/* SPDX-License-Identifier: GPL-2.0 */

/** \file ipc.c Inter-process communication and shared memory helpers. */

#include "para.h"
#include "error.h"
#include "ipc.h"
#include <sys/types.h>
#include <sys/param.h>

#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>

/**
 * Define a new mutex.
 *
 * \return The identifier for the new mutex on success, a negative error code
 * on errors.
 *
 * \sa semget(2).
 */
int mutex_new(void)
{
	int ret = semget(IPC_PRIVATE, 1, IPC_CREAT | 0666);
	return ret < 0? -ERRNO_TO_PARA_ERROR(errno) : ret;
}

/**
 * Destroy a mutex.
 *
 * \param id The identifier of the mutex to be destroyed.
 *
 * \sa semctl(2)
 */
void mutex_destroy(int id)
{
	if (semctl(id, 0, IPC_RMID) < 0)
		PARA_WARNING_LOG("%s\n", para_strerror(errno));
}

static void para_semop(int id, struct sembuf *sops, int num)
{
	do {
		if (semop(id, sops, num) >= 0)
			return;
	} while (errno == EINTR);
	if (errno == EIDRM) {
		PARA_CRIT_LOG("semaphore set %d was removed\n", id);
		return;
	}
	PARA_EMERG_LOG("fatal semop error %s: pid %d\n", strerror(errno),
		(int)getpid());
	exit(EXIT_FAILURE);
}

/**
 * Lock the given mutex.
 *
 * \param id The identifier of the shared memory area to lock.
 *
 * This function either succeeds or aborts.
 *
 * \sa semop(2), struct \ref misc_meta_data.
 */
void mutex_lock(int id)
{
	struct sembuf sops[2] = {
		{
			.sem_num = 0,
			.sem_op = 0,
			.sem_flg = SEM_UNDO
		},
		{
			.sem_num = 0,
			.sem_op = 1,
			.sem_flg = SEM_UNDO
		}
	};
	para_semop(id, sops, 2);
}

/**
 * Unlock a mutex.
 *
 * \param id The identifier of the mutex.
 *
 * This function either succeeds or aborts.
 *
 * \sa semop(2), struct \ref misc_meta_data.
 */
void mutex_unlock(int id)
{
	struct sembuf sops[1] = {
		{
			.sem_num = 0,
			.sem_op = -1,
			.sem_flg = SEM_UNDO
		},
	};
	para_semop(id, sops, 1);
}

/**
 * Create a new shared memory area of given size.
 *
 * \param size The size of the shared memory area to create.
 *
 * \return The id of the shared memory array on success, a negative error
 * code on errors.
 *
 * \sa shmget(2).
 */
int shm_new(size_t size)
{
	int ret = shmget(IPC_PRIVATE, size, IPC_CREAT | IPC_EXCL | 0600);
	return ret < 0 ? -ERRNO_TO_PARA_ERROR(errno) : ret;
}

/**
 * Destroy the given shared memory area.
 *
 * \param id The shared memory identifier.
 *
 * \return The return value of the underlying shmctl() call on success,
 * a negative error code on errors.
 *
 * \sa shmctl(2).
 */
int shm_destroy(int id)
{
	struct shmid_ds shm_desc;
	int ret = shmctl(id, IPC_RMID, &shm_desc);
	return ret < 0? -ERRNO_TO_PARA_ERROR(errno) : ret;
}

/**
 * Attach a shared memory segment.
 *
 * \param id The identifier of the shared memory segment to attach.
 * \param mode Either ATTACH_RO (read only) or ATTACH_RW (read/write).
 * \param result Points to the attached area just attached on success.
 *
 * \return Standard.
 *
 * \sa shmat(2).
 */
int shm_attach(int id, enum shm_attach_mode mode, void **result)
{
	if (mode == ATTACH_RW)
		*result = shmat(id, NULL, 0);
	else
		*result = shmat(id, NULL, SHM_RDONLY);
	return *result == (void *) -1? -ERRNO_TO_PARA_ERROR(errno) : 1;
}

/**
 * Get the size of a shared memory segment.
 *
 * \param id The shared memory segment identifier.
 * \param result Size in bytes is returned here, zero on errors.
 *
 * \return Standard.
 *
 * \sa shmctl(2).
 */
int shm_size(int id, size_t *result)
{
	struct shmid_ds ds; /* data structure */

	*result = 0;
	if (shmctl(id, IPC_STAT, &ds) < 0)
		return -ERRNO_TO_PARA_ERROR(errno);
	*result = ds.shm_segsz;
	return 1;
}

/**
 * Detach a shared memory segment.
 *
 * \param addr The address of the attached segment.
 *
 * \return Standard.
 *
 * \sa shmdt(2).
 */
int shm_detach(void *addr)
{
	int ret = shmdt(addr);
	return ret < 0? -ERRNO_TO_PARA_ERROR(errno) : 1;
}

# if defined __FreeBSD__ || defined __NetBSD__
#include <sys/sysctl.h>
# 	define SYSCTL_SHMMAX_VARIABLE "kern.ipc.shmmax"
# else
#	undef SYSCTL_SHMMAX_VARIABLE
# endif

/**
 * Get the maximal size of a shared memory area.
 *
 * The value is only computed once when the function is called for the first
 * time.  Subsequent calls return the number which was computed during the
 * first call.
 *
 * \return A number suitable as an argument to \ref shm_new().
 */
size_t shm_get_shmmax(void)
{
	static size_t shmmax;

	if (shmmax > 0) /* only dance once */
		return shmmax;
#ifdef __linux__ /* get it from proc fs */
	{
		int fd = open("/proc/sys/kernel/shmmax", O_RDONLY);
		if (fd >= 0) {
			char buf[100];
			int ret = read(fd, buf, sizeof(buf) - 1);
			if (ret > 0) {
				buf[ret] = '\0';
				shmmax = strtoul(buf, NULL, 10);
			}
			close(fd);
		}
	}
#elif defined SYSCTL_SHMMAX_VARIABLE
	{
		size_t len = sizeof(shmmax);
		sysctlbyname(SYSCTL_SHMMAX_VARIABLE, &shmmax, &len, NULL, 0);
	}
#elif defined SHMMAX
	shmmax = SHMMAX;
#endif
	/*
	 * The value may be too large for allocating memory. In particular, on
	 * 32 bit Linux it is almost 4G.
	 */
	shmmax = PARA_MIN((size_t)10 * 1024 * 1024, shmmax);
	if (shmmax == 0) {
		PARA_WARNING_LOG("unable to determine shmmax\n");
		shmmax = 65535; /* last resort */
	}
	PARA_INFO_LOG("shmmax: %zu\n", shmmax);
	return shmmax;
}