open.c

基于UNIX6的文件系统模拟程序

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


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

	int user_id = getid(u_id);

	dinodeid = namei(filename);
	if(dinodeid == NULL) /* no such file */
	{
		printf("\nfile does not existed!!\n");
		return NULL;
	}
	inode = iget(dinodeid);
	if(!access(user_id,inode,openmode)) /* access denied */
	{
		printf("\nfile open has no access !!");
		iput(inode);
		return NULL;
	}

	/* alloc the sys_ofile item */
	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 NULL;
	}
	sys_ofile[i].f_inode = inode;
	sys_ofile[i].f_flag = 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;

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

	/* if APPEND, free the block of the file before 
	if(openmode & FAPPEND)
	{
		for(i=0;i<inode->di_size/BLOCKSIZ+1;i++)
			bfree(inode->di_addr[i]);
		inode->di_size=0;
	}*/
	return j;

}