Merge branch 't/rename_system_files'

[dss.git] / sig.c

diff --git a/sig.c b/sig.c
new file mode 100644 (file)
index 0000000..2f6f7dd
--- /dev/null
+++ b/sig.c
@@ -0,0 +1,159 @@
+/*
+ * Copyright (C) 2004-2010 Andre Noll <maan@systemlinux.org>
+ *
+ * Licensed under the GPL v2. For licencing details see COPYING.
+ */
+
+#include <string.h>
+#include <errno.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <dirent.h>
+#include <assert.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <sys/select.h>
+
+
+#include "gcc-compat.h"
+#include "err.h"
+#include "log.h"
+#include "str.h"
+#include "file.h"
+#include "sig.h"
+
+static int signal_pipe[2];
+
+/**
+ * Initialize the signal subsystem.
+ *
+ * This function creates a pipe, the signal pipe, to deliver pending signals to
+ * the application (Bernstein's trick). It should be called during the
+ * application's startup part, followed by subsequent calls to
+ * install_sighandler() for each signal that should be caught.
+ *
+ * signal_init() installs a generic signal handler which is used for all
+ * signals simultaneously. When a signal arrives, this generic signal handler
+ * writes the corresponding signal number to the signal pipe so that the
+ * application can test for pending signals simply by checking the signal pipe
+ * for reading, e.g. by using the select(2) system call.
+ *
+ * \return This function either succeeds or calls exit(2) to terminate
+ * the current process. On success, the file descriptor of the signal pipe is
+ * returned.
+ */
+int signal_init(void)
+{
+       int ret;
+       if (pipe(signal_pipe) < 0) {
+               ret = -ERRNO_TO_DSS_ERROR(errno);
+               goto err_out;
+       }
+       ret = mark_fd_nonblocking(signal_pipe[0]);
+       if (ret < 0)
+               goto err_out;
+       ret = mark_fd_nonblocking(signal_pipe[1]);
+       if (ret < 0)
+               goto err_out;
+       return signal_pipe[0];
+err_out:
+       DSS_EMERG_LOG(("%s\n", dss_strerror(-ret)));
+       exit(EXIT_FAILURE);
+}
+
+/*
+ * just write one integer to signal pipe
+ */
+static void generic_signal_handler(int s)
+{
+       write(signal_pipe[1], &s, sizeof(int));
+}
+
+/**
+ * Reap one child.
+ *
+ * \param pid In case a child died, its pid is returned here.
+ *
+ * Call waitpid() and print a log message containing the pid and the cause of
+ * the child's death.
+ *
+ * \return A (negative) error code on errors, zero, if no child died, one
+ * otherwise. If and only if the function returns one, the content of \a pid is
+ * meaningful.
+ *
+ * \sa waitpid(2)
+ */
+int reap_child(pid_t *pid, int *status)
+{
+       *pid = waitpid(-1, status, WNOHANG);
+
+       if (!*pid)
+               return 0;
+       if (*pid < 0)
+               return -ERRNO_TO_DSS_ERROR(errno);
+       if (WIFEXITED(*status))
+               DSS_DEBUG_LOG(("child %i exited. Exit status: %i\n", (int)*pid,
+                       WEXITSTATUS(*status)));
+       else if (WIFSIGNALED(*status))
+               DSS_DEBUG_LOG(("child %i was killed by signal %i\n", (int)*pid,
+                       WTERMSIG(*status)));
+       else
+               DSS_WARNING_LOG(("child %i terminated abormally\n", (int)*pid));
+       return 1;
+}
+
+/**
+ * Wrapper around signal(2)
+ *
+ * \param sig The number of the signal to catch.
+ *
+ * This installs the generic signal handler for the given signal.
+ *
+ * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
+ * \sa signal(2)
+ */
+int install_sighandler(int sig)
+{
+       DSS_DEBUG_LOG(("catching signal %d\n", sig));
+       if (signal(sig, &generic_signal_handler) != SIG_ERR)
+               return 1;
+       return -E_SIGNAL_SIG_ERR;
+}
+
+/**
+ * Return number of next pending signal.
+ *
+ * This should be called if the fd for the signal pipe is ready for reading.
+ *
+ * \return On success, the number of the received signal is returned.
+ * If the read was interrupted by another signal the function returns 0.
+ * Otherwise a negative error code is returned.
+ */
+int next_signal(void)
+{
+       int s, err;
+       ssize_t r;
+
+       r = read(signal_pipe[0], &s, sizeof(s));
+       if (r == sizeof(s)) {
+               DSS_DEBUG_LOG(("next signal: %d\n", s));
+               return s;
+       }
+       err = errno;
+       assert(r < 0);
+       if (err == EAGAIN)
+               return 0;
+       DSS_ERROR_LOG(("failed to read from signal pipe\n"));
+       return -ERRNO_TO_DSS_ERROR(err);
+}
+
+/**
+ * Close the signal pipe.
+ */
+void signal_shutdown(void)
+{
+       close(signal_pipe[1]);
+}