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Lab9: file system
作业地址：Lab: file system (mit.edu)
文件系统的实验，需要对提前阅读fs.c\bio.c\sysfile.c以及相关头文件
Large files (moderate)
本实验为xv6的文件系统添加大文件支持
原本的xv6文件系统的每个inode结构体，采用混合索引的方式记录数据所在的盘块号，如下图。
对于文件的前12KB数据，可以通过直接访问inode得到盘块号（每个盘块1024字节），address1~12，对于大于12个盘块的文件，会分配一个一级索引表（一个盘块，1024KB大小，用于存储这部分数据的所在盘块号。），一个一级索引表可以包含BSIZE/4 = 256个盘块号，加上直接索引的12个盘块号， 总共是268个盘块。也就是说一个文件最多268KB。
本实验实现系统的大文件，减少一个直接索引的盘块，改成二级索引表（占一个盘块，可以包含256个一级索引表，每个一级索引表又包含256个盘块号，也就是最大的文件大小变为11+256+256*256）个块，也就是65803KB。
跟前面的页表有点像
1、修改NDIRECT和MAXFILE，修改dinode和inode结构体addrs数组长度
// fs.h
#define NDIRECT 11
#define NINDIRECT (BSIZE / sizeof(uint))
#define MAXFILE (NDIRECT + NINDIRECT + NINDIRECT * NINDIRECT)// On-disk inode structure
struct dinode {short type; // File typeshort major; // Major device number (T_DEVICE only)short minor; // Minor device number (T_DEVICE only)short nlink; // Number of links to inode in file systemuint size; // Size of file (bytes)uint addrs[NDIRECT + 2]; // Data block addresses
};
//file.h
struct inode {uint dev; // Device numberuint inum; // Inode numberint ref; // Reference countstruct sleeplock lock; // protects everything below hereint valid; // inode has been read from disk?short type; // copy of disk inodeshort major;short minor;short nlink;uint size;uint addrs[NDIRECT+2];
};
2、修改bmap，使其能够识别二级索引，当查出一级块号后，需将一级块的数据读入，再次查询
static uint
bmap(struct inode *ip, uint bn)
{uint addr, *a;struct buf *bp;// printf("bn = %d\n", bn);if(bn < NDIRECT){ // NDIRECTif((addr = ip->addrs[bn]) == 0)ip->addrs[bn] = addr = balloc(ip->dev);return addr;}bn -= NDIRECT;// printf("bn = %d, NINDIRECT = %d\n", bn + NDIRECT, NINDIRECT); // 256if(bn < NINDIRECT) { // 第一级可以直接搞定// Load indirect block, allocating if necessary.if((addr = ip->addrs[NDIRECT]) == 0){// printf("here1\n");ip->addrs[NDIRECT] = addr = balloc(ip->dev); //申请一个block for indirect block}bp = bread(ip->dev, addr); // 从磁盘中读取数据到block中,addr是indirect的地址a = (uint*)bp->data; // buf中的数据头，也就是说a里面有256项if((addr = a[bn]) == 0){a[bn] = addr = balloc(ip->dev);log_write(bp);}brelse(bp);return addr;}else{bn -= NINDIRECT;// printf("%d\n", bn);if(bn < NINDIRECT * NINDIRECT) {// printf("bn=%d\n",bn+ NDIRECT - 1+NINDIRECT);if((addr = ip->addrs[NDIRECT + 1]) == 0) {ip->addrs[NDIRECT + 1] = addr = balloc(ip->dev); // 申请一个block for double-indirect block// printf("here2:addr = %d\n", addr);}int i = bn / NINDIRECT, j = bn % NINDIRECT;bp = bread(ip->dev, addr);a = (uint*)bp->data; // 此时a中存放的是二级块的地址if((addr = a[i]) == 0) // 如果此时一级块指向的block地址为空，则 {a[i] = addr = balloc(ip->dev); // 再申请一个blocklog_write(bp);} brelse(bp); // 及时释放struct buf *bp_double = bread(ip->dev, addr); // 再次查询！a = (uint*)bp_double->data; // 再次查询！if((addr = a[j]) == 0) {a[j] = addr = balloc(ip->dev);log_write(bp_double);}brelse(bp_double);// printf("%p\n", addr);return addr;}}panic("bmap: out of range");
}
3、修改itrunc，释放所有的块，包括直接、一级、二级索引的表
void
itrunc(struct inode *ip)
{int i, j;struct buf *bp;uint *a;for(i = 0; i < NDIRECT; i++){ // NDIRECTif(ip->addrs[i]){bfree(ip->dev, ip->addrs[i]);ip->addrs[i] = 0;}}if(ip->addrs[NDIRECT]){ // NDIRECTbp = bread(ip->dev, ip->addrs[NDIRECT - 1]); // NDIRECTa = (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]); // NDIRECTip->addrs[NDIRECT] = 0; // NDIRECT}if(ip->addrs[NDIRECT + 1]) {bp = bread(ip->dev, ip->addrs[NDIRECT + 1]); a = (uint*)bp->data;for(j = 0; j < NINDIRECT; j++){if(a[j]){struct buf *bp_double = bread(ip->dev, a[j]);uint* a_double = (uint*)bp_double->data;for(int k = 0; k < NINDIRECT; k++){if(a_double[k]) {bfree(ip->dev, a_double[k]);a_double[k] = 0;} }brelse(bp_double);bfree(ip->dev, a[j]);a[j] = 0;}}brelse(bp);bfree(ip->dev, ip->addrs[NDIRECT + 1]); // NDIRECTip->addrs[NDIRECT + 1] = 0; // NDIRECT}ip->size = 0;iupdate(ip);
}
测试通过
$ bigfile
...
wrote 65803 blocks
bigfile done; ok
$ usertests
usertests starting
test manywrites: OK
test execout: OK
...
test forktest: OK
test bigdir: OK
ALL TESTS PASSED
Symbolic links (moderate)
使用symlink系统调用（和lab1一样的流程创建系统调用），创建符号链接，符号链接和其他文件一样，使用inode块，使用第一个块存储符号链接指向的文件
uint64 sys_symlink(void) //symlink(char *target, char *path)
{char target[MAXPATH], path[MAXPATH];if(argstr(0, target, MAXPATH) < 0 || argstr(1, path, MAXPATH) < 0)return -1;// printf("target = %s, path = %s\n", target, path);// 创建软连接 path -> target// 不需要判断 target是否存在struct inode* ip;begin_op();ip = create(path, T_SYMLINK, 0, 0);if(ip == 0){end_op();return -1;}if(writei(ip, 0, (uint64)target, 0, strlen(target)) < 0){ //写入targetend_op();return -1;}iunlockput(ip);end_op();return 0;
}
在fcntl.h中补齐O_NOFOLLOW的定义
#define O_RDONLY 0x000
#define O_WRONLY 0x001
#define O_RDWR 0x002
#define O_CREATE 0x200
#define O_TRUNC 0x400
#define O_NOFOLLOW 0x800
修改sys_open函数，使其在遇到符号链接，并且没有O_NOFOLLOW标志时，递归地寻找直到非符号链接的inode
uint64
sys_open(void)
{char path[MAXPATH];int fd, omode;struct file *f;struct inode *ip;int n;if((n = argstr(0, path, MAXPATH)) < 0 || argint(1, &omode) < 0)return -1;begin_op();if(omode & O_CREATE){ip = create(path, T_FILE, 0, 0);if(ip == 0){end_op();return -1;}} else { // add beginif((ip = namei(path)) == 0){end_op();return -1;}ilock(ip);if(ip->type == T_SYMLINK && !(omode & O_NOFOLLOW)) { // 如果是符号链接并且没有不跟随标志int max_depth = 10; // 定义最大递归深度char target[MAXPATH];int found = 0;for(int i = 0; i < max_depth; i++) {if(readi(ip, 0, (uint64)target, 0, MAXPATH) < 0) {iunlockput(ip);end_op();return -1;}iunlockput(ip);ip = namei(target);if(ip == 0) break;if(ip->type == T_SYMLINK) ilock(ip);else{found = 1;ilock(ip);break;}}if(!found){end_op();return -1;}}// add endif(ip->type == T_DIR && omode != O_RDONLY){iunlockput(ip);end_op();return -1;}}...
}
测试：
$ symlinktest
Start: test symlinks
test symlinks: ok
Start: test concurrent symlinks
test concurrent symlinks: ok
$ usertests
usertests starting
test manywrites: OK
test execout: OK
test copyin: OK
test copyout: OK
...
test iref: OK
test forktest: OK
test bigdir: OK
ALL TESTS PASSED
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