manual: Remove outdated sentence about para_afh.

[paraslash.git] / signal.c

diff --git a/signal.c b/signal.c
index f02c453a04a02e5d3e1c8a9c791aba8275a60671..3b202a2c8ba6a62b23fa46f7e99ed207c4f08750 100644 (file)
--- a/signal.c
+++ b/signal.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2004-2011 Andre Noll <maan@systemlinux.org>
+ * Copyright (C) 2004-2013 Andre Noll <maan@systemlinux.org>
  *
  * Licensed under the GPL v2. For licencing details see COPYING.
  */
@@ -22,15 +22,15 @@ static int signal_pipe[2];
  * during the application's startup part, followed by subsequent calls
  * to para_install_sighandler() for each signal that should be caught.
  *
- * para_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.
+ * A generic signal handler is used for all signals simultaneously. When a
+ * signal arrives, the signal handler writes the number of the signal received
+ * to one end of the signal pipe. The application can test for pending signals
+ * by checking if the file descriptor of the other end of the signal pipe is
+ * ready for reading, see select(2).
  *
- * \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.
+ * \return This function either succeeds or calls exit(2) to terminate the
+ * current process. On success, the file descriptor of the read end of the
+ * signal pipe is returned.
  */
 int para_signal_init(void)
 {
@@ -51,15 +51,22 @@ err_out:
        exit(EXIT_FAILURE);
 }
 
-/*
- * just write one integer to signal pipe
- */
+/* Write the signal number to signal pipe. */
 static void generic_signal_handler(int s)
 {
+       /*
+        * Signal handlers that make system calls must save a copy of errno on
+        * entry to the handler and restore it on exit, to prevent the
+        * possibility of overwriting a errno value that had previously been
+        * set in the main program.
+        */
+       int save_errno = errno;
        ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
 
-       if (ret == sizeof(int))
+       if (ret == sizeof(int)) {
+               errno = save_errno;
                return;
+       }
        if (ret < 0)
                PARA_EMERG_LOG("%s\n", strerror(errno));
        else
@@ -147,10 +154,50 @@ void para_install_sighandler(int sig)
        para_sigaction(sig, &generic_signal_handler);
 }
 
+/**
+ * Block a signal for the caller.
+ *
+ * \param sig The signal to block.
+ *
+ * This sets the given signal in the current signal mask of the calling process
+ * to prevent this signal from delivery.
+ *
+ * \sa \ref para_unblock_signal(), sigprocmask(2), sigaddset(3).
+ */
+void para_block_signal(int sig)
+{
+       sigset_t set;
+
+       PARA_DEBUG_LOG("blocking signal %d\n", sig);
+       sigemptyset(&set);
+       sigaddset(&set, sig);
+       sigprocmask(SIG_BLOCK, &set, NULL);
+}
+
+/**
+ * Unblock a signal.
+ *
+ * \param sig The signal to unblock.
+ *
+ * This function removes the given signal from the current set of blocked
+ * signals.
+ *
+ * \sa \ref para_block_signal(), sigprocmask(2), sigaddset(3).
+ */
+void para_unblock_signal(int sig)
+{
+       sigset_t set;
+
+       PARA_DEBUG_LOG("unblocking signal %d\n", sig);
+       sigemptyset(&set);
+       sigaddset(&set, sig);
+       sigprocmask(SIG_UNBLOCK, &set, NULL);
+}
+
 /**
  * Return the number of the next pending signal.
  *
- * \param rfds Th fd_set containing the signal pipe.
+ * \param rfds The fd_set containing the signal pipe.
  *
  * \return On success, the number of the received signal is returned. If there
  * is no signal currently pending, the function returns zero. On read errors