the day of reckoning has come for the debug port "Shutdown" hack.

instead of mucking with ACPI or using a new hack, the student will now write
sys_date() using the cmosgetdate() helper.

Previously, these were inconsistent: they used their struct proc
argument for bounds checking, but always copied the argument from the
current address space (and hence the current process).  Drop the
struct proc argument and always use the current proc.

Suggested by Carmi Merimovich.

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)

Get rid of last instances of linear address and "la"
Get ready for detecting physical memory dynamically

Allocate proper kernel page table immediately in main using boot allocator
Remove pginit
Simplify address space layout a tiny bit
More to come (e.g., superpages to simplify static table)

Very important to give qemu memory through PHYSTOP :(

Passes usertests and stressfs
Seems to recover correctly in a number of simple cases

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.

usertest that passes too many arguments, break exec

delete most comments from bootother.S (since copy of bootasm.S)
ksegment() -> seginit()
move more stuff from main() to mainc()

Simplify allocuvm/deallocuvm to operate in a contiguous memory model.  This makes their interface match up better with proc->sz and also simplifies the callers (it even gets the main body of exec on one page).

kinit() knows about end and PHYSTOP
map all of kernel read/write (rather than r/o instructions)
thanks, austin

do not keep sorted contiguous free list

increase PHYSTOP

put an invalid page below the stack
have fork() handle invalid pages

fix corner cases with alignment when mapping kernel ELF file

replace jstack with asm()s

(maybe this never worked, but it works now)

Includes code for TLB shootdown (which actually seems unnecessary for xv6)

memcpy directly.