NetBSD/sys/kern/kern_fork.c

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/* $NetBSD: kern_fork.c,v 1.31 1997/02/18 01:30:37 mrg Exp $ */
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/*
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* Copyright (c) 1982, 1986, 1989, 1991, 1993
* The Regents of the University of California. All rights reserved.
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* (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
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*/
#include <sys/param.h>
#include <sys/systm.h>
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#include <sys/map.h>
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#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
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#include <sys/mount.h>
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#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/acct.h>
#include <sys/ktrace.h>
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#include <sys/syscallargs.h>
#include <vm/vm.h>
int nprocs = 1; /* process 0 */
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int fork1 __P((struct proc *, int, register_t *));
/*ARGSUSED*/
int
sys_fork(p, v, retval)
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struct proc *p;
void *v;
register_t *retval;
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{
return (fork1(p, 0, retval));
}
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/*ARGSUSED*/
int
sys_vfork(p, v, retval)
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struct proc *p;
void *v;
register_t *retval;
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{
return (fork1(p, 1, retval));
}
int
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fork1(p1, isvfork, retval)
register struct proc *p1;
int isvfork;
register_t *retval;
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{
register struct proc *p2;
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register uid_t uid;
struct proc *newproc;
int count;
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static int nextpid, pidchecked = 0;
/*
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* Although process entries are dynamically created, we still keep
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* 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
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* exceed the limit. The variable nprocs is the current number of
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* processes, maxproc is the limit.
*/
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uid = p1->p_cred->p_ruid;
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if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) {
tablefull("proc");
return (EAGAIN);
}
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/*
* 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);
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return (EAGAIN);
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}
/* Allocate new proc. */
MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK);
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/*
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* Find an unused process ID. We remember a range of unused IDs
* ready to use (from nextpid+1 through pidchecked-1).
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*/
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;
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again:
for (; p2 != 0; p2 = p2->p_list.le_next) {
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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;
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goto again;
}
}
nprocs++;
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p2 = newproc;
p2->p_stat = SIDL; /* protect against others */
p2->p_pid = nextpid;
LIST_INSERT_HEAD(&allproc, p2, p_list);
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p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */
LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
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/*
* 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));
/*
* Duplicate sub-structures as needed.
* Increase reference counts on shared objects.
* The p_stats and p_sigacts substructs are set in vm_fork.
*/
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p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID);
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p2->p_emul = p1->p_emul;
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if (p1->p_flag & P_PROFIL)
startprofclock(p2);
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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);
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/* bump references to the text vnode (for procfs) */
p2->p_textvp = p1->p_textvp;
if (p2->p_textvp)
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VREF(p2->p_textvp);
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 (isvfork)
p2->p_flag |= P_PPWAIT;
LIST_INSERT_AFTER(p1, p2, p_pglist);
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p2->p_pptr = p1;
LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling);
LIST_INIT(&p2->p_children);
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#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
/*
* This begins the section where we must prevent the parent
* from being swapped.
*/
PHOLD(p1);
#ifdef __FORK_BRAINDAMAGE
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/*
* Set return values for child before vm_fork,
* so they can be copied to child stack.
* We return 0, rather than the traditional behaviour of modifying the
* return value in the system call stub.
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* 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] = 0;
retval[1] = 1;
if (vm_fork(p1, p2))
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return (0);
#else
/*
* Finish creating the child process. It will return through a
* different path later.
*/
vm_fork(p1, p2);
#endif
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/*
* Make child runnable, set start time, and add to run queue.
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*/
(void) splstatclock();
p2->p_stats->p_start = time;
p2->p_acflag = AFORK;
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p2->p_stat = SRUN;
setrunqueue(p2);
(void) spl0();
/*
* Now can be swapped.
*/
PRELE(p1);
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/*
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* 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).
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*/
if (isvfork)
while (p2->p_flag & P_PPWAIT)
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tsleep(p1, PWAIT, "ppwait", 0);
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/*
* Return child pid to parent process,
* marking us as parent via retval[1].
*/
retval[0] = p2->p_pid;
retval[1] = 0;
return (0);
}