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 
21 	if((flags&(RFPROC|RFFDG|RFMEM)) == (RFPROC|RFFDG)){
22 		/* check other flags before we commit */
23 		flags &= ~(RFPROC|RFFDG);
24 		n = (flags & ~(RFNOTEG|RFNAMEG|RFNOWAIT));
25 		if(n){
26 			werrstr("unknown flags %08ux in rfork", n);
27 			return -1;
28 		}
29 		if(flags&RFNOWAIT){
30 			/*
31 			 * BUG - should put the signal handler back after we
32 			 * finish, but I just don't care.  If a program calls with
33 			 * NOWAIT once, they're not likely to want child notes
34 			 * after that.
35 			 */
36 			signal(SIGCHLD, nop);
37 			if(pipe(p) < 0)
38 				return -1;
39 		}
40 		pid = fork();
41 		if(pid == -1)
42 			return -1;
43 		if(flags&RFNOWAIT){
44 			flags &= ~RFNOWAIT;
45 			if(pid){
46 				/*
47 				 * Parent - wait for child to fork wait-free child.
48 				 * Then read pid from pipe.  Assume pipe buffer can absorb the write.
49 				 */
50 				close(p[1]);
51 				status = 0;
52 				if(wait4(pid, &status, 0, 0) < 0){
53 					werrstr("pipe dance - wait4 - %r");
54 					close(p[0]);
55 					return -1;
56 				}
57 				n = readn(p[0], buf, sizeof buf-1);
58 				close(p[0]);
59 				if(!WIFEXITED(status) || WEXITSTATUS(status)!=0 || n <= 0){
60 					if(!WIFEXITED(status))
61 						werrstr("pipe dance - !exited 0x%ux", status);
62 					else if(WEXITSTATUS(status) != 0)
63 						werrstr("pipe dance - non-zero status 0x%ux", status);
64 					else if(n < 0)
65 						werrstr("pipe dance - pipe read error - %r");
66 					else if(n == 0)
67 						werrstr("pipe dance - pipe read eof");
68 					else
69 						werrstr("pipe dance - unknown failure");
70 					return -1;
71 				}
72 				buf[n] = 0;
73 				if(buf[0] == 'x'){
74 					werrstr("%s", buf+2);
75 					return -1;
76 				}
77 				pid = strtol(buf, &q, 0);
78 			}else{
79 				/*
80 				 * Child - fork a new child whose wait message can't 
81 				 * get back to the parent because we're going to exit!
82 				 */
83 				signal(SIGCHLD, SIG_IGN);
84 				close(p[0]);
85 				pid = fork();
86 				if(pid){
87 					/* Child parent - send status over pipe and exit. */
88 					if(pid > 0)
89 						fprint(p[1], "%d", pid);
90 					else
91 						fprint(p[1], "x %r");
92 					close(p[1]);
93 					_exit(0);
94 				}else{
95 					/* Child child - close pipe. */
96 					close(p[1]);
97 				}
98 			}
99 		}
100 		if(pid != 0)
101 			return pid;
102 	}
103 	if(flags&RFPROC){
104 		werrstr("cannot use rfork for shared memory -- use ffork");
105 		return -1;
106 	}
107 	if(flags&RFNAMEG){
108 		/* XXX set $NAMESPACE to a new directory */
109 		flags &= ~RFNAMEG;
110 	}
111 	if(flags&RFNOTEG){
112 		setpgid(0, getpid());
113 		flags &= ~RFNOTEG;
114 	}
115 	if(flags&RFNOWAIT){
116 		werrstr("cannot use RFNOWAIT without RFPROC");
117 		return -1;
118 	}
119 	if(flags){
120 		werrstr("unknown flags %08ux in rfork", flags);
121 		return -1;
122 	}
123 	return 0;
124 }