4.4BSD/usr/src/sys/kern/kern_fork.c
/*
* Copyright (c) 1982, 1986, 1989, 1991, 1993
* The 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.
*
* @(#)kern_fork.c 8.1 (Berkeley) 6/10/93
*/
#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/proc.h>
#include <sys/resourcevar.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/acct.h>
#include <sys/ktrace.h>
struct fork_args {
int dummy;
};
/* ARGSUSED */
fork(p, uap, retval)
struct proc *p;
struct fork_args *uap;
int retval[];
{
return (fork1(p, 0, retval));
}
/* ARGSUSED */
vfork(p, uap, retval)
struct proc *p;
struct fork_args *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 uid_t uid;
struct proc *newproc;
struct proc **hash;
int count;
static int nextpid, pidchecked = 0;
/*
* 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 bring the system within one of the global
* limit; 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 || uid == 0 && nprocs >= maxproc + 1) {
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 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 = (struct proc *)allproc;
again:
for (; p2 != NULL; p2 = p2->p_nxt) {
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;
goto again;
}
}
/*
* Link onto allproc (this should probably be delayed).
* Heavy use of volatile here to prevent the compiler from
* rearranging code. Yes, it *is* terribly ugly, but at least
* it works.
*/
nprocs++;
p2 = newproc;
#define Vp2 ((volatile struct proc *)p2)
Vp2->p_stat = SIDL; /* protect against others */
Vp2->p_pid = nextpid;
/*
* This is really:
* p2->p_nxt = allproc;
* allproc->p_prev = &p2->p_nxt;
* p2->p_prev = &allproc;
* allproc = p2;
* The assignment via allproc is legal since it is never NULL.
*/
*(volatile struct proc **)&Vp2->p_nxt = allproc;
*(volatile struct proc ***)&allproc->p_prev =
(volatile struct proc **)&Vp2->p_nxt;
*(volatile struct proc ***)&Vp2->p_prev = &allproc;
allproc = Vp2;
#undef Vp2
p2->p_link = NULL; /* shouldn't be necessary */
p2->p_rlink = NULL; /* shouldn't be necessary */
/* Insert on the hash chain. */
hash = &pidhash[PIDHASH(p2->p_pid)];
p2->p_hash = *hash;
*hash = p2;
/*
* 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.
*/
p2->p_flag = SLOAD;
if (p1->p_flag & SPROFIL)
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);
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 & SCTTY)
p2->p_flag |= SCTTY;
if (isvfork)
p2->p_flag |= SPPWAIT;
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
/*
* 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);
}