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