1 #include <u.h>
2 #include <sys/wait.h>
3 #include <signal.h>
4 #include <libc.h>
5 #undef rfork
6 
7 int
8 p9rfork(int flags)
9 {
10 	int pid, status;
11 	int p[2];
12 	int n;
13 	char buf[128], *q;
14 
15 	if((flags&(RFPROC|RFFDG|RFMEM)) == (RFPROC|RFFDG)){
16 		/* check other flags before we commit */
17 		flags &= ~(RFPROC|RFFDG);
18 		n = (flags & ~(RFNOTEG|RFNAMEG|RFNOWAIT));
19 		if(n){
20 			werrstr("unknown flags %08ux in rfork", n);
21 			return -1;
22 		}
23 		if(flags&RFNOWAIT){
24 			if(pipe(p) < 0)
25 				return -1;
26 		}
27 		pid = fork();
28 		if(pid == -1)
29 			return -1;
30 		if(flags&RFNOWAIT){
31 			flags &= ~RFNOWAIT;
32 			if(pid){
33 				/*
34 				 * Parent - wait for child to fork wait-free child.
35 				 * Then read pid from pipe.  Assume pipe buffer can absorb the write.
36 				 */
37 				close(p[1]);
38 				wait4(pid, &status, 0, 0);
39 				n = readn(p[0], buf, sizeof buf-1);
40 				close(p[0]);
41 				if(!WIFEXITED(status) || WEXITSTATUS(status)!=0 || n <= 0){
42 					werrstr("pipe dance failed in rfork");
43 					return -1;
44 				}
45 				buf[n] = 0;
46 				n = strtol(buf, &q, 0);
47 				if(*q != 0){
48 					werrstr("%s", q);
49 					return -1;
50 				}
51 				pid = n;
52 			}else{
53 				/*
54 				 * Child - fork a new child whose wait message can't 
55 				 * get back to the parent because we're going to exit!
56 				 */
57 				signal(SIGCHLD, SIG_IGN);
58 				close(p[0]);
59 				pid = fork();
60 				if(pid){
61 					/* Child parent - send status over pipe and exit. */
62 					if(pid > 0)
63 						fprint(p[1], "%d", pid);
64 					else
65 						fprint(p[1], " %r");
66 					close(p[1]);
67 					_exit(0);
68 				}else{
69 					/* Child child - close pipe. */
70 					close(p[1]);
71 				}
72 			}
73 		}
74 		if(pid != 0)
75 			return pid;
76 	}
77 	if(flags&RFPROC){
78 		werrstr("cannot use rfork for shared memory -- use ffork");
79 		return -1;
80 	}
81 	if(flags&RFNAMEG){
82 		/* XXX set $NAMESPACE to a new directory */
83 		flags &= ~RFNAMEG;
84 	}
85 	if(flags&RFNOTEG){
86 		setpgid(0, getpid());
87 		flags &= ~RFNOTEG;
88 	}
89 	if(flags&RFNOWAIT){
90 		werrstr("cannot use RFNOWAIT without RFPROC");
91 		return -1;
92 	}
93 	if(flags){
94 		werrstr("unknown flags %08ux in rfork", flags);
95 		return -1;
96 	}
97 	return 0;
98 }