xv6-riscv/kernel/proc.c

#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "riscv.h"
#include "spinlock.h"
#include "proc.h"
#include "defs.h"

struct proc proc[NPROC];

struct proc *initproc;

extern void forkret(void);
void freeproc(struct proc *p);

extern char trampoline[]; // trampoline.S

// helps ensure that wakeups of wait()ing
// parents are not lost. helps obey the
// memory model when using p->parent.
// must be acquired before any p->lock.
struct spinlock wait_lock;

// Allocate a page for each process's kernel stack.
// Map it high in memory, followed by an invalid
// guard page.
void
proc_mapstacks(pagetable_t kpgtbl)
{
  struct proc *p;
  
  for(p = proc; p < &proc[NPROC]; p++) {
    char *pa = kalloc();
    if(pa == 0)
      panic("kalloc");
    uint64 va = KSTACK((int) (p - proc));
    kvmmap(kpgtbl, va, (uint64)pa, PGSIZE, PTE_R | PTE_W);
  }
}

// initialize the proc table.
void
procinit(void)
{
  struct proc *p;

  initlock(&wait_lock, "wait_lock");
  for(p = proc; p < &proc[NPROC]; p++) {
      initlock(&p->lock, "proc");
      p->state = UNUSED;
      p->kstack = KSTACK((int) (p - proc));
  }
}

// Look in the process table for an UNUSED proc.
// If found, initialize state required to run in the kernel,
// and return with p->lock held.
// If there are no free procs, or a memory allocation fails, return 0.
struct proc *allocproc(void);

// Create a user page table for a given process, with no user memory,
// but with trampoline and trapframe pages.
pagetable_t proc_pagetable(struct proc *p);

// Free a process's page table, and free the
// physical memory it refers to.
void proc_freepagetable(pagetable_t pagetable, uint64 sz);

// a user program that calls exec("/init")
// assembled from ../user/initcode.S
// od -t xC ../user/initcode
uchar initcode[] = {
  0x17, 0x05, 0x00, 0x00, 0x13, 0x05, 0x45, 0x02,
  0x97, 0x05, 0x00, 0x00, 0x93, 0x85, 0x35, 0x02,
  0x93, 0x08, 0x70, 0x00, 0x73, 0x00, 0x00, 0x00,
  0x93, 0x08, 0x20, 0x00, 0x73, 0x00, 0x00, 0x00,
  0xef, 0xf0, 0x9f, 0xff, 0x2f, 0x69, 0x6e, 0x69,
  0x74, 0x00, 0x00, 0x24, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00
};

// Set up first user process.
void
userinit(void)
{
  struct proc *p;

  p = allocproc();
  initproc = p;
  
  // allocate one user page and copy initcode's instructions
  // and data into it.
  uvmfirst(p->pagetable, initcode, sizeof(initcode));
  p->sz = PGSIZE;

  // prepare for the very first "return" from kernel to user.
  p->trapframe->epc = 0;      // user program counter
  p->trapframe->sp = PGSIZE;  // user stack pointer

  safestrcpy(p->name, "initcode", sizeof(p->name));
  p->cwd = namei("/");

  p->state = RUNNABLE;

  release(&p->lock);
}

// Create a new process, copying the parent.
// Sets up child kernel stack to return as if from fork() system call.
int
fork(void)
{
  int i, pid;
  struct proc *np;
  struct proc *p = myproc();

  // Allocate process.
  if((np = allocproc()) == 0){
    return -1;
  }

  // Copy user memory from parent to child.
  if(uvmcopy(p->pagetable, np->pagetable, p->sz) < 0){
    freeproc(np);
    release(&np->lock);
    return -1;
  }
  np->sz = p->sz;

  // copy saved user registers.
  *(np->trapframe) = *(p->trapframe);

  // Cause fork to return 0 in the child.
  np->trapframe->a0 = 0;

  // increment reference counts on open file descriptors.
  for(i = 0; i < NOFILE; i++)
    if(p->ofile[i])
      np->ofile[i] = filedup(p->ofile[i]);
  np->cwd = idup(p->cwd);

  safestrcpy(np->name, p->name, sizeof(p->name));

  pid = np->pid;

  release(&np->lock);

  acquire(&wait_lock);
  np->parent = p;
  release(&wait_lock);

  acquire(&np->lock);
  np->state = RUNNABLE;
  release(&np->lock);

  return pid;
}

// Pass p's abandoned children to init.
// Caller must hold wait_lock.
void reparent(struct proc *p);

// Exit the current process.  Does not return.
// An exited process remains in the zombie state
// until its parent calls wait().
void
exit(int status)
{
  struct proc *p = myproc();

  if(p == initproc)
    panic("init exiting");

  // Close all open files.
  for(int fd = 0; fd < NOFILE; fd++){
    if(p->ofile[fd]){
      struct file *f = p->ofile[fd];
      fileclose(f);
      p->ofile[fd] = 0;
    }
  }

  begin_op();
  iput(p->cwd);
  end_op();
  p->cwd = 0;

  acquire(&wait_lock);

  // Give any children to init.
  reparent(p);

  // Parent might be sleeping in wait().
  wakeup(p->parent);
  
  acquire(&p->lock);

  p->xstate = status;
  p->state = ZOMBIE;

  release(&wait_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)
{
  struct proc *pp;
  int havekids, pid;
  struct proc *p = myproc();

  acquire(&wait_lock);

  for(;;){
    // Scan through table looking for exited children.
    havekids = 0;
    for(pp = proc; pp < &proc[NPROC]; pp++){
      if(pp->parent == p){
        // make sure the child isn't still in exit() or swtch().
        acquire(&pp->lock);

        havekids = 1;
        if(pp->state == ZOMBIE){
          // Found one.
          pid = pp->pid;
          if(addr != 0 && copyout(p->pagetable, addr, (char *)&pp->xstate,
                                  sizeof(pp->xstate)) < 0) {
            release(&pp->lock);
            release(&wait_lock);
            return -1;
          }
          freeproc(pp);
          release(&pp->lock);
          release(&wait_lock);
          return pid;
        }
        release(&pp->lock);
      }
    }

    // No point waiting if we don't have any children.
    if(!havekids || killed(p)){
      release(&wait_lock);
      return -1;
    }
    
    // Wait for a child to exit.
    sleep_lock(p, &wait_lock); // DOC: wait-sleep
  }
}

// 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.
//  - eventually that process transfers control
//    via swtch back to the scheduler.
void
scheduler(void)
{
  struct proc *p;
  struct cpu *c = mycpu();
  
  c->proc = 0;
  for(;;){
    // 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->context, &p->context);

        // Process is done running for now.
        // It should have changed its p->state before coming back.
        c->proc = 0;
      }
      release(&p->lock);
    }
  }
}

// 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);

// A fork child's very first scheduling by scheduler()
// will swtch to forkret.
void
forkret(void)
{
  static int first = 1;

  // 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
    // be run from main().
    first = 0;
    fsinit(ROOTDEV);
  }

  usertrapret();
}

// Atomically release lock and sleep on chan.
// Reacquires lock when awakened.
void sleep_lock(void *chan, struct spinlock *lk);

// 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++) {
    if(p != myproc()){
      acquire(&p->lock);
      if(p->state == SLEEPING && p->chan == chan) {
        p->state = RUNNABLE;
      }
      release(&p->lock);
    }
  }
}

// Kill the process with the given pid.
// The victim won't exit until it tries to return
// to user space (see usertrap() in trap.c).
int kill(int pid);
void setkilled(struct proc *p);
int killed(struct proc *p);

// Copy to either a user address, or kernel address,
// depending on usr_dst.
// Returns 0 on success, -1 on error.
int
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);
    return 0;
  }
}

// Copy from either a user address, or kernel address,
// depending on usr_src.
// Returns 0 on success, -1 on error.
int
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);
    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",
  [USED]      "used",
  [SLEEPING]  "sleep ",
  [RUNNABLE]  "runble",
  [RUNNING]   "run   ",
  [ZOMBIE]    "zombie"
  };
  struct proc *p;
  char *state;

  printstr("\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 = "???";

    printint(p->pid);
    printstr(" ");
    printstr(state);
    printstr(" ");
    printstr(p->name);
    printstr("\n");
  }
}