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