kern_fork.c revision 1.26
1 /* $NetBSD: kern_fork.c,v 1.26 1995/12/09 04:23:07 mycroft 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 8.6 (Berkeley) 4/8/94 41 */ 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/map.h> 46 #include <sys/filedesc.h> 47 #include <sys/kernel.h> 48 #include <sys/malloc.h> 49 #include <sys/proc.h> 50 #include <sys/resourcevar.h> 51 #include <sys/vnode.h> 52 #include <sys/file.h> 53 #include <sys/acct.h> 54 #include <sys/ktrace.h> 55 56 int nprocs = 1; /* process 0 */ 57 58 int 59 sys_fork(p, v, retval) 60 struct proc *p; 61 void *v; 62 register_t *retval; 63 { 64 65 return (fork1(p, 0, retval)); 66 } 67 68 int 69 sys_vfork(p, v, retval) 70 struct proc *p; 71 void *v; 72 register_t *retval; 73 { 74 75 return (fork1(p, 1, retval)); 76 } 77 78 int 79 fork1(p1, isvfork, retval) 80 register struct proc *p1; 81 int isvfork; 82 register_t *retval; 83 { 84 register struct proc *p2; 85 register uid_t uid; 86 struct proc *newproc; 87 struct proc **hash; 88 int count; 89 static int nextpid, pidchecked = 0; 90 91 /* 92 * Although process entries are dynamically created, we still keep 93 * a global limit on the maximum number we will create. Don't allow 94 * a nonprivileged user to use the last process; don't let root 95 * exceed the limit. The variable nprocs is the current number of 96 * processes, maxproc is the limit. 97 */ 98 uid = p1->p_cred->p_ruid; 99 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 100 tablefull("proc"); 101 return (EAGAIN); 102 } 103 104 /* 105 * Increment the count of procs running with this uid. Don't allow 106 * a nonprivileged user to exceed their current limit. 107 */ 108 count = chgproccnt(uid, 1); 109 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 110 (void)chgproccnt(uid, -1); 111 return (EAGAIN); 112 } 113 114 /* Allocate new proc. */ 115 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 116 117 /* 118 * Find an unused process ID. We remember a range of unused IDs 119 * ready to use (from nextpid+1 through pidchecked-1). 120 */ 121 nextpid++; 122 retry: 123 /* 124 * If the process ID prototype has wrapped around, 125 * restart somewhat above 0, as the low-numbered procs 126 * tend to include daemons that don't exit. 127 */ 128 if (nextpid >= PID_MAX) { 129 nextpid = 100; 130 pidchecked = 0; 131 } 132 if (nextpid >= pidchecked) { 133 int doingzomb = 0; 134 135 pidchecked = PID_MAX; 136 /* 137 * Scan the active and zombie procs to check whether this pid 138 * is in use. Remember the lowest pid that's greater 139 * than nextpid, so we can avoid checking for a while. 140 */ 141 p2 = allproc.lh_first; 142 again: 143 for (; p2 != 0; p2 = p2->p_list.le_next) { 144 while (p2->p_pid == nextpid || 145 p2->p_pgrp->pg_id == nextpid) { 146 nextpid++; 147 if (nextpid >= pidchecked) 148 goto retry; 149 } 150 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 151 pidchecked = p2->p_pid; 152 if (p2->p_pgrp->pg_id > nextpid && 153 pidchecked > p2->p_pgrp->pg_id) 154 pidchecked = p2->p_pgrp->pg_id; 155 } 156 if (!doingzomb) { 157 doingzomb = 1; 158 p2 = zombproc.lh_first; 159 goto again; 160 } 161 } 162 163 nprocs++; 164 p2 = newproc; 165 p2->p_stat = SIDL; /* protect against others */ 166 p2->p_pid = nextpid; 167 LIST_INSERT_HEAD(&allproc, p2, p_list); 168 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 169 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 170 171 /* 172 * Make a proc table entry for the new process. 173 * Start by zeroing the section of proc that is zero-initialized, 174 * then copy the section that is copied directly from the parent. 175 */ 176 bzero(&p2->p_startzero, 177 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 178 bcopy(&p1->p_startcopy, &p2->p_startcopy, 179 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 180 181 /* 182 * Duplicate sub-structures as needed. 183 * Increase reference counts on shared objects. 184 * The p_stats and p_sigacts substructs are set in vm_fork. 185 */ 186 p2->p_flag = P_INMEM; 187 p2->p_emul = p1->p_emul; 188 if (p1->p_flag & P_PROFIL) 189 startprofclock(p2); 190 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 191 M_SUBPROC, M_WAITOK); 192 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 193 p2->p_cred->p_refcnt = 1; 194 crhold(p1->p_ucred); 195 196 /* bump references to the text vnode (for procfs) */ 197 p2->p_textvp = p1->p_textvp; 198 if (p2->p_textvp) 199 VREF(p2->p_textvp); 200 201 p2->p_fd = fdcopy(p1); 202 /* 203 * If p_limit is still copy-on-write, bump refcnt, 204 * otherwise get a copy that won't be modified. 205 * (If PL_SHAREMOD is clear, the structure is shared 206 * copy-on-write.) 207 */ 208 if (p1->p_limit->p_lflags & PL_SHAREMOD) 209 p2->p_limit = limcopy(p1->p_limit); 210 else { 211 p2->p_limit = p1->p_limit; 212 p2->p_limit->p_refcnt++; 213 } 214 215 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 216 p2->p_flag |= P_CONTROLT; 217 if (isvfork) 218 p2->p_flag |= P_PPWAIT; 219 LIST_INSERT_AFTER(p1, p2, p_pglist); 220 p2->p_pptr = p1; 221 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 222 LIST_INIT(&p2->p_children); 223 224 #ifdef KTRACE 225 /* 226 * Copy traceflag and tracefile if enabled. 227 * If not inherited, these were zeroed above. 228 */ 229 if (p1->p_traceflag&KTRFAC_INHERIT) { 230 p2->p_traceflag = p1->p_traceflag; 231 if ((p2->p_tracep = p1->p_tracep) != NULL) 232 VREF(p2->p_tracep); 233 } 234 #endif 235 236 /* 237 * This begins the section where we must prevent the parent 238 * from being swapped. 239 */ 240 p1->p_holdcnt++; 241 242 #ifdef __FORK_BRAINDAMAGE 243 /* 244 * Set return values for child before vm_fork, 245 * so they can be copied to child stack. 246 * We return 0, rather than the traditional behaviour of modifying the 247 * return value in the system call stub. 248 * NOTE: the kernel stack may be at a different location in the child 249 * process, and thus addresses of automatic variables (including retval) 250 * may be invalid after vm_fork returns in the child process. 251 */ 252 retval[0] = 0; 253 retval[1] = 0; 254 if (vm_fork(p1, p2)) 255 return (0); 256 #else 257 /* 258 * Finish creating the child process. It will return through a 259 * different path later. 260 */ 261 vm_fork(p1, p2); 262 #endif 263 264 /* 265 * Make child runnable, set start time, and add to run queue. 266 */ 267 (void) splstatclock(); 268 p2->p_stats->p_start = time; 269 p2->p_acflag = AFORK; 270 p2->p_stat = SRUN; 271 setrunqueue(p2); 272 (void) spl0(); 273 274 /* 275 * Now can be swapped. 276 */ 277 p1->p_holdcnt--; 278 279 /* 280 * Preserve synchronization semantics of vfork. If waiting for 281 * child to exec or exit, set P_PPWAIT on child, and sleep on our 282 * proc (in case of exit). 283 */ 284 if (isvfork) 285 while (p2->p_flag & P_PPWAIT) 286 tsleep(p1, PWAIT, "ppwait", 0); 287 288 /* 289 * Return child pid to parent process, 290 * marking us as parent via retval[1]. 291 */ 292 retval[0] = p2->p_pid; 293 retval[1] = 0; 294 return (0); 295 } 296
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