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原帖由 huntrsky 于 2006-11-19 14:54 发表
谁人把fork()函数的源码贴出来研究一下啊~~~不胜感激
我把它贴出来,只怕你看不懂。
- /* $OpenBSD: kern_fork.c,v 1.44 2001/10/14 14:39:03 art Exp $ */
- /* $NetBSD: kern_fork.c,v 1.29 1996/02/09 18:59:34 christos Exp $ */
- /*
- * 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
- */
- #include <sys/param.h>
- #include <sys/systm.h>
- #include <sys/map.h>
- #include <sys/filedesc.h>
- #include <sys/kernel.h>
- #include <sys/malloc.h>
- #include <sys/mount.h>
- #include <sys/proc.h>
- #include <sys/resourcevar.h>
- #include <sys/signalvar.h>
- #include <sys/vnode.h>
- #include <sys/file.h>
- #include <sys/acct.h>
- #include <sys/ktrace.h>
- #include <sys/sched.h>
- #include <dev/rndvar.h>
- #include <sys/pool.h>
- #include <sys/syscallargs.h>
- #include <vm/vm.h>
- #include <uvm/uvm_extern.h>
- #include <uvm/uvm_map.h>
- int nprocs = 1; /* process 0 */
- int randompid; /* when set to 1, pid's go random */
- pid_t lastpid;
- struct forkstat forkstat;
- /*ARGSUSED*/
- int
- sys_fork(p, v, retval)
- struct proc *p;
- void *v;
- register_t *retval;
- {
- return (fork1(p, SIGCHLD, FORK_FORK, NULL, 0, retval));
- }
- /*ARGSUSED*/
- int
- sys_vfork(p, v, retval)
- struct proc *p;
- void *v;
- register_t *retval;
- {
- return (fork1(p, SIGCHLD, FORK_VFORK|FORK_PPWAIT, NULL, 0, retval));
- }
- int
- sys_rfork(p, v, retval)
- struct proc *p;
- void *v;
- register_t *retval;
- {
- struct sys_rfork_args /* {
- syscallarg(int) flags;
- } */ *uap = v;
- int rforkflags;
- int flags;
- flags = FORK_RFORK;
- rforkflags = SCARG(uap, flags);
- if ((rforkflags & RFPROC) == 0)
- return (EINVAL);
- switch(rforkflags & (RFFDG|RFCFDG)) {
- case (RFFDG|RFCFDG):
- return EINVAL;
- case RFCFDG:
- flags |= FORK_CLEANFILES;
- break;
- case RFFDG:
- break;
- default:
- flags |= FORK_SHAREFILES;
- break;
- }
- if (rforkflags & RFNOWAIT)
- flags |= FORK_NOZOMBIE;
- if (rforkflags & RFMEM)
- flags |= FORK_VMNOSTACK;
- return (fork1(p, SIGCHLD, flags, NULL, 0, retval));
- }
- int
- fork1(p1, exitsig, flags, stack, stacksize, retval)
- register struct proc *p1;
- int exitsig;
- int flags;
- void *stack;
- size_t stacksize;
- register_t *retval;
- {
- struct proc *p2;
- uid_t uid;
- struct proc *newproc;
- struct vmspace *vm;
- int count;
- static int pidchecked = 0;
- vaddr_t uaddr;
- int s;
- extern void endtsleep __P((void *));
- extern void realitexpire __P((void *));
- #ifndef RFORK_FDSHARE
- /* XXX - Too dangerous right now. */
- if (flags & FORK_SHAREFILES) {
- return (EOPNOTSUPP);
- }
- #endif
- /*
- * Although process entries are dynamically created, we still keep
- * a global limit on the maximum number we will create. We reserve
- * the last 5 processes to root. The variable nprocs is the current
- * number of processes, maxproc is the limit.
- */
- uid = p1->p_cred->p_ruid;
- if ((nprocs >= maxproc - 5 && uid != 0) || nprocs >= maxproc) {
- tablefull("proc");
- return (EAGAIN);
- }
- /*
- * 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);
- return (EAGAIN);
- }
- /*
- * Allocate a pcb and kernel stack for the process
- */
- uaddr = uvm_km_valloc(kernel_map, USPACE);
- if (uaddr == 0)
- return ENOMEM;
- /* Allocate new proc. */
- newproc = pool_get(&proc_pool, PR_WAITOK);
- lastpid++;
- if (randompid)
- lastpid = PID_MAX;
- 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 (lastpid >= PID_MAX) {
- lastpid = arc4random() % PID_MAX;
- pidchecked = 0;
- }
- if (lastpid >= 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 lastpid, so we can avoid checking for a while.
- */
- p2 = LIST_FIRST(&allproc);
- again:
- for (; p2 != 0; p2 = LIST_NEXT(p2, p_list)) {
- while (p2->p_pid == lastpid ||
- p2->p_pgrp->pg_id == lastpid) {
- lastpid++;
- if (lastpid >= pidchecked)
- goto retry;
- }
- if (p2->p_pid > lastpid && pidchecked > p2->p_pid)
- pidchecked = p2->p_pid;
- if (p2->p_pgrp->pg_id > lastpid &&
- pidchecked > p2->p_pgrp->pg_id)
- pidchecked = p2->p_pgrp->pg_id;
- }
- if (!doingzomb) {
- doingzomb = 1;
- p2 = LIST_FIRST(&zombproc);
- goto again;
- }
- }
- nprocs++;
- p2 = newproc;
- p2->p_stat = SIDL; /* protect against others */
- p2->p_pid = lastpid;
- p2->p_exitsig = exitsig;
- LIST_INSERT_HEAD(&allproc, p2, p_list);
- p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */
- 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));
- /*
- * Initialize the timeouts.
- */
- timeout_set(&p2->p_sleep_to, endtsleep, p2);
- timeout_set(&p2->p_realit_to, realitexpire, p2);
- /*
- * 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;
- p2->p_emul = p1->p_emul;
- if (p1->p_flag & P_PROFIL)
- startprofclock(p2);
- p2->p_flag |= (p1->p_flag & (P_SUGID | P_SUGIDEXEC));
- 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 & FORK_CLEANFILES)
- p2->p_fd = fdinit(p1);
- else if (flags & FORK_SHAREFILES)
- p2->p_fd = fdshare(p1);
- else
- 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++;
- }
- if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
- p2->p_flag |= P_CONTROLT;
- if (flags & FORK_PPWAIT)
- p2->p_flag |= P_PPWAIT;
- LIST_INSERT_AFTER(p1, p2, p_pglist);
- p2->p_pptr = p1;
- if (flags & FORK_NOZOMBIE)
- p2->p_flag |= P_NOZOMBIE;
- LIST_INSERT_HEAD(&p1->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
- * XXX should move p_estcpu into the region of struct proc which gets
- * copied.
- */
- scheduler_fork_hook(p1, p2);
- /*
- * Create signal actions for the child process.
- */
- if (flags & FORK_SIGHAND)
- sigactsshare(p1, p2);
- else
- p2->p_sigacts = sigactsinit(p1);
- /*
- * This begins the section where we must prevent the parent
- * from being swapped.
- */
- PHOLD(p1);
- if (flags & FORK_VMNOSTACK) {
- /* share as much address space as possible */
- (void) uvm_map_inherit(&p1->p_vmspace->vm_map,
- VM_MIN_ADDRESS, VM_MAXUSER_ADDRESS - MAXSSIZ,
- VM_INHERIT_SHARE);
- }
- p2->p_addr = (struct user *)uaddr;
- /*
- * Finish creating the child process. It will return through a
- * different path later.
- */
- uvm_fork(p1, p2, ((flags & FORK_SHAREVM) ? TRUE : FALSE), stack,
- stacksize);
- vm = p2->p_vmspace;
- if (flags & FORK_FORK) {
- forkstat.cntfork++;
- forkstat.sizfork += vm->vm_dsize + vm->vm_ssize;
- } else if (flags & FORK_VFORK) {
- forkstat.cntvfork++;
- forkstat.sizvfork += vm->vm_dsize + vm->vm_ssize;
- } else if (flags & FORK_RFORK) {
- forkstat.cntrfork++;
- forkstat.sizrfork += vm->vm_dsize + vm->vm_ssize;
- } else {
- forkstat.cntkthread++;
- forkstat.sizkthread += vm->vm_dsize + vm->vm_ssize;
- }
- /*
- * Make child runnable, set start time, and add to run queue.
- */
- s = splstatclock();
- p2->p_stats->p_start = time;
- p2->p_acflag = AFORK;
- p2->p_stat = SRUN;
- setrunqueue(p2);
- splx(s);
- /*
- * Now can be swapped.
- */
- PRELE(p1);
- uvmexp.forks++;
- if (flags & FORK_PPWAIT)
- uvmexp.forks_ppwait++;
- if (flags & FORK_SHAREVM)
- uvmexp.forks_sharevm++;
- /*
- * tell any interested parties about the new process
- */
- KNOTE(&p1->p_klist, NOTE_FORK | p2->p_pid);
- /*
- * 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).
- */
- if (flags & FORK_PPWAIT)
- 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);
- }
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