1 /* $NetBSD: kern_fork.c,v 1.54 1999/03/24 05:51:23 mrg 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 /* 280 * If p_limit is still copy-on-write, bump refcnt, 281 * otherwise get a copy that won't be modified. 282 * (If PL_SHAREMOD is clear, the structure is shared 283 * copy-on-write.) 284 */ 285 if (p1->p_limit->p_lflags & PL_SHAREMOD) 286 p2->p_limit = limcopy(p1->p_limit); 287 else { 288 p2->p_limit = p1->p_limit; 289 p2->p_limit->p_refcnt++; 290 } 291 292 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 293 p2->p_flag |= P_CONTROLT; 294 if (flags & FORK_PPWAIT) 295 p2->p_flag |= P_PPWAIT; 296 LIST_INSERT_AFTER(p1, p2, p_pglist); 297 p2->p_pptr = p1; 298 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 299 LIST_INIT(&p2->p_children); 300 301 #ifdef KTRACE 302 /* 303 * Copy traceflag and tracefile if enabled. 304 * If not inherited, these were zeroed above. 305 */ 306 if (p1->p_traceflag&KTRFAC_INHERIT) { 307 p2->p_traceflag = p1->p_traceflag; 308 if ((p2->p_tracep = p1->p_tracep) != NULL) 309 ktradref(p2); 310 } 311 #endif 312 scheduler_fork_hook(p1, p2); 313 314 /* 315 * This begins the section where we must prevent the parent 316 * from being swapped. 317 */ 318 PHOLD(p1); 319 320 /* 321 * Finish creating the child process. It will return through a 322 * different path later. 323 */ 324 p2->p_addr = (struct user *)uaddr; 325 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 326 327 /* 328 * Make child runnable, set start time, and add to run queue. 329 */ 330 s = splstatclock(); 331 p2->p_stats->p_start = time; 332 p2->p_acflag = AFORK; 333 p2->p_stat = SRUN; 334 setrunqueue(p2); 335 splx(s); 336 337 /* 338 * Now can be swapped. 339 */ 340 PRELE(p1); 341 342 /* 343 * Update stats now that we know the fork was successful. 344 */ 345 uvmexp.forks++; 346 if (flags & FORK_PPWAIT) 347 uvmexp.forks_ppwait++; 348 if (flags & FORK_SHAREVM) 349 uvmexp.forks_sharevm++; 350 351 /* 352 * Pass a pointer to the new process to the caller. 353 */ 354 if (rnewprocp != NULL) 355 *rnewprocp = p2; 356 357 /* 358 * Preserve synchronization semantics of vfork. If waiting for 359 * child to exec or exit, set P_PPWAIT on child, and sleep on our 360 * proc (in case of exit). 361 */ 362 if (flags & FORK_PPWAIT) 363 while (p2->p_flag & P_PPWAIT) 364 tsleep(p1, PWAIT, "ppwait", 0); 365 366 /* 367 * Return child pid to parent process, 368 * marking us as parent via retval[1]. 369 */ 370 if (retval != NULL) { 371 retval[0] = p2->p_pid; 372 retval[1] = 0; 373 } 374 return (0); 375 } 376