X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=signal.c;h=3b202a2c8ba6a62b23fa46f7e99ed207c4f08750;hp=aa63c8b5461a9627c021a514b83b7c8ee1067067;hb=d87806284b9f6be9aab71ccbf0280d273b57eeb3;hpb=c29457cf28486bc455c437e300bcfd0c7582c605

diff --git a/signal.c b/signal.c
index aa63c8b5..3b202a2c 100644
--- 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