Introduce para_sigaction().
[paraslash.git] / signal.c
1 /*
2 * Copyright (C) 2004-2009 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_nonblocking(signal_pipe[0]);
44 if (ret < 0)
45 goto err_out;
46 ret = mark_fd_nonblocking(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 ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
61
62 if (ret == sizeof(int))
63 return;
64 if (ret < 0)
65 PARA_EMERG_LOG("%s\n", strerror(errno));
66 else
67 PARA_EMERG_LOG("short write to signal pipe\n");
68 exit(EXIT_FAILURE);
69 }
70
71 /**
72 * Reap one child.
73 *
74 * \param pid In case a child died, its pid is returned here.
75 *
76 * Call waitpid() and print a log message containing the pid and the cause of
77 * the child's death.
78 *
79 * \return A (negative) paraslash error code on errors, zero, if no child died,
80 * one otherwise. If and only if the function returns one, the content of \a
81 * pid is meaningful.
82 *
83 * \sa waitpid(2).
84 */
85 int para_reap_child(pid_t *pid)
86 {
87 int status;
88 *pid = waitpid(-1, &status, WNOHANG);
89
90 if (!*pid)
91 return 0;
92 if (*pid < 0)
93 return -ERRNO_TO_PARA_ERROR(errno);
94 if (WIFEXITED(status))
95 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
96 WEXITSTATUS(status));
97 else if (WIFSIGNALED(status))
98 PARA_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
99 WTERMSIG(status));
100 else
101 PARA_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
102 return 1;
103 }
104
105 /**
106 * Paraslash's zombie killer.
107 *
108 * It just calls \p para_reap_child() until there are no more children left to
109 * reap.
110 */
111 void para_reap_children(void)
112 {
113 pid_t pid;
114
115 while (para_reap_child(&pid) > 0)
116 ; /* nothing */
117 }
118
119 /**
120 * Install the given handler for the given signal.
121 *
122 * \param sig The number of the signal to catch.
123 * \param handler to be installed, \p SIG_IGN, or \p SIG_DFL.
124 *
125 * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on
126 * errors.
127 *
128 * \sa sigaction(2).
129 */
130 int para_sigaction(int sig, void (*handler)(int))
131 {
132 struct sigaction act;
133
134 PARA_DEBUG_LOG("catching signal %d\n", sig);
135 act.sa_handler = handler;
136 sigemptyset(&act.sa_mask);
137 act.sa_flags = 0;
138 if (sig == SIGALRM) {
139 #ifdef SA_INTERRUPT /* SunOS */
140 act.sa_flags |= SA_INTERRUPT;
141 #endif
142 } else {
143 #ifdef SA_RESTART /* BSD */
144 act.sa_flags |= SA_RESTART;
145 #endif
146 }
147 if (sigaction(sig, &act, NULL) < 0)
148 return -E_SIGNAL_SIG_ERR;
149 return 1;
150 }
151
152 /**
153 * Install the generic signal handler for the given signal number.
154 *
155 * \param sig The number of the signal to catch.
156 *
157 * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on
158 * errors.
159 *
160 * \sa signal(2), sigaction(2).
161 */
162 int para_install_sighandler(int sig)
163 {
164 return para_sigaction(sig, &generic_signal_handler);
165 }
166
167 /**
168 * Return the number of next pending signal.
169 *
170 * This should be called if the fd for the signal pipe is ready for reading.
171 *
172 * \return On success, the number of the received signal is returned. If the
173 * read returned zero or was interrupted by another signal the function returns
174 * 0. Otherwise, a negative error value is returned.
175 */
176 int para_next_signal(void)
177 {
178 int s;
179 ssize_t r = read(signal_pipe[0], &s, sizeof(s));
180
181 if (!r) {
182 PARA_CRIT_LOG("read from signal pipe returned zero\n");
183 return 0;
184 }
185 if (r < 0) {
186 if (errno == EAGAIN || errno == EINTR)
187 return 0;
188 return -ERRNO_TO_PARA_ERROR(errno);
189 }
190 assert(r == sizeof(s));
191 PARA_DEBUG_LOG("next signal: %d\n", s);
192 return s;
193 }
194
195 /**
196 * Close the write end of the signal pipe.
197 */
198 void para_signal_shutdown(void)
199 {
200 close(signal_pipe[1]);
201 }