2 * Copyright (C) 2004-2010 Andre Noll <maan@systemlinux.org>
4 * Licensed under the GPL v2. For licencing details see COPYING.
10 #include <sys/types.h>
18 #include <sys/select.h>
21 #include "gcc-compat.h"
28 static int signal_pipe[2];
31 * Initialize the signal subsystem.
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.
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.
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
51 if (pipe(signal_pipe) < 0) {
52 ret = -ERRNO_TO_DSS_ERROR(errno);
55 ret = mark_fd_nonblocking(signal_pipe[0]);
58 ret = mark_fd_nonblocking(signal_pipe[1]);
61 return signal_pipe[0];
63 DSS_EMERG_LOG(("%s\n", dss_strerror(-ret)));
68 * just write one integer to signal pipe
70 static void generic_signal_handler(int s)
72 write(signal_pipe[1], &s, sizeof(int));
78 * \param pid In case a child died, its pid is returned here.
80 * Call waitpid() and print a log message containing the pid and the cause of
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
89 int reap_child(pid_t *pid, int *status)
91 *pid = waitpid(-1, status, WNOHANG);
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,
104 DSS_WARNING_LOG(("child %i terminated abormally\n", (int)*pid));
109 * Wrapper around signal(2)
111 * \param sig The number of the signal to catch.
113 * This installs the generic signal handler for the given signal.
115 * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
118 int install_sighandler(int sig)
120 DSS_DEBUG_LOG(("catching signal %d\n", sig));
121 if (signal(sig, &generic_signal_handler) != SIG_ERR)
123 return -E_SIGNAL_SIG_ERR;
127 * Return number of next pending signal.
129 * This should be called if the fd for the signal pipe is ready for reading.
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.
135 int next_signal(void)
140 r = read(signal_pipe[0], &s, sizeof(s));
141 if (r == sizeof(s)) {
142 DSS_DEBUG_LOG(("next signal: %d\n", s));
149 DSS_ERROR_LOG(("failed to read from signal pipe\n"));
150 return -ERRNO_TO_DSS_ERROR(err);
154 * Close the signal pipe.
156 void signal_shutdown(void)
158 close(signal_pipe[1]);