introduce mark_fd_nonblock()
[paraslash.git] / signal.c
1 /*
2 * Copyright (C) 2004-2006 Andre Noll <maan@systemlinux.org>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
17 */
18 /** \file signal.c signal handling functions */
19
20 #include "para.h"
21 #include "fd.h"
22 #include "error.h"
23 static int signal_pipe[2];
24
25 /**
26 * initialize the paraslash signal subsystem
27 *
28 * This function creates a pipe, the signal pipe, to deliver pending
29 * signals to the application (Bernstein's trick). It should be called
30 * during the application's startup part, followed by subsequent calls
31 * to para_install_sighandler() for each signal that should be caught.
32 *
33 * para_signal_init() installs a generic signal handler which is used for all
34 * signals simultaneously. When a signal arrives, this generic signal handler
35 * writes the corresponding signal number to the signal pipe so that the
36 * application can test for pending signals simply by checking the signal pipe
37 * for reading, e.g. by using the select(2) system call.
38 *
39 * \return This function either succeeds or calls exit(2) to terminate
40 * the current process. On success, the file descriptor of the signal pipe is
41 * returned.
42 */
43 int para_signal_init(void)
44 {
45 int ret = -E_SIGNAL_PIPE;
46 if (pipe(signal_pipe))
47 goto err_out;
48 ret = mark_fd_nonblock(signal_pipe[0]);
49 if (ret < 0)
50 goto err_out;
51 ret = mark_fd_nonblock(signal_pipe[1]);
52 if (ret < 0)
53 goto err_out;
54 return signal_pipe[0];
55 err_out:
56 PARA_EMERG_LOG("%s\n", PARA_STRERROR(-ret));
57 exit(EXIT_FAILURE);
58 }
59
60 /*
61 * just write one integer to signal pipe
62 */
63 static void generic_signal_handler(int s)
64 {
65 write(signal_pipe[1], &s, sizeof(int));
66 //fprintf(stderr, "got sig %i, write returned %d\n", s, ret);
67 }
68
69 /**
70 * reap one child
71 *
72 * call waitpid() and print a log message containing the pid
73 * and the cause of the child's death.
74 *
75 * \return Like \p waitpid(), this function returns the process ID of the
76 * terminated child; on error, \p -E_WAITPID is returned.
77 * \sa waitpid(2)
78 */
79 pid_t para_reap_child(void)
80 {
81 int status;
82 pid_t pid = waitpid(-1, &status, WNOHANG);
83
84 if (pid <= 0) {
85 if (pid < 0)
86 pid = -E_WAITPID;
87 return 0;
88 }
89 if (WIFEXITED(status))
90 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", pid,
91 WEXITSTATUS(status));
92 else if (WIFSIGNALED(status))
93 PARA_DEBUG_LOG("child %i was killed by signal %i\n", pid,
94 WTERMSIG(status));
95 else
96 PARA_WARNING_LOG("child %i terminated abormally\n", pid);
97 return pid;
98 }
99
100 /**
101 * paraslash's zombie killer
102 *
103 * It just calls \p para_reap_child() until there are no more children left to
104 * reap.
105 */
106 void para_reap_children(void)
107 {
108 while (para_reap_child() > 0)
109 ; /* nothing */
110 }
111
112 /**
113 * wrapper around signal(2)
114 * \param sig the number of the signal to catch
115 *
116 * This installs the generic signal handler for the given signal.
117 * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
118 * \sa signal(2)
119 */
120 int para_install_sighandler(int sig)
121 {
122 PARA_DEBUG_LOG("catching signal %d\n", sig);
123 return signal(sig, &generic_signal_handler) == SIG_ERR? -E_SIGNAL_SIG_ERR : 1;
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. \p
132 * -E_SIGNAL_READ is returned if a read error occured while reading the signal
133 * pipe. If the read was interrupted by another signal the function returns 0.
134 */
135 int para_next_signal(void)
136 {
137 int s;
138 ssize_t r;
139
140 if ((r = read(signal_pipe[0], &s, sizeof(s)) == sizeof(s)) > 0) {
141 PARA_DEBUG_LOG("next signal: %d\n", s);
142 return s;
143 }
144 return r < 0 && (errno != EAGAIN)? 0 : -E_SIGNAL_READ;
145 }