/* 
 * Copyright 2010 Stefan Lankes, Chair for Operating Systems,
 *                               RWTH Aachen University
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * This file is part of MetalSVM.
 *
 */

/** 
 * @author Stefan Lankes
 * @file arch/x86/include/asm/tasks.h
 * @brief Task-related functions for forking and scheduling
 *
 * This file contains functions needed for task switching, scheduling and task creation.
 */

#ifndef __ARCH_TASKS__
#define __ARCH_TASKS__

#include <metalsvm/stddef.h>
#include <metalsvm/tasks_types.h>

#ifdef __cplusplus
extern "C" {
#endif

/** @brief Fork a task from current task
 *
 * @param task Pointer to the task structure to fork to
 * @return 
 * - 0 on success
 * - -EINVAL (-22) on failure
 */
int arch_fork(task_t* task);

/** @brief Setup a default frame for a new task
 *
 * @param task Pointer to the task structure
 * @param ep The entry point for code execution
 * @param arg Arguments list pointer for the task's stack
 * @return 
 * - 0 on success
 * - -EINVAL (-22) on failure
 */
int create_default_frame(task_t* task, entry_point_t ep, void* arg);

/** @brief Register a task's TSS at GDT
 *
 * @param task Pointer to task structure
 * @return
 * - 0 on success
 * - -EINVAL (-22) on failure
 */
int register_task(task_t* task);

/** @brief Call to rescheduling
 *
 * This is a purely assembled procedure for rescheduling
 */
void reschedule(void);

/** @brief Jump back to user code
 *
 * This function runs the user code after stopping it just as if
 * it was a return from a procedure.
 *
 * @return 0 in any case
 */
static inline int jump_to_user_code(uint32_t ep, uint32_t stack)
{
	asm volatile ("mov %0, %%ds; mov %0, %%fs; mov %0, %%gs; mov %0, %%es" :: "r"(0x23));
	asm volatile ("push $0x23; push %0; push $0x1B; push %1" :: "r"(stack), "r"(ep));
	asm volatile ("lret");

	return 0;
}

#ifdef __cplusplus
}
#endif

#endif