My changes have a race with re-used bufs and the code doesn't seem to get shorter
Keep the changes that fixed ip->off race

This reverts commit 3a5fa7ed.

Conflicts:

	defs.h
	file.c
	file.h

Remove I_BUSY, B_BUSY, and intrans defs and usages
One spinlock per buf to avoid ugly loop in bget
fix race in filewrite (don't update f->off after releasing lock)

Very important to give qemu memory through PHYSTOP :(

Variable declarations at top of function,
separate from initialization.

Use == 0 instead of ! for checking pointers.

Consistent spacing around {, *, casts.

Declare 0-parameter functions as (void) not ().

Integer valued functions return -1 on failure, 0 on success.

 * rename c/cp to cpu/proc
 * rename cpu.context to cpu.scheduler
 * fix some comments
 * formatting for printout

group locks into structs they protect.
few naming nits.

Rename B_WRITE to B_DIRTY and then let ide.c
maintain the B_VALID and B_DIRTY flags.

nits in comments

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

don't use the same name for two different pieces of code

lots of cleanup

so fast interrupts overflow the kernel stack
fix: cli() before lapic_eoi()

fix acquire() to cli() *before* incrementing nlock
make T_SYSCALL a trap gate, not an interrupt gate
sadly, various crashes if you hold down a keyboard key...