/*
 * Copyright (C) 2006-2007 Andre Noll <maan@systemlinux.org>
 *
 * Licensed under the GPL v2. For licencing details see COPYING.
 */

/** \file ipc.c interprocess communication and shared memory helpers */

#include "para.h"
#include "error.h"
#include "ipc.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 -E_SEM_GET
 * on errors.
 *
 * \sa semget(2)
 */
int mutex_new(void)
{
	int ret = semget(IPC_PRIVATE, 1, IPC_CREAT | 0666);
	return ret < 0?  -E_SEM_GET : ret;
}

/**
 * destroy a mutex
 *
 * \param id the identifier of the mutex to be destroyed
 *
 * \return Positive on success, \a -E_SEM_REMOVE on errors.
 *
 * \sa semctl(2)
 */
int mutex_destroy(int id)
{
	int ret = semctl(id, 0, IPC_RMID);
	return ret < 0? -E_SEM_REMOVE : 1;
}

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_NOTICE_LOG("semaphore set %d was removed\n", id);
		return;
	}
	PARA_EMERG_LOG("fatal semop error %s: pid %d\n", strerror(errno), getpid());
	exit(EXIT_FAILURE);
}

/**
 * lock the given mutex
 *
 * \param id of the shared memory area to lock
 *
 * This function either succeeds or aborts.
 *
 * \sa semop(2), struct 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 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 areay on success, \a -E_SHM_GET 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 ? -E_SHM_GET : ret;
}

/**
 * destroy the given shared memory area
 *
 * \param id the shared memory id
 *
 * \return The return value of the underlying shmctl() call on success,
 * \a -E_SHM_DESTROY 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? -E_SHM_DESTROY : 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
 *
 * \return positive on success, \a -E_SHM_ATTACH on errors.
 *
 * \sa shmat(2)
 */
int shm_attach(int id, enum shm_attach_mode mode, void **result)
{
	if (mode == ATTACH_RW) {
		*result = shmat(id, NULL, 0);
		return *result? 1 : -E_SHM_ATTACH;
	}
	*result = shmat(id, NULL, SHM_RDONLY);
	return *result? 1 : -E_SHM_ATTACH;
}

/**
 * detach a shared memory segment
 *
 * \param addr the address of the attached segment
 *
 * \return positive on success, \a -E_SHM_DETACH on errors.
 *
 * \sa shmdt(2)
 */
int shm_detach(void *addr)
{
	int ret = shmdt(addr);
	return ret < 0? -E_SHM_DETACH : 1;
}