src/select.c

/*! \file select.c
 * select filedescriptor handling.
 * Taken from:
 * userspace logging daemon for the iptables ULOG target
 * of the linux 2.4 netfilter subsystem. */
/*
 * (C) 2000-2009 by Harald Welte <laforge@gnumonks.org>
 * All Rights Reserverd.
 *
 * SPDX-License-Identifier: GPL-2.0+
 *
 *  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 2 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, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 *  MA  02110-1301, USA.
 */

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>

#include <osmocom/core/select.h>
#include <osmocom/core/linuxlist.h>
#include <osmocom/core/timer.h>

#include "../config.h"

#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>

/*! \addtogroup select
 *  @{
 *  select() loop abstraction
 *
 * \file select.c */

static int maxfd = 0;
static LLIST_HEAD(osmo_fds);
static int unregistered_count;

/*! Set up an osmo-fd. Will not register it.
 *  \param[inout] ofd Osmo FD to be set-up
 *  \param[in] fd OS-level file descriptor number
 *  \param[in] when bit-mask of BSC_FD_{READ,WRITE,EXECEPT}
 *  \param[in] cb Call-back function to be called
 *  \param[in] data Private context pointer
 *  \param[in] priv_nr Private number
 */
void osmo_fd_setup(struct osmo_fd *ofd, int fd, unsigned int when,
		   int (*cb)(struct osmo_fd *fd, unsigned int what),
		   void *data, unsigned int priv_nr)
{
	ofd->fd = fd;
	ofd->when = when;
	ofd->cb = cb;
	ofd->data = data;
	ofd->priv_nr = priv_nr;
}

/*! Check if a file descriptor is already registered
 *  \param[in] fd osmocom file descriptor to be checked
 *  \returns true if registered; otherwise false
 */
bool osmo_fd_is_registered(struct osmo_fd *fd)
{
	struct osmo_fd *entry;
	llist_for_each_entry(entry, &osmo_fds, list) {
		if (entry == fd) {
			return true;
		}
	}

	return false;
}

/*! Register a new file descriptor with select loop abstraction
 *  \param[in] fd osmocom file descriptor to be registered
 *  \returns 0 on success; negative in case of error
 */
int osmo_fd_register(struct osmo_fd *fd)
{
	int flags;

	/* make FD nonblocking */
	flags = fcntl(fd->fd, F_GETFL);
	if (flags < 0)
		return flags;
	flags |= O_NONBLOCK;
	flags = fcntl(fd->fd, F_SETFL, flags);
	if (flags < 0)
		return flags;

	/* set close-on-exec flag */
	flags = fcntl(fd->fd, F_GETFD);
	if (flags < 0)
		return flags;
	flags |= FD_CLOEXEC;
	flags = fcntl(fd->fd, F_SETFD, flags);
	if (flags < 0)
		return flags;

	/* Register FD */
	if (fd->fd > maxfd)
		maxfd = fd->fd;

#ifdef BSC_FD_CHECK
	if (osmo_fd_is_registered(fd)) {
		fprintf(stderr, "Adding a osmo_fd that is already in the list.\n");
		return 0;
	}
#endif

	llist_add_tail(&fd->list, &osmo_fds);

	return 0;
}

/*! Unregister a file descriptor from select loop abstraction
 *  \param[in] fd osmocom file descriptor to be unregistered
 */
void osmo_fd_unregister(struct osmo_fd *fd)
{
	/* Note: when fd is inside the osmo_fds list (not registered before)
	 * this function will crash! If in doubt, check file descriptor with
	 * osmo_fd_is_registered() */
	unregistered_count++;
	llist_del(&fd->list);
}

/*! Close a file descriptor, mark it as closed + unregister from select loop abstraction
 *  \param[in] fd osmocom file descriptor to be unregistered + closed
 *
 *  If \a fd is registered, we unregister it from the select() loop
 *  abstraction.  We then close the fd and set it to -1, as well as
 *  unsetting any 'when' flags */
void osmo_fd_close(struct osmo_fd *fd)
{
	if (osmo_fd_is_registered(fd))
		osmo_fd_unregister(fd);
	if (fd->fd != -1)
		close(fd->fd);
	fd->fd = -1;
	fd->when = 0;
}

/*! Populate the fd_sets and return the highest fd number
 *  \param[in] _rset The readfds to populate
 *  \param[in] _wset The wrtiefds to populate
 *  \param[in] _eset The errorfds to populate
 *
 *  \returns The highest file descriptor seen or 0 on an empty list
 */
inline int osmo_fd_fill_fds(void *_rset, void *_wset, void *_eset)
{
	fd_set *readset = _rset, *writeset = _wset, *exceptset = _eset;
	struct osmo_fd *ufd;
	int highfd = 0;

	llist_for_each_entry(ufd, &osmo_fds, list) {
		if (ufd->when & BSC_FD_READ)
			FD_SET(ufd->fd, readset);

		if (ufd->when & BSC_FD_WRITE)
			FD_SET(ufd->fd, writeset);

		if (ufd->when & BSC_FD_EXCEPT)
			FD_SET(ufd->fd, exceptset);

		if (ufd->fd > highfd)
			highfd = ufd->fd;
	}

	return highfd;
}

inline int osmo_fd_disp_fds(void *_rset, void *_wset, void *_eset)
{
	struct osmo_fd *ufd, *tmp;
	int work = 0;
	fd_set *readset = _rset, *writeset = _wset, *exceptset = _eset;

restart:
	unregistered_count = 0;
	llist_for_each_entry_safe(ufd, tmp, &osmo_fds, list) {
		int flags = 0;

		if (FD_ISSET(ufd->fd, readset)) {
			flags |= BSC_FD_READ;
			FD_CLR(ufd->fd, readset);
		}

		if (FD_ISSET(ufd->fd, writeset)) {
			flags |= BSC_FD_WRITE;
			FD_CLR(ufd->fd, writeset);
		}

		if (FD_ISSET(ufd->fd, exceptset)) {
			flags |= BSC_FD_EXCEPT;
			FD_CLR(ufd->fd, exceptset);
		}

		if (flags) {
			work = 1;
			ufd->cb(ufd, flags);
		}
		/* ugly, ugly hack. If more than one filedescriptor was
		 * unregistered, they might have been consecutive and
		 * llist_for_each_entry_safe() is no longer safe */
		/* this seems to happen with the last element of the list as well */
		if (unregistered_count >= 1)
			goto restart;
	}

	return work;
}

/*! select main loop integration
 *  \param[in] polling should we pollonly (1) or block on select (0)
 *  \returns 0 if no fd handled; 1 if fd handled; negative in case of error
 */
int osmo_select_main(int polling)
{
	fd_set readset, writeset, exceptset;
	int rc;
	struct timeval no_time = {0, 0};

	FD_ZERO(&readset);
	FD_ZERO(&writeset);
	FD_ZERO(&exceptset);

	/* prepare read and write fdsets */
	osmo_fd_fill_fds(&readset, &writeset, &exceptset);

	if (!polling)
		osmo_timers_prepare();
	rc = select(maxfd+1, &readset, &writeset, &exceptset, polling ? &no_time : osmo_timers_nearest());
	if (rc < 0)
		return 0;

	/* fire timers */
	osmo_timers_update();

	/* call registered callback functions */
	return osmo_fd_disp_fds(&readset, &writeset, &exceptset);
}

/*! find an osmo_fd based on the integer fd
 *  \param[in] fd file descriptor to use as search key
 *  \returns \ref osmo_fd for \ref fd; NULL in case it doesn't exist */
struct osmo_fd *osmo_fd_get_by_fd(int fd)
{
	struct osmo_fd *ofd;

	llist_for_each_entry(ofd, &osmo_fds, list) {
		if (ofd->fd == fd)
			return ofd;
	}
	return NULL;
}

/*! @} */

#endif /* _HAVE_SYS_SELECT_H */