/*
* release an inode.
* decrease the reference count, write updates to disk if nessary.
* also check the link count, if zero, trucate it.
* */
void iput(struct inode *ip){
ushort dev;
if(ip==NULL)
panic("bad struct inode*");
ip->i_flag |= I_LOCK;
if (ip->i_count > 0) {
ip->i_count--;
}
if (ip->i_count==0){
if (ip->i_nlink==0) {
itrunc(ip);
ifree(ip->i_dev, ip->i_num);
}
// if it's a device file, the dev number is stored in zone[0].
dev = ip->i_zone[0];
switch (ip->i_mode & S_IFMT) {
case S_IFBLK:
(*bdevsw[MAJOR(dev)].d_close)(dev);
break;
case S_IFCHR:
(*cdevsw[MAJOR(dev)].d_close)(dev);
break;
}
iupdate(ip);
ip->i_flag = 0;
ip->i_num = 0;
}
unlk_ino(ip);
}
/*
* open a file. flag indicated opened type like O_RDONLY, O_TRUNC, O_CREAT and blah. And
* mode only used in the O_CREAT scenary, indicated the file (inode) type.
*
* each proc has got one user file table(p_ofile[NOFILE]), it's each entry is also a number,
* indicated the number in the system file table(file[NFILE]). when user opened a file, it
* first allocate a user file table entry(aka. file descriptor), then attach it with a system
* file table entry. It's reference count is increased in fork() or dup().
* */
int do_open(char *path, uint flag, uint mode){
struct inode *ip;
struct file *fp;
ushort dev;
int fd;
// on create a new file.
if (flag & O_CREAT){
ip = namei(path, 1);
// if file is not existing yet.
if (ip->i_nlink==0) {
ip->i_mode = mode;
ip->i_uid = cu->p_euid;
ip->i_gid = cu->p_egid;
ip->i_mtime = time();
ip->i_nlink = 1;
iupdate(ip);
}
}
// an existing file.
else {
ip = namei(path, 0);
if (ip == NULL){
syserr(ENFILE);
return -1;
}
// TODO: check access
// if it's a device file, the dev number is stored in zone[0].
dev = ip->i_zone[0];
switch(ip->i_mode & S_IFMT) {
case S_IFBLK:
(*bdevsw[MAJOR(dev)].d_open)(dev);
break;
case S_IFCHR:
(*cdevsw[MAJOR(dev)].d_open)(dev);
break;
}
}
if (((fd=ufalloc())<0) || (fp=falloc(fd))==NULL) {
iput(ip);
return -1;
}
if (flag & O_TRUNC){
itrunc(ip);
}
unlk_ino(ip);
fp->f_oflag = flag;
fp->f_ino = ip;
cu->p_fdflag[fd] = FD_CLOEXEC;
return fd;
}
