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 1.10 1995/01/21 15:08:57 bde 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 /* ARGSUSED */ 59 int 60 fork(p, uap, retval) 61 struct proc *p; 62 struct fork_args *uap; 63 int retval[]; 64 { 65 66 return (fork1(p, 0, retval)); 67 } 68 69 /* ARGSUSED */ 70 int 71 vfork(p, uap, retval) 72 struct proc *p; 73 struct fork_args *uap; 74 int retval[]; 75 { 76 77 return (fork1(p, 1, retval)); 78 } 79 80 int nprocs = 1; /* process 0 */ 81 82 static int 83 fork1(p1, isvfork, retval) 84 register struct proc *p1; 85 int isvfork, retval[]; 86 { 87 register struct proc *p2; 88 register uid_t uid; 89 struct proc *newproc; 90 struct proc **hash; 91 int count; 92 static int nextpid, pidchecked = 0; 93 94 /* 95 * Although process entries are dynamically created, we still keep 96 * a global limit on the maximum number we will create. Don't allow 97 * a nonprivileged user to use the last process; don't let root 98 * exceed the limit. The variable nprocs is the current number of 99 * processes, maxproc is the limit. 100 */ 101 uid = p1->p_cred->p_ruid; 102 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 103 tablefull("proc"); 104 return (EAGAIN); 105 } 106 /* 107 * Increment the count of procs running with this uid. Don't allow 108 * a nonprivileged user to exceed their current limit. 109 */ 110 count = chgproccnt(uid, 1); 111 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 112 (void)chgproccnt(uid, -1); 113 return (EAGAIN); 114 } 115 116 /* Allocate new proc. */ 117 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 118 119 /* 120 * Find an unused process ID. We remember a range of unused IDs 121 * ready to use (from nextpid+1 through pidchecked-1). 122 */ 123 nextpid++; 124 retry: 125 /* 126 * If the process ID prototype has wrapped around, 127 * restart somewhat above 0, as the low-numbered procs 128 * tend to include daemons that don't exit. 129 */ 130 if (nextpid >= PID_MAX) { 131 nextpid = 100; 132 pidchecked = 0; 133 } 134 if (nextpid >= pidchecked) { 135 int doingzomb = 0; 136 137 pidchecked = PID_MAX; 138 /* 139 * Scan the active and zombie procs to check whether this pid 140 * is in use. Remember the lowest pid that's greater 141 * than nextpid, so we can avoid checking for a while. 142 */ 143 p2 = (struct proc *)allproc; 144 again: 145 for (; p2 != NULL; p2 = p2->p_next) { 146 while (p2->p_pid == nextpid || 147 p2->p_pgrp->pg_id == nextpid) { 148 nextpid++; 149 if (nextpid >= pidchecked) 150 goto retry; 151 } 152 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 153 pidchecked = p2->p_pid; 154 if (p2->p_pgrp->pg_id > nextpid && 155 pidchecked > p2->p_pgrp->pg_id) 156 pidchecked = p2->p_pgrp->pg_id; 157 } 158 if (!doingzomb) { 159 doingzomb = 1; 160 p2 = zombproc; 161 goto again; 162 } 163 } 164 165 166 /* 167 * Link onto allproc (this should probably be delayed). 168 * Heavy use of volatile here to prevent the compiler from 169 * rearranging code. Yes, it *is* terribly ugly, but at least 170 * it works. 171 */ 172 nprocs++; 173 p2 = newproc; 174 #define Vp2 ((volatile struct proc *)p2) 175 Vp2->p_stat = SIDL; /* protect against others */ 176 Vp2->p_pid = nextpid; 177 /* 178 * This is really: 179 * p2->p_next = allproc; 180 * allproc->p_prev = &p2->p_next; 181 * p2->p_prev = &allproc; 182 * allproc = p2; 183 * The assignment via allproc is legal since it is never NULL. 184 */ 185 *(volatile struct proc **)&Vp2->p_next = allproc; 186 *(volatile struct proc ***)&allproc->p_prev = 187 (volatile struct proc **)&Vp2->p_next; 188 *(volatile struct proc ***)&Vp2->p_prev = &allproc; 189 allproc = Vp2; 190 #undef Vp2 191 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 192 193 /* Insert on the hash chain. */ 194 hash = &pidhash[PIDHASH(p2->p_pid)]; 195 p2->p_hash = *hash; 196 *hash = p2; 197 198 /* 199 * Make a proc table entry for the new process. 200 * Start by zeroing the section of proc that is zero-initialized, 201 * then copy the section that is copied directly from the parent. 202 */ 203 bzero(&p2->p_startzero, 204 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 205 bcopy(&p1->p_startcopy, &p2->p_startcopy, 206 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 207 208 /* 209 * Duplicate sub-structures as needed. 210 * Increase reference counts on shared objects. 211 * The p_stats and p_sigacts substructs are set in vm_fork. 212 */ 213 p2->p_flag = P_INMEM; 214 if (p1->p_flag & P_PROFIL) 215 startprofclock(p2); 216 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 217 M_SUBPROC, M_WAITOK); 218 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 219 p2->p_cred->p_refcnt = 1; 220 crhold(p1->p_ucred); 221 222 /* bump references to the text vnode (for procfs) */ 223 p2->p_textvp = p1->p_textvp; 224 if (p2->p_textvp) 225 VREF(p2->p_textvp); 226 227 p2->p_fd = fdcopy(p1); 228 /* 229 * If p_limit is still copy-on-write, bump refcnt, 230 * otherwise get a copy that won't be modified. 231 * (If PL_SHAREMOD is clear, the structure is shared 232 * copy-on-write.) 233 */ 234 if (p1->p_limit->p_lflags & PL_SHAREMOD) 235 p2->p_limit = limcopy(p1->p_limit); 236 else { 237 p2->p_limit = p1->p_limit; 238 p2->p_limit->p_refcnt++; 239 } 240 241 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 242 p2->p_flag |= P_CONTROLT; 243 if (isvfork) 244 p2->p_flag |= P_PPWAIT; 245 p2->p_pgrpnxt = p1->p_pgrpnxt; 246 p1->p_pgrpnxt = p2; 247 p2->p_pptr = p1; 248 p2->p_osptr = p1->p_cptr; 249 if (p1->p_cptr) 250 p1->p_cptr->p_ysptr = p2; 251 p1->p_cptr = p2; 252 #ifdef KTRACE 253 /* 254 * Copy traceflag and tracefile if enabled. 255 * If not inherited, these were zeroed above. 256 */ 257 if (p1->p_traceflag&KTRFAC_INHERIT) { 258 p2->p_traceflag = p1->p_traceflag; 259 if ((p2->p_tracep = p1->p_tracep) != NULL) 260 VREF(p2->p_tracep); 261 } 262 #endif 263 264 /* 265 * set priority of child to be that of parent 266 */ 267 p2->p_estcpu = p1->p_estcpu; 268 269 /* 270 * This begins the section where we must prevent the parent 271 * from being swapped. 272 */ 273 p1->p_flag |= P_NOSWAP; 274 275 /* 276 * Set return values for child before vm_fork, 277 * so they can be copied to child stack. 278 * We return parent pid, and mark as child in retval[1]. 279 * NOTE: the kernel stack may be at a different location in the child 280 * process, and thus addresses of automatic variables (including retval) 281 * may be invalid after vm_fork returns in the child process. 282 */ 283 retval[0] = p1->p_pid; 284 retval[1] = 1; 285 if (vm_fork(p1, p2, isvfork)) { 286 /* 287 * Child process. Set start time and get to work. 288 */ 289 microtime(&runtime); 290 p2->p_stats->p_start = runtime; 291 p2->p_acflag = AFORK; 292 return (0); 293 } 294 295 /* 296 * Make child runnable and add to run queue. 297 */ 298 (void) splhigh(); 299 p2->p_stat = SRUN; 300 setrunqueue(p2); 301 (void) spl0(); 302 303 /* 304 * Now can be swapped. 305 */ 306 p1->p_flag &= ~P_NOSWAP; 307 308 /* 309 * Preserve synchronization semantics of vfork. If waiting for 310 * child to exec or exit, set P_PPWAIT on child, and sleep on our 311 * proc (in case of exit). 312 */ 313 if (isvfork) 314 while (p2->p_flag & P_PPWAIT) 315 tsleep(p1, PWAIT, "ppwait", 0); 316 317 /* 318 * Return child pid to parent process, 319 * marking us as parent via retval[1]. 320 */ 321 retval[0] = p2->p_pid; 322 retval[1] = 0; 323 return (0); 324 } 325