kern_fork.c revision 1.41
1 /* $NetBSD: kern_fork.c,v 1.41 1998/04/09 00:23:38 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_uvm.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/mount.h> 52 #include <sys/proc.h> 53 #include <sys/resourcevar.h> 54 #include <sys/vnode.h> 55 #include <sys/file.h> 56 #include <sys/acct.h> 57 #include <sys/ktrace.h> 58 #include <sys/vmmeter.h> 59 60 #include <sys/syscallargs.h> 61 62 #include <vm/vm.h> 63 #include <vm/vm_kern.h> 64 65 #if defined(UVM) 66 #include <uvm/uvm_extern.h> 67 #endif 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; 123 vm_offset_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 #if defined(UVM) 156 uaddr = uvm_km_valloc(kernel_map, USPACE); 157 #else 158 uaddr = kmem_alloc_pageable(kernel_map, USPACE); 159 #endif 160 if (uaddr == 0) { 161 (void)chgproccnt(uid, -1); 162 return (ENOMEM); 163 } 164 165 /* 166 * We are now committed to the fork. From here on, we may 167 * block on resources, but resource allocation may NOT fail. 168 */ 169 170 /* Allocate new proc. */ 171 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 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 int doingzomb = 0; 190 191 pidchecked = PID_MAX; 192 /* 193 * Scan the active and zombie procs 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 p2 = allproc.lh_first; 198 again: 199 for (; p2 != 0; p2 = p2->p_list.le_next) { 200 while (p2->p_pid == nextpid || 201 p2->p_pgrp->pg_id == nextpid || 202 p2->p_session->s_sid == nextpid) { 203 nextpid++; 204 if (nextpid >= pidchecked) 205 goto retry; 206 } 207 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 208 pidchecked = p2->p_pid; 209 210 if (p2->p_pgrp->pg_id > nextpid && 211 pidchecked > p2->p_pgrp->pg_id) 212 pidchecked = p2->p_pgrp->pg_id; 213 214 if (p2->p_session->s_sid > nextpid && 215 pidchecked > p2->p_session->s_sid) 216 pidchecked = p2->p_session->s_sid; 217 } 218 if (!doingzomb) { 219 doingzomb = 1; 220 p2 = zombproc.lh_first; 221 goto again; 222 } 223 } 224 225 nprocs++; 226 p2 = newproc; 227 p2->p_stat = SIDL; /* protect against others */ 228 p2->p_pid = nextpid; 229 LIST_INSERT_HEAD(&allproc, p2, p_list); 230 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 231 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 232 233 /* 234 * Make a proc table entry for the new process. 235 * Start by zeroing the section of proc that is zero-initialized, 236 * then copy the section that is copied directly from the parent. 237 */ 238 bzero(&p2->p_startzero, 239 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 240 bcopy(&p1->p_startcopy, &p2->p_startcopy, 241 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 242 243 /* 244 * Duplicate sub-structures as needed. 245 * Increase reference counts on shared objects. 246 * The p_stats and p_sigacts substructs are set in vm_fork. 247 */ 248 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID); 249 p2->p_emul = p1->p_emul; 250 if (p1->p_flag & P_PROFIL) 251 startprofclock(p2); 252 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 253 M_SUBPROC, M_WAITOK); 254 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 255 p2->p_cred->p_refcnt = 1; 256 crhold(p1->p_ucred); 257 258 /* bump references to the text vnode (for procfs) */ 259 p2->p_textvp = p1->p_textvp; 260 if (p2->p_textvp) 261 VREF(p2->p_textvp); 262 263 p2->p_fd = fdcopy(p1); 264 /* 265 * If p_limit is still copy-on-write, bump refcnt, 266 * otherwise get a copy that won't be modified. 267 * (If PL_SHAREMOD is clear, the structure is shared 268 * copy-on-write.) 269 */ 270 if (p1->p_limit->p_lflags & PL_SHAREMOD) 271 p2->p_limit = limcopy(p1->p_limit); 272 else { 273 p2->p_limit = p1->p_limit; 274 p2->p_limit->p_refcnt++; 275 } 276 277 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 278 p2->p_flag |= P_CONTROLT; 279 if (flags & FORK_PPWAIT) 280 p2->p_flag |= P_PPWAIT; 281 LIST_INSERT_AFTER(p1, p2, p_pglist); 282 p2->p_pptr = p1; 283 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 284 LIST_INIT(&p2->p_children); 285 286 #ifdef KTRACE 287 /* 288 * Copy traceflag and tracefile if enabled. 289 * If not inherited, these were zeroed above. 290 */ 291 if (p1->p_traceflag&KTRFAC_INHERIT) { 292 p2->p_traceflag = p1->p_traceflag; 293 if ((p2->p_tracep = p1->p_tracep) != NULL) 294 VREF(p2->p_tracep); 295 } 296 #endif 297 298 /* 299 * This begins the section where we must prevent the parent 300 * from being swapped. 301 */ 302 PHOLD(p1); 303 304 /* 305 * Finish creating the child process. It will return through a 306 * different path later. 307 */ 308 p2->p_addr = (struct user *)uaddr; 309 #if defined(UVM) 310 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 311 #else 312 vm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 313 #endif 314 315 /* 316 * Make child runnable, set start time, and add to run queue. 317 */ 318 (void) splstatclock(); 319 p2->p_stats->p_start = time; 320 p2->p_acflag = AFORK; 321 p2->p_stat = SRUN; 322 setrunqueue(p2); 323 (void) spl0(); 324 325 /* 326 * Now can be swapped. 327 */ 328 PRELE(p1); 329 330 /* 331 * Update stats now that we know the fork was successful. 332 */ 333 #if defined(UVM) 334 uvmexp.forks++; 335 if (flags & FORK_PPWAIT) 336 uvmexp.forks_ppwait++; 337 if (flags & FORK_SHAREVM) 338 uvmexp.forks_sharevm++; 339 #else 340 cnt.v_forks++; 341 if (flags & FORK_PPWAIT) 342 cnt.v_forks_ppwait++; 343 if (flags & FORK_SHAREVM) 344 cnt.v_forks_sharevm++; 345 #endif 346 347 /* 348 * Pass a pointer to the new process to the caller. 349 */ 350 if (rnewprocp != NULL) 351 *rnewprocp = p2; 352 353 /* 354 * Preserve synchronization semantics of vfork. If waiting for 355 * child to exec or exit, set P_PPWAIT on child, and sleep on our 356 * proc (in case of exit). 357 */ 358 if (flags & FORK_PPWAIT) 359 while (p2->p_flag & P_PPWAIT) 360 tsleep(p1, PWAIT, "ppwait", 0); 361 362 /* 363 * Return child pid to parent process, 364 * marking us as parent via retval[1]. 365 */ 366 if (retval != NULL) { 367 retval[0] = p2->p_pid; 368 retval[1] = 0; 369 } 370 return (0); 371 } 372
Indexes created Mon Sep 22 13:09:51 GMT 2025