kern_fork.c revision 1.53
1 /* $NetBSD: kern_fork.c,v 1.53 1999/02/23 02:57:18 ross 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 #include "opt_uvm.h" 45 46 #include <sys/param.h> 47 #include <sys/systm.h> 48 #include <sys/map.h> 49 #include <sys/filedesc.h> 50 #include <sys/kernel.h> 51 #include <sys/malloc.h> 52 #include <sys/pool.h> 53 #include <sys/mount.h> 54 #include <sys/proc.h> 55 #include <sys/resourcevar.h> 56 #include <sys/vnode.h> 57 #include <sys/file.h> 58 #include <sys/acct.h> 59 #include <sys/ktrace.h> 60 #include <sys/vmmeter.h> 61 #include <sys/sched.h> 62 63 #include <sys/syscallargs.h> 64 65 #include <vm/vm.h> 66 #include <vm/vm_kern.h> 67 68 #if defined(UVM) 69 #include <uvm/uvm_extern.h> 70 #endif 71 72 int nprocs = 1; /* process 0 */ 73 74 /*ARGSUSED*/ 75 int 76 sys_fork(p, v, retval) 77 struct proc *p; 78 void *v; 79 register_t *retval; 80 { 81 82 return (fork1(p, 0, retval, NULL)); 83 } 84 85 /* 86 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM). 87 * Address space is not shared, but parent is blocked until child exit. 88 */ 89 /*ARGSUSED*/ 90 int 91 sys_vfork(p, v, retval) 92 struct proc *p; 93 void *v; 94 register_t *retval; 95 { 96 97 return (fork1(p, FORK_PPWAIT, retval, NULL)); 98 } 99 100 /* 101 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2) 102 * semantics. Address space is shared, and parent is blocked until child exit. 103 */ 104 /*ARGSUSED*/ 105 int 106 sys___vfork14(p, v, retval) 107 struct proc *p; 108 void *v; 109 register_t *retval; 110 { 111 112 return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, retval, NULL)); 113 } 114 115 int 116 fork1(p1, flags, retval, rnewprocp) 117 register struct proc *p1; 118 int flags; 119 register_t *retval; 120 struct proc **rnewprocp; 121 { 122 register struct proc *p2; 123 register uid_t uid; 124 struct proc *newproc; 125 int count, s; 126 vaddr_t uaddr; 127 static int nextpid, pidchecked = 0; 128 129 /* 130 * Although process entries are dynamically created, we still keep 131 * a global limit on the maximum number we will create. Don't allow 132 * a nonprivileged user to use the last process; don't let root 133 * exceed the limit. The variable nprocs is the current number of 134 * processes, maxproc is the limit. 135 */ 136 uid = p1->p_cred->p_ruid; 137 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 138 tablefull("proc"); 139 return (EAGAIN); 140 } 141 142 /* 143 * Increment the count of procs running with this uid. Don't allow 144 * a nonprivileged user to exceed their current limit. 145 */ 146 count = chgproccnt(uid, 1); 147 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 148 (void)chgproccnt(uid, -1); 149 return (EAGAIN); 150 } 151 152 /* 153 * Allocate virtual address space for the U-area now, while it 154 * is still easy to abort the fork operation if we're out of 155 * kernel virtual address space. The actual U-area pages will 156 * be allocated and wired in vm_fork(). 157 */ 158 #if defined(UVM) 159 uaddr = uvm_km_valloc(kernel_map, USPACE); 160 #else 161 uaddr = kmem_alloc_pageable(kernel_map, USPACE); 162 #endif 163 if (uaddr == 0) { 164 (void)chgproccnt(uid, -1); 165 return (ENOMEM); 166 } 167 168 /* 169 * We are now committed to the fork. From here on, we may 170 * block on resources, but resource allocation may NOT fail. 171 */ 172 173 /* Allocate new proc. */ 174 newproc = pool_get(&proc_pool, PR_WAITOK); 175 176 /* 177 * BEGIN PID ALLOCATION. (Lock PID allocation variables eventually). 178 */ 179 180 /* 181 * Find an unused process ID. We remember a range of unused IDs 182 * ready to use (from nextpid+1 through pidchecked-1). 183 */ 184 nextpid++; 185 retry: 186 /* 187 * If the process ID prototype has wrapped around, 188 * restart somewhat above 0, as the low-numbered procs 189 * tend to include daemons that don't exit. 190 */ 191 if (nextpid >= PID_MAX) { 192 nextpid = 100; 193 pidchecked = 0; 194 } 195 if (nextpid >= pidchecked) { 196 const struct proclist_desc *pd; 197 198 pidchecked = PID_MAX; 199 /* 200 * Scan the process lists to check whether this pid 201 * is in use. Remember the lowest pid that's greater 202 * than nextpid, so we can avoid checking for a while. 203 */ 204 pd = proclists; 205 again: 206 for (p2 = LIST_FIRST(pd->pd_list); p2 != 0; 207 p2 = LIST_NEXT(p2, p_list)) { 208 while (p2->p_pid == nextpid || 209 p2->p_pgrp->pg_id == nextpid || 210 p2->p_session->s_sid == nextpid) { 211 nextpid++; 212 if (nextpid >= pidchecked) 213 goto retry; 214 } 215 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 216 pidchecked = p2->p_pid; 217 218 if (p2->p_pgrp->pg_id > nextpid && 219 pidchecked > p2->p_pgrp->pg_id) 220 pidchecked = p2->p_pgrp->pg_id; 221 222 if (p2->p_session->s_sid > nextpid && 223 pidchecked > p2->p_session->s_sid) 224 pidchecked = p2->p_session->s_sid; 225 } 226 227 /* 228 * If there's another list, scan it. If we have checked 229 * them all, we've found one! 230 */ 231 pd++; 232 if (pd->pd_list != NULL) 233 goto again; 234 } 235 236 nprocs++; 237 p2 = newproc; 238 239 /* Record the pid we've allocated. */ 240 p2->p_pid = nextpid; 241 242 /* 243 * Put the proc on allproc before unlocking PID allocation 244 * so that waiters won't grab it as soon as we unlock. 245 */ 246 LIST_INSERT_HEAD(&allproc, p2, p_list); 247 248 /* 249 * END PID ALLOCATION. (Unlock PID allocation variables). 250 */ 251 252 p2->p_stat = SIDL; /* protect against others */ 253 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 254 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 255 256 /* 257 * Make a proc table entry for the new process. 258 * Start by zeroing the section of proc that is zero-initialized, 259 * then copy the section that is copied directly from the parent. 260 */ 261 memset(&p2->p_startzero, 0, 262 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 263 memcpy(&p2->p_startcopy, &p1->p_startcopy, 264 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 265 266 /* 267 * Duplicate sub-structures as needed. 268 * Increase reference counts on shared objects. 269 * The p_stats and p_sigacts substructs are set in vm_fork. 270 */ 271 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID); 272 p2->p_emul = p1->p_emul; 273 if (p1->p_flag & P_PROFIL) 274 startprofclock(p2); 275 p2->p_cred = pool_get(&pcred_pool, PR_WAITOK); 276 memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred)); 277 p2->p_cred->p_refcnt = 1; 278 crhold(p1->p_ucred); 279 280 /* bump references to the text vnode (for procfs) */ 281 p2->p_textvp = p1->p_textvp; 282 if (p2->p_textvp) 283 VREF(p2->p_textvp); 284 285 p2->p_fd = fdcopy(p1); 286 /* 287 * If p_limit is still copy-on-write, bump refcnt, 288 * otherwise get a copy that won't be modified. 289 * (If PL_SHAREMOD is clear, the structure is shared 290 * copy-on-write.) 291 */ 292 if (p1->p_limit->p_lflags & PL_SHAREMOD) 293 p2->p_limit = limcopy(p1->p_limit); 294 else { 295 p2->p_limit = p1->p_limit; 296 p2->p_limit->p_refcnt++; 297 } 298 299 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 300 p2->p_flag |= P_CONTROLT; 301 if (flags & FORK_PPWAIT) 302 p2->p_flag |= P_PPWAIT; 303 LIST_INSERT_AFTER(p1, p2, p_pglist); 304 p2->p_pptr = p1; 305 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 306 LIST_INIT(&p2->p_children); 307 308 #ifdef KTRACE 309 /* 310 * Copy traceflag and tracefile if enabled. 311 * If not inherited, these were zeroed above. 312 */ 313 if (p1->p_traceflag&KTRFAC_INHERIT) { 314 p2->p_traceflag = p1->p_traceflag; 315 if ((p2->p_tracep = p1->p_tracep) != NULL) 316 ktradref(p2); 317 } 318 #endif 319 scheduler_fork_hook(p1, p2); 320 321 /* 322 * This begins the section where we must prevent the parent 323 * from being swapped. 324 */ 325 PHOLD(p1); 326 327 /* 328 * Finish creating the child process. It will return through a 329 * different path later. 330 */ 331 p2->p_addr = (struct user *)uaddr; 332 #if defined(UVM) 333 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 334 #else 335 vm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 336 #endif 337 338 /* 339 * Make child runnable, set start time, and add to run queue. 340 */ 341 s = splstatclock(); 342 p2->p_stats->p_start = time; 343 p2->p_acflag = AFORK; 344 p2->p_stat = SRUN; 345 setrunqueue(p2); 346 splx(s); 347 348 /* 349 * Now can be swapped. 350 */ 351 PRELE(p1); 352 353 /* 354 * Update stats now that we know the fork was successful. 355 */ 356 #if defined(UVM) 357 uvmexp.forks++; 358 if (flags & FORK_PPWAIT) 359 uvmexp.forks_ppwait++; 360 if (flags & FORK_SHAREVM) 361 uvmexp.forks_sharevm++; 362 #else 363 cnt.v_forks++; 364 if (flags & FORK_PPWAIT) 365 cnt.v_forks_ppwait++; 366 if (flags & FORK_SHAREVM) 367 cnt.v_forks_sharevm++; 368 #endif 369 370 /* 371 * Pass a pointer to the new process to the caller. 372 */ 373 if (rnewprocp != NULL) 374 *rnewprocp = p2; 375 376 /* 377 * Preserve synchronization semantics of vfork. If waiting for 378 * child to exec or exit, set P_PPWAIT on child, and sleep on our 379 * proc (in case of exit). 380 */ 381 if (flags & FORK_PPWAIT) 382 while (p2->p_flag & P_PPWAIT) 383 tsleep(p1, PWAIT, "ppwait", 0); 384 385 /* 386 * Return child pid to parent process, 387 * marking us as parent via retval[1]. 388 */ 389 if (retval != NULL) { 390 retval[0] = p2->p_pid; 391 retval[1] = 0; 392 } 393 return (0); 394 } 395
Indexes created Sun Sep 21 20:09:37 GMT 2025