xv6/proc.c

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#include "types.h"
#include "mmu.h"
#include "x86.h"
#include "param.h"
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#include "file.h"
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#include "proc.h"
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#include "defs.h"
#include "spinlock.h"
struct spinlock proc_table_lock;
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struct proc proc[NPROC];
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struct proc *curproc[NCPU];
int next_pid = 1;
extern void forkret(void);
extern void forkret1(struct trapframe*);
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void
pinit(void)
{
initlock(&proc_table_lock, "proc_table");
}
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// Set up CPU's segment descriptors and task state for a
// given process.
// If p==0, set up for "idle" state for when scheduler()
// is idling, not running any process.
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void
setupsegs(struct proc *p)
{
struct cpu *c = &cpus[cpu()];
c->ts.ss0 = SEG_KDATA << 3;
if(p){
c->ts.esp0 = (uint)(p->kstack + KSTACKSIZE);
} else {
c->ts.esp0 = 0xffffffff;
}
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c->gdt[0] = SEG_NULL;
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c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0x100000 + 64*1024, 0);
c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
c->gdt[SEG_TSS] = SEG16(STS_T32A, (uint) &c->ts, sizeof(c->ts), 0);
c->gdt[SEG_TSS].s = 0;
if(p){
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c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (uint)p->mem, p->sz, DPL_USER);
c->gdt[SEG_UDATA] = SEG(STA_W, (uint)p->mem, p->sz, DPL_USER);
} else {
c->gdt[SEG_UCODE] = SEG_NULL;
c->gdt[SEG_UDATA] = SEG_NULL;
}
lgdt(c->gdt, sizeof c->gdt);
ltr(SEG_TSS << 3);
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}
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// Grow current process's memory by n bytes.
// Return old size on success, -1 on failure.
int
growproc(int n)
{
struct proc *cp = curproc[cpu()];
char *newmem, *oldmem;
newmem = kalloc(cp->sz + n);
if(newmem == 0)
return 0xffffffff;
memmove(newmem, cp->mem, cp->sz);
memset(newmem + cp->sz, 0, n);
oldmem = cp->mem;
cp->mem = newmem;
kfree(oldmem, cp->sz);
cp->sz += n;
return cp->sz - n;
}
// 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;
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for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state == UNUSED){
p->state = EMBRYO;
return p;
}
}
return 0;
}
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// Create a new process copying p as the parent.
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// 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).
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struct proc*
copyproc(struct proc *p)
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{
int i;
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struct proc *np;
// Allocate process.
acquire(&proc_table_lock);
if((np = allocproc()) == 0){
release(&proc_table_lock);
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return 0;
}
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np->pid = next_pid++;
np->ppid = p->pid;
release(&proc_table_lock);
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// Copy user memory.
np->sz = p->sz;
np->mem = kalloc(np->sz);
if(np->mem == 0){
np->state = UNUSED;
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return 0;
}
memmove(np->mem, p->mem, np->sz);
// Allocate kernel stack.
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np->kstack = kalloc(KSTACKSIZE);
if(np->kstack == 0){
kfree(np->mem, np->sz);
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np->mem = 0;
np->state = UNUSED;
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return 0;
}
// Copy trapframe registers from parent.
np->tf = (struct trapframe*)(np->kstack + KSTACKSIZE) - 1;
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memmove(np->tf, p->tf, sizeof(*np->tf));
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// Clear %eax so that fork system call returns 0 in child.
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np->tf->eax = 0;
// Set up new jmpbuf to start executing at forkret (see below).
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memset(&np->jmpbuf, 0, sizeof np->jmpbuf);
np->jmpbuf.eip = (uint)forkret;
np->jmpbuf.esp = (uint)np->tf - 4;
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// Copy file descriptors
for(i = 0; i < NOFILE; i++){
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np->ofile[i] = p->ofile[i];
if(np->ofile[i])
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fileincref(np->ofile[i]);
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}
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np->cwd = iincref(p->cwd);
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return np;
}
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//PAGEBREAK: 42
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// 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 scheduler.
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void
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scheduler(void)
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{
struct proc *p;
int i;
for(;;){
// Loop over process table looking for process to run.
acquire(&proc_table_lock);
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for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state != RUNNABLE)
continue;
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// Switch to chosen process. It is the process's job
// to release proc_table_lock and then reacquire it
// before jumping back to us.
setupsegs(p);
curproc[cpu()] = p;
p->state = RUNNING;
if(setjmp(&cpus[cpu()].jmpbuf) == 0)
longjmp(&p->jmpbuf);
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// Process is done running for now.
// It should have changed its p->state before coming back.
curproc[cpu()] = 0;
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setupsegs(0);
}
release(&proc_table_lock);
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}
}
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// Enter scheduler. Must already hold proc_table_lock
// and have changed curproc[cpu()]->state.
void
sched(void)
{
struct proc *p = curproc[cpu()];
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if(p->state == RUNNING)
panic("sched running");
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if(!holding(&proc_table_lock))
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panic("sched proc_table_lock");
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if(cpus[cpu()].nlock != 1)
panic("sched locks");
if(setjmp(&p->jmpbuf) == 0)
longjmp(&cpus[cpu()].jmpbuf);
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}
// Give up the CPU for one scheduling round.
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void
yield(void)
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{
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struct proc *p = curproc[cpu()];
acquire(&proc_table_lock);
p->state = RUNNABLE;
sched();
release(&proc_table_lock);
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}
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// A fork child's very first scheduling by scheduler()
// will longjmp here. "Return" to user space.
void
forkret(void)
{
// Still holding proc_table_lock from scheduler.
release(&proc_table_lock);
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// Jump into assembly, never to return.
forkret1(curproc[cpu()]->tf);
}
// Atomically release lock and sleep on chan.
// Reacquires lock when reawakened.
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void
sleep(void *chan, struct spinlock *lk)
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{
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struct proc *p = curproc[cpu()];
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if(p == 0)
panic("sleep");
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if(lk == 0)
panic("sleep without lk");
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// Must acquire proc_table_lock in order to
// change p->state and then call sched.
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// 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.
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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);
}
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}
// Wake up all processes sleeping on chan.
// Proc_table_lock must be held.
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void
wakeup1(void *chan)
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{
struct proc *p;
for(p = proc; p < &proc[NPROC]; p++)
if(p->state == SLEEPING && p->chan == chan)
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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);
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}
// 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.
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// Exited processes remain in the zombie state
// until their parent calls wait() to find out they exited.
void
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proc_exit(void)
{
struct proc *p;
struct proc *cp = curproc[cpu()];
int fd;
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if(cp->pid == 1)
panic("init exiting");
// Close all open files.
for(fd = 0; fd < NOFILE; fd++){
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if(cp->ofile[fd]){
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fileclose(cp->ofile[fd]);
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cp->ofile[fd] = 0;
}
}
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idecref(cp->cwd);
cp->cwd = 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++)
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if(p->ppid == cp->pid){
p->ppid = 1;
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wakeup1(&proc[1]); // init
}
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// Jump into the scheduler, never to return.
cp->killed = 0;
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(;;){
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// Scan through table looking for zombie children.
havekids = 0;
for(i = 0; i < NPROC; i++){
p = &proc[i];
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if(p->state == UNUSED)
continue;
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;
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p->ppid = 0;
p->name[0] = 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;
}
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// Wait for children to exit. (See wakeup1 call in proc_exit.)
sleep(cp, &proc_table_lock);
}
}
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// Print a process listing to console. For debugging.
// Runs when user types ^P on console.
// No lock to avoid wedging a stuck machine further.
void
procdump(void)
{
static char *states[] = {
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[UNUSED] "unused",
[EMBRYO] "embryo",
[SLEEPING] "sleep ",
[RUNNABLE] "runble",
[RUNNING] "run ",
[ZOMBIE] "zombie"
};
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int i;
struct proc *p;
char *state;
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for(i = 0; i < NPROC; i++) {
p = &proc[i];
if(p->state == UNUSED)
continue;
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if(p->state >= 0 && p->state < NELEM(states) && states[p->state])
state = states[p->state];
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else
state = "???";
cprintf("%d %s %s\n", p->pid, state, p->name);
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}
}
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