Homework: Files and Disk I/O

Read: readi, writei, fileread, filewrite, create, and dirlink, and code related to these calls in fs.c, bio.c, ide.c, file.c, and sysfile.c

Hand-In Procedure

You are to turn in this homework before lecture. Please email your answers to 6.828-homework@pdos.csail.mit.edu, preferably in plain text.

File and Disk I/O

Insert a print statement in bwrite so that you get a print every time a block is written to disk:

  cprintf("bwrite sector %d\n", b->sector);

Build and boot a new kernel and run these three commands at the shell:

  echo > a
  echo x > a
  rm a
  mkdir d

(Try rm d if you are curious; it should look much the same as rm a.)

You should see a sequence of bwrite prints after running each command.

Submit: Record the list and annotate it with the calling function and what block is being written (for example, "file's i-node block", "file's data block", &c).

Hint: an easy way to get the name of the calling function is to add a string argument to bwrite, edit all the calls to bwrite to pass the name of the calling function, and just print it. You should be able to reason about what kind of block is being written just from the calling function.

You need not write the following up, but try to understand why each write is happening. This will help your understanding of the file system layout and the code.