events_standard.c

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/* 
   Unix SMB/CIFS implementation.
   main select loop and event handling
   Copyright (C) Andrew Tridgell	2003-2005
   Copyright (C) Stefan Metzmacher	2005
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.
   
   This program 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 General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program.  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()
*/

#if _SAMBA_BUILD_
#include "includes.h"
#include "lib/util/dlinklist.h"
#else
#include "replace.h"
#include "events_util.h"
#endif
#include "system/filesys.h"
#include "system/network.h"
#include "system/select.h" /* needed for HAVE_EVENTS_EPOLL */
#include "events.h"
#include "events_internal.h"

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

	/* list of filedescriptor events */
	struct fd_event *fd_events;

	/* 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	   handler needs to assume that the linked list is no longer
	   valid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_EVENTS_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)
{
	DEBUG(0,("%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 EVENT_FD_* to EPOLLIN/EPOLLOUT
*/
static uint32_t epoll_map_flags(uint16_t flags)
{
	uint32_t ret = 0;
	if (flags & EVENT_FD_READ) ret |= (EPOLLIN | EPOLLERR | EPOLLHUP);
	if (flags & EVENT_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 fd_event *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 fd_event *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) {
		DEBUG(0,("Failed to recreate epoll handle after fork\n"));
		return;
	}
	std_ev->pid = getpid();
	for (fde=std_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 fd_event *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 & EVENT_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 fd_event *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 fd_event *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 & EVENT_FD_READ) {
		fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;
	}
}

static void epoll_change_event(struct std_event_context *std_ev, struct fd_event *fde)
{
	bool got_error = (fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_GOT_ERROR);
	bool want_read = (fde->flags & EVENT_FD_READ);
	bool want_write= (fde->flags & EVENT_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->num_signal_handlers && 
	    common_event_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->num_signal_handlers) {
		if (common_event_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 */
		common_event_loop_timer_delay(std_ev->ev);
		return 0;
	}

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