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 1.12 1995/05/30 08:05:27 rgrimes Exp $ 40 */ 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/filedesc.h> 45 #include <sys/kernel.h> 46 #include <sys/malloc.h> 47 #include <sys/proc.h> 48 #include <sys/resourcevar.h> 49 #include <sys/vnode.h> 50 #include <sys/file.h> 51 #include <sys/acct.h> 52 #include <sys/ktrace.h> 53 54 #include <vm/vm.h> 55 56 static int fork1(struct proc *, int, int *); 57 58 struct fork_args { 59 int dummy; 60 }; 61 62 /* ARGSUSED */ 63 int 64 fork(p, uap, retval) 65 struct proc *p; 66 struct fork_args *uap; 67 int retval[]; 68 { 69 70 return (fork1(p, 0, retval)); 71 } 72 73 /* ARGSUSED */ 74 int 75 vfork(p, uap, retval) 76 struct proc *p; 77 struct fork_args *uap; 78 int retval[]; 79 { 80 81 return (fork1(p, 1, retval)); 82 } 83 84 int nprocs = 1; /* process 0 */ 85 86 static int 87 fork1(p1, isvfork, retval) 88 register struct proc *p1; 89 int isvfork, retval[]; 90 { 91 register struct proc *p2; 92 register uid_t uid; 93 struct proc *newproc; 94 struct proc **hash; 95 int count; 96 static int nextpid, pidchecked = 0; 97 98 /* 99 * Although process entries are dynamically created, we still keep 100 * a global limit on the maximum number we will create. Don't allow 101 * a nonprivileged user to use the last process; don't let root 102 * exceed the limit. The variable nprocs is the current number of 103 * processes, maxproc is the limit. 104 */ 105 uid = p1->p_cred->p_ruid; 106 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 107 tablefull("proc"); 108 return (EAGAIN); 109 } 110 /* 111 * Increment the count of procs running with this uid. Don't allow 112 * a nonprivileged user to exceed their current limit. 113 */ 114 count = chgproccnt(uid, 1); 115 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 116 (void)chgproccnt(uid, -1); 117 return (EAGAIN); 118 } 119 120 /* Allocate new proc. */ 121 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 122 123 /* 124 * Find an unused process ID. We remember a range of unused IDs 125 * ready to use (from nextpid+1 through pidchecked-1). 126 */ 127 nextpid++; 128 retry: 129 /* 130 * If the process ID prototype has wrapped around, 131 * restart somewhat above 0, as the low-numbered procs 132 * tend to include daemons that don't exit. 133 */ 134 if (nextpid >= PID_MAX) { 135 nextpid = 100; 136 pidchecked = 0; 137 } 138 if (nextpid >= pidchecked) { 139 int doingzomb = 0; 140 141 pidchecked = PID_MAX; 142 /* 143 * Scan the active and zombie procs to check whether this pid 144 * is in use. Remember the lowest pid that's greater 145 * than nextpid, so we can avoid checking for a while. 146 */ 147 p2 = (struct proc *)allproc; 148 again: 149 for (; p2 != NULL; p2 = p2->p_next) { 150 while (p2->p_pid == nextpid || 151 p2->p_pgrp->pg_id == nextpid) { 152 nextpid++; 153 if (nextpid >= pidchecked) 154 goto retry; 155 } 156 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 157 pidchecked = p2->p_pid; 158 if (p2->p_pgrp->pg_id > nextpid && 159 pidchecked > p2->p_pgrp->pg_id) 160 pidchecked = p2->p_pgrp->pg_id; 161 } 162 if (!doingzomb) { 163 doingzomb = 1; 164 p2 = zombproc; 165 goto again; 166 } 167 } 168 169 170 /* 171 * Link onto allproc (this should probably be delayed). 172 * Heavy use of volatile here to prevent the compiler from 173 * rearranging code. Yes, it *is* terribly ugly, but at least 174 * it works. 175 */ 176 nprocs++; 177 p2 = newproc; 178 #define Vp2 ((volatile struct proc *)p2) 179 Vp2->p_stat = SIDL; /* protect against others */ 180 Vp2->p_pid = nextpid; 181 /* 182 * This is really: 183 * p2->p_next = allproc; 184 * allproc->p_prev = &p2->p_next; 185 * p2->p_prev = &allproc; 186 * allproc = p2; 187 * The assignment via allproc is legal since it is never NULL. 188 */ 189 *(volatile struct proc **)&Vp2->p_next = allproc; 190 *(volatile struct proc ***)&allproc->p_prev = 191 (volatile struct proc **)&Vp2->p_next; 192 *(volatile struct proc ***)&Vp2->p_prev = &allproc; 193 allproc = Vp2; 194 #undef Vp2 195 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 196 197 /* Insert on the hash chain. */ 198 hash = &pidhash[PIDHASH(p2->p_pid)]; 199 p2->p_hash = *hash; 200 *hash = p2; 201 202 /* 203 * Make a proc table entry for the new process. 204 * Start by zeroing the section of proc that is zero-initialized, 205 * then copy the section that is copied directly from the parent. 206 */ 207 bzero(&p2->p_startzero, 208 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 209 bcopy(&p1->p_startcopy, &p2->p_startcopy, 210 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 211 212 /* 213 * Duplicate sub-structures as needed. 214 * Increase reference counts on shared objects. 215 * The p_stats and p_sigacts substructs are set in vm_fork. 216 */ 217 p2->p_flag = P_INMEM; 218 if (p1->p_flag & P_PROFIL) 219 startprofclock(p2); 220 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 221 M_SUBPROC, M_WAITOK); 222 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 223 p2->p_cred->p_refcnt = 1; 224 crhold(p1->p_ucred); 225 226 /* bump references to the text vnode (for procfs) */ 227 p2->p_textvp = p1->p_textvp; 228 if (p2->p_textvp) 229 VREF(p2->p_textvp); 230 231 p2->p_fd = fdcopy(p1); 232 /* 233 * If p_limit is still copy-on-write, bump refcnt, 234 * otherwise get a copy that won't be modified. 235 * (If PL_SHAREMOD is clear, the structure is shared 236 * copy-on-write.) 237 */ 238 if (p1->p_limit->p_lflags & PL_SHAREMOD) 239 p2->p_limit = limcopy(p1->p_limit); 240 else { 241 p2->p_limit = p1->p_limit; 242 p2->p_limit->p_refcnt++; 243 } 244 245 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 246 p2->p_flag |= P_CONTROLT; 247 if (isvfork) 248 p2->p_flag |= P_PPWAIT; 249 p2->p_pgrpnxt = p1->p_pgrpnxt; 250 p1->p_pgrpnxt = p2; 251 p2->p_pptr = p1; 252 p2->p_osptr = p1->p_cptr; 253 if (p1->p_cptr) 254 p1->p_cptr->p_ysptr = p2; 255 p1->p_cptr = p2; 256 #ifdef KTRACE 257 /* 258 * Copy traceflag and tracefile if enabled. 259 * If not inherited, these were zeroed above. 260 */ 261 if (p1->p_traceflag&KTRFAC_INHERIT) { 262 p2->p_traceflag = p1->p_traceflag; 263 if ((p2->p_tracep = p1->p_tracep) != NULL) 264 VREF(p2->p_tracep); 265 } 266 #endif 267 268 /* 269 * set priority of child to be that of parent 270 */ 271 p2->p_estcpu = p1->p_estcpu; 272 273 /* 274 * This begins the section where we must prevent the parent 275 * from being swapped. 276 */ 277 p1->p_flag |= P_NOSWAP; 278 279 /* 280 * Set return values for child before vm_fork, 281 * so they can be copied to child stack. 282 * We return parent pid, and mark as child in retval[1]. 283 * NOTE: the kernel stack may be at a different location in the child 284 * process, and thus addresses of automatic variables (including retval) 285 * may be invalid after vm_fork returns in the child process. 286 */ 287 retval[0] = p1->p_pid; 288 retval[1] = 1; 289 if (vm_fork(p1, p2, isvfork)) { 290 /* 291 * Child process. Set start time and get to work. 292 */ 293 microtime(&runtime); 294 p2->p_stats->p_start = runtime; 295 p2->p_acflag = AFORK; 296 return (0); 297 } 298 299 /* 300 * Make child runnable and add to run queue. 301 */ 302 (void) splhigh(); 303 p2->p_stat = SRUN; 304 setrunqueue(p2); 305 (void) spl0(); 306 307 /* 308 * Now can be swapped. 309 */ 310 p1->p_flag &= ~P_NOSWAP; 311 312 /* 313 * Preserve synchronization semantics of vfork. If waiting for 314 * child to exec or exit, set P_PPWAIT on child, and sleep on our 315 * proc (in case of exit). 316 */ 317 if (isvfork) 318 while (p2->p_flag & P_PPWAIT) 319 tsleep(p1, PWAIT, "ppwait", 0); 320 321 /* 322 * Return child pid to parent process, 323 * marking us as parent via retval[1]. 324 */ 325 retval[0] = p2->p_pid; 326 retval[1] = 0; 327 return (0); 328 } 329