FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_fork.c

     /*
      * Copyright (c) 1982, 1986, 1989, 1991, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
      * the permission of UNIX System Laboratories, Inc.
      *
     * 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.
     *
     *      @(#)kern_fork.c 8.6 (Berkeley) 4/8/94
     * $FreeBSD: src/sys/kern/kern_fork.c,v 1.27.2.3 1999/09/05 08:14:54 peter Exp $
     */
    
    #include "opt_ktrace.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/sysproto.h>
    #include <sys/filedesc.h>
    #include <sys/kernel.h>
    #include <sys/malloc.h>
    #include <sys/proc.h>
    #include <sys/resourcevar.h>
    #include <sys/vnode.h>
    #include <sys/acct.h>
    #include <sys/ktrace.h>
    #include <sys/unistd.h> 
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/lock.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_inherit.h>
    
    static int fork1 __P((struct proc *p, int flags, int *retval));
    
    /*
     * These are the stuctures used to create a callout list for things to do
     * when forking a process
     */
    typedef struct fork_list_element {
            struct fork_list_element *next;
            forklist_fn function;
    } *fle_p;
    
    static fle_p    fork_list;
    
    #ifndef _SYS_SYSPROTO_H_
    struct fork_args {
            int     dummy;
    };
    #endif
    
    /* ARGSUSED */
    int
    fork(p, uap, retval)
            struct proc *p;
            struct fork_args *uap;
            int retval[];
    {
            return (fork1(p, (RFFDG|RFPROC), retval));
    }
    
    /* ARGSUSED */
    int
    vfork(p, uap, retval)
            struct proc *p;
            struct vfork_args *uap;
            int retval[];
   {
           return (fork1(p, (RFFDG|RFPROC|RFPPWAIT), retval));
   }
   
   /* ARGSUSED */
   int
   rfork(p, uap, retval)
           struct proc *p;
           struct rfork_args *uap;
           int retval[];
   {
           return (fork1(p, uap->flags, retval));
   }
   
   
   int     nprocs = 1;             /* process 0 */
   static int nextpid = 0;
   
   static int
   fork1(p1, flags, retval)
           register struct proc *p1;
           int flags;
           int retval[];
   {
           register struct proc *p2, *pptr;
           register uid_t uid;
           struct proc *newproc;
           int count;
           static int pidchecked = 0;
           fle_p ep ;
   
           ep = fork_list;
           if ((flags & RFPROC) == 0)
                   return (EINVAL);
           if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
                   return (EINVAL);
   
           /*
            * Although process entries are dynamically created, we still keep
            * a global limit on the maximum number we will create.  Don't allow
            * a nonprivileged user to use the last process; don't let root
            * exceed the limit. The variable nprocs is the current number of
            * processes, maxproc is the limit.
            */
           uid = p1->p_cred->p_ruid;
           if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) {
                   tablefull("proc");
                   return (EAGAIN);
           }
           /*
            * Increment the nprocs resource before blocking can occur.  There
            * are hard-limits as to the number of processes that can run.
            */
           nprocs++;
   
           /*
            * Increment the count of procs running with this uid. Don't allow
            * a nonprivileged user to exceed their current limit.
            */
           count = chgproccnt(uid, 1);
           if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) {
                   (void)chgproccnt(uid, -1);
                   /*
                    * Back out the process count
                    */
                   nprocs--;
                   return (EAGAIN);
           }
   
           /* Allocate new proc. */
           MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK);
   
           /*
            * 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.lh_first;
   again:
                   for (; p2 != 0; p2 = p2->p_list.le_next) {
                           while (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.lh_first;
                           goto again;
                   }
           }
   
           p2 = newproc;
           p2->p_stat = SIDL;                      /* protect against others */
           p2->p_pid = nextpid;
           LIST_INSERT_HEAD(&allproc, p2, p_list);
           LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
   
           /*
            * 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));
   
           /*
            * XXX: this should be done as part of the startzero above
            */
           p2->p_vmspace = 0;              /* XXX */
   
           /*
            * Duplicate sub-structures as needed.
            * Increase reference counts on shared objects.
            * The p_stats and p_sigacts substructs are set in vm_fork.
            */
           p2->p_flag = P_INMEM;
           if (p1->p_flag & P_PROFIL)
                   startprofclock(p2);
           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);
   
           /* bump references to the text vnode (for procfs) */
           p2->p_textvp = p1->p_textvp;
           if (p2->p_textvp)
                   VREF(p2->p_textvp);
   
           if (flags & RFCFDG)
                   p2->p_fd = fdinit(p1);
           else if (flags & RFFDG)
                   p2->p_fd = fdcopy(p1);
           else
                   p2->p_fd = fdshare(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++;
           }
   
           /*
            * Preserve some flags in subprocess.
            */
           p2->p_flag |= p1->p_flag & P_SUGID;
           if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
                   p2->p_flag |= P_CONTROLT;
           if (flags & RFPPWAIT)
                   p2->p_flag |= P_PPWAIT;
           LIST_INSERT_AFTER(p1, p2, p_pglist);
   
           /*
            * Attach the new process to its parent.
            *
            * If RFNOWAIT is set, the newly created process becomes a child
            * of init.  This effectively disassociates the child from the
            * parent.
            */
           if (flags & RFNOWAIT)
                   pptr = initproc;
           else
                   pptr = p1;
           p2->p_pptr = pptr;
           LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
           LIST_INIT(&p2->p_children);
   
   #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
   
           /*
            * set priority of child to be that of parent
            */
           p2->p_estcpu = p1->p_estcpu;
   
           /*
            * This begins the section where we must prevent the parent
            * from being swapped.
            */
           p1->p_flag |= P_NOSWAP;
   
           /*
            * share as much address space as possible
            * XXX this should probably go in vm_fork()
            */
           if (flags & RFMEM)
                   (void) vm_map_inherit(&p1->p_vmspace->vm_map,
                       VM_MIN_ADDRESS, VM_MAXUSER_ADDRESS - MAXSSIZ,
                       VM_INHERIT_SHARE);
   
           /*
            * 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)) {
                   /*
                    * Child process.  Set start time and get to work.
                    */
                   microtime(&runtime);
                   (void) spl0();
                   p2->p_stats->p_start = runtime;
                   p2->p_acflag = AFORK;
                   return (0);
           }
   
           /*
            * Both processes are set up, now check if any LKMs want
            * to adjust anything.
            *   What if they have an error? XXX
            */
           while (ep) {
                   (*ep->function)(p1, p2, flags);
                   ep = ep->next;
           }
   
           /*
            * Make child runnable and add to run queue.
            */
           (void) splhigh();
           p2->p_stat = SRUN;
           setrunqueue(p2);
           (void) spl0();
   
           /*
            * Now can be swapped.
            */
           p1->p_flag &= ~P_NOSWAP;
   
           /*
            * Preserve synchronization semantics of vfork.  If waiting for
            * child to exec or exit, set P_PPWAIT on child, and sleep on our
            * proc (in case of exit).
            */
           while (p2->p_flag & P_PPWAIT)
                   tsleep(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);
   }
   
   /*
    * The next two functionms are general routines to handle adding/deleting
    * items on the fork callout list.
    *
    * at_fork():
    * Take the arguments given and put them onto the fork callout list,
    * However first make sure that it's not already there.
    * Returns 0 on success or a standard error number.
    */
   int
   at_fork(forklist_fn function)
   {
           fle_p ep;
   
           /* let the programmer know if he's been stupid */
           if (rm_at_fork(function)) 
                   printf("fork callout entry already present\n");
           ep = malloc(sizeof(*ep), M_TEMP, M_NOWAIT);
           if (ep == NULL)
                   return (ENOMEM);
           ep->next = fork_list;
           ep->function = function;
           fork_list = ep;
           return (0);
   }
   
   /*
    * Scan the exit callout list for the given items and remove them.
    * Returns the number of items removed.
    * Theoretically this value can only be 0 or 1.
    */
   int
   rm_at_fork(forklist_fn function)
   {
           fle_p *epp, ep;
           int count;
   
           count= 0;
           epp = &fork_list;
           ep = *epp;
           while (ep) {
                   if (ep->function == function) {
                           *epp = ep->next;
                           free(ep, M_TEMP);
                           count++;
                   } else {
                           epp = &ep->next;
                   }
                   ep = *epp;
           }
           return (count);
   }
   
   

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