Files and the VFS · File Systems on Disk

1. TODO 1 in myls_starter.c: opendir, then readdir until NULL; build "dir/name" with snprintf
2. TODO 2: lstat the path; print inode, mode, links, owner (getpwuid), size, name
3. TODO 3: mode_string: the type letter, then rwx three times from the bits 0400 … 0001
4. TODO 4: for a symlink, readlink and print " -> target" (add the '\0' yourself)
5. Compare with ls -lia on your home directory, /dev and /proc/self/fd

./myls proj (reference; real)

  959483 drwxr-xr-x  2 root   4096 src
  959482 drwxr-xr-x  4 root   4096 .
  959486 -rw-r--r--  1 root      6 notes.txt
  959356 drwxr-xr-x  4 root   4096 ..
  959484 drwxr-xr-x  2 root   4096 docs
  959487 lrwxrwxrwx  1 root      9 readme
                       -> notes.txt
$ ls -lia proj
959482 drwxr-xr-x 4 root root 4096 .
959356 drwxr-xr-x 4 root root 4096 ..
959484 drwxr-xr-x 2 root root 4096 docs
959486 -rw-r--r-- 1 root root    6 notes.txt
959487 lrwxrwxrwx 1 root root    9 readme -> …

lstat, not stat: stat follows a symlink and describes the target; for readme -> notes.txt you would print a regular file and never see the "l".

1. ./mkimage.sh (or use the disk.img in the zip); look at it with dumpe2fs and debugfs -R "ls -l /"
2. TODO 1: read the superblock at byte 1024; check 0xEF53; bs = 1024 << s_log_block_size
3. TODO 2: read_inode: group and index, the group descriptor, then the inode
4. TODO 3: walk a directory block with rec_len; compare names with memcmp
5. TODO 4: print i_size bytes from the direct blocks. Test /hello.txt, /docs/notes.txt

reference, real

$ ./ext2cat disk.img /docs
block size 1024, 1024 inodes per group, …
  docs  in inode 2 -> inode 12
inode    12  rec_len   12  .
inode     2  rec_len   12  ..
inode    13  rec_len   16  big.txt
inode    14  rec_len   20  notes.txt
inode    15  rec_len   20  numbers.txt
inode    16  rec_len  944  readme
$ ./ext2cat disk.img /docs/notes.txt
Lab 12.2 notes
line two
$ ./ext2cat disk.img /docs/numbers.txt
block 12 needs an indirect block: Homework 12.2

Check every step with the tools: debugfs -R "stat /hello.txt" disk.img prints the inode you should find; od -A d -t x1 -j BYTE -N 64 disk.img shows the raw bytes.