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)

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

nits in comments

no more cons_put system calls
usertests tests two processes writing files

iget
mkfs makes a file system image
put this in your .bochsrc:
ata0-slave: type=disk, mode=flat, path="fs.img", cylinders=1024, heads=1, spt=1