kern_fork.c revision 1.55 1 /* $NetBSD: kern_fork.c,v 1.55 1999/04/30 18:42:59 thorpej Exp $ */
2
3 /*
4 * Copyright (c) 1982, 1986, 1989, 1991, 1993
5 * The Regents of the University of California. All rights reserved.
6 * (c) UNIX System Laboratories, Inc.
7 * All or some portions of this file are derived from material licensed
8 * to the University of California by American Telephone and Telegraph
9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
10 * the permission of UNIX System Laboratories, Inc.
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. All advertising materials mentioning features or use of this software
21 * must display the following acknowledgement:
22 * This product includes software developed by the University of
23 * California, Berkeley and its contributors.
24 * 4. Neither the name of the University nor the names of its contributors
25 * may be used to endorse or promote products derived from this software
26 * without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
38 * SUCH DAMAGE.
39 *
40 * @(#)kern_fork.c 8.8 (Berkeley) 2/14/95
41 */
42
43 #include "opt_ktrace.h"
44
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/map.h>
48 #include <sys/filedesc.h>
49 #include <sys/kernel.h>
50 #include <sys/malloc.h>
51 #include <sys/pool.h>
52 #include <sys/mount.h>
53 #include <sys/proc.h>
54 #include <sys/resourcevar.h>
55 #include <sys/vnode.h>
56 #include <sys/file.h>
57 #include <sys/acct.h>
58 #include <sys/ktrace.h>
59 #include <sys/vmmeter.h>
60 #include <sys/sched.h>
61
62 #include <sys/syscallargs.h>
63
64 #include <vm/vm.h>
65 #include <vm/vm_kern.h>
66
67 #include <uvm/uvm_extern.h>
68
69 int nprocs = 1; /* process 0 */
70
71 /*ARGSUSED*/
72 int
73 sys_fork(p, v, retval)
74 struct proc *p;
75 void *v;
76 register_t *retval;
77 {
78
79 return (fork1(p, 0, retval, NULL));
80 }
81
82 /*
83 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM).
84 * Address space is not shared, but parent is blocked until child exit.
85 */
86 /*ARGSUSED*/
87 int
88 sys_vfork(p, v, retval)
89 struct proc *p;
90 void *v;
91 register_t *retval;
92 {
93
94 return (fork1(p, FORK_PPWAIT, retval, NULL));
95 }
96
97 /*
98 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2)
99 * semantics. Address space is shared, and parent is blocked until child exit.
100 */
101 /*ARGSUSED*/
102 int
103 sys___vfork14(p, v, retval)
104 struct proc *p;
105 void *v;
106 register_t *retval;
107 {
108
109 return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, retval, NULL));
110 }
111
112 int
113 fork1(p1, flags, retval, rnewprocp)
114 register struct proc *p1;
115 int flags;
116 register_t *retval;
117 struct proc **rnewprocp;
118 {
119 register struct proc *p2;
120 register uid_t uid;
121 struct proc *newproc;
122 int count, s;
123 vaddr_t uaddr;
124 static int nextpid, pidchecked = 0;
125
126 /*
127 * Although process entries are dynamically created, we still keep
128 * a global limit on the maximum number we will create. Don't allow
129 * a nonprivileged user to use the last process; don't let root
130 * exceed the limit. The variable nprocs is the current number of
131 * processes, maxproc is the limit.
132 */
133 uid = p1->p_cred->p_ruid;
134 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) {
135 tablefull("proc");
136 return (EAGAIN);
137 }
138
139 /*
140 * Increment the count of procs running with this uid. Don't allow
141 * a nonprivileged user to exceed their current limit.
142 */
143 count = chgproccnt(uid, 1);
144 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) {
145 (void)chgproccnt(uid, -1);
146 return (EAGAIN);
147 }
148
149 /*
150 * Allocate virtual address space for the U-area now, while it
151 * is still easy to abort the fork operation if we're out of
152 * kernel virtual address space. The actual U-area pages will
153 * be allocated and wired in vm_fork().
154 */
155 uaddr = uvm_km_valloc(kernel_map, USPACE);
156 if (uaddr == 0) {
157 (void)chgproccnt(uid, -1);
158 return (ENOMEM);
159 }
160
161 /*
162 * We are now committed to the fork. From here on, we may
163 * block on resources, but resource allocation may NOT fail.
164 */
165
166 /* Allocate new proc. */
167 newproc = pool_get(&proc_pool, PR_WAITOK);
168
169 /*
170 * BEGIN PID ALLOCATION. (Lock PID allocation variables eventually).
171 */
172
173 /*
174 * Find an unused process ID. We remember a range of unused IDs
175 * ready to use (from nextpid+1 through pidchecked-1).
176 */
177 nextpid++;
178 retry:
179 /*
180 * If the process ID prototype has wrapped around,
181 * restart somewhat above 0, as the low-numbered procs
182 * tend to include daemons that don't exit.
183 */
184 if (nextpid >= PID_MAX) {
185 nextpid = 100;
186 pidchecked = 0;
187 }
188 if (nextpid >= pidchecked) {
189 const struct proclist_desc *pd;
190
191 pidchecked = PID_MAX;
192 /*
193 * Scan the process lists to check whether this pid
194 * is in use. Remember the lowest pid that's greater
195 * than nextpid, so we can avoid checking for a while.
196 */
197 pd = proclists;
198 again:
199 for (p2 = LIST_FIRST(pd->pd_list); p2 != 0;
200 p2 = LIST_NEXT(p2, p_list)) {
201 while (p2->p_pid == nextpid ||
202 p2->p_pgrp->pg_id == nextpid ||
203 p2->p_session->s_sid == nextpid) {
204 nextpid++;
205 if (nextpid >= pidchecked)
206 goto retry;
207 }
208 if (p2->p_pid > nextpid && pidchecked > p2->p_pid)
209 pidchecked = p2->p_pid;
210
211 if (p2->p_pgrp->pg_id > nextpid &&
212 pidchecked > p2->p_pgrp->pg_id)
213 pidchecked = p2->p_pgrp->pg_id;
214
215 if (p2->p_session->s_sid > nextpid &&
216 pidchecked > p2->p_session->s_sid)
217 pidchecked = p2->p_session->s_sid;
218 }
219
220 /*
221 * If there's another list, scan it. If we have checked
222 * them all, we've found one!
223 */
224 pd++;
225 if (pd->pd_list != NULL)
226 goto again;
227 }
228
229 nprocs++;
230 p2 = newproc;
231
232 /* Record the pid we've allocated. */
233 p2->p_pid = nextpid;
234
235 /*
236 * Put the proc on allproc before unlocking PID allocation
237 * so that waiters won't grab it as soon as we unlock.
238 */
239 LIST_INSERT_HEAD(&allproc, p2, p_list);
240
241 /*
242 * END PID ALLOCATION. (Unlock PID allocation variables).
243 */
244
245 p2->p_stat = SIDL; /* protect against others */
246 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */
247 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash);
248
249 /*
250 * Make a proc table entry for the new process.
251 * Start by zeroing the section of proc that is zero-initialized,
252 * then copy the section that is copied directly from the parent.
253 */
254 memset(&p2->p_startzero, 0,
255 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero));
256 memcpy(&p2->p_startcopy, &p1->p_startcopy,
257 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy));
258
259 /*
260 * Duplicate sub-structures as needed.
261 * Increase reference counts on shared objects.
262 * The p_stats and p_sigacts substructs are set in vm_fork.
263 */
264 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID);
265 p2->p_emul = p1->p_emul;
266 if (p1->p_flag & P_PROFIL)
267 startprofclock(p2);
268 p2->p_cred = pool_get(&pcred_pool, PR_WAITOK);
269 memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred));
270 p2->p_cred->p_refcnt = 1;
271 crhold(p1->p_ucred);
272
273 /* bump references to the text vnode (for procfs) */
274 p2->p_textvp = p1->p_textvp;
275 if (p2->p_textvp)
276 VREF(p2->p_textvp);
277
278 p2->p_fd = fdcopy(p1);
279 p2->p_cwdi = cwdinit(p1);
280
281 /*
282 * If p_limit is still copy-on-write, bump refcnt,
283 * otherwise get a copy that won't be modified.
284 * (If PL_SHAREMOD is clear, the structure is shared
285 * copy-on-write.)
286 */
287 if (p1->p_limit->p_lflags & PL_SHAREMOD)
288 p2->p_limit = limcopy(p1->p_limit);
289 else {
290 p2->p_limit = p1->p_limit;
291 p2->p_limit->p_refcnt++;
292 }
293
294 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
295 p2->p_flag |= P_CONTROLT;
296 if (flags & FORK_PPWAIT)
297 p2->p_flag |= P_PPWAIT;
298 LIST_INSERT_AFTER(p1, p2, p_pglist);
299 p2->p_pptr = p1;
300 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling);
301 LIST_INIT(&p2->p_children);
302
303 #ifdef KTRACE
304 /*
305 * Copy traceflag and tracefile if enabled.
306 * If not inherited, these were zeroed above.
307 */
308 if (p1->p_traceflag&KTRFAC_INHERIT) {
309 p2->p_traceflag = p1->p_traceflag;
310 if ((p2->p_tracep = p1->p_tracep) != NULL)
311 ktradref(p2);
312 }
313 #endif
314 scheduler_fork_hook(p1, p2);
315
316 /*
317 * This begins the section where we must prevent the parent
318 * from being swapped.
319 */
320 PHOLD(p1);
321
322 /*
323 * Finish creating the child process. It will return through a
324 * different path later.
325 */
326 p2->p_addr = (struct user *)uaddr;
327 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE);
328
329 /*
330 * Make child runnable, set start time, and add to run queue.
331 */
332 s = splstatclock();
333 p2->p_stats->p_start = time;
334 p2->p_acflag = AFORK;
335 p2->p_stat = SRUN;
336 setrunqueue(p2);
337 splx(s);
338
339 /*
340 * Now can be swapped.
341 */
342 PRELE(p1);
343
344 /*
345 * Update stats now that we know the fork was successful.
346 */
347 uvmexp.forks++;
348 if (flags & FORK_PPWAIT)
349 uvmexp.forks_ppwait++;
350 if (flags & FORK_SHAREVM)
351 uvmexp.forks_sharevm++;
352
353 /*
354 * Pass a pointer to the new process to the caller.
355 */
356 if (rnewprocp != NULL)
357 *rnewprocp = p2;
358
359 /*
360 * Preserve synchronization semantics of vfork. If waiting for
361 * child to exec or exit, set P_PPWAIT on child, and sleep on our
362 * proc (in case of exit).
363 */
364 if (flags & FORK_PPWAIT)
365 while (p2->p_flag & P_PPWAIT)
366 tsleep(p1, PWAIT, "ppwait", 0);
367
368 /*
369 * Return child pid to parent process,
370 * marking us as parent via retval[1].
371 */
372 if (retval != NULL) {
373 retval[0] = p2->p_pid;
374 retval[1] = 0;
375 }
376 return (0);
377 }
378