/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (C) 2010 David Xu <davidxu@freebsd.org>.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice(s), this list of conditions and the following disclaimer as
 *    the first lines of this file unmodified other than the possible
 *    addition of one or more copyright notices.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice(s), this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "namespace.h"
#include <sys/types.h>
#include <sys/queue.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <errno.h>
#include <machine/atomic.h>
#include <sys/umtx.h>
#include <limits.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <semaphore.h>
#include <unistd.h>
#include "un-namespace.h"
#include "libc_private.h"

__weak_reference(_sem_close, sem_close);
__weak_reference(_sem_destroy, sem_destroy);
__weak_reference(_sem_getvalue, sem_getvalue);
__weak_reference(_sem_init, sem_init);
__weak_reference(_sem_open, sem_open);
__weak_reference(_sem_post, sem_post);
__weak_reference(_sem_timedwait, sem_timedwait);
__weak_reference(_sem_clockwait_np, sem_clockwait_np);
__weak_reference(_sem_trywait, sem_trywait);
__weak_reference(_sem_unlink, sem_unlink);
__weak_reference(_sem_wait, sem_wait);

#define SEM_PREFIX      "/tmp/SEMD"
#define SEM_MAGIC       ((u_int32_t)0x73656d32)

_Static_assert(SEM_VALUE_MAX <= USEM_MAX_COUNT, "SEM_VALUE_MAX too large");

struct sem_nameinfo {
        int open_count;
        char *name;
        dev_t dev;
        ino_t ino;
        sem_t *sem;
        LIST_ENTRY(sem_nameinfo) next;
};

static pthread_once_t once = PTHREAD_ONCE_INIT;
static pthread_mutex_t sem_llock;
static LIST_HEAD(, sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);

static void
sem_prefork(void)
{
        
        _pthread_mutex_lock(&sem_llock);
}

static void
sem_postfork(void)
{

        _pthread_mutex_unlock(&sem_llock);
}

static void
sem_child_postfork(void)
{

        _pthread_mutex_unlock(&sem_llock);
}

static void
sem_module_init(void)
{

        _pthread_mutex_init(&sem_llock, NULL);
        _pthread_atfork(sem_prefork, sem_postfork, sem_child_postfork);
}

static inline int
sem_check_validity(sem_t *sem)
{

        if (sem->_magic == SEM_MAGIC)
                return (0);
        errno = EINVAL;
        return (-1);
}

int
_sem_init(sem_t *sem, int pshared, unsigned int value)
{

        if (value > SEM_VALUE_MAX) {
                errno = EINVAL;
                return (-1);
        }
 
        bzero(sem, sizeof(sem_t));
        sem->_magic = SEM_MAGIC;
        sem->_kern._count = (u_int32_t)value;
        sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
        return (0);
}

sem_t *
_sem_open(const char *name, int flags, ...)
{
        char path[PATH_MAX];
        struct stat sb;
        va_list ap;
        struct sem_nameinfo *ni;
        sem_t *sem, tmp;
        int errsave, fd, len, mode, value;

        ni = NULL;
        sem = NULL;
        fd = -1;
        value = 0;

        if (name[0] != '/') {
                errno = EINVAL;
                return (SEM_FAILED);
        }
        name++;
        strcpy(path, SEM_PREFIX);
        if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
                errno = ENAMETOOLONG;
                return (SEM_FAILED);
        }
        if (flags & ~(O_CREAT|O_EXCL)) {
                errno = EINVAL;
                return (SEM_FAILED);
        }
        if ((flags & O_CREAT) != 0) {
                va_start(ap, flags);
                mode = va_arg(ap, int);
                value = va_arg(ap, int);
                va_end(ap);
        }
        fd = -1;
        _pthread_once(&once, sem_module_init);

        _pthread_mutex_lock(&sem_llock);
        LIST_FOREACH(ni, &sem_list, next) {
                if (ni->name != NULL && strcmp(name, ni->name) == 0) {
                        fd = _open(path, flags | O_RDWR | O_CLOEXEC |
                            O_EXLOCK, mode);
                        if (fd == -1 || _fstat(fd, &sb) == -1) {
                                ni = NULL;
                                goto error;
                        }
                        if ((flags & (O_CREAT | O_EXCL)) == (O_CREAT |
                            O_EXCL) || ni->dev != sb.st_dev ||
                            ni->ino != sb.st_ino) {
                                ni->name = NULL;
                                ni = NULL;
                                break;
                        }
                        ni->open_count++;
                        sem = ni->sem;
                        _pthread_mutex_unlock(&sem_llock);
                        _close(fd);
                        return (sem);
                }
        }

        len = sizeof(*ni) + strlen(name) + 1;
        ni = (struct sem_nameinfo *)malloc(len);
        if (ni == NULL) {
                errno = ENOSPC;
                goto error;
        }

        ni->name = (char *)(ni+1);
        strcpy(ni->name, name);

        if (fd == -1) {
                fd = _open(path, flags | O_RDWR | O_CLOEXEC | O_EXLOCK, mode);
                if (fd == -1 || _fstat(fd, &sb) == -1)
                        goto error;
        }
        if (sb.st_size < sizeof(sem_t)) {
                tmp._magic = SEM_MAGIC;
                tmp._kern._count = value;
                tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
                if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp))
                        goto error;
        }
        flock(fd, LOCK_UN);
        sem = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE,
            MAP_SHARED | MAP_NOSYNC, fd, 0);
        if (sem == MAP_FAILED) {
                sem = NULL;
                if (errno == ENOMEM)
                        errno = ENOSPC;
                goto error;
        }
        if (sem->_magic != SEM_MAGIC) {
                errno = EINVAL;
                goto error;
        }
        ni->open_count = 1;
        ni->sem = sem;
        ni->dev = sb.st_dev;
        ni->ino = sb.st_ino;
        LIST_INSERT_HEAD(&sem_list, ni, next);
        _close(fd);
        _pthread_mutex_unlock(&sem_llock);
        return (sem);

error:
        errsave = errno;
        if (fd != -1)
                _close(fd);
        if (sem != NULL)
                munmap(sem, sizeof(sem_t));
        free(ni);
        _pthread_mutex_unlock(&sem_llock);
        errno = errsave;
        return (SEM_FAILED);
}

int
_sem_close(sem_t *sem)
{
        struct sem_nameinfo *ni;
        bool last;

        if (sem_check_validity(sem) != 0)
                return (-1);

        if (!(sem->_kern._flags & SEM_NAMED)) {
                errno = EINVAL;
                return (-1);
        }

        _pthread_once(&once, sem_module_init);

        _pthread_mutex_lock(&sem_llock);
        LIST_FOREACH(ni, &sem_list, next) {
                if (sem == ni->sem) {
                        last = --ni->open_count == 0;
                        if (last)
                                LIST_REMOVE(ni, next);
                        _pthread_mutex_unlock(&sem_llock);
                        if (last) {
                                munmap(sem, sizeof(*sem));
                                free(ni);
                        }
                        return (0);
                }
        }
        _pthread_mutex_unlock(&sem_llock);
        errno = EINVAL;
        return (-1);
}

int
_sem_unlink(const char *name)
{
        char path[PATH_MAX];

        if (name[0] != '/') {
                errno = ENOENT;
                return -1;
        }
        name++;
        strcpy(path, SEM_PREFIX);
        if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
                errno = ENAMETOOLONG;
                return (-1);
        }

        return (unlink(path));
}

int
_sem_destroy(sem_t *sem)
{

        if (sem_check_validity(sem) != 0)
                return (-1);

        if (sem->_kern._flags & SEM_NAMED) {
                errno = EINVAL;
                return (-1);
        }
        sem->_magic = 0;
        return (0);
}

int
_sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
{

        if (sem_check_validity(sem) != 0)
                return (-1);

        *sval = (int)USEM_COUNT(sem->_kern._count);
        return (0);
}

static __inline int
usem_wake(struct _usem2 *sem)
{

        return (_umtx_op(sem, UMTX_OP_SEM2_WAKE, 0, NULL, NULL));
}

static __inline int
usem_wait(struct _usem2 *sem, clockid_t clock_id, int flags,
    const struct timespec *rqtp, struct timespec *rmtp)
{
        struct {
                struct _umtx_time timeout;
                struct timespec remain;
        } tms;
        void *tm_p;
        size_t tm_size;
        int retval;

        if (rqtp == NULL) {
                tm_p = NULL;
                tm_size = 0;
        } else {
                tms.timeout._clockid = clock_id;
                tms.timeout._flags = (flags & TIMER_ABSTIME) ? UMTX_ABSTIME : 0;
                tms.timeout._timeout = *rqtp;
                tm_p = &tms;
                tm_size = sizeof(tms);
        }
        retval = _umtx_op(sem, UMTX_OP_SEM2_WAIT, 0, (void *)tm_size, tm_p);
        if (retval == -1 && errno == EINTR && (flags & TIMER_ABSTIME) == 0 &&
            rqtp != NULL && rmtp != NULL) {
                *rmtp = tms.remain;
        }

        return (retval);
}

int
_sem_trywait(sem_t *sem)
{
        int val;

        if (sem_check_validity(sem) != 0)
                return (-1);

        while (USEM_COUNT(val = sem->_kern._count) > 0) {
                if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
                        return (0);
        }
        errno = EAGAIN;
        return (-1);
}

int
_sem_clockwait_np(sem_t * __restrict sem, clockid_t clock_id, int flags,
        const struct timespec *rqtp, struct timespec *rmtp)
{
        int val, retval;

        if (sem_check_validity(sem) != 0)
                return (-1);

        retval = 0;
        _pthread_testcancel();
        for (;;) {
                while (USEM_COUNT(val = sem->_kern._count) > 0) {
                        if (atomic_cmpset_acq_int(&sem->_kern._count, val,
                            val - 1))
                                return (0);
                }

                if (retval) {
                        _pthread_testcancel();
                        break;
                }

                /*
                 * The timeout argument is only supposed to
                 * be checked if the thread would have blocked.
                 */
                if (rqtp != NULL) {
                        if (rqtp->tv_nsec >= 1000000000 || rqtp->tv_nsec < 0) {
                                errno = EINVAL;
                                return (-1);
                        }
                }
                _pthread_cancel_enter(1);
                retval = usem_wait(&sem->_kern, clock_id, flags, rqtp, rmtp);
                _pthread_cancel_leave(0);
        }
        return (retval);
}

int
_sem_timedwait(sem_t * __restrict sem,
        const struct timespec * __restrict abstime)
{

        return (_sem_clockwait_np(sem, CLOCK_REALTIME, TIMER_ABSTIME, abstime,
            NULL));
};

int
_sem_wait(sem_t *sem)
{

        return (_sem_timedwait(sem, NULL));
}

/*
 * POSIX:
 * The sem_post() interface is reentrant with respect to signals and may be
 * invoked from a signal-catching function. 
 * The implementation does not use lock, so it should be safe.
 */
int
_sem_post(sem_t *sem)
{
        unsigned int count;

        if (sem_check_validity(sem) != 0)
                return (-1);

        do {
                count = sem->_kern._count;
                if (USEM_COUNT(count) + 1 > SEM_VALUE_MAX) {
                        errno = EOVERFLOW;
                        return (-1);
                }
        } while (!atomic_cmpset_rel_int(&sem->_kern._count, count, count + 1));
        if (count & USEM_HAS_WAITERS)
                usem_wake(&sem->_kern);
        return (0);
}