NAME section for manpage
[dss.git] / signal.c
1 /*
2 * Copyright (C) 2004-2008 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 <string.h>
9 #include <errno.h>
10 #include <signal.h>
11 #include <sys/types.h>
12 #include <sys/wait.h>
13 #include <dirent.h>
14 #include <assert.h>
15 #include <stdio.h>
16 #include <unistd.h>
17 #include <signal.h>
18 #include <stdlib.h>
19 #include <sys/select.h>
20
21
22 #include "gcc-compat.h"
23 #include "error.h"
24 #include "log.h"
25 #include "string.h"
26 #include "fd.h"
27
28 static int signal_pipe[2];
29
30 /**
31 * Initialize the signal subsystem.
32 *
33 * This function creates a pipe, the signal pipe, to deliver pending signals to
34 * the application (Bernstein's trick). It should be called during the
35 * application's startup part, followed by subsequent calls to
36 * install_sighandler() for each signal that should be caught.
37 *
38 * signal_init() installs a generic signal handler which is used for all
39 * signals simultaneously. When a signal arrives, this generic signal handler
40 * writes the corresponding signal number to the signal pipe so that the
41 * application can test for pending signals simply by checking the signal pipe
42 * for reading, e.g. by using the select(2) system call.
43 *
44 * \return This function either succeeds or calls exit(2) to terminate
45 * the current process. On success, the file descriptor of the signal pipe is
46 * returned.
47 */
48 int signal_init(void)
49 {
50 int ret;
51 if (pipe(signal_pipe) < 0) {
52 ret = -ERRNO_TO_DSS_ERROR(errno);
53 goto err_out;
54 }
55 ret = mark_fd_nonblocking(signal_pipe[0]);
56 if (ret < 0)
57 goto err_out;
58 ret = mark_fd_nonblocking(signal_pipe[1]);
59 if (ret < 0)
60 goto err_out;
61 return signal_pipe[0];
62 err_out:
63 DSS_EMERG_LOG("%s\n", dss_strerror(-ret));
64 exit(EXIT_FAILURE);
65 }
66
67 /*
68 * just write one integer to signal pipe
69 */
70 static void generic_signal_handler(int s)
71 {
72 write(signal_pipe[1], &s, sizeof(int));
73 //fprintf(stderr, "got sig %i\n", s);
74 }
75
76 /**
77 * Reap one child.
78 *
79 * \param pid In case a child died, its pid is returned here.
80 *
81 * Call waitpid() and print a log message containing the pid and the cause of
82 * the child's death.
83 *
84 * \return A (negative) error code on errors, zero, if no child died, one
85 * otherwise. If and only if the function returns one, the content of \a pid is
86 * meaningful.
87 *
88 * \sa waitpid(2)
89 */
90 int reap_child(pid_t *pid, int *status)
91 {
92 *pid = waitpid(-1, status, WNOHANG);
93
94 if (!*pid)
95 return 0;
96 if (*pid < 0)
97 return -ERRNO_TO_DSS_ERROR(errno);
98 if (WIFEXITED(*status))
99 DSS_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
100 WEXITSTATUS(*status));
101 else if (WIFSIGNALED(*status))
102 DSS_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
103 WTERMSIG(*status));
104 else
105 DSS_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
106 return 1;
107 }
108
109 /**
110 * Wrapper around signal(2)
111 *
112 * \param sig The number of the signal to catch.
113 *
114 * This installs the generic signal handler for the given signal.
115 *
116 * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
117 * \sa signal(2)
118 */
119 int install_sighandler(int sig)
120 {
121 DSS_DEBUG_LOG("catching signal %d\n", sig);
122 if (signal(sig, &generic_signal_handler) != SIG_ERR)
123 return 1;
124 return -E_SIGNAL_SIG_ERR;
125 }
126
127 /**
128 * Return number of next pending signal.
129 *
130 * This should be called if the fd for the signal pipe is ready for reading.
131 *
132 * \return On success, the number of the received signal is returned.
133 * If the read was interrupted by another signal the function returns 0.
134 * Otherwise a negative error code is returned.
135 */
136 int next_signal(void)
137 {
138 int s, err;
139 ssize_t r;
140
141 r = read(signal_pipe[0], &s, sizeof(s));
142 if (r == sizeof(s)) {
143 DSS_DEBUG_LOG("next signal: %d\n", s);
144 return s;
145 }
146 err = errno;
147 assert(r < 0);
148 if (err == EAGAIN)
149 return 0;
150 DSS_ERROR_LOG("failed to read from signal pipe\n");
151 return -ERRNO_TO_DSS_ERROR(err);
152 }
153
154 /**
155 * Close the signal pipe.
156 */
157 void signal_shutdown(void)
158 {
159 close(signal_pipe[1]);
160 }