kern_fork.c revision 1.48
1 /* $NetBSD: kern_fork.c,v 1.48 1998/09/08 23:50:14 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 #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 62 #include <sys/syscallargs.h> 63 64 #include <vm/vm.h> 65 #include <vm/vm_kern.h> 66 67 #if defined(UVM) 68 #include <uvm/uvm_extern.h> 69 #endif 70 71 int nprocs = 1; /* process 0 */ 72 73 /*ARGSUSED*/ 74 int 75 sys_fork(p, v, retval) 76 struct proc *p; 77 void *v; 78 register_t *retval; 79 { 80 81 return (fork1(p, 0, retval, NULL)); 82 } 83 84 /* 85 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM). 86 * Address space is not shared, but parent is blocked until child exit. 87 */ 88 /*ARGSUSED*/ 89 int 90 sys_vfork(p, v, retval) 91 struct proc *p; 92 void *v; 93 register_t *retval; 94 { 95 96 return (fork1(p, FORK_PPWAIT, retval, NULL)); 97 } 98 99 /* 100 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2) 101 * semantics. Address space is shared, and parent is blocked until child exit. 102 */ 103 /*ARGSUSED*/ 104 int 105 sys___vfork14(p, v, retval) 106 struct proc *p; 107 void *v; 108 register_t *retval; 109 { 110 111 return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, retval, NULL)); 112 } 113 114 int 115 fork1(p1, flags, retval, rnewprocp) 116 register struct proc *p1; 117 int flags; 118 register_t *retval; 119 struct proc **rnewprocp; 120 { 121 register struct proc *p2; 122 register uid_t uid; 123 struct proc *newproc; 124 int count; 125 vaddr_t uaddr; 126 static int nextpid, pidchecked = 0; 127 128 /* 129 * Although process entries are dynamically created, we still keep 130 * a global limit on the maximum number we will create. Don't allow 131 * a nonprivileged user to use the last process; don't let root 132 * exceed the limit. The variable nprocs is the current number of 133 * processes, maxproc is the limit. 134 */ 135 uid = p1->p_cred->p_ruid; 136 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 137 tablefull("proc"); 138 return (EAGAIN); 139 } 140 141 /* 142 * Increment the count of procs running with this uid. Don't allow 143 * a nonprivileged user to exceed their current limit. 144 */ 145 count = chgproccnt(uid, 1); 146 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 147 (void)chgproccnt(uid, -1); 148 return (EAGAIN); 149 } 150 151 /* 152 * Allocate virtual address space for the U-area now, while it 153 * is still easy to abort the fork operation if we're out of 154 * kernel virtual address space. The actual U-area pages will 155 * be allocated and wired in vm_fork(). 156 */ 157 #if defined(UVM) 158 uaddr = uvm_km_valloc(kernel_map, USPACE); 159 #else 160 uaddr = kmem_alloc_pageable(kernel_map, USPACE); 161 #endif 162 if (uaddr == 0) { 163 (void)chgproccnt(uid, -1); 164 return (ENOMEM); 165 } 166 167 /* 168 * We are now committed to the fork. From here on, we may 169 * block on resources, but resource allocation may NOT fail. 170 */ 171 172 /* Allocate new proc. */ 173 newproc = pool_get(&proc_pool, PR_WAITOK); 174 175 /* 176 * BEGIN PID ALLOCATION. (Lock PID allocation variables eventually). 177 */ 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 /* 242 * Put the proc on allproc before unlocking PID allocation 243 * so that waiters won't grab it as soon as we unlock. 244 */ 245 LIST_INSERT_HEAD(&allproc, p2, p_list); 246 247 /* 248 * END PID ALLOCATION. (Unlock PID allocation variables). 249 */ 250 251 p2->p_stat = SIDL; /* protect against others */ 252 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 253 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 254 255 /* 256 * Make a proc table entry for the new process. 257 * Start by zeroing the section of proc that is zero-initialized, 258 * then copy the section that is copied directly from the parent. 259 */ 260 memset(&p2->p_startzero, 0, 261 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 262 memcpy(&p2->p_startcopy, &p1->p_startcopy, 263 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 264 265 /* 266 * Duplicate sub-structures as needed. 267 * Increase reference counts on shared objects. 268 * The p_stats and p_sigacts substructs are set in vm_fork. 269 */ 270 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID); 271 p2->p_emul = p1->p_emul; 272 if (p1->p_flag & P_PROFIL) 273 startprofclock(p2); 274 p2->p_cred = pool_get(&pcred_pool, PR_WAITOK); 275 memcpy(p2->p_cred, p1->p_cred, sizeof(*p2->p_cred)); 276 p2->p_cred->p_refcnt = 1; 277 crhold(p1->p_ucred); 278 279 /* bump references to the text vnode (for procfs) */ 280 p2->p_textvp = p1->p_textvp; 281 if (p2->p_textvp) 282 VREF(p2->p_textvp); 283 284 p2->p_fd = fdcopy(p1); 285 /* 286 * If p_limit is still copy-on-write, bump refcnt, 287 * otherwise get a copy that won't be modified. 288 * (If PL_SHAREMOD is clear, the structure is shared 289 * copy-on-write.) 290 */ 291 if (p1->p_limit->p_lflags & PL_SHAREMOD) 292 p2->p_limit = limcopy(p1->p_limit); 293 else { 294 p2->p_limit = p1->p_limit; 295 p2->p_limit->p_refcnt++; 296 } 297 298 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 299 p2->p_flag |= P_CONTROLT; 300 if (flags & FORK_PPWAIT) 301 p2->p_flag |= P_PPWAIT; 302 LIST_INSERT_AFTER(p1, p2, p_pglist); 303 p2->p_pptr = p1; 304 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 305 LIST_INIT(&p2->p_children); 306 307 #ifdef KTRACE 308 /* 309 * Copy traceflag and tracefile if enabled. 310 * If not inherited, these were zeroed above. 311 */ 312 if (p1->p_traceflag&KTRFAC_INHERIT) { 313 p2->p_traceflag = p1->p_traceflag; 314 if ((p2->p_tracep = p1->p_tracep) != NULL) 315 ktradref(p2); 316 } 317 #endif 318 319 /* 320 * This begins the section where we must prevent the parent 321 * from being swapped. 322 */ 323 PHOLD(p1); 324 325 /* 326 * Finish creating the child process. It will return through a 327 * different path later. 328 */ 329 p2->p_addr = (struct user *)uaddr; 330 #if defined(UVM) 331 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 332 #else 333 vm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 334 #endif 335 336 /* 337 * Make child runnable, set start time, and add to run queue. 338 */ 339 (void) splstatclock(); 340 p2->p_stats->p_start = time; 341 p2->p_acflag = AFORK; 342 p2->p_stat = SRUN; 343 setrunqueue(p2); 344 (void) spl0(); 345 346 /* 347 * Now can be swapped. 348 */ 349 PRELE(p1); 350 351 /* 352 * Update stats now that we know the fork was successful. 353 */ 354 #if defined(UVM) 355 uvmexp.forks++; 356 if (flags & FORK_PPWAIT) 357 uvmexp.forks_ppwait++; 358 if (flags & FORK_SHAREVM) 359 uvmexp.forks_sharevm++; 360 #else 361 cnt.v_forks++; 362 if (flags & FORK_PPWAIT) 363 cnt.v_forks_ppwait++; 364 if (flags & FORK_SHAREVM) 365 cnt.v_forks_sharevm++; 366 #endif 367 368 /* 369 * Pass a pointer to the new process to the caller. 370 */ 371 if (rnewprocp != NULL) 372 *rnewprocp = p2; 373 374 /* 375 * Preserve synchronization semantics of vfork. If waiting for 376 * child to exec or exit, set P_PPWAIT on child, and sleep on our 377 * proc (in case of exit). 378 */ 379 if (flags & FORK_PPWAIT) 380 while (p2->p_flag & P_PPWAIT) 381 tsleep(p1, PWAIT, "ppwait", 0); 382 383 /* 384 * Return child pid to parent process, 385 * marking us as parent via retval[1]. 386 */ 387 if (retval != NULL) { 388 retval[0] = p2->p_pid; 389 retval[1] = 0; 390 } 391 return (0); 392 } 393
Indexes created Tue Sep 23 14:10:03 GMT 2025