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 1.8 1994/10/09 07:34:55 davidg 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 /* ARGSUSED */ 62 int 63 fork(p, uap, retval) 64 struct proc *p; 65 struct fork_args *uap; 66 int retval[]; 67 { 68 69 return (fork1(p, 0, retval)); 70 } 71 72 /* ARGSUSED */ 73 int 74 vfork(p, uap, retval) 75 struct proc *p; 76 struct fork_args *uap; 77 int retval[]; 78 { 79 80 return (fork1(p, 1, retval)); 81 } 82 83 int nprocs = 1; /* process 0 */ 84 85 static int 86 fork1(p1, isvfork, retval) 87 register struct proc *p1; 88 int isvfork, retval[]; 89 { 90 register struct proc *p2; 91 register uid_t uid; 92 struct proc *newproc; 93 struct proc **hash; 94 int count; 95 static int nextpid, pidchecked = 0; 96 97 /* 98 * Although process entries are dynamically created, we still keep 99 * a global limit on the maximum number we will create. Don't allow 100 * a nonprivileged user to use the last process; don't let root 101 * exceed the limit. The variable nprocs is the current number of 102 * processes, maxproc is the limit. 103 */ 104 uid = p1->p_cred->p_ruid; 105 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 106 tablefull("proc"); 107 return (EAGAIN); 108 } 109 /* 110 * Increment the count of procs running with this uid. Don't allow 111 * a nonprivileged user to exceed their current limit. 112 */ 113 count = chgproccnt(uid, 1); 114 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 115 (void)chgproccnt(uid, -1); 116 return (EAGAIN); 117 } 118 119 /* Allocate new proc. */ 120 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 121 122 /* 123 * Find an unused process ID. We remember a range of unused IDs 124 * ready to use (from nextpid+1 through pidchecked-1). 125 */ 126 nextpid++; 127 retry: 128 /* 129 * If the process ID prototype has wrapped around, 130 * restart somewhat above 0, as the low-numbered procs 131 * tend to include daemons that don't exit. 132 */ 133 if (nextpid >= PID_MAX) { 134 nextpid = 100; 135 pidchecked = 0; 136 } 137 if (nextpid >= pidchecked) { 138 int doingzomb = 0; 139 140 pidchecked = PID_MAX; 141 /* 142 * Scan the active and zombie procs to check whether this pid 143 * is in use. Remember the lowest pid that's greater 144 * than nextpid, so we can avoid checking for a while. 145 */ 146 p2 = (struct proc *)allproc; 147 again: 148 for (; p2 != NULL; p2 = p2->p_next) { 149 while (p2->p_pid == nextpid || 150 p2->p_pgrp->pg_id == nextpid) { 151 nextpid++; 152 if (nextpid >= pidchecked) 153 goto retry; 154 } 155 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 156 pidchecked = p2->p_pid; 157 if (p2->p_pgrp->pg_id > nextpid && 158 pidchecked > p2->p_pgrp->pg_id) 159 pidchecked = p2->p_pgrp->pg_id; 160 } 161 if (!doingzomb) { 162 doingzomb = 1; 163 p2 = zombproc; 164 goto again; 165 } 166 } 167 168 169 /* 170 * Link onto allproc (this should probably be delayed). 171 * Heavy use of volatile here to prevent the compiler from 172 * rearranging code. Yes, it *is* terribly ugly, but at least 173 * it works. 174 */ 175 nprocs++; 176 p2 = newproc; 177 #define Vp2 ((volatile struct proc *)p2) 178 Vp2->p_stat = SIDL; /* protect against others */ 179 Vp2->p_pid = nextpid; 180 /* 181 * This is really: 182 * p2->p_next = allproc; 183 * allproc->p_prev = &p2->p_next; 184 * p2->p_prev = &allproc; 185 * allproc = p2; 186 * The assignment via allproc is legal since it is never NULL. 187 */ 188 *(volatile struct proc **)&Vp2->p_next = allproc; 189 *(volatile struct proc ***)&allproc->p_prev = 190 (volatile struct proc **)&Vp2->p_next; 191 *(volatile struct proc ***)&Vp2->p_prev = &allproc; 192 allproc = Vp2; 193 #undef Vp2 194 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 195 196 /* Insert on the hash chain. */ 197 hash = &pidhash[PIDHASH(p2->p_pid)]; 198 p2->p_hash = *hash; 199 *hash = p2; 200 201 /* 202 * Make a proc table entry for the new process. 203 * Start by zeroing the section of proc that is zero-initialized, 204 * then copy the section that is copied directly from the parent. 205 */ 206 bzero(&p2->p_startzero, 207 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 208 bcopy(&p1->p_startcopy, &p2->p_startcopy, 209 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 210 211 /* 212 * Duplicate sub-structures as needed. 213 * Increase reference counts on shared objects. 214 * The p_stats and p_sigacts substructs are set in vm_fork. 215 */ 216 p2->p_flag = P_INMEM; 217 if (p1->p_flag & P_PROFIL) 218 startprofclock(p2); 219 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 220 M_SUBPROC, M_WAITOK); 221 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 222 p2->p_cred->p_refcnt = 1; 223 crhold(p1->p_ucred); 224 225 /* bump references to the text vnode (for procfs) */ 226 p2->p_textvp = p1->p_textvp; 227 if (p2->p_textvp) 228 VREF(p2->p_textvp); 229 230 p2->p_fd = fdcopy(p1); 231 /* 232 * If p_limit is still copy-on-write, bump refcnt, 233 * otherwise get a copy that won't be modified. 234 * (If PL_SHAREMOD is clear, the structure is shared 235 * copy-on-write.) 236 */ 237 if (p1->p_limit->p_lflags & PL_SHAREMOD) 238 p2->p_limit = limcopy(p1->p_limit); 239 else { 240 p2->p_limit = p1->p_limit; 241 p2->p_limit->p_refcnt++; 242 } 243 244 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 245 p2->p_flag |= P_CONTROLT; 246 if (isvfork) 247 p2->p_flag |= P_PPWAIT; 248 p2->p_pgrpnxt = p1->p_pgrpnxt; 249 p1->p_pgrpnxt = p2; 250 p2->p_pptr = p1; 251 p2->p_osptr = p1->p_cptr; 252 if (p1->p_cptr) 253 p1->p_cptr->p_ysptr = p2; 254 p1->p_cptr = p2; 255 #ifdef KTRACE 256 /* 257 * Copy traceflag and tracefile if enabled. 258 * If not inherited, these were zeroed above. 259 */ 260 if (p1->p_traceflag&KTRFAC_INHERIT) { 261 p2->p_traceflag = p1->p_traceflag; 262 if ((p2->p_tracep = p1->p_tracep) != NULL) 263 VREF(p2->p_tracep); 264 } 265 #endif 266 267 /* 268 * set priority of child to be that of parent 269 */ 270 p2->p_estcpu = p1->p_estcpu; 271 272 /* 273 * This begins the section where we must prevent the parent 274 * from being swapped. 275 */ 276 p1->p_flag |= P_NOSWAP; 277 278 /* 279 * Set return values for child before vm_fork, 280 * so they can be copied to child stack. 281 * We return parent pid, and mark as child in retval[1]. 282 * NOTE: the kernel stack may be at a different location in the child 283 * process, and thus addresses of automatic variables (including retval) 284 * may be invalid after vm_fork returns in the child process. 285 */ 286 retval[0] = p1->p_pid; 287 retval[1] = 1; 288 if (vm_fork(p1, p2, isvfork)) { 289 /* 290 * Child process. Set start time and get to work. 291 */ 292 (void) splclock(); 293 p2->p_stats->p_start = time; 294 (void) spl0(); 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