		if (fde == NULL) {
			epoll_fallback_to_select(std_ev, "epoll_wait() gave bad data");
			return -1;
		}
		if (events[i].events & (EPOLLHUP|EPOLLERR)) {
			fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_GOT_ERROR;
			/*
			 * if we only wait for TEVENT_FD_WRITE, we should not tell the
			 * event handler about it, and remove the epoll_event,
			 * as we only report errors when waiting for read events,
			 * to match the select() behavior
			 */
			if (!(fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR)) {
				epoll_del_event(std_ev, fde);
				continue;
			}
			flags |= TEVENT_FD_READ;
		}
		if (events[i].events & EPOLLIN) flags |= TEVENT_FD_READ;
		if (events[i].events & EPOLLOUT) flags |= TEVENT_FD_WRITE;
		if (flags) {
			fde->handler(std_ev->ev, fde, flags, fde->private_data);
			if (destruction_count != std_ev->destruction_count) {
				break;
			}
		}
	}

	return 0;
}
#else
#define epoll_init_ctx(std_ev) 
#define epoll_add_event(std_ev,fde)
#define epoll_del_event(std_ev,fde)
#define epoll_change_event(std_ev,fde)
#define epoll_event_loop(std_ev,tvalp) (-1)
#define epoll_check_reopen(std_ev)
#endif

/*
  create a std_event_context structure.
*/
static int std_event_context_init(struct tevent_context *ev)
{
	struct std_event_context *std_ev;

	std_ev = talloc_zero(ev, struct std_event_context);
	if (!std_ev) return -1;
	std_ev->ev = ev;
	std_ev->epoll_fd = -1;

	epoll_init_ctx(std_ev);

	ev->additional_data = std_ev;
	return 0;
}

/*
  recalculate the maxfd
*/
static void calc_maxfd(struct std_event_context *std_ev)
{
	struct tevent_fd *fde;

	std_ev->maxfd = 0;
	for (fde = std_ev->ev->fd_events; fde; fde = fde->next) {
		if (fde->fd > std_ev->maxfd) {
			std_ev->maxfd = fde->fd;
		}
	}
}


/* to mark the ev->maxfd invalid
 * this means we need to recalculate it
 */
#define EVENT_INVALID_MAXFD (-1)

/*
  destroy an fd_event
*/
static int std_event_fd_destructor(struct tevent_fd *fde)
{
	struct tevent_context *ev = fde->event_ctx;
	struct std_event_context *std_ev = NULL;

	if (ev) {
		std_ev = talloc_get_type(ev->additional_data,
					 struct std_event_context);

		epoll_check_reopen(std_ev);

		if (std_ev->maxfd == fde->fd) {
			std_ev->maxfd = EVENT_INVALID_MAXFD;
		}

		std_ev->destruction_count++;

		epoll_del_event(std_ev, fde);
	}

	return tevent_common_fd_destructor(fde);
}

/*
  add a fd based event
  return NULL on failure (memory allocation error)
*/
static struct tevent_fd *std_event_add_fd(struct tevent_context *ev, TALLOC_CTX *mem_ctx,
					  int fd, uint16_t flags,
					  tevent_fd_handler_t handler,
					  void *private_data,
					  const char *handler_name,
					  const char *location)
{
	struct std_event_context *std_ev = talloc_get_type(ev->additional_data,
							   struct std_event_context);
	struct tevent_fd *fde;

	epoll_check_reopen(std_ev);

	fde = tevent_common_add_fd(ev, mem_ctx, fd, flags,
				   handler, private_data,
				   handler_name, location);
	if (!fde) return NULL;

	if ((std_ev->maxfd != EVENT_INVALID_MAXFD)
	    && (fde->fd > std_ev->maxfd)) {
		std_ev->maxfd = fde->fd;
	}
	talloc_set_destructor(fde, std_event_fd_destructor);

	epoll_add_event(std_ev, fde);

	return fde;
}

/*
  set the fd event flags
*/
static void std_event_set_fd_flags(struct tevent_fd *fde, uint16_t flags)
{
	struct tevent_context *ev;
	struct std_event_context *std_ev;

	if (fde->flags == flags) return;

	ev = fde->event_ctx;
	std_ev = talloc_get_type(ev->additional_data, struct std_event_context);

	fde->flags = flags;

	epoll_check_reopen(std_ev);

	epoll_change_event(std_ev, fde);
}

/*
  event loop handling using select()
*/
static int std_event_loop_select(struct std_event_context *std_ev, struct timeval *tvalp)
{
	fd_set r_fds, w_fds;
	struct tevent_fd *fde;
	int selrtn;
	uint32_t destruction_count = ++std_ev->destruction_count;

	/* we maybe need to recalculate the maxfd */
	if (std_ev->maxfd == EVENT_INVALID_MAXFD) {
		calc_maxfd(std_ev);
	}

	FD_ZERO(&r_fds);
	FD_ZERO(&w_fds);

	/* setup any fd events */
	for (fde = std_ev->ev->fd_events; fde; fde = fde->next) {
		if (fde->flags & TEVENT_FD_READ) {
			FD_SET(fde->fd, &r_fds);
		}
		if (fde->flags & TEVENT_FD_WRITE) {
			FD_SET(fde->fd, &w_fds);
		}
	}

	if (std_ev->ev->signal_events &&
	    tevent_common_check_signal(std_ev->ev)) {
		return 0;
	}

	selrtn = select(std_ev->maxfd+1, &r_fds, &w_fds, NULL, tvalp);

	if (selrtn == -1 && errno == EINTR && 
	    std_ev->ev->signal_events) {
		tevent_common_check_signal(std_ev->ev);
		return 0;
	}

	if (selrtn == -1 && errno == EBADF) {
		/* the socket is dead! this should never
		   happen as the socket should have first been
		   made readable and that should have removed
		   the event, so this must be a bug. This is a
		   fatal error. */
		tevent_debug(std_ev->ev, TEVENT_DEBUG_FATAL,
			     "ERROR: EBADF on std_event_loop_once\n");
		std_ev->exit_code = EBADF;
		return -1;
	}

	if (selrtn == 0 && tvalp) {
		/* we don't care about a possible delay here */
		tevent_common_loop_timer_delay(std_ev->ev);
		return 0;
	}

	if (selrtn > 0) {
		/* at least one file descriptor is ready - check
		   which ones and call the handler, being careful to allow
		   the handler to remove itself when called */
		for (fde = std_ev->ev->fd_events; fde; fde = fde->next) {
			uint16_t flags = 0;

			if (FD_ISSET(fde->fd, &r_fds)) flags |= TEVENT_FD_READ;
			if (FD_ISSET(fde->fd, &w_fds)) flags |= TEVENT_FD_WRITE;
			if (flags) {
				fde->handler(std_ev->ev, fde, flags, fde->private_data);
				if (destruction_count != std_ev->destruction_count) {
					break;
				}
			}
		}
	}

	return 0;
}		

/*
  do a single event loop using the events defined in ev 
*/
static int std_event_loop_once(struct tevent_context *ev, const char *location)
{
	struct std_event_context *std_ev = talloc_get_type(ev->additional_data,
		 					   struct std_event_context);
	struct timeval tval;

	tval = tevent_common_loop_timer_delay(ev);
	if (tevent_timeval_is_zero(&tval)) {
		return 0;
	}

	epoll_check_reopen(std_ev);

	if (epoll_event_loop(std_ev, &tval) == 0) {
		return 0;
	}

	return std_event_loop_select(std_ev, &tval);
}

/*
  return on failure or (with 0) if all fd events are removed
*/
static int std_event_loop_wait(struct tevent_context *ev, const char *location)
{
	struct std_event_context *std_ev = talloc_get_type(ev->additional_data,
							   struct std_event_context);
	std_ev->exit_code = 0;

	while (ev->fd_events && std_ev->exit_code == 0) {
		if (std_event_loop_once(ev, location) != 0) {
			break;
		}
	}

	return std_ev->exit_code;
}

static const struct tevent_ops std_event_ops = {
	.context_init	= std_event_context_init,
	.add_fd		= std_event_add_fd,
	.set_fd_close_fn= tevent_common_fd_set_close_fn,
	.get_fd_flags	= tevent_common_fd_get_flags,
	.set_fd_flags	= std_event_set_fd_flags,
	.add_timer	= tevent_common_add_timer,
	.add_signal	= tevent_common_add_signal,
	.loop_once	= std_event_loop_once,
	.loop_wait	= std_event_loop_wait,
};


bool tevent_standard_init(void)
{
	return tevent_register_backend("standard", &std_event_ops);
}