PDF at http://am.lcs.mit.edu/~rsc/xv6.pdf

Various changes made while offline.

 + bwrite sector argument is redundant; use b->sector.
 + reformatting of files for nicer PDF page breaks
 + distinguish between locked, unlocked inodes in type signatures
 + change FD_FILE to FD_INODE
 + move userinit (nee proc0init) to proc.c
 + move ROOTDEV to param.h
 + always parenthesize sizeof argument

Various cleanup:

 - Got rid of dummy proc[0].  Now proc[0] is init.
 - Added initcode.S to exec /init, so that /init is
   just a regular binary.
 - Moved exec out of sysfile to exec.c
 - Moved code dealing with fs guts (like struct inode)
   from sysfile.c to fs.c.  Code dealing with system call
   arguments stays in sysfile.c
 - Refactored directory routines in fs.c; should be simpler.
 - Changed iget to return *unlocked* inode structure.
   This solves the lookup-then-use race in namei
   without introducing deadlocks.
   It also enabled getting rid of the dummy proc[0].

if no lapic available, use 8253pit for clock
now xv6 runs both on qemu (uniprocessor) and bochs (uniprocessor and MP)

lots of cleanup

delete unused functions
a few comments

fix race in mknod / creat
use last component in dirent in mknod, not path

nit in sbrk
indirect block
fix dup to share fd struct

better parsing of sh commands (copied from jos sh)
cat: read from 1 if no args
sbrk system call, but untested
getpid system call
moved locks in keyboard intr, but why do we get intr w. null characters from keyboard?

renumber system calls (run gmake clean!)
skeleton for dup system call

don't hold fd table lock across idecref() (latter does block i/o)
idecref calls iput() in case last ref -> freeing inode
dir size is 512 * # blocks, so readi/writei &c work
unlink deletes dirent even if ip->nlink > 0

don't increase length of directory

no more cons_put system calls
usertests tests two processes writing files

primitive ls

remove console init code from userfs

working unlink, but doesn't free dir blocks that become empty
remove out-of-date comment in ioapic