Get rid of E_SIGNAL_PIPE.
[paraslash.git] / signal.c
1 /*
2 * Copyright (C) 2004-2006 Andre Noll <maan@systemlinux.org>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6 /** \file signal.c signal handling functions */
7
8 #include <signal.h>
9 #include <sys/types.h>
10 #include <dirent.h>
11
12 #include "para.h"
13 #include "error.h"
14 #include "fd.h"
15
16 static int signal_pipe[2];
17
18 /**
19 * Initialize the paraslash signal subsystem.
20 *
21 * This function creates a pipe, the signal pipe, to deliver pending
22 * signals to the application (Bernstein's trick). It should be called
23 * during the application's startup part, followed by subsequent calls
24 * to para_install_sighandler() for each signal that should be caught.
25 *
26 * para_signal_init() installs a generic signal handler which is used for all
27 * signals simultaneously. When a signal arrives, this generic signal handler
28 * writes the corresponding signal number to the signal pipe so that the
29 * application can test for pending signals simply by checking the signal pipe
30 * for reading, e.g. by using the select(2) system call.
31 *
32 * \return This function either succeeds or calls exit(2) to terminate
33 * the current process. On success, the file descriptor of the signal pipe is
34 * returned.
35 */
36 int para_signal_init(void)
37 {
38 int ret;
39 if (pipe(signal_pipe) < 0) {
40 ret = -ERRNO_TO_PARA_ERROR(errno);
41 goto err_out;
42 }
43 ret = mark_fd_nonblock(signal_pipe[0]);
44 if (ret < 0)
45 goto err_out;
46 ret = mark_fd_nonblock(signal_pipe[1]);
47 if (ret < 0)
48 goto err_out;
49 return signal_pipe[0];
50 err_out:
51 PARA_EMERG_LOG("%s\n", PARA_STRERROR(-ret));
52 exit(EXIT_FAILURE);
53 }
54
55 /*
56 * just write one integer to signal pipe
57 */
58 static void generic_signal_handler(int s)
59 {
60 write(signal_pipe[1], &s, sizeof(int));
61 //fprintf(stderr, "got sig %i, write returned %d\n", s, ret);
62 }
63
64 /**
65 * reap one child
66 *
67 * call waitpid() and print a log message containing the pid
68 * and the cause of the child's death.
69 *
70 * \return Like \p waitpid(), this function returns the process ID of the
71 * terminated child; on error, \p -E_WAITPID is returned.
72 * \sa waitpid(2)
73 */
74 pid_t para_reap_child(void)
75 {
76 int status;
77 pid_t pid = waitpid(-1, &status, WNOHANG);
78
79 if (pid <= 0) {
80 if (pid < 0)
81 pid = -E_WAITPID;
82 return pid;
83 }
84 if (WIFEXITED(status))
85 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", pid,
86 WEXITSTATUS(status));
87 else if (WIFSIGNALED(status))
88 PARA_DEBUG_LOG("child %i was killed by signal %i\n", pid,
89 WTERMSIG(status));
90 else
91 PARA_WARNING_LOG("child %i terminated abormally\n", pid);
92 return pid;
93 }
94
95 /**
96 * paraslash's zombie killer
97 *
98 * It just calls \p para_reap_child() until there are no more children left to
99 * reap.
100 */
101 void para_reap_children(void)
102 {
103 while (para_reap_child() > 0)
104 ; /* nothing */
105 }
106
107 /**
108 * wrapper around signal(2)
109 * \param sig the number of the signal to catch
110 *
111 * This installs the generic signal handler for the given signal.
112 * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
113 * \sa signal(2)
114 */
115 int para_install_sighandler(int sig)
116 {
117 PARA_DEBUG_LOG("catching signal %d\n", sig);
118 return signal(sig, &generic_signal_handler) == SIG_ERR? -E_SIGNAL_SIG_ERR : 1;
119 }
120
121 /**
122 * return number of next pending signal
123 *
124 * This should be called if the fd for the signal pipe is ready for reading.
125 *
126 * \return On success, the number of the received signal is returned. \p
127 * -E_SIGNAL_READ is returned if a read error occurred while reading the signal
128 * pipe. If the read was interrupted by another signal the function returns 0.
129 */
130 int para_next_signal(void)
131 {
132 int s;
133 ssize_t r;
134
135 if ((r = read(signal_pipe[0], &s, sizeof(s)) == sizeof(s)) > 0) {
136 PARA_DEBUG_LOG("next signal: %d\n", s);
137 return s;
138 }
139 return r < 0 && (errno != EAGAIN)? 0 : -E_SIGNAL_READ;
140 }