open.h

Linux 的最重要的特徵之一是它的为许多不同的文件系统的支持。这使其非常灵活从而与许多另外的操作系统可以很好的共存。linux采用的是树型结构。最上层是根目录

#include <stdio.h>
#include "structure.h"

unsigned short open(user_id,filename,openmode)
int user_id;
char *filename;
unsigned short openmode;
{
	unsigned int dinodeid;
	struct inode *inode;
	int i,j;

	dinodeid=namei(filename);
	if(dinodeid!=(int)NULL)
	{
		printf("\nfile does not existed!!!\n");
		return (int)NULL;
	}
	inode=iget(dinodeid);
	if(!access(user_id,inode,openmode))
	{
		printf("\nfile open has not access!!!\n");
		iput(inode);
		return (int)NULL;
	}

	for(i=1;i<SYSOPENFILE;i++)
		if(sys_ofile[i].f_count==0) break;
	if(i==SYSOPENFILE)
	{
		printf("\nsystem open file too much\n");
		iput(inode);
		return (int)NULL;
	}
	sys_ofile[i].f_inode=inode;
	sys_ofile[i].f_flag=(char)openmode;
	sys_ofile[i].f_count=1;
	if(openmode&FAPPEND)
		sys_ofile[i].f_off=inode->di_size;
	else
		sys_ofile[i].f_off=0;

	for(j=0;j<NOFILE;j++)
		if(user[user_id].u_ofile[j]==0) break;
	if(j==NOFILE)
	{
		printf("\nuser open file too much!!!\n");
			sys_ofile[i].f_count=0;
		iput(inode);
		return (int)NULL;
	}
	user[user_id].u_ofile[j]=1;

	if(openmode&FAPPEND)
	{
		for(i=0;j<inode->di_size/BLOCKSIZ+1;i++)
			bfree(inode->di_addr[i]);
		inode->di_size=0;
	}
	return j;
}