Review Session 9

Ex1. FUSE (Filesystem in Userspace)
  If your FUSE driver code have bugs, will it crash the whole system?
  What if FUSE library has bugs? What if FUSE kernel module has bugs?

Ex2. Super Block
  struct superblock {
  	uint32_t    s_magic; // Magic number: FS_MAGIC.
  	uint32_t    s_nblocks; // Total number of blocks on disk.
  	uint32_t    s_root; // Inum of the root directory inode.
  } __attribute__((packed));

Q: What if our file system crash and s_magic is wrong?
   What if s_nblocks is wrong? What if s_root is wrong?

Ex3. Free Block Bitmap
  Suppose "uint32_t *bitmap;" is the pointer point to the head of bitmap.
  And we want to check whether blockno (int blockno = 202) is free or not.

Q: write a line of valid C code to check:
  if (                            ) { 
	  printf("block 202 is used\n");
  } else {
	  printf("block 202 is free\n");
  }

Ex4. Inode
  struct inode {
    uid_t       i_owner; // Owner of inode.
    gid_t       i_group; // Group membership of inode.
    mode_t      i_mode; // Permissions and type of inode.
    dev_t       i_rdev; // Device represented by inode, if any.
    uint16_t    i_nlink; // The number of hard links.
    int64_t     i_atime; // Access time (reads).
    int64_t     i_ctime; // Change time (chmod, chown).
    int64_t     i_mtime; // Modification time (writes).
    uint32_t    i_size; // The size of the inode in bytes.
    
    // Block pointers.
    // A block is allocated iff its value is != 0.
    uint32_t    i_direct[N_DIRECT]; // Direct blocks.
    uint32_t    i_indirect; // Indirect block.
    uint32_t    i_double; // Double-indirect block.
  } __attribute__((packed));

Q: When N_DIRECT is 10, what's the maximum number of blocks 
   can one file in our filesystem have?

Ex5. Directory
  struct dirent {
    uint32_t    d_inum; // Block number of the referenced inode.
    char        d_name[NAME_MAX]; // File name.
  } __attribute__((packed));

Q: When NAME_MAX is 124, how many files can one directory have?
   (based on the maximum file size on Ex4)

Ex6. Path Walk
  If we want to open file "/home/cs202/hello", 
  how many direcotries should we query?