xv6-cs450/proc.c

387 lines
9.3 KiB
C

#include "types.h"
#include "mmu.h"
#include "x86.h"
#include "param.h"
#include "fd.h"
#include "proc.h"
#include "defs.h"
#include "spinlock.h"
struct spinlock proc_table_lock;
struct proc proc[NPROC];
struct proc *curproc[NCPU];
int next_pid = 1;
extern void forkret(void);
extern void forkret1(struct Trapframe*);
/*
* set up a process's task state and segment descriptors
* correctly, given its current size and address in memory.
* this should be called whenever the latter change.
* doesn't change the cpu's current segmentation setup.
*/
void
setupsegs(struct proc *p)
{
memset(&p->ts, 0, sizeof(struct Taskstate));
p->ts.ss0 = SEG_KDATA << 3;
p->ts.esp0 = (unsigned)(p->kstack + KSTACKSIZE);
// XXX it may be wrong to modify the current segment table!
p->gdt[0] = SEG_NULL;
p->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, 0);
p->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
p->gdt[SEG_TSS] = SEG16(STS_T32A, (unsigned) &p->ts,
sizeof(p->ts), 0);
p->gdt[SEG_TSS].s = 0;
p->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (unsigned)p->mem, p->sz, 3);
p->gdt[SEG_UDATA] = SEG(STA_W, (unsigned)p->mem, p->sz, 3);
p->gdt_pd._garbage = 0;
p->gdt_pd.lim = sizeof(p->gdt) - 1;
p->gdt_pd.base = (unsigned) p->gdt;
}
// Look in the process table for an UNUSED proc.
// If found, change state to EMBRYO and return it.
// Otherwise return 0.
struct proc*
allocproc(void)
{
int i;
struct proc *p;
for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state == UNUSED){
p->state = EMBRYO;
return p;
}
}
return 0;
}
// Create a new process copying p as the parent.
// Does not copy the kernel stack.
// Instead, sets up stack to return as if from system call.
// Caller must arrange for process to run (set state to RUNNABLE).
struct proc *
copyproc(struct proc* p)
{
int i;
struct proc *np;
// Allocate process.
acquire(&proc_table_lock);
if((np = allocproc()) == 0){
release(&proc_table_lock);
return 0;
}
np->pid = next_pid++;
np->ppid = p->pid;
release(&proc_table_lock);
// Copy process image memory.
np->sz = p->sz;
np->mem = kalloc(np->sz);
if(np->mem == 0){
np->state = UNUSED;
return 0;
}
memmove(np->mem, p->mem, np->sz);
// Allocate kernel stack.
np->kstack = kalloc(KSTACKSIZE);
if(np->kstack == 0){
kfree(np->mem, np->sz);
np->state = UNUSED;
return 0;
}
// Initialize segment table.
setupsegs(np);
// Copy trapframe registers from parent.
np->tf = (struct Trapframe*)(np->kstack + KSTACKSIZE) - 1;
*np->tf = *p->tf;
// Clear %eax so that fork system call returns 0 in child.
np->tf->regs.eax = 0;
// Set up new jmpbuf to start executing at forkret (see below).
memset(&np->jmpbuf, 0, sizeof np->jmpbuf);
np->jmpbuf.eip = (unsigned)forkret;
np->jmpbuf.esp = (unsigned)np->tf;
// Copy file descriptors
for(i = 0; i < NOFILE; i++){
np->fds[i] = p->fds[i];
if(np->fds[i])
fd_incref(np->fds[i]);
}
return np;
}
// Per-CPU process scheduler.
// Each CPU calls scheduler() after setting itself up.
// Scheduler never returns. It loops, doing:
// - choose a process to run
// - longjmp to start running that process
// - eventually that process transfers control back
// via longjmp back to the top of scheduler.
void
scheduler(void)
{
struct proc *p;
int i;
cprintf("start scheduler on cpu %d jmpbuf %p\n", cpu(), &cpus[cpu()].jmpbuf);
cpus[cpu()].lastproc = &proc[0];
for(;;){
// Loop over process table looking for process to run.
acquire(&proc_table_lock);
for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state != RUNNABLE)
continue;
// Run this process.
// XXX move this into swtch or trapret or something.
// It can run on the other stack.
// h/w sets busy bit in TSS descriptor sometimes, and faults
// if it's set in LTR. so clear tss descriptor busy bit.
p->gdt[SEG_TSS].type = STS_T32A;
// XXX should probably have an lgdt() function in x86.h
// to confine all the inline assembly.
// XXX probably ought to lgdt on trap return too, in case
// a system call has moved a program or changed its size.
asm volatile("lgdt %0" : : "g" (p->gdt_pd.lim));
ltr(SEG_TSS << 3);
// Switch to chosen process. It is the process's job
// to release proc_table_lock and then reacquire it
// before jumping back to us.
if(0) cprintf("cpu%d: run %d\n", cpu(), p-proc);
curproc[cpu()] = p;
p->state = RUNNING;
if(setjmp(&cpus[cpu()].jmpbuf) == 0)
longjmp(&p->jmpbuf);
// Process is done running for now.
// It should have changed its p->state before coming back.
curproc[cpu()] = 0;
if(p->state == RUNNING)
panic("swtch to scheduler with state=RUNNING");
// XXX if not holding proc_table_lock panic.
}
release(&proc_table_lock);
if(cpus[cpu()].nlock != 0)
panic("holding locks in scheduler");
// With proc_table_lock released, there are no
// locks held on this cpu, so interrupts are enabled.
// Hardware interrupts can happen here.
// Also, releasing the lock here lets the other CPUs
// look for runnable processes too.
}
}
// Enter scheduler. Must already hold proc_table_lock
// and have changed curproc[cpu()]->state.
void
sched(void)
{
if(setjmp(&curproc[cpu()]->jmpbuf) == 0)
longjmp(&cpus[cpu()].jmpbuf);
}
// Give up the CPU for one scheduling round.
void
yield(void)
{
struct proc *p;
if((p=curproc[cpu()]) == 0 || curproc[cpu()]->state != RUNNING)
panic("yield");
acquire(&proc_table_lock);
p->state = RUNNABLE;
sched();
release(&proc_table_lock);
}
// A process's very first scheduling by scheduler()
// will longjmp here to do the first jump into user space.
void
forkret(void)
{
// Still holding proc_table_lock from scheduler.
release(&proc_table_lock);
// Jump into assembly, never to return.
forkret1(curproc[cpu()]->tf);
}
// Atomically release lock and sleep on chan.
// Reacquires lock when reawakened.
void
sleep(void *chan, struct spinlock *lk)
{
struct proc *p = curproc[cpu()];
if(p == 0)
panic("sleep");
// Must acquire proc_table_lock in order to
// change p->state and then call sched.
// Once we hold proc_table_lock, we can be
// guaranteed that we won't miss any wakeup
// (wakeup runs with proc_table_lock locked),
// so it's okay to release lk.
if(lk != &proc_table_lock){
acquire(&proc_table_lock);
release(lk);
}
// Go to sleep.
p->chan = chan;
p->state = SLEEPING;
sched();
// Tidy up.
p->chan = 0;
// Reacquire original lock.
if(lk != &proc_table_lock){
release(&proc_table_lock);
acquire(lk);
}
}
// Wake up all processes sleeping on chan.
// Proc_table_lock must be held.
void
wakeup1(void *chan)
{
struct proc *p;
for(p = proc; p < &proc[NPROC]; p++)
if(p->state == SLEEPING && p->chan == chan)
p->state = RUNNABLE;
}
// Wake up all processes sleeping on chan.
// Proc_table_lock is acquired and released.
void
wakeup(void *chan)
{
acquire(&proc_table_lock);
wakeup1(chan);
release(&proc_table_lock);
}
// Kill the process with the given pid.
// Process won't actually exit until it returns
// to user space (see trap in trap.c).
int
proc_kill(int pid)
{
struct proc *p;
acquire(&proc_table_lock);
for(p = proc; p < &proc[NPROC]; p++){
if(p->pid == pid){
p->killed = 1;
// Wake process from sleep if necessary.
if(p->state == SLEEPING)
p->state = RUNNABLE;
release(&proc_table_lock);
return 0;
}
}
release(&proc_table_lock);
return -1;
}
// Exit the current process. Does not return.
// Exited processes remain in the zombie state
// until their parent calls wait() to find out they exited.
void
proc_exit()
{
struct proc *p;
struct proc *cp = curproc[cpu()];
int fd;
// Close all open files.
for(fd = 0; fd < NOFILE; fd++){
if(cp->fds[fd]){
fd_close(cp->fds[fd]);
cp->fds[fd] = 0;
}
}
acquire(&proc_table_lock);
// Wake up our parent.
for(p = proc; p < &proc[NPROC]; p++)
if(p->pid == cp->ppid)
wakeup1(p);
// Reparent our children to process 1.
for(p = proc; p < &proc[NPROC]; p++)
if(p->ppid == cp->pid)
p->ppid = 1;
// Jump into the scheduler, never to return.
cp->state = ZOMBIE;
sched();
panic("zombie exit");
}
// Wait for a child process to exit and return its pid.
// Return -1 if this process has no children.
int
proc_wait(void)
{
struct proc *p;
struct proc *cp = curproc[cpu()];
int i, havekids, pid;
acquire(&proc_table_lock);
for(;;){
// Scan through table looking zombie children.
havekids = 0;
for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->ppid == cp->pid){
if(p->state == ZOMBIE){
// Found one.
kfree(p->mem, p->sz);
kfree(p->kstack, KSTACKSIZE);
pid = p->pid;
p->state = UNUSED;
p->pid = 0;
release(&proc_table_lock);
return pid;
}
havekids = 1;
}
}
// No point waiting if we don't have any children.
if(!havekids){
release(&proc_table_lock);
return -1;
}
// Wait for children to exit. (See wakeup1 call in proc_exit.)
sleep(cp, &proc_table_lock);
}
}