lab-fs
Large files
修改fs.h中关于直接块间接块的定义，前11块为直接快，第12块为一级间接块，第13块为二级间接块。
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| #define NDIRECT 11
#define NINDIRECT (BSIZE / sizeof(uint))
#define NDUBINDIRECT (BSIZE / sizeof(uint)) * (BSIZE / sizeof(uint))
#define MAXFILE (NDIRECT + NINDIRECT + NDUBINDIRECT)
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当要访问的bn(block number)大于NDIRECT + NINDIRECT时，访问二级间接块，仿照一级间接块的查询方式即可，注意需要查询两级地址。
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| static uint
bmap(struct inode *ip, uint bn)
{
uint addr, *a;
struct buf *bp;
if(bn < NDIRECT){
if((addr = ip->addrs[bn]) == 0)
ip->addrs[bn] = addr = balloc(ip->dev);
return addr;
}
bn -= NDIRECT;
if(bn < NINDIRECT) {
if((addr = ip->addrs[NDIRECT]) == 0)
ip->addrs[NDIRECT] = addr = balloc(ip->dev);
bp = bread(ip->dev, addr);
a = (uint*)bp->data;
if((addr = a[bn]) == 0){
a[bn] = addr = balloc(ip->dev);
log_write(bp);
}
brelse(bp);
return addr;
}
bn -= NINDIRECT;
if (bn < NDUBINDIRECT)
{
if((addr = ip->addrs[NDIRECT + 1]) == 0) {
ip->addrs[NDIRECT + 1] = addr = balloc(ip->dev);
}
uint indirect_index = bn / (NINDIRECT);
uint offset = bn % NINDIRECT;
bp = bread(ip->dev, addr);
a = (uint*)bp->data;
if((addr = a[indirect_index]) == 0) {
a[indirect_index] = addr = balloc(ip->dev);
log_write(bp);
}
brelse(bp);
bp = bread(ip->dev,addr);
a = (uint*)bp->data;
if((addr = a[offset]) == 0) {
a[offset] = addr = balloc(ip->dev);
log_write(bp);
}
brelse(bp);
return addr;
}
panic("bmap: out of range");
}
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确保itrunc释放文件的所有块，包括二级间接块。
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| void
itrunc(struct inode *ip)
{
int i, j;
struct buf *bp;
struct buf *indirect_bp;
uint *a;
uint *b;
int indirect_index,offset;
for(i = 0; i < NDIRECT; i++){
if(ip->addrs[i]){
bfree(ip->dev, ip->addrs[i]);
ip->addrs[i] = 0;
}
}
if(ip->addrs[NDIRECT]){
bp = bread(ip->dev, ip->addrs[NDIRECT]);
a = (uint*)bp->data;
for(j = 0; j < NINDIRECT; j++){
if(a[j])
bfree(ip->dev, a[j]);
}
brelse(bp);
bfree(ip->dev, ip->addrs[NDIRECT]);
ip->addrs[NDIRECT] = 0;
}
if(ip->addrs[NDIRECT + 1]) {
bp = bread(ip->dev, ip->addrs[NDIRECT + 1]);
a = (uint*)bp->data;
for(indirect_index = 0; indirect_index < NINDIRECT; indirect_index++) {
if(a[indirect_index]) {
indirect_bp = bread(ip->dev,a[indirect_index]);
b = (uint*)indirect_bp->data;
for(offset = 0; offset < NINDIRECT; offset++) {
if(b[offset]) {
bfree(ip->dev,b[offset]);
}
}
brelse(indirect_bp);
bfree(ip->dev,a[indirect_index]);
}
}
brelse(bp);
}
ip->size = 0;
iupdate(ip);
}
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Symbolic links
在stat.h内定义 T_SYMLINK 类型。
在fcntl.h定于新标志O_NOFOLLOW。
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| #define O_NOFOLLOW 0x1000
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仿照其他文件系统调用，实现sys_symlink。在新创建的inode的数据块中保存目标路径target字符串。
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| uint64
sys_symlink(void)
{
char taget[MAXPATH], path[MAXPATH];
struct inode *ip;
begin_op();
if(argstr(0, taget, MAXPATH) < 0 || argstr(1, path, MAXPATH) < 0)
return -1;
if ((ip = create(path, T_SYMLINK, 0, 0)) == 0) {
end_op();
return -1;
}
if(writei(ip,0,(uint64)taget,0,MAXPATH) < MAXPATH) {
end_op();
return -1;
}
iunlockput(ip);
end_op();
return 0;
}
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修改sys_open。当打开文件类型为T_SYMLINK时，首先判断是否指定标志O_NOFOLLOW，如果制定了，则按照打开其他类型文件一样处理。否则需要不断递归查询真实文件路径。
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| uint64
sys_open(void)
{
...
if(ip->type == T_DEVICE && (ip->major < 0 || ip->major >= NDEV)){
iunlockput(ip);
end_op();
return -1;
}
if(ip->type == T_SYMLINK) {
if(!(omode & O_NOFOLLOW)) {
int cnt = 0;
char target[MAXPATH];
while(ip->type == T_SYMLINK) {
if(cnt >= 10) {
iunlockput(ip);
end_op();
return -1;
}
cnt++;
readi(ip,0,(uint64)target,0,MAXPATH);
iunlockput(ip);
if((ip = namei(target)) == 0) {
end_op();
return -1;
}
ilock(ip);
}
}
}
...
}
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