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	rfork.c - 9base - revived minimalist port of Plan 9 userland to Unix
	git clone git://git.suckless.org/9base
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	rfork.c (2824B)
	---
	1 #include <u.h>
	2 #include <sys/wait.h>
	3 #include <signal.h>
	4 #include <libc.h>
	5 #undef rfork
	6
	7 static void
	8 nop(int x)
	9 {
	10 USED(x);
	11 }
	12
	13 int
	14 p9rfork(int flags)
	15 {
	16 int pid, status;
	17 int p[2];
	18 int n;
	19 char buf[128], *q;
	20 extern char **environ;
	21
	22 if((flags&(RFPROC\|RFFDG\|RFMEM)) == (RFPROC\|RFFDG)){
	23 /* check other flags before we commit */
	24 flags &= ~(RFPROC\|RFFDG\|RFENVG);
	25 n = (flags & ~(RFNOTEG\|RFNAMEG\|RFNOWAIT\|RFCENVG));
	26 if(n){
	27 werrstr("unknown flags %08ux in rfork", n);
	28 return -1;
	29 }
	30 if(flags&RFNOWAIT){
	31 /*
	32 * BUG - should put the signal handler back afte…
	33 * finish, but I just don't care. If a program …
	34 * NOWAIT once, they're not likely to want child…
	35 * after that.
	36 */
	37 signal(SIGCHLD, nop);
	38 if(pipe(p) < 0)
	39 return -1;
	40 }
	41 pid = fork();
	42 if(pid == -1)
	43 return -1;
	44 if(flags&RFNOWAIT){
	45 flags &= ~RFNOWAIT;
	46 if(pid){
	47 /*
	48 * Parent - wait for child to fork wait-…
	49 * Then read pid from pipe. Assume pipe…
	50 */
	51 close(p[1]);
	52 status = 0;
	53 if(wait4(pid, &status, 0, 0) < 0){
	54 werrstr("pipe dance - wait4 - %r…
	55 close(p[0]);
	56 return -1;
	57 }
	58 n = readn(p[0], buf, sizeof buf-1);
	59 close(p[0]);
	60 if(!WIFEXITED(status) \|\| WEXITSTATUS(sta…
	61 if(!WIFEXITED(status))
	62 werrstr("pipe dance - !e…
	63 else if(WEXITSTATUS(status) != 0)
	64 werrstr("pipe dance - no…
	65 else if(n < 0)
	66 werrstr("pipe dance - pi…
	67 else if(n == 0)
	68 werrstr("pipe dance - pi…
	69 else
	70 werrstr("pipe dance - un…
	71 return -1;
	72 }
	73 buf[n] = 0;
	74 if(buf[0] == 'x'){
	75 werrstr("%s", buf+2);
	76 return -1;
	77 }
	78 pid = strtol(buf, &q, 0);
	79 }else{
	80 /*
	81 * Child - fork a new child whose wait m…
	82 * get back to the parent because we're …
	83 */
	84 signal(SIGCHLD, SIG_IGN);
	85 close(p[0]);
	86 pid = fork();
	87 if(pid){
	88 /* Child parent - send status ov…
	89 if(pid > 0)
	90 fprint(p[1], "%d", pid);
	91 else
	92 fprint(p[1], "x %r");
	93 close(p[1]);
	94 _exit(0);
	95 }else{
	96 /* Child child - close pipe. */
	97 close(p[1]);
	98 }
	99 }
	100 }
	101 if(pid != 0)
	102 return pid;
	103 if(flags&RFCENVG)
	104 if(environ)
	105 *environ = nil;
	106 }
	107 if(flags&RFPROC){
	108 werrstr("cannot use rfork for shared memory -- use libth…
	109 return -1;
	110 }
	111 if(flags&RFNAMEG){
	112 /* XXX set $NAMESPACE to a new directory */
	113 flags &= ~RFNAMEG;
	114 }
	115 if(flags&RFNOTEG){
	116 setpgid(0, getpid());
	117 flags &= ~RFNOTEG;
	118 }
	119 if(flags&RFNOWAIT){
	120 werrstr("cannot use RFNOWAIT without RFPROC");
	121 return -1;
	122 }
	123 if(flags){
	124 werrstr("unknown flags %08ux in rfork", flags);
	125 return -1;
	126 }
	127 return 0;
	128 }