1 /* $NetBSD: kern_fork.c,v 1.61 1999/07/22 21:08:31 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 #include <sys/signalvar.h> 62 63 #include <sys/syscallargs.h> 64 65 #include <vm/vm.h> 66 #include <vm/vm_kern.h> 67 68 #include <uvm/uvm_extern.h> 69 70 int nprocs = 1; /* process 0 */ 71 72 /*ARGSUSED*/ 73 int 74 sys_fork(p, v, retval) 75 struct proc *p; 76 void *v; 77 register_t *retval; 78 { 79 80 return (fork1(p, 0, SIGCHLD, NULL, 0, retval, NULL)); 81 } 82 83 /* 84 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM). 85 * Address space is not shared, but parent is blocked until child exit. 86 */ 87 /*ARGSUSED*/ 88 int 89 sys_vfork(p, v, retval) 90 struct proc *p; 91 void *v; 92 register_t *retval; 93 { 94 95 return (fork1(p, FORK_PPWAIT, SIGCHLD, NULL, 0, retval, NULL)); 96 } 97 98 /* 99 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2) 100 * semantics. Address space is shared, and parent is blocked until child exit. 101 */ 102 /*ARGSUSED*/ 103 int 104 sys___vfork14(p, v, retval) 105 struct proc *p; 106 void *v; 107 register_t *retval; 108 { 109 110 return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, SIGCHLD, NULL, 0, 111 retval, NULL)); 112 } 113 114 int 115 fork1(p1, flags, exitsig, stack, stacksize, retval, rnewprocp) 116 register struct proc *p1; 117 int flags; 118 int exitsig; 119 void *stack; 120 size_t stacksize; 121 register_t *retval; 122 struct proc **rnewprocp; 123 { 124 register struct proc *p2; 125 register uid_t uid; 126 struct proc *newproc; 127 int count, s; 128 vaddr_t uaddr; 129 static int nextpid, pidchecked = 0; 130 131 /* 132 * Although process entries are dynamically created, we still keep 133 * a global limit on the maximum number we will create. Don't allow 134 * a nonprivileged user to use the last process; don't let root 135 * exceed the limit. The variable nprocs is the current number of 136 * processes, maxproc is the limit. 137 */ 138 uid = p1->p_cred->p_ruid; 139 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 140 tablefull("proc"); 141 return (EAGAIN); 142 } 143 144 /* 145 * Increment the count of procs running with this uid. Don't allow 146 * a nonprivileged user to exceed their current limit. 147 */ 148 count = chgproccnt(uid, 1); 149 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 150 (void)chgproccnt(uid, -1); 151 return (EAGAIN); 152 } 153 154 /* 155 * Allocate virtual address space for the U-area now, while it 156 * is still easy to abort the fork operation if we're out of 157 * kernel virtual address space. The actual U-area pages will 158 * be allocated and wired in vm_fork(). 159 */ 160 uaddr = uvm_km_valloc(kernel_map, USPACE); 161 if (uaddr == 0) { 162 (void)chgproccnt(uid, -1); 163 return (ENOMEM); 164 } 165 166 /* 167 * We are now committed to the fork. From here on, we may 168 * block on resources, but resource allocation may NOT fail. 169 */ 170 171 /* Allocate new proc. */ 172 newproc = pool_get(&proc_pool, PR_WAITOK); 173 174 /* 175 * BEGIN PID ALLOCATION. 176 */ 177 s = proclist_lock_write(); 178 179 /* 180 * Find an unused process ID. We remember a range of unused IDs 181 * ready to use (from nextpid+1 through pidchecked-1). 182 */ 183 nextpid++; 184 retry: 185 /* 186 * If the process ID prototype has wrapped around, 187 * restart somewhat above 0, as the low-numbered procs 188 * tend to include daemons that don't exit. 189 */ 190 if (nextpid >= PID_MAX) { 191 nextpid = 100; 192 pidchecked = 0; 193 } 194 if (nextpid >= pidchecked) { 195 const struct proclist_desc *pd; 196 197 pidchecked = PID_MAX; 198 /* 199 * Scan the process lists to check whether this pid 200 * is in use. Remember the lowest pid that's greater 201 * than nextpid, so we can avoid checking for a while. 202 */ 203 pd = proclists; 204 again: 205 for (p2 = LIST_FIRST(pd->pd_list); p2 != 0; 206 p2 = LIST_NEXT(p2, p_list)) { 207 while (p2->p_pid == nextpid || 208 p2->p_pgrp->pg_id == nextpid || 209 p2->p_session->s_sid == nextpid) { 210 nextpid++; 211 if (nextpid >= pidchecked) 212 goto retry; 213 } 214 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 215 pidchecked = p2->p_pid; 216 217 if (p2->p_pgrp->pg_id > nextpid && 218 pidchecked > p2->p_pgrp->pg_id) 219 pidchecked = p2->p_pgrp->pg_id; 220 221 if (p2->p_session->s_sid > nextpid && 222 pidchecked > p2->p_session->s_sid) 223 pidchecked = p2->p_session->s_sid; 224 } 225 226 /* 227 * If there's another list, scan it. If we have checked 228 * them all, we've found one! 229 */ 230 pd++; 231 if (pd->pd_list != NULL) 232 goto again; 233 } 234 235 nprocs++; 236 p2 = newproc; 237 238 /* Record the pid we've allocated. */ 239 p2->p_pid = nextpid; 240 241 /* Record the signal to be delivered to the parent on exit. */ 242 p2->p_exitsig = exitsig; 243 244 /* 245 * Put the proc on allproc before unlocking PID allocation 246 * so that waiters won't grab it as soon as we unlock. 247 */ 248 249 p2->p_stat = SIDL; /* protect against others */ 250 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 251 252 LIST_INSERT_HEAD(&allproc, p2, p_list); 253 254 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 255 256 /* 257 * END PID ALLOCATION. 258 */ 259 proclist_unlock_write(s); 260 261 /* 262 * Make a proc table entry for the new process. 263 * Start by zeroing the section of proc that is zero-initialized, 264 * then copy the section that is copied directly from the parent. 265 */ 266 memset(&p2->p_startzero, 0, 267 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 268 memcpy(&p2->p_startcopy, &p1->p_startcopy, 269 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 270 271 /* 272 * Duplicate sub-structures as needed. 273 * Increase reference counts on shared objects. 274 * The p_stats and p_sigacts substructs are set in vm_fork. 275 */ 276 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID); 277 p2->p_emul = p1->p_emul; 278 if (p1->p_flag & P_PROFIL) 279 startprofclock(p2); 280 p2->p_cred = pool_get(&pcred_pool, PR_WAITOK); 281 memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred)); 282 p2->p_cred->p_refcnt = 1; 283 crhold(p1->p_ucred); 284 285 /* bump references to the text vnode (for procfs) */ 286 p2->p_textvp = p1->p_textvp; 287 if (p2->p_textvp) 288 VREF(p2->p_textvp); 289 290 if (flags & FORK_SHAREFILES) 291 fdshare(p1, p2); 292 else 293 p2->p_fd = fdcopy(p1); 294 295 if (flags & FORK_SHARECWD) 296 cwdshare(p1, p2); 297 else 298 p2->p_cwdi = cwdinit(p1); 299 300 /* 301 * If p_limit is still copy-on-write, bump refcnt, 302 * otherwise get a copy that won't be modified. 303 * (If PL_SHAREMOD is clear, the structure is shared 304 * copy-on-write.) 305 */ 306 if (p1->p_limit->p_lflags & PL_SHAREMOD) 307 p2->p_limit = limcopy(p1->p_limit); 308 else { 309 p2->p_limit = p1->p_limit; 310 p2->p_limit->p_refcnt++; 311 } 312 313 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 314 p2->p_flag |= P_CONTROLT; 315 if (flags & FORK_PPWAIT) 316 p2->p_flag |= P_PPWAIT; 317 LIST_INSERT_AFTER(p1, p2, p_pglist); 318 p2->p_pptr = p1; 319 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 320 LIST_INIT(&p2->p_children); 321 322 #ifdef KTRACE 323 /* 324 * Copy traceflag and tracefile if enabled. 325 * If not inherited, these were zeroed above. 326 */ 327 if (p1->p_traceflag&KTRFAC_INHERIT) { 328 p2->p_traceflag = p1->p_traceflag; 329 if ((p2->p_tracep = p1->p_tracep) != NULL) 330 ktradref(p2); 331 } 332 #endif 333 scheduler_fork_hook(p1, p2); 334 335 /* 336 * Create signal actions for the child process. 337 */ 338 if (flags & FORK_SHARESIGS) 339 sigactsshare(p1, p2); 340 else 341 p2->p_sigacts = sigactsinit(p1); 342 343 /* 344 * This begins the section where we must prevent the parent 345 * from being swapped. 346 */ 347 PHOLD(p1); 348 349 /* 350 * Finish creating the child process. It will return through a 351 * different path later. 352 */ 353 p2->p_addr = (struct user *)uaddr; 354 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE, 355 stack, stacksize); 356 357 /* 358 * Make child runnable, set start time, and add to run queue. 359 */ 360 s = splstatclock(); 361 p2->p_stats->p_start = time; 362 p2->p_acflag = AFORK; 363 p2->p_stat = SRUN; 364 setrunqueue(p2); 365 splx(s); 366 367 /* 368 * Now can be swapped. 369 */ 370 PRELE(p1); 371 372 /* 373 * Update stats now that we know the fork was successful. 374 */ 375 uvmexp.forks++; 376 if (flags & FORK_PPWAIT) 377 uvmexp.forks_ppwait++; 378 if (flags & FORK_SHAREVM) 379 uvmexp.forks_sharevm++; 380 381 /* 382 * Pass a pointer to the new process to the caller. 383 */ 384 if (rnewprocp != NULL) 385 *rnewprocp = p2; 386 387 /* 388 * Preserve synchronization semantics of vfork. If waiting for 389 * child to exec or exit, set P_PPWAIT on child, and sleep on our 390 * proc (in case of exit). 391 */ 392 if (flags & FORK_PPWAIT) 393 while (p2->p_flag & P_PPWAIT) 394 tsleep(p1, PWAIT, "ppwait", 0); 395 396 /* 397 * Return child pid to parent process, 398 * marking us as parent via retval[1]. 399 */ 400 if (retval != NULL) { 401 retval[0] = p2->p_pid; 402 retval[1] = 0; 403 } 404 return (0); 405 } 406