sys/kern/kern_fork.c

/*
 * Copyright (c) 1982, 1986, 1989, 1991 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from: @(#)kern_fork.c   7.29 (Berkeley) 5/15/91
 *      $Id$
 */

#include "param.h"
#include "systm.h"
#include "filedesc.h"
#include "kernel.h"
#include "malloc.h"
#include "proc.h"
#include "resourcevar.h"
#include "vnode.h"
#include "file.h"
#include "acct.h"
#include "ktrace.h"
#include "vm/vm.h"

/* ARGSUSED */
fork(p, uap, retval)
        struct proc *p;
        void *uap;
        int retval[];
{

        return (fork1(p, 0, retval));
}

/* ARGSUSED */
vfork(p, uap, retval)
        struct proc *p;
        void *uap;
        int retval[];
{

        return (fork1(p, 1, retval));
}

int     nprocs = 1;             /* process 0 */

fork1(p1, isvfork, retval)
        register struct proc *p1;
        int isvfork, retval[];
{
        register struct proc *p2;
        register int count, uid;
        static int nextpid, pidchecked = 0;

        count = 0;
        if ((uid = p1->p_ucred->cr_uid) != 0) {
                for (p2 = allproc; p2; p2 = p2->p_nxt)
                        if (p2->p_ucred->cr_uid == uid)
                                count++;
                for (p2 = zombproc; p2; p2 = p2->p_nxt)
                        if (p2->p_ucred->cr_uid == uid)
                                count++;
        }
        /*
         * Although process entries are dynamically entries,
         * we still keep a global limit on the maximum number
         * we will create.  Don't allow a nonprivileged user
         * to exceed its current limit or to bring us within one
         * of the global limit; don't let root exceed the limit.
         * nprocs is the current number of processes,
         * maxproc is the limit.
         */
        if (nprocs >= maxproc || uid == 0 && nprocs >= maxproc + 1) {
                tablefull("proc");
                return (EAGAIN);
        }
        if (count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur)
                return (EAGAIN);

        /*
         * Find an unused process ID.
         * We remember a range of unused IDs ready to use
         * (from nextpid+1 through pidchecked-1).
         */
        nextpid++;
retry:
        /*
         * If the process ID prototype has wrapped around,
         * restart somewhat above 0, as the low-numbered procs
         * tend to include daemons that don't exit.
         */
        if (nextpid >= PID_MAX) {
                nextpid = 100;
                pidchecked = 0;
        }
        if (nextpid >= pidchecked) {
                int doingzomb = 0;

                pidchecked = PID_MAX;
                /*
                 * Scan the active and zombie procs to check whether this pid
                 * is in use.  Remember the lowest pid that's greater
                 * than nextpid, so we can avoid checking for a while.
                 */
                p2 = allproc;
again:
                for (; p2 != NULL; p2 = p2->p_nxt) {
                        if (p2->p_pid == nextpid ||
                            p2->p_pgrp->pg_id == nextpid) {
                                nextpid++;
                                if (nextpid >= pidchecked)
                                        goto retry;
                        }
                        if (p2->p_pid > nextpid && pidchecked > p2->p_pid)
                                pidchecked = p2->p_pid;
                        if (p2->p_pgrp->pg_id > nextpid &&
                            pidchecked > p2->p_pgrp->pg_id)
                                pidchecked = p2->p_pgrp->pg_id;
                }
                if (!doingzomb) {
                        doingzomb = 1;
                        p2 = zombproc;
                        goto again;
                }
        }


        /*
         * Allocate new proc.
         * Link onto allproc (this should probably be delayed).
         */
        MALLOC(p2, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK);
        nprocs++;
        p2->p_nxt = allproc;
        p2->p_nxt->p_prev = &p2->p_nxt;         /* allproc is never NULL */
        p2->p_prev = &allproc;
        allproc = p2;
        p2->p_link = NULL;                      /* shouldn't be necessary */
        p2->p_rlink = NULL;                     /* shouldn't be necessary */

        /*
         * Make a proc table entry for the new process.
         * Start by zeroing the section of proc that is zero-initialized,
         * then copy the section that is copied directly from the parent.
         */
        bzero(&p2->p_startzero,
            (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
        bcopy(&p1->p_startcopy, &p2->p_startcopy,
            (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
        p2->p_spare[0] = 0;     /* XXX - should be in zero range */
        p2->p_spare[1] = 0;     /* XXX - should be in zero range */
        p2->p_spare[2] = 0;     /* XXX - should be in zero range */
        p2->p_spare[3] = 0;     /* XXX - should be in zero range */

        /*
         * Duplicate sub-structures as needed.
         * Increase reference counts on shared objects.
         * The p_stats and p_sigacts substructs are set in vm_fork.
         */
        MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred),
            M_SUBPROC, M_WAITOK);
        bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred));
        p2->p_cred->p_refcnt = 1;
        crhold(p1->p_ucred);

        p2->p_fd = fdcopy(p1);
        /*
         * If p_limit is still copy-on-write, bump refcnt,
         * otherwise get a copy that won't be modified.
         * (If PL_SHAREMOD is clear, the structure is shared
         * copy-on-write.)
         */
        if (p1->p_limit->p_lflags & PL_SHAREMOD)
                p2->p_limit = limcopy(p1->p_limit);
        else {
                p2->p_limit = p1->p_limit;
                p2->p_limit->p_refcnt++;
        }

        p2->p_flag = SLOAD | (p1->p_flag & SHPUX);
        if (p1->p_session->s_ttyvp != NULL && p1->p_flag & SCTTY)
                p2->p_flag |= SCTTY;
        if (isvfork)
                p2->p_flag |= SPPWAIT;
        p2->p_stat = SIDL;
        p2->p_pid = nextpid;
        {
        struct proc **hash = &pidhash[PIDHASH(p2->p_pid)];

        p2->p_hash = *hash;
        *hash = p2;
        }
        p2->p_pgrpnxt = p1->p_pgrpnxt;
        p1->p_pgrpnxt = p2;
        p2->p_pptr = p1;
        p2->p_osptr = p1->p_cptr;
        if (p1->p_cptr)
                p1->p_cptr->p_ysptr = p2;
        p1->p_cptr = p2;
#ifdef KTRACE
        /*
         * Copy traceflag and tracefile if enabled.
         * If not inherited, these were zeroed above.
         */
        if (p1->p_traceflag&KTRFAC_INHERIT) {
                p2->p_traceflag = p1->p_traceflag;
                if ((p2->p_tracep = p1->p_tracep) != NULL)
                        VREF(p2->p_tracep);
        }
#endif

#if defined(tahoe)
        p2->p_vmspace->p_ckey = p1->p_vmspace->p_ckey; /* XXX move this */
#endif

        /*
         * This begins the section where we must prevent the parent
         * from being swapped.
         */
        p1->p_flag |= SKEEP;
        /*
         * Set return values for child before vm_fork,
         * so they can be copied to child stack.
         * We return parent pid, and mark as child in retval[1].
         * NOTE: the kernel stack may be at a different location in the child
         * process, and thus addresses of automatic variables (including retval)
         * may be invalid after vm_fork returns in the child process.
         */
        retval[0] = p1->p_pid;
        retval[1] = 1;
        if (vm_fork(p1, p2, isvfork)) {
                /*
                 * Child process.  Set start time and get to work.
                 */
                (void) splclock();
                p2->p_stats->p_start = time;
                (void) spl0();
                p2->p_acflag = AFORK;
                return (0);
        }

        /*
         * Make child runnable and add to run queue.
         */
        (void) splhigh();
        p2->p_stat = SRUN;
        setrq(p2);
        (void) spl0();

        /*
         * Now can be swapped.
         */
        p1->p_flag &= ~SKEEP;

        /*
         * Preserve synchronization semantics of vfork.
         * If waiting for child to exec or exit, set SPPWAIT
         * on child, and sleep on our proc (in case of exit).
         */
        if (isvfork)
                while (p2->p_flag & SPPWAIT)
                        tsleep((caddr_t)p1, PWAIT, "ppwait", 0);

        /*
         * Return child pid to parent process,
         * marking us as parent via retval[1].
         */
        retval[0] = p2->p_pid;
        retval[1] = 0;
        return (0);
}