1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
|
#include <u.h>
#include <sys/wait.h>
#include <signal.h>
#include <libc.h>
#undef rfork
static void
nop(int x)
{
USED(x);
}
int
p9rfork(int flags)
{
int pid, status;
int p[2];
int n;
char buf[128], *q;
extern char **environ;
struct sigaction oldchld;
memset(&oldchld, 0, sizeof oldchld);
if((flags&(RFPROC|RFFDG|RFMEM)) == (RFPROC|RFFDG)){
/* check other flags before we commit */
flags &= ~(RFPROC|RFFDG|RFENVG);
n = (flags & ~(RFNOTEG|RFNAMEG|RFNOWAIT|RFCENVG));
if(n){
werrstr("unknown flags %08ux in rfork", n);
return -1;
}
if(flags&RFNOWAIT){
sigaction(SIGCHLD, nil, &oldchld);
signal(SIGCHLD, nop);
if(pipe(p) < 0)
return -1;
}
pid = fork();
if(pid == -1)
return -1;
if(flags&RFNOWAIT){
flags &= ~RFNOWAIT;
if(pid){
/*
* Parent - wait for child to fork wait-free child.
* Then read pid from pipe. Assume pipe buffer can absorb the write.
*/
close(p[1]);
status = 0;
if(wait4(pid, &status, 0, 0) < 0){
werrstr("pipe dance - wait4 - %r");
close(p[0]);
return -1;
}
n = readn(p[0], buf, sizeof buf-1);
close(p[0]);
if(!WIFEXITED(status) || WEXITSTATUS(status)!=0 || n <= 0){
if(!WIFEXITED(status))
werrstr("pipe dance - !exited 0x%ux", status);
else if(WEXITSTATUS(status) != 0)
werrstr("pipe dance - non-zero status 0x%ux", status);
else if(n < 0)
werrstr("pipe dance - pipe read error - %r");
else if(n == 0)
werrstr("pipe dance - pipe read eof");
else
werrstr("pipe dance - unknown failure");
return -1;
}
buf[n] = 0;
if(buf[0] == 'x'){
werrstr("%s", buf+2);
return -1;
}
pid = strtol(buf, &q, 0);
}else{
/*
* Child - fork a new child whose wait message can't
* get back to the parent because we're going to exit!
*/
signal(SIGCHLD, SIG_IGN);
close(p[0]);
pid = fork();
if(pid){
/* Child parent - send status over pipe and exit. */
if(pid > 0)
fprint(p[1], "%d", pid);
else
fprint(p[1], "x %r");
close(p[1]);
_exit(0);
}else{
/* Child child - close pipe. */
close(p[1]);
}
}
sigaction(SIGCHLD, &oldchld, nil);
}
if(pid != 0)
return pid;
if(flags&RFCENVG)
if(environ)
*environ = nil;
}
if(flags&RFPROC){
werrstr("cannot use rfork for shared memory -- use libthread");
return -1;
}
if(flags&RFNAMEG){
/* XXX set $NAMESPACE to a new directory */
flags &= ~RFNAMEG;
}
if(flags&RFNOTEG){
setpgid(0, getpid());
flags &= ~RFNOTEG;
}
if(flags&RFNOWAIT){
werrstr("cannot use RFNOWAIT without RFPROC");
return -1;
}
if(flags){
werrstr("unknown flags %08ux in rfork", flags);
return -1;
}
return 0;
}
|