/*
 *  linux/kernel/sys.c
 *
 *  (C) 1991  Linus Torvalds
 */

#include <errno.h>

#include <linux/sched.h>	//调度程序头文件。定义了任务结构task_struct,任务0的数据,
							//还有一些有关描述符参数设置和获取的嵌入式汇编函数宏语言
#include <linux/tty.h>
#include <linux/kernel.h>	//内核头文件
#include <asm/segment.h>
#include <sys/times.h>
#include <sys/utsname.h>	//系统名称结构头文件

int sys_ftime()
{
	return -ENOSYS;
}

int sys_break()
{
	return -ENOSYS;
}

int sys_ptrace()
{
	return -ENOSYS;
}

int sys_stty()
{
	return -ENOSYS;
}

int sys_gtty()
{
	return -ENOSYS;
}

int sys_rename()
{
	return -ENOSYS;
}

int sys_prof()
{
	return -ENOSYS;
}

int sys_setregid(int rgid, int egid)
{
	if (rgid>0) {
		if ((current->gid == rgid) || 
		    suser())
			current->gid = rgid;
		else
			return(-EPERM);
	}
	if (egid>0) {
		if ((current->gid == egid) ||
		    (current->egid == egid) ||
		    suser()) {
			current->egid = egid;
			current->sgid = egid;
		} else
			return(-EPERM);
	}
	return 0;
}
//设置进程组号
int sys_setgid(int gid)
{
/*	return(sys_setregid(gid, gid)); */
	if (suser())
		current->gid = current->egid = current->sgid = gid;
	else if ((gid == current->gid) || (gid == current->sgid))
		current->egid = gid;
	else
		return -EPERM;
	return 0;
}

int sys_acct()
{
	return -ENOSYS;
}

int sys_phys()
{
	return -ENOSYS;
}

int sys_lock()
{
	return -ENOSYS;
}

int sys_mpx()
{
	return -ENOSYS;
}

int sys_ulimit()
{
	return -ENOSYS;
}
//返回从1970年1月1号 开始记时的时间值(s)
int sys_time(long * tloc)
{
	int i;

	i = CURRENT_TIME;
	if (tloc) {
		verify_area(tloc,4);
		put_fs_long(i,(unsigned long *)tloc);	//把时间值存储到用户空间
		//段寄存器fs被默认地指向用户数据空间，因此此函数可利用fs段寄存器来访问用户空间中的值
	}
	return i;
}

/*
 * Unprivileged users may change the real user id to the effective uid
 * or vice versa.
 */
int sys_setreuid(int ruid, int euid)
{
	int old_ruid = current->uid;
	
	if (ruid>0) {
		if ((current->euid==ruid) ||
                    (old_ruid == ruid) ||
		    suser())
			current->uid = ruid;
		else
			return(-EPERM);
	}
	if (euid>0) {
		if ((old_ruid == euid) ||
                    (current->euid == euid) ||
		    suser()) {
			current->euid = euid;
			current->suid = euid;
		} else {
			current->uid = old_ruid;
			return(-EPERM);
		}
	}
	return 0;
}

int sys_setuid(int uid)
{
/*	return(sys_setreuid(uid, uid)); */
	if (suser())
		current->uid = current->euid = current->suid = uid;
	else if ((uid == current->uid) || (uid == current->suid))
		current->euid = uid;
	else
		return -EPERM;
	return(0);
}

int sys_stime(long * tptr)
{
	if (!suser())
		return -EPERM;
	startup_time = get_fs_long((unsigned long *)tptr) - jiffies/HZ;
	return 0;
}
//获取当前任务运行时间统计值
int sys_times(struct tms * tbuf)
{
	if (tbuf) {
		verify_area(tbuf,sizeof *tbuf);
		put_fs_long(current->utime,(unsigned long *)&tbuf->tms_utime);
		put_fs_long(current->stime,(unsigned long *)&tbuf->tms_stime);
		put_fs_long(current->cutime,(unsigned long *)&tbuf->tms_cutime);
		put_fs_long(current->cstime,(unsigned long *)&tbuf->tms_cstime);
	}
	return jiffies;
}
//设置程序在内存中的末端位置
int sys_brk(unsigned long end_data_seg)
{
	//如果参数值大于代码结尾，并且小于（堆栈-16kb），则设置新数据段结尾值
	if (end_data_seg >= current->end_code &&
	    end_data_seg < current->start_stack - 16384)
		current->brk = end_data_seg;
	return current->brk;
}

/*
 * This needs some heave checking ...
 * I just haven't get the stomach for it. I also don't fully
 * understand sessions/pgrp etc. Let somebody who does explain it.
 */
int sys_setpgid(int pid, int pgid)
{
	int i;

	if (!pid)
		pid = current->pid;
	if (!pgid)
		pgid = current->pid;
	for (i=0 ; i<NR_TASKS ; i++)
		if (task[i] && task[i]->pid==pid) {
			if (task[i]->leader)
				return -EPERM;
			if (task[i]->session != current->session)
				return -EPERM;
			task[i]->pgrp = pgid;
			return 0;
		}
	return -ESRCH;
}

int sys_getpgrp(void)
{
	return current->pgrp;
}

int sys_setsid(void)
{
	if (current->leader && !suser())
		return -EPERM;
	current->leader = 1;
	current->session = current->pgrp = current->pid;
	current->tty = -1;
	return current->pgrp;
}

int sys_getgroups()
{
	return -ENOSYS;
}

int sys_setgroups()
{
	return -ENOSYS;
}

int sys_uname(struct utsname * name)
{
	static struct utsname thisname = {
		"linux .0","nodename","release ","version ","machine "
	};
	int i;

	if (!name) return -ERROR;
	verify_area(name,sizeof *name);
	for(i=0;i<sizeof *name;i++)
		put_fs_byte(((char *) &thisname)[i],i+(char *) name);
	return 0;
}

int sys_sethostname()
{
	return -ENOSYS;
}

int sys_getrlimit()
{
	return -ENOSYS;
}

int sys_setrlimit()
{
	return -ENOSYS;
}

int sys_getrusage()
{
	return -ENOSYS;
}

int sys_gettimeofday()
{
	return -ENOSYS;
}

int sys_settimeofday()
{
	return -ENOSYS;
}


int sys_umask(int mask)
{
	int old = current->umask;

	current->umask = mask & 0777;
	return (old);
}

int sys_pipe2(void){
	return 0;
}

int sys_sleep(unsigned int seconds){
	sys_signal(SIGALRM,SIG_IGN);
	sys_alarm(seconds);
	sys_pause();
	return 0;
}

int sys_execve2(){
	return 0;
}
//获取目录的目录项
int sys_getdents(int fd,struct linux_dirent *dirp,unsigned int count){
	return 0;
}

int sys_getcwd(char* buf,size_t size){
    //char cwd[BUF_MAX];
    if(buf == NULL){
        buf = get_free_page();
    }
    else buf = malloc(size);
	if(!buf)return -1;
    unsigned current_depth = 0;
    struct m_inode* current_ino;
    struct m_inode* parent_ino;
    for(;;){
        current_ino = namei(".");
        parent_ino = namei("..");
        if(current_ino == parent_ino)
            break;
        sys_chdir("..");
        //read_inode(current_ino);		这是个静态函数
        //buf[current_depth++] = read_inode(current_ino);//根据节点号，在当前目录查找文件read_inode
		current_depth++;
    }
    int i = current_depth-1;
    for(i;i >= 0;i--){
        printk("/%s",buf[i]);
    }
    printk("%s\n",current_depth==0?"/":"");
    //复制过来
    return 0;
}