2 * Copyright (C) 2004-2013 Andre Noll <maan@systemlinux.org>
4 * Licensed under the GPL v2. For licencing details see COPYING.
6 /** \file signal.c Signal handling functions. */
18 static int signal_pipe
[2];
21 * Initialize the paraslash signal subsystem.
23 * This function creates a pipe, the signal pipe, to deliver pending
24 * signals to the application (Bernstein's trick). It should be called
25 * during the application's startup part, followed by subsequent calls
26 * to para_install_sighandler() for each signal that should be caught.
28 * A generic signal handler is used for all signals simultaneously. When a
29 * signal arrives, the signal handler writes the number of the signal received
30 * to one end of the signal pipe. The application can test for pending signals
31 * by checking if the file descriptor of the other end of the signal pipe is
32 * ready for reading, see select(2).
34 * \return This function either succeeds or calls exit(2) to terminate the
35 * current process. On success, the file descriptor of the read end of the
36 * signal pipe is returned.
38 int para_signal_init(void)
41 if (pipe(signal_pipe
) < 0) {
42 ret
= -ERRNO_TO_PARA_ERROR(errno
);
45 ret
= mark_fd_nonblocking(signal_pipe
[0]);
48 ret
= mark_fd_nonblocking(signal_pipe
[1]);
51 return signal_pipe
[0];
53 PARA_EMERG_LOG("%s\n", para_strerror(-ret
));
57 /* Write the signal number to signal pipe. */
58 static void generic_signal_handler(int s
)
61 * Signal handlers that make system calls must save a copy of errno on
62 * entry to the handler and restore it on exit, to prevent the
63 * possibility of overwriting a errno value that had previously been
64 * set in the main program.
66 int save_errno
= errno
;
67 ssize_t ret
= write(signal_pipe
[1], &s
, sizeof(int));
69 if (ret
== sizeof(int)) {
74 PARA_EMERG_LOG("%s\n", strerror(errno
));
76 PARA_EMERG_LOG("short write to signal pipe\n");
83 * \param pid In case a child died, its pid is returned here.
85 * Call waitpid() and print a log message containing the pid and the cause of
88 * \return A (negative) paraslash error code on errors, zero, if no child died,
89 * one otherwise. If and only if the function returns one, the content of \a
94 int para_reap_child(pid_t
*pid
)
97 *pid
= waitpid(-1, &status
, WNOHANG
);
102 return -ERRNO_TO_PARA_ERROR(errno
);
103 if (WIFEXITED(status
))
104 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid
,
105 WEXITSTATUS(status
));
106 else if (WIFSIGNALED(status
))
107 PARA_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid
,
110 PARA_WARNING_LOG("child %i terminated abormally\n", (int)*pid
);
115 * Install the given handler for the given signal.
117 * \param sig The number of the signal to catch.
118 * \param handler to be installed, \p SIG_IGN, or \p SIG_DFL.
120 * This either succeeds or calls exit(EXIT_FAILURE).
124 void para_sigaction(int sig
, void (*handler
)(int))
126 struct sigaction act
;
128 PARA_DEBUG_LOG("catching signal %d\n", sig
);
129 act
.sa_handler
= handler
;
130 sigemptyset(&act
.sa_mask
);
132 if (sig
== SIGALRM
) {
133 #ifdef SA_INTERRUPT /* SunOS */
134 act
.sa_flags
|= SA_INTERRUPT
;
137 #ifdef SA_RESTART /* BSD */
138 act
.sa_flags
|= SA_RESTART
;
141 if (sigaction(sig
, &act
, NULL
) >= 0)
143 PARA_EMERG_LOG("failed to install signal handler for signal %d\n",
149 * Install the generic signal handler for the given signal number.
151 * \param sig The number of the signal to catch.
153 * \sa signal(2), sigaction(2).
155 void para_install_sighandler(int sig
)
157 para_sigaction(sig
, &generic_signal_handler
);
161 * Block a signal for the caller.
163 * \param sig The signal to block.
165 * This sets the given signal in the current signal mask of the calling process
166 * to prevent this signal from delivery.
168 * \sa \ref para_unblock_signal(), sigprocmask(2), sigaddset(3).
170 void para_block_signal(int sig
)
174 PARA_DEBUG_LOG("blocking signal %d\n", sig
);
176 sigaddset(&set
, sig
);
177 sigprocmask(SIG_BLOCK
, &set
, NULL
);
183 * \param sig The signal to unblock.
185 * This function removes the given signal from the current set of blocked
188 * \sa \ref para_block_signal(), sigprocmask(2), sigaddset(3).
190 void para_unblock_signal(int sig
)
194 PARA_DEBUG_LOG("unblocking signal %d\n", sig
);
196 sigaddset(&set
, sig
);
197 sigprocmask(SIG_UNBLOCK
, &set
, NULL
);
201 * Return the number of the next pending signal.
203 * \param rfds The fd_set containing the signal pipe.
205 * \return On success, the number of the received signal is returned. If there
206 * is no signal currently pending, the function returns zero. On read errors
207 * from the signal pipe, the process is terminated.
209 int para_next_signal(fd_set
*rfds
)
212 int s
, ret
= read_nonblock(signal_pipe
[0], &s
, sizeof(s
), rfds
, &n
);
215 PARA_EMERG_LOG("%s\n", para_strerror(-ret
));
220 assert(n
== sizeof(s
));
221 PARA_DEBUG_LOG("next signal: %d\n", s
);
226 * Close the write end of the signal pipe.
228 void para_signal_shutdown(void)
230 close(signal_pipe
[1]);