open.c

自已看吧

#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <utime.h>
#include <sys/stat.h>

#include <linux/sched.h>
#include <linux/tty.h>
#include <linux/kernel.h>
#include <asm/segment.h>

int sys_utime(char * filename, struct utimbuf * times)		//将times的时间设置给filename文件
{
	struct m_inode * inode;
	long actime,modtime;

	if (!(inode=namei(filename)))				//取该文件的inode
		return -ENOENT;
	if (times) {
		actime = get_fs_long((unsigned long *) &times->actime);
		modtime = get_fs_long((unsigned long *) &times->modtime);
	} else
		actime = modtime = CURRENT_TIME;
	inode->i_atime = actime;
	inode->i_mtime = modtime;
	inode->i_dirt = 1;
	iput(inode);
	return 0;
}

int sys_access(const char * filename,int mode)			//用mode模式是否可访问filename表示的文件
{
	struct m_inode * inode;
	int res;

	mode &= 0007;
	if (!(inode=namei(filename)))
		return -EACCES;
	res = inode->i_mode & 0777;
	iput(inode);
	if (!(current->euid && current->uid))
		if (res & 0111)
			res = 0777;
		else
			res = 0666;
	if (current->euid == inode->i_uid)
		res >>= 6;
	else if (current->egid == inode->i_gid)
		res >>= 6;
	if ((res & 0007 & mode) == mode)
		return 0;
	return -EACCES;
}

int sys_chdir(const char * filename)				//将当前进程的pwd指向filename代表的目录
{
	struct m_inode * inode;

	if (!(inode = namei(filename)))
		return -ENOENT;
	if (!S_ISDIR(inode->i_mode)) {
		iput(inode);
		return -ENOTDIR;
	}
	iput(current->pwd);
	current->pwd = inode;
	return (0);
}

int sys_chroot(const char * filename)				//将当前进程的root指向filename代表的目录
{
	struct m_inode * inode;

	if (!(inode=namei(filename)))
		return -ENOENT;
	if (!S_ISDIR(inode->i_mode)) {
		iput(inode);
		return -ENOTDIR;
	}
	iput(current->root);
	current->root = inode;
	return (0);
}

int sys_chmod(const char * filename,int mode)			//将指定filename的文件或目录的mode替换成参数mode的模式
{
	struct m_inode * inode;

	if (!(inode=namei(filename)))
		return -ENOENT;
	if (current->uid && current->euid)
		if (current->uid!=inode->i_uid && current->euid!=inode->i_uid) {
			iput(inode);
			return -EACCES;
		} else 
			mode = (mode & 0777) | (inode->i_mode & 07000);
	inode->i_mode = (mode & 07777) | (inode->i_mode & ~07777);
	inode->i_dirt = 1;
	iput(inode);
	return 0;
}

int sys_chown(const char * filename,int uid,int gid)		//将指定的filename的用户标识和用户组标识改变成指定的uid和gid
{
	struct m_inode * inode;

	if (!(inode=namei(filename)))
		return -ENOENT;
	if (current->uid && current->euid) {
		iput(inode);
		return -EACCES;
	}
	inode->i_uid=uid;
	inode->i_gid=gid;
	inode->i_dirt=1;
	iput(inode);
	return 0;
}

int sys_open(const char * filename,int flag,int mode)
{
	struct m_inode * inode;
	struct file * f;
	int i,fd;

	mode &= 0777 & ~current->umask;
	for(fd=0 ; fd<NR_OPEN ; fd++)				//取得一个当前进程未用的filp，准备指向该文件
		if (!current->filp[fd])
			break;
	if (fd>=NR_OPEN)
		return -EINVAL;
	current->close_on_exec &= ~(1<<fd);			//在close_on_exec中标记该位已占用
	f=0+file_table;						//将指针指向文件表的开始
	for (i=0 ; i<NR_FILE ; i++,f++)				//取得一个未用的file_table表项
		if (!f->f_count) break;
	if (i>=NR_FILE)
		return -EINVAL;
	(current->filp[fd]=f)->f_count++;				//标记在用
	if ((i=open_namei(filename,flag,mode,&inode))<0) {	//根据文件名来打开文件的inode
		current->filp[fd]=NULL;
		f->f_count=0;
		return i;
	}
/* ttys are somewhat special (ttyxx major==4, tty major==5) */
	if (S_ISCHR(inode->i_mode))
		if (MAJOR(inode->i_zone[0])==4) {			//如果是ttyxx设备文件，修改当前进程的tty并将tty登记入tty_table
			if (current->leader && current->tty<0) {
				current->tty = MINOR(inode->i_zone[0]);
				tty_table[current->tty].pgrp = current->pgrp;
			}
		} else if (MAJOR(inode->i_zone[0])==5)		//是tty设备文件
			if (current->tty<0) {
				iput(inode);
				current->filp[fd]=NULL;
				f->f_count=0;
				return -EPERM;
			}
	f->f_mode = inode->i_mode;
	f->f_flags = flag;
	f->f_count = 1;
	f->f_inode = inode;
	f->f_pos = 0;
	return (fd);
}

int sys_creat(const char * pathname, int mode)
{
	return sys_open(pathname, O_CREAT | O_TRUNC, mode);
}

int sys_close(unsigned int fd)
{	
	struct file * filp;

	if (fd >= NR_OPEN)					//一个进程最多只能打开20个文件
		return -EINVAL;
	current->close_on_exec &= ~(1<<fd);		//屏蔽该文件在close_on_exec中的占位
	if (!(filp = current->filp[fd]))
		return -EINVAL;
	current->filp[fd] = NULL;				//令该进程指向的该文件指针为空
	if (filp->f_count == 0)
		panic("Close: file count is 0");
	if (--filp->f_count)					//如果有其他进程用该文件，就直接返回
		return (0);
	iput(filp->f_inode);					//释放该文件的inode
	return (0);
}