1 #include <fcntl.h>
2 #include <unistd.h>
3 #include "threadimpl.h"
4 
5 static void efork(int[3], int[2], char*, char**);
6 void
7 threadexec(Channel *pidc, int fd[3], char *prog, char *args[])
8 {
9 	int pfd[2];
10 	int n, pid;
11 	char exitstr[ERRMAX];
12 
13 	_threaddebug(DBGEXEC, "threadexec %s", prog);
14 	
15 	/*
16 	 * We want threadexec to behave like exec; if exec succeeds,
17 	 * never return, and if it fails, return with errstr set.
18 	 * Unfortunately, the exec happens in another proc since
19 	 * we have to wait for the exec'ed process to finish.
20 	 * To provide the semantics, we open a pipe with the 
21 	 * write end close-on-exec and hand it to the proc that
22 	 * is doing the exec.  If the exec succeeds, the pipe will
23 	 * close so that our read below fails.  If the exec fails,
24 	 * then the proc doing the exec sends the errstr down the
25 	 * pipe to us.
26 	 */
27 	if(pipe(pfd) < 0)
28 		goto Bad;
29 	if(fcntl(pfd[0], F_SETFD, 1) < 0)
30 		goto Bad;
31 	if(fcntl(pfd[1], F_SETFD, 1) < 0)
32 		goto Bad;
33 
34 	switch(pid = fork()){
35 	case -1:
36 		close(pfd[0]);
37 		close(pfd[1]);
38 		goto Bad;
39 	case 0:
40 		efork(fd, pfd, prog, args);
41 		_exit(0);
42 	default:
43 		break;
44 	}
45 
46 	close(pfd[1]);
47 	if((n = read(pfd[0], exitstr, ERRMAX-1)) > 0){	/* exec failed */
48 		exitstr[n] = '\0';
49 		errstr(exitstr, ERRMAX);
50 		close(pfd[0]);
51 		goto Bad;
52 	}
53 	close(pfd[0]);
54 	close(fd[0]);
55 	if(fd[1] != fd[0])
56 		close(fd[1]);
57 	if(fd[2] != fd[1] && fd[2] != fd[0])
58 		close(fd[2]);
59 	if(pidc)
60 		sendul(pidc, pid);
61 
62 	_threaddebug(DBGEXEC, "threadexec schedexecwait");
63 	threadexits(0);
64 
65 Bad:
66 	_threaddebug(DBGEXEC, "threadexec bad %r");
67 	if(pidc)
68 		sendul(pidc, ~0);
69 }
70 
71 void
72 threadexecl(Channel *pidc, int fd[3], char *f, ...)
73 {
74 	threadexec(pidc, fd, f, &f+1);
75 }
76 
77 static void
78 efork(int stdfd[3], int fd[2], char *prog, char **args)
79 {
80 	char buf[ERRMAX];
81 	int i;
82 
83 	_threaddebug(DBGEXEC, "_schedexec %s -- calling execv", prog);
84 	dup(stdfd[0], 0);
85 	dup(stdfd[1], 1);
86 	dup(stdfd[2], 2);
87 	for(i=3; i<40; i++)
88 		if(i != fd[1])
89 			close(i);
90 	rfork(RFNOTEG);
91 	execvp(prog, args);
92 	_threaddebug(DBGEXEC, "_schedexec failed: %r");
93 	rerrstr(buf, sizeof buf);
94 	if(buf[0]=='\0')
95 		strcpy(buf, "exec failed");
96 	write(fd[1], buf, strlen(buf));
97 	close(fd[1]);
98 	_exits(buf);
99 }
100