1 /* 2 * Copyright (c) 1982, 1986, 1989, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * (c) UNIX System Laboratories, Inc. 5 * All or some portions of this file are derived from material licensed 6 * to the University of California by American Telephone and Telegraph 7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 8 * the permission of UNIX System Laboratories, Inc. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94 39 * $Id: kern_fork.c,v 1.13 1995/10/08 00:06:05 swallace Exp $ 40 */ 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/sysproto.h> 45 #include <sys/filedesc.h> 46 #include <sys/kernel.h> 47 #include <sys/malloc.h> 48 #include <sys/proc.h> 49 #include <sys/resourcevar.h> 50 #include <sys/vnode.h> 51 #include <sys/file.h> 52 #include <sys/acct.h> 53 #include <sys/ktrace.h> 54 55 #include <vm/vm.h> 56 57 static int fork1(struct proc *, int, int *); 58 59 #ifndef _SYS_SYSPROTO_H_ 60 struct fork_args { 61 int dummy; 62 }; 63 #endif 64 65 /* ARGSUSED */ 66 int 67 fork(p, uap, retval) 68 struct proc *p; 69 struct fork_args *uap; 70 int retval[]; 71 { 72 73 return (fork1(p, 0, retval)); 74 } 75 76 /* ARGSUSED */ 77 int 78 vfork(p, uap, retval) 79 struct proc *p; 80 struct fork_args *uap; 81 int retval[]; 82 { 83 84 return (fork1(p, 1, retval)); 85 } 86 87 int nprocs = 1; /* process 0 */ 88 89 static int 90 fork1(p1, isvfork, retval) 91 register struct proc *p1; 92 int isvfork, retval[]; 93 { 94 register struct proc *p2; 95 register uid_t uid; 96 struct proc *newproc; 97 struct proc **hash; 98 int count; 99 static int nextpid, pidchecked = 0; 100 101 /* 102 * Although process entries are dynamically created, we still keep 103 * a global limit on the maximum number we will create. Don't allow 104 * a nonprivileged user to use the last process; don't let root 105 * exceed the limit. The variable nprocs is the current number of 106 * processes, maxproc is the limit. 107 */ 108 uid = p1->p_cred->p_ruid; 109 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 110 tablefull("proc"); 111 return (EAGAIN); 112 } 113 /* 114 * Increment the count of procs running with this uid. Don't allow 115 * a nonprivileged user to exceed their current limit. 116 */ 117 count = chgproccnt(uid, 1); 118 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 119 (void)chgproccnt(uid, -1); 120 return (EAGAIN); 121 } 122 123 /* Allocate new proc. */ 124 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 125 126 /* 127 * Find an unused process ID. We remember a range of unused IDs 128 * ready to use (from nextpid+1 through pidchecked-1). 129 */ 130 nextpid++; 131 retry: 132 /* 133 * If the process ID prototype has wrapped around, 134 * restart somewhat above 0, as the low-numbered procs 135 * tend to include daemons that don't exit. 136 */ 137 if (nextpid >= PID_MAX) { 138 nextpid = 100; 139 pidchecked = 0; 140 } 141 if (nextpid >= pidchecked) { 142 int doingzomb = 0; 143 144 pidchecked = PID_MAX; 145 /* 146 * Scan the active and zombie procs to check whether this pid 147 * is in use. Remember the lowest pid that's greater 148 * than nextpid, so we can avoid checking for a while. 149 */ 150 p2 = (struct proc *)allproc; 151 again: 152 for (; p2 != NULL; p2 = p2->p_next) { 153 while (p2->p_pid == nextpid || 154 p2->p_pgrp->pg_id == nextpid) { 155 nextpid++; 156 if (nextpid >= pidchecked) 157 goto retry; 158 } 159 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 160 pidchecked = p2->p_pid; 161 if (p2->p_pgrp->pg_id > nextpid && 162 pidchecked > p2->p_pgrp->pg_id) 163 pidchecked = p2->p_pgrp->pg_id; 164 } 165 if (!doingzomb) { 166 doingzomb = 1; 167 p2 = zombproc; 168 goto again; 169 } 170 } 171 172 173 /* 174 * Link onto allproc (this should probably be delayed). 175 * Heavy use of volatile here to prevent the compiler from 176 * rearranging code. Yes, it *is* terribly ugly, but at least 177 * it works. 178 */ 179 nprocs++; 180 p2 = newproc; 181 #define Vp2 ((volatile struct proc *)p2) 182 Vp2->p_stat = SIDL; /* protect against others */ 183 Vp2->p_pid = nextpid; 184 /* 185 * This is really: 186 * p2->p_next = allproc; 187 * allproc->p_prev = &p2->p_next; 188 * p2->p_prev = &allproc; 189 * allproc = p2; 190 * The assignment via allproc is legal since it is never NULL. 191 */ 192 *(volatile struct proc **)&Vp2->p_next = allproc; 193 *(volatile struct proc ***)&allproc->p_prev = 194 (volatile struct proc **)&Vp2->p_next; 195 *(volatile struct proc ***)&Vp2->p_prev = &allproc; 196 allproc = Vp2; 197 #undef Vp2 198 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 199 200 /* Insert on the hash chain. */ 201 hash = &pidhash[PIDHASH(p2->p_pid)]; 202 p2->p_hash = *hash; 203 *hash = p2; 204 205 /* 206 * Make a proc table entry for the new process. 207 * Start by zeroing the section of proc that is zero-initialized, 208 * then copy the section that is copied directly from the parent. 209 */ 210 bzero(&p2->p_startzero, 211 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 212 bcopy(&p1->p_startcopy, &p2->p_startcopy, 213 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 214 215 /* 216 * Duplicate sub-structures as needed. 217 * Increase reference counts on shared objects. 218 * The p_stats and p_sigacts substructs are set in vm_fork. 219 */ 220 p2->p_flag = P_INMEM; 221 if (p1->p_flag & P_PROFIL) 222 startprofclock(p2); 223 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 224 M_SUBPROC, M_WAITOK); 225 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 226 p2->p_cred->p_refcnt = 1; 227 crhold(p1->p_ucred); 228 229 /* bump references to the text vnode (for procfs) */ 230 p2->p_textvp = p1->p_textvp; 231 if (p2->p_textvp) 232 VREF(p2->p_textvp); 233 234 p2->p_fd = fdcopy(p1); 235 /* 236 * If p_limit is still copy-on-write, bump refcnt, 237 * otherwise get a copy that won't be modified. 238 * (If PL_SHAREMOD is clear, the structure is shared 239 * copy-on-write.) 240 */ 241 if (p1->p_limit->p_lflags & PL_SHAREMOD) 242 p2->p_limit = limcopy(p1->p_limit); 243 else { 244 p2->p_limit = p1->p_limit; 245 p2->p_limit->p_refcnt++; 246 } 247 248 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 249 p2->p_flag |= P_CONTROLT; 250 if (isvfork) 251 p2->p_flag |= P_PPWAIT; 252 p2->p_pgrpnxt = p1->p_pgrpnxt; 253 p1->p_pgrpnxt = p2; 254 p2->p_pptr = p1; 255 p2->p_osptr = p1->p_cptr; 256 if (p1->p_cptr) 257 p1->p_cptr->p_ysptr = p2; 258 p1->p_cptr = p2; 259 #ifdef KTRACE 260 /* 261 * Copy traceflag and tracefile if enabled. 262 * If not inherited, these were zeroed above. 263 */ 264 if (p1->p_traceflag&KTRFAC_INHERIT) { 265 p2->p_traceflag = p1->p_traceflag; 266 if ((p2->p_tracep = p1->p_tracep) != NULL) 267 VREF(p2->p_tracep); 268 } 269 #endif 270 271 /* 272 * set priority of child to be that of parent 273 */ 274 p2->p_estcpu = p1->p_estcpu; 275 276 /* 277 * This begins the section where we must prevent the parent 278 * from being swapped. 279 */ 280 p1->p_flag |= P_NOSWAP; 281 282 /* 283 * Set return values for child before vm_fork, 284 * so they can be copied to child stack. 285 * We return parent pid, and mark as child in retval[1]. 286 * NOTE: the kernel stack may be at a different location in the child 287 * process, and thus addresses of automatic variables (including retval) 288 * may be invalid after vm_fork returns in the child process. 289 */ 290 retval[0] = p1->p_pid; 291 retval[1] = 1; 292 if (vm_fork(p1, p2, isvfork)) { 293 /* 294 * Child process. Set start time and get to work. 295 */ 296 microtime(&runtime); 297 p2->p_stats->p_start = runtime; 298 p2->p_acflag = AFORK; 299 return (0); 300 } 301 302 /* 303 * Make child runnable and add to run queue. 304 */ 305 (void) splhigh(); 306 p2->p_stat = SRUN; 307 setrunqueue(p2); 308 (void) spl0(); 309 310 /* 311 * Now can be swapped. 312 */ 313 p1->p_flag &= ~P_NOSWAP; 314 315 /* 316 * Preserve synchronization semantics of vfork. If waiting for 317 * child to exec or exit, set P_PPWAIT on child, and sleep on our 318 * proc (in case of exit). 319 */ 320 if (isvfork) 321 while (p2->p_flag & P_PPWAIT) 322 tsleep(p1, PWAIT, "ppwait", 0); 323 324 /* 325 * Return child pid to parent process, 326 * marking us as parent via retval[1]. 327 */ 328 retval[0] = p2->p_pid; 329 retval[1] = 0; 330 return (0); 331 } 332