xv6-65oo2/kernel/proc.c

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#include "types.h"
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#include "param.h"
#include "memlayout.h"
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#include "riscv.h"
#include "spinlock.h"
#include "proc.h"
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#include "defs.h"
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struct cpu cpus[NCPU];
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struct proc proc[NPROC];
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struct proc *initproc;
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int nextpid = 1;
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struct spinlock pid_lock;
extern void forkret(void);
static void wakeup1(struct proc *chan);
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extern char trampoline[]; // trampoline.S
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void
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procinit(void)
{
struct proc *p;
initlock(&pid_lock, "nextpid");
for(p = proc; p < &proc[NPROC]; p++) {
initlock(&p->lock, "proc");
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// Allocate a page for the process's kernel stack.
// Map it high in memory, followed by an invalid
// guard page.
char *pa = kalloc();
if(pa == 0)
panic("kalloc");
uint64 va = KSTACK((int) (p - proc));
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kvmmap(va, (uint64)pa, PGSIZE, PTE_R | PTE_W);
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p->kstack = va;
}
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kvminithart();
}
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// Must be called with interrupts disabled,
// to prevent race with process being moved
// to a different CPU.
int
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cpuid()
{
int id = r_tp();
return id;
}
// Return this CPU's cpu struct.
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// Interrupts must be disabled.
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struct cpu*
mycpu(void) {
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int id = cpuid();
struct cpu *c = &cpus[id];
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return c;
}
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// Return the current struct proc *, or zero if none.
struct proc*
myproc(void) {
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push_off();
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struct cpu *c = mycpu();
struct proc *p = c->proc;
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pop_off();
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return p;
}
int
allocpid() {
int pid;
acquire(&pid_lock);
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pid = nextpid;
nextpid = nextpid + 1;
release(&pid_lock);
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return pid;
}
// Look in the process table for an UNUSED proc.
// If found, initialize state required to run in the kernel,
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// and return with p->lock held.
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// If there are no free procs, return 0.
static struct proc*
allocproc(void)
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{
struct proc *p;
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for(p = proc; p < &proc[NPROC]; p++) {
acquire(&p->lock);
if(p->state == UNUSED) {
goto found;
} else {
release(&p->lock);
}
}
return 0;
found:
p->pid = allocpid();
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// Allocate a trapframe page.
if((p->tf = (struct trapframe *)kalloc()) == 0){
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release(&p->lock);
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return 0;
}
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// An empty user page table.
p->pagetable = proc_pagetable(p);
// Set up new context to start executing at forkret,
// which returns to user space.
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memset(&p->context, 0, sizeof(p->context));
p->context.ra = (uint64)forkret;
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p->context.sp = p->kstack + PGSIZE;
return p;
}
// free a proc structure and the data hanging from it,
// including user pages.
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// p->lock must be held.
static void
freeproc(struct proc *p)
{
if(p->tf)
kfree((void*)p->tf);
p->tf = 0;
if(p->pagetable)
proc_freepagetable(p->pagetable, p->sz);
p->pagetable = 0;
p->sz = 0;
p->pid = 0;
p->parent = 0;
p->name[0] = 0;
p->chan = 0;
p->killed = 0;
p->xstate = 0;
p->state = UNUSED;
}
// Create a page table for a given process,
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// with no user pages, but with trampoline pages.
pagetable_t
proc_pagetable(struct proc *p)
{
pagetable_t pagetable;
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// An empty page table.
pagetable = uvmcreate();
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// map the trampoline code (for system call return)
// at the highest user virtual address.
// only the supervisor uses it, on the way
// to/from user space, so not PTE_U.
mappages(pagetable, TRAMPOLINE, PGSIZE,
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(uint64)trampoline, PTE_R | PTE_X);
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// map the trapframe just below TRAMPOLINE, for trampoline.S.
mappages(pagetable, TRAPFRAME, PGSIZE,
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(uint64)(p->tf), PTE_R | PTE_W);
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return pagetable;
}
// Free a process's page table, and free the
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// physical memory it refers to.
void
proc_freepagetable(pagetable_t pagetable, uint64 sz)
{
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uvmunmap(pagetable, TRAMPOLINE, PGSIZE, 0);
uvmunmap(pagetable, TRAPFRAME, PGSIZE, 0);
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uvmfree(pagetable, sz);
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}
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// a user program that calls exec("/init")
// od -t xC initcode
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uchar initcode[] = {
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0x17, 0x05, 0x00, 0x00, 0x13, 0x05, 0x05, 0x02,
0x97, 0x05, 0x00, 0x00, 0x93, 0x85, 0x05, 0x02,
0x9d, 0x48, 0x73, 0x00, 0x00, 0x00, 0x89, 0x48,
0x73, 0x00, 0x00, 0x00, 0xef, 0xf0, 0xbf, 0xff,
0x2f, 0x69, 0x6e, 0x69, 0x74, 0x00, 0x00, 0x01,
0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00
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};
// Set up first user process.
void
userinit(void)
{
struct proc *p;
p = allocproc();
initproc = p;
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// allocate one user page and copy init's instructions
// and data into it.
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uvminit(p->pagetable, initcode, sizeof(initcode));
p->sz = PGSIZE;
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// prepare for the very first "return" from kernel to user.
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p->tf->epc = 0; // user program counter
p->tf->sp = PGSIZE; // user stack pointer
safestrcpy(p->name, "initcode", sizeof(p->name));
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p->cwd = namei("/");
p->state = RUNNABLE;
release(&p->lock);
}
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// Grow or shrink user memory by n bytes.
// Return 0 on success, -1 on failure.
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int
growproc(int n)
{
uint sz;
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struct proc *p = myproc();
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sz = p->sz;
if(n > 0){
if((sz = uvmalloc(p->pagetable, sz, sz + n)) == 0) {
return -1;
}
} else if(n < 0){
sz = uvmdealloc(p->pagetable, sz, sz + n);
}
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p->sz = sz;
return 0;
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}
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// Create a new process, copying the parent.
// Sets up child kernel stack to return as if from fork() system call.
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int
fork(void)
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{
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int i, pid;
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struct proc *np;
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struct proc *p = myproc();
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// Allocate process.
if((np = allocproc()) == 0){
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return -1;
}
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// Copy user memory from parent to child.
if(uvmcopy(p->pagetable, np->pagetable, p->sz) < 0){
freeproc(np);
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release(&np->lock);
return -1;
}
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np->sz = p->sz;
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np->parent = p;
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// copy saved user registers.
*(np->tf) = *(p->tf);
// Cause fork to return 0 in the child.
np->tf->a0 = 0;
// increment reference counts on open file descriptors.
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for(i = 0; i < NOFILE; i++)
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if(p->ofile[i])
np->ofile[i] = filedup(p->ofile[i]);
np->cwd = idup(p->cwd);
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safestrcpy(np->name, p->name, sizeof(p->name));
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pid = np->pid;
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np->state = RUNNABLE;
release(&np->lock);
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return pid;
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}
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// Pass p's abandoned children to init.
// Caller must hold p->lock.
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void
reparent(struct proc *p)
{
struct proc *pp;
for(pp = proc; pp < &proc[NPROC]; pp++){
// this code uses pp->parent without holding pp->lock.
// acquiring the lock first could cause a deadlock
// if pp or a child of pp were also in exit()
// and about to try to lock p.
if(pp->parent == p){
// pp->parent can't change between the check and the acquire()
// because only the parent changes it, and we're the parent.
acquire(&pp->lock);
pp->parent = initproc;
// we should wake up init here, but that would require
// initproc->lock, which would be a deadlock, since we hold
// the lock on one of init's children (pp). this is why
// exit() always wakes init (before acquiring any locks).
release(&pp->lock);
}
}
}
// Exit the current process. Does not return.
// An exited process remains in the zombie state
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// until its parent calls wait().
void
exit(int status)
{
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struct proc *p = myproc();
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if(p == initproc)
panic("init exiting");
// Close all open files.
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for(int fd = 0; fd < NOFILE; fd++){
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if(p->ofile[fd]){
struct file *f = p->ofile[fd];
fileclose(f);
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p->ofile[fd] = 0;
}
}
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begin_op();
iput(p->cwd);
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end_op();
p->cwd = 0;
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// we might re-parent a child to init. we can't be precise about
// waking up init, since we can't acquire its lock once we've
// acquired any other proc lock. so wake up init whether that's
// necessary or not. init may miss this wakeup, but that seems
// harmless.
acquire(&initproc->lock);
wakeup1(initproc);
release(&initproc->lock);
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// grab a copy of p->parent, to ensure that we unlock the same
// parent we locked. in case our parent gives us away to init while
// we're waiting for the parent lock. we may then race with an
// exiting parent, but the result will be a harmless spurious wakeup
// to a dead or wrong process; proc structs are never re-allocated
// as anything else.
acquire(&p->lock);
struct proc *original_parent = p->parent;
release(&p->lock);
// we need the parent's lock in order to wake it up from wait().
// the parent-then-child rule says we have to lock it first.
acquire(&original_parent->lock);
acquire(&p->lock);
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// Give any children to init.
reparent(p);
// Parent might be sleeping in wait().
wakeup1(original_parent);
p->xstate = status;
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p->state = ZOMBIE;
release(&original_parent->lock);
// Jump into the scheduler, never to return.
sched();
panic("zombie exit");
}
// Wait for a child process to exit and return its pid.
// Return -1 if this process has no children.
int
wait(uint64 addr)
{
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struct proc *np;
int havekids, pid;
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struct proc *p = myproc();
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// hold p->lock for the whole time to avoid lost
// wakeups from a child's exit().
acquire(&p->lock);
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for(;;){
// Scan through table looking for exited children.
havekids = 0;
for(np = proc; np < &proc[NPROC]; np++){
// this code uses np->parent without holding np->lock.
// acquiring the lock first would cause a deadlock,
// since np might be an ancestor, and we already hold p->lock.
if(np->parent == p){
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// np->parent can't change between the check and the acquire()
// because only the parent changes it, and we're the parent.
acquire(&np->lock);
havekids = 1;
if(np->state == ZOMBIE){
// Found one.
pid = np->pid;
if(addr != 0 && copyout(p->pagetable, addr, (char *)&np->xstate,
sizeof(np->xstate)) < 0) {
release(&np->lock);
release(&p->lock);
return -1;
}
freeproc(np);
release(&np->lock);
release(&p->lock);
return pid;
}
release(&np->lock);
}
}
// No point waiting if we don't have any children.
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if(!havekids || p->killed){
release(&p->lock);
return -1;
}
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// Wait for a child to exit.
sleep(p, &p->lock); //DOC: wait-sleep
}
}
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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.
// - swtch to start running that process.
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// - eventually that process transfers control
// via swtch back to the scheduler.
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void
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scheduler(void)
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{
struct proc *p;
struct cpu *c = mycpu();
c->proc = 0;
for(;;){
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// Avoid deadlock by ensuring that devices can interrupt.
intr_on();
for(p = proc; p < &proc[NPROC]; p++) {
acquire(&p->lock);
if(p->state == RUNNABLE) {
// Switch to chosen process. It is the process's job
// to release its lock and then reacquire it
// before jumping back to us.
p->state = RUNNING;
c->proc = p;
swtch(&c->scheduler, &p->context);
// Process is done running for now.
// It should have changed its p->state before coming back.
c->proc = 0;
}
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release(&p->lock);
}
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}
}
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// Switch to scheduler. Must hold only p->lock
// and have changed proc->state. Saves and restores
// intena because intena is a property of this
// kernel thread, not this CPU. It should
// be proc->intena and proc->noff, but that would
// break in the few places where a lock is held but
// there's no process.
void
sched(void)
{
int intena;
struct proc *p = myproc();
if(!holding(&p->lock))
panic("sched p->lock");
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if(mycpu()->noff != 1)
panic("sched locks");
if(p->state == RUNNING)
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panic("sched running");
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if(intr_get())
panic("sched interruptible");
intena = mycpu()->intena;
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swtch(&p->context, &mycpu()->scheduler);
mycpu()->intena = intena;
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}
// Give up the CPU for one scheduling round.
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void
yield(void)
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{
struct proc *p = myproc();
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acquire(&p->lock);
p->state = RUNNABLE;
sched();
release(&p->lock);
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}
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// A fork child's very first scheduling by scheduler()
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// will swtch to forkret.
void
forkret(void)
{
static int first = 1;
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// Still holding p->lock from scheduler.
release(&myproc()->lock);
if (first) {
// File system initialization must be run in the context of a
// regular process (e.g., because it calls sleep), and thus cannot
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// be run from main().
first = 0;
fsinit(ROOTDEV);
}
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usertrapret();
}
// Atomically release lock and sleep on chan.
// Reacquires lock when awakened.
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void
sleep(void *chan, struct spinlock *lk)
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{
struct proc *p = myproc();
// Must acquire p->lock in order to
// change p->state and then call sched.
// Once we hold p->lock, we can be
// guaranteed that we won't miss any wakeup
// (wakeup locks p->lock),
// so it's okay to release lk.
if(lk != &p->lock){ //DOC: sleeplock0
acquire(&p->lock); //DOC: sleeplock1
release(lk);
}
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// Go to sleep.
p->chan = chan;
p->state = SLEEPING;
sched();
// Tidy up.
p->chan = 0;
// Reacquire original lock.
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if(lk != &p->lock){
release(&p->lock);
acquire(lk);
}
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}
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// Wake up all processes sleeping on chan.
// Must be called without any p->lock.
void
wakeup(void *chan)
{
struct proc *p;
for(p = proc; p < &proc[NPROC]; p++) {
acquire(&p->lock);
if(p->state == SLEEPING && p->chan == chan) {
p->state = RUNNABLE;
}
release(&p->lock);
}
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}
// Wake up p if it is sleeping in wait(); used by exit().
// Caller must hold p->lock.
static void
wakeup1(struct proc *p)
{
if(!holding(&p->lock))
panic("wakeup1");
if(p->chan == p && p->state == SLEEPING) {
p->state = RUNNABLE;
}
}
// Kill the process with the given pid.
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// The victim won't exit until it tries to return
// to user space (see usertrap() in trap.c).
int
kill(int pid)
{
struct proc *p;
for(p = proc; p < &proc[NPROC]; p++){
acquire(&p->lock);
if(p->pid == pid){
p->killed = 1;
if(p->state == SLEEPING){
// Wake process from sleep().
p->state = RUNNABLE;
}
release(&p->lock);
return 0;
}
release(&p->lock);
}
return -1;
}
// Copy to either a user address, or kernel address,
// depending on usr_dst.
// Returns 0 on success, -1 on error.
int
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either_copyout(int user_dst, uint64 dst, void *src, uint64 len)
{
struct proc *p = myproc();
if(user_dst){
return copyout(p->pagetable, dst, src, len);
} else {
memmove((char *)dst, src, len);
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return 0;
}
}
// Copy from either a user address, or kernel address,
// depending on usr_src.
// Returns 0 on success, -1 on error.
int
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either_copyin(void *dst, int user_src, uint64 src, uint64 len)
{
struct proc *p = myproc();
if(user_src){
return copyin(p->pagetable, dst, src, len);
} else {
memmove(dst, (char*)src, len);
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return 0;
}
}
// 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[] = {
[UNUSED] "unused",
[SLEEPING] "sleep ",
[RUNNABLE] "runble",
[RUNNING] "run ",
[ZOMBIE] "zombie"
};
struct proc *p;
char *state;
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printf("\n");
for(p = proc; p < &proc[NPROC]; p++){
if(p->state == UNUSED)
continue;
if(p->state >= 0 && p->state < NELEM(states) && states[p->state])
state = states[p->state];
else
state = "???";
printf("%d %s %s", p->pid, state, p->name);
printf("\n");
}
}