xv6-65oo2/proc.c

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

struct {
  struct spinlock lock;
  struct proc proc[NPROC];
} ptable;

// XXX riscv move somewhere else
struct cpu cpus[NCPU];

struct proc *initproc;

int nextpid = 1;
extern void forkret(void);

// for returning  out of the kernel
extern void sysexit(void);

static void wakeup1(void *chan);

extern char trampout[]; // trampoline.S

void
procinit(void)
{
  initlock(&ptable.lock, "ptable");
}

// Must be called with interrupts disabled.
// XXX riscv
int
cpuid() {
  return 0;
}

// Return this core's cpu struct.
// XXX riscv
struct cpu*
mycpu(void) {
  struct cpu *c;
  c = &cpus[0];
  return c;
}

// Disable interrupts so that we are not rescheduled
// while reading proc from the cpu structure
// XXX riscv
struct proc*
myproc(void) {
  return cpus[0].proc;
}

//PAGEBREAK: 32
// Look in the process table for an UNUSED proc.
// If found, change state to EMBRYO and initialize
// state required to run in the kernel.
// Otherwise return 0.
static struct proc*
allocproc(void)
{
  struct proc *p;

  acquire(&ptable.lock);

  for(p = ptable.proc; p < &ptable.proc[NPROC]; p++)
    if(p->state == UNUSED)
      goto found;

  release(&ptable.lock);
  return 0;

found:
  p->state = EMBRYO;
  p->pid = nextpid++;

  release(&ptable.lock);

  // Allocate a page for the kernel stack.
  if((p->kstack = kalloc()) == 0){
    p->state = UNUSED;
    return 0;
  }

  // Allocate a trapframe page.
  if((p->tf = (struct trapframe *)kalloc()) == 0){
    p->state = UNUSED;
    return 0;
  }

  // An empty user page table.
  p->pagetable = proc_pagetable(p);

  // Set up new context to start executing at forkret,
  // which returns to user space.
  memset(&p->context, 0, sizeof p->context);
  p->context.ra = (uint64)forkret;
  p->context.sp = (uint64)p->kstack + PGSIZE;

  return p;
}

// Create a page table for a given process,
// with no users pages, but with trampoline pages.
// Called both when creating a process, and
// by exec() when building tentative new memory image,
// which might fail.
pagetable_t
proc_pagetable(struct proc *p)
{
  pagetable_t pagetable;

  // An empty user page table.
  pagetable = uvmcreate();

  // 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,
           (uint64)trampout, PTE_R | PTE_X);

  // map the trapframe, for trampoline.S.
  mappages(pagetable, (TRAMPOLINE - PGSIZE), PGSIZE,
           (uint64)(p->tf), PTE_R | PTE_W);

  return pagetable;
}

// Free a process's page table, and free the
// physical memory the page table refers to.
// Called both when a process exits and from
// exec() if it fails.
void
proc_freepagetable(pagetable_t pagetable, uint64 sz)
{
  unmappages(pagetable, TRAMPOLINE, PGSIZE, 0);
  unmappages(pagetable, TRAMPOLINE-PGSIZE, PGSIZE, 0);
  uvmfree(pagetable, sz);
}

// a user program that calls exec("/init")
// od -t xC initcode
unsigned char initcode[] = {
  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,
  0x00, 0x00, 0x00
};

//PAGEBREAK: 32
// Set up first user process.
void
userinit(void)
{
  struct proc *p;

  p = allocproc();
  initproc = p;
  
  uvminit(p->pagetable, initcode, sizeof(initcode));
  p->sz = PGSIZE;

  // prepare for the very first kernel->user.
  p->tf->epc = 0;
  p->tf->sp = PGSIZE;

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

  // this assignment to p->state lets other cores
  // run this process. the acquire forces the above
  // writes to be visible, and the lock is also needed
  // because the assignment might not be atomic.
  acquire(&ptable.lock);

  p->state = RUNNABLE;

  release(&ptable.lock);
}

#if 0

// Grow current process's memory by n bytes.
// Return 0 on success, -1 on failure.
int
growproc(int n)
{
  uint sz;
  struct proc *p = myproc();

  sz = p->sz;
  if(n > 0){
    if((sz = allocuvm(p->pagetable, sz, sz + n)) == 0)
      return -1;
  } else if(n < 0){
    if((sz = uvmdealloc(p->pagetable, sz, sz + n)) == 0)
      return -1;
  }
  p->sz = sz;
  switchuvm(p);
  return 0;
}
#endif

// Create a new process, copying p as the parent.
// Sets up child kernel stack to return as if from 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.
  uvmcopy(p->pagetable, np->pagetable, p->sz);
  np->sz = p->sz;

  np->parent = p;

  // 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.
  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;

  acquire(&ptable.lock);

  np->state = RUNNABLE;

  release(&ptable.lock);

  return pid;
}

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

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

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

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

  acquire(&ptable.lock);

  // Parent might be sleeping in wait().
  wakeup1(p->parent);

  // Pass abandoned children to init.
  for(pp = ptable.proc; pp < &ptable.proc[NPROC]; pp++){
    if(pp->parent == p){
      pp->parent = initproc;
      if(pp->state == ZOMBIE)
        wakeup1(initproc);
    }
  }

  // Jump into the scheduler, never to return.
  p->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
wait(void)
{
  struct proc *np;
  int havekids, pid;
  struct proc *p = myproc();
  
  acquire(&ptable.lock);
  for(;;){
    // Scan through table looking for exited children.
    havekids = 0;
    for(np = ptable.proc; np < &ptable.proc[NPROC]; np++){
      if(np->parent != p)
        continue;
      havekids = 1;
      if(np->state == ZOMBIE){
        // Found one.
        pid = np->pid;
        kfree(np->kstack);
        np->kstack = 0;
        kfree((void*)np->tf);
        np->tf = 0;
        proc_freepagetable(np->pagetable, np->sz);
        np->pagetable = 0;
        np->pid = 0;
        np->parent = 0;
        np->name[0] = 0;
        np->killed = 0;
        np->state = UNUSED;
        release(&ptable.lock);
        return pid;
      }
    }

    // No point waiting if we don't have any children.
    if(!havekids || p->killed){
      release(&ptable.lock);
      return -1;
    }

    // Wait for children to exit.  (See wakeup1 call in proc_exit.)
    sleep(p, &ptable.lock);  //DOC: wait-sleep
  }
}

//PAGEBREAK: 42
// 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(;;){
    // Enable interrupts on this processor.
    // XXX riscv
    //sti();
    
    // Loop over process table looking for process to run.
    acquire(&ptable.lock);
    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
      if(p->state != RUNNABLE)
        continue;

      // Switch to chosen process.  It is the process's job
      // to release ptable.lock and then reacquire it
      // before jumping back to us.
      c->proc = p;
      p->state = RUNNING;

      printf("switch...\n");
      swtch(&c->scheduler, &p->context);
      printf("switch returned\n");

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

  }
}

// Enter scheduler.  Must hold only ptable.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->ncli, 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(&ptable.lock))
    panic("sched ptable.lock");
  if(p->state == RUNNING)
    panic("sched running");
  intena = mycpu()->intena;
  swtch(&p->context, &mycpu()->scheduler);
  mycpu()->intena = intena;
}

// Give up the CPU for one scheduling round.
void
yield(void)
{
  acquire(&ptable.lock);  //DOC: yieldlock
  myproc()->state = RUNNABLE;
  sched();
  release(&ptable.lock);
}

// A fork child's very first scheduling by scheduler()
// will swtch to forkret.
void
forkret(void)
{
  struct proc *p = myproc();

  static int first = 1;
  // Still holding ptable.lock from scheduler.
  release(&ptable.lock);

  printf("entering forkret\n");

  if (first) {
    // Some initialization functions must be run in the context
    // of a regular process (e.g., they call sleep), and thus cannot
    // be run from main().
    first = 0;
    iinit(ROOTDEV);
    initlog(ROOTDEV);
  }

  usertrapret();
}

// Atomically release lock and sleep on chan.
// Reacquires lock when awakened.
void
sleep(void *chan, struct spinlock *lk)
{
  struct proc *p = myproc();
  
  if(p == 0)
    panic("sleep");

  if(lk == 0)
    panic("sleep without lk");

  // Must acquire ptable.lock in order to
  // change p->state and then call sched.
  // Once we hold ptable.lock, we can be
  // guaranteed that we won't miss any wakeup
  // (wakeup runs with ptable.lock locked),
  // so it's okay to release lk.
  if(lk != &ptable.lock){  //DOC: sleeplock0
    acquire(&ptable.lock);  //DOC: sleeplock1
    release(lk);
  }
  // Go to sleep.
  p->chan = chan;
  p->state = SLEEPING;

  sched();

  // Tidy up.
  p->chan = 0;

  // Reacquire original lock.
  if(lk != &ptable.lock){  //DOC: sleeplock2
    release(&ptable.lock);
    acquire(lk);
  }
}

//PAGEBREAK!
// Wake up all processes sleeping on chan.
// The ptable lock must be held.
static void
wakeup1(void *chan)
{
  struct proc *p;

  for(p = ptable.proc; p < &ptable.proc[NPROC]; p++)
    if(p->state == SLEEPING && p->chan == chan)
      p->state = RUNNABLE;
}

// Wake up all processes sleeping on chan.
void
wakeup(void *chan)
{
  acquire(&ptable.lock);
  wakeup1(chan);
  release(&ptable.lock);
}

#if 0

// Kill the process with the given pid.
// Process won't exit until it returns
// to user space (see trap in trap.c).
int
kill(int pid)
{
  struct proc *p;

  acquire(&ptable.lock);
  for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
    if(p->pid == pid){
      p->killed = 1;
      // Wake process from sleep if necessary.
      if(p->state == SLEEPING)
        p->state = RUNNABLE;
      release(&ptable.lock);
      return 0;
    }
  }
  release(&ptable.lock);
  return -1;
}

//PAGEBREAK: 36
// 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",
  [EMBRYO]    "embryo",
  [SLEEPING]  "sleep ",
  [RUNNABLE]  "runble",
  [RUNNING]   "run   ",
  [ZOMBIE]    "zombie"
  };
  int i;
  struct proc *p;
  char *state;
  uint64 pc[10];

  for(p = ptable.proc; p < &ptable.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);
    if(p->state == SLEEPING){
      getcallerpcs((uint64*)p->context->rbp+2, pc);
      for(i=0; i<10 && pc[i] != 0; i++)
        printf(" %p", pc[i]);
    }
    printf("\n");
  }
}

#endif