4.2BSD/usr/src/sys/sys/kern_fork.c

/*	kern_fork.c	6.1	83/07/29	*/

#include "../machine/reg.h"
#include "../machine/pte.h"
#include "../machine/psl.h"

#include "../h/param.h"
#include "../h/systm.h"
#include "../h/map.h"
#include "../h/dir.h"
#include "../h/user.h"
#include "../h/kernel.h"
#include "../h/proc.h"
#include "../h/inode.h"
#include "../h/seg.h"
#include "../h/vm.h"
#include "../h/text.h"
#include "../h/file.h"
#include "../h/acct.h"
#include "../h/quota.h"

/*
 * fork system call.
 */
fork()
{

	u.u_cdmap = zdmap;
	u.u_csmap = zdmap;
	if (swpexpand(u.u_dsize, u.u_ssize, &u.u_cdmap, &u.u_csmap) == 0) {
		u.u_r.r_val2 = 0;
		return;
	}
	fork1(0);
}

vfork()
{

	fork1(1);
}

fork1(isvfork)
	int isvfork;
{
	register struct proc *p1, *p2;
	register a;

	a = 0;
	p2 = NULL;
	for (p1 = proc; p1 < procNPROC; p1++) {
		if (p1->p_stat==NULL && p2==NULL)
			p2 = p1;
		else {
			if (p1->p_uid==u.u_uid && p1->p_stat!=NULL)
				a++;
		}
	}
	/*
	 * Disallow if
	 *  No processes at all;
	 *  not su and too many procs owned; or
	 *  not su and would take last slot.
	 */
	if (p2==NULL)
		tablefull("proc");
	if (p2==NULL || (u.u_uid!=0 && (p2==procNPROC-1 || a>MAXUPRC))) {
		u.u_error = EAGAIN;
		if (!isvfork) {
			(void) vsexpand(0, &u.u_cdmap, 1);
			(void) vsexpand(0, &u.u_csmap, 1);
		}
		goto out;
	}
	p1 = u.u_procp;
	if (newproc(isvfork)) {
		u.u_r.r_val1 = p1->p_pid;
		u.u_r.r_val2 = 1;  /* child */
		u.u_start = time.tv_sec;
		u.u_acflag = AFORK;
		return;
	}
	u.u_r.r_val1 = p2->p_pid;

out:
	u.u_r.r_val2 = 0;
}

/*
 * Create a new process-- the internal version of
 * sys fork.
 * It returns 1 in the new process, 0 in the old.
 */
newproc(isvfork)
	int isvfork;
{
	register struct proc *p;
	register struct proc *rpp, *rip;
	register int n;
	register struct file *fp;

	p = NULL;
	/*
	 * First, just locate a slot for a process
	 * and copy the useful info from this process into it.
	 * The panic "cannot happen" because fork has already
	 * checked for the existence of a slot.
	 */
retry:
	mpid++;
	if (mpid >= 30000) {
		mpid = 0;
		goto retry;
	}
	for (rpp = proc; rpp < procNPROC; rpp++) {
		if (rpp->p_stat == NULL && p==NULL)
			p = rpp;
		if (rpp->p_pid==mpid || rpp->p_pgrp==mpid)
			goto retry;
	}
	if ((rpp = p) == NULL)
		panic("no procs");

	/*
	 * Make a proc table entry for the new process.
	 */
	rip = u.u_procp;
#ifdef QUOTA
	rpp->p_quota = rip->p_quota;
	rpp->p_quota->q_cnt++;
#endif
	rpp->p_stat = SIDL;
	timerclear(&rpp->p_realtimer.it_value);
	rpp->p_flag = SLOAD | (rip->p_flag & (SPAGI|SOUSIG));
	if (isvfork) {
		rpp->p_flag |= SVFORK;
		rpp->p_ndx = rip->p_ndx;
	} else
		rpp->p_ndx = rpp - proc;
	rpp->p_uid = rip->p_uid;
	rpp->p_pgrp = rip->p_pgrp;
	rpp->p_nice = rip->p_nice;
	rpp->p_textp = isvfork ? 0 : rip->p_textp;
	rpp->p_pid = mpid;
	rpp->p_ppid = rip->p_pid;
	rpp->p_pptr = rip;
	rpp->p_osptr = rip->p_cptr;
	if (rip->p_cptr)
		rip->p_cptr->p_ysptr = rpp;
	rpp->p_ysptr = NULL;
	rpp->p_cptr = NULL;
	rip->p_cptr = rpp;
	rpp->p_time = 0;
	rpp->p_cpu = 0;
	rpp->p_sigmask = rip->p_sigmask;
	rpp->p_sigcatch = rip->p_sigcatch;
	rpp->p_sigignore = rip->p_sigignore;
	/* take along any pending signals like stops? */
	if (isvfork) {
		rpp->p_tsize = rpp->p_dsize = rpp->p_ssize = 0;
		rpp->p_szpt = clrnd(ctopt(UPAGES));
		forkstat.cntvfork++;
		forkstat.sizvfork += rip->p_dsize + rip->p_ssize;
	} else {
		rpp->p_tsize = rip->p_tsize;
		rpp->p_dsize = rip->p_dsize;
		rpp->p_ssize = rip->p_ssize;
		rpp->p_szpt = rip->p_szpt;
		forkstat.cntfork++;
		forkstat.sizfork += rip->p_dsize + rip->p_ssize;
	}
	rpp->p_rssize = 0;
	rpp->p_maxrss = rip->p_maxrss;
	rpp->p_wchan = 0;
	rpp->p_slptime = 0;
	rpp->p_pctcpu = 0;
	rpp->p_cpticks = 0;
	n = PIDHASH(rpp->p_pid);
	p->p_idhash = pidhash[n];
	pidhash[n] = rpp - proc;
	multprog++;

	/*
	 * Increase reference counts on shared objects.
	 */
	for (n = 0; n < NOFILE; n++) {
		fp = u.u_ofile[n];
		if (fp == NULL)
			continue;
		fp->f_count++;
	}
	u.u_cdir->i_count++;
	if (u.u_rdir)
		u.u_rdir->i_count++;

	/*
	 * Partially simulate the environment
	 * of the new process so that when it is actually
	 * created (by copying) it will look right.
	 * This begins the section where we must prevent the parent
	 * from being swapped.
	 */
	rip->p_flag |= SKEEP;
	if (procdup(rpp, isvfork))
		return (1);

	/*
	 * Make child runnable and add to run queue.
	 */
	(void) spl6();
	rpp->p_stat = SRUN;
	setrq(rpp);
	(void) spl0();

	/*
	 * Cause child to take a non-local goto as soon as it runs.
	 * On older systems this was done with SSWAP bit in proc
	 * table; on VAX we use u.u_pcb.pcb_sswap so don't need
	 * to do rpp->p_flag |= SSWAP.  Actually do nothing here.
	 */
	/* rpp->p_flag |= SSWAP; */

	/*
	 * Now can be swapped.
	 */
	rip->p_flag &= ~SKEEP;

	/*
	 * If vfork make chain from parent process to child
	 * (where virtal memory is temporarily).  Wait for
	 * child to finish, steal virtual memory back,
	 * and wakeup child to let it die.
	 */
	if (isvfork) {
		u.u_procp->p_xlink = rpp;
		u.u_procp->p_flag |= SNOVM;
		while (rpp->p_flag & SVFORK)
			sleep((caddr_t)rpp, PZERO - 1);
		if ((rpp->p_flag & SLOAD) == 0)
			panic("newproc vfork");
		uaccess(rpp, Vfmap, &vfutl);
		u.u_procp->p_xlink = 0;
		vpassvm(rpp, u.u_procp, &vfutl, &u, Vfmap);
		u.u_procp->p_flag &= ~SNOVM;
		rpp->p_ndx = rpp - proc;
		rpp->p_flag |= SVFDONE;
		wakeup((caddr_t)rpp);
	}

	/*
	 * 0 return means parent.
	 */
	return (0);
}