lib: Add close_low_fd

This factors out the essential code from close_low_fds for one file
descriptor: Redirect a fd to /dev/null

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

2 files changed, 48 insertions, 0 deletions

diff --git a/lib/util/become_daemon.c b/lib/util/become_daemon.c
index 0671a1ef8ed..eba0cae579e 100644
--- a/lib/util/become_daemon.c
+++ b/lib/util/become_daemon.c
@@ -32,6 +32,49 @@
  Close the low 3 fd's and open dev/null in their place.
 ********************************************************************/
 
+_PUBLIC_ int close_low_fd(int fd)
+{
+#ifndef VALGRIND
+	int ret, dev_null;
+
+	dev_null = open("/dev/null", O_RDWR, 0);
+
+	if ((dev_null == -1) && (errno = ENFILE)) {
+		/*
+		 * Try to free up an fd
+		 */
+		ret = close(fd);
+		if (ret != 0) {
+			return errno;
+		}
+	}
+
+	dev_null = open("/dev/null", O_RDWR, 0);
+	if (dev_null == -1) {
+		dev_null = open("/dev/null", O_WRONLY, 0);
+	}
+	if (dev_null == -1) {
+		return errno;
+	}
+
+	if (dev_null == fd) {
+		/*
+		 * This can happen in the ENFILE case above
+		 */
+		return 0;
+	}
+
+	ret = dup2(dev_null, fd);
+	if (ret == -1) {
+		int err = errno;
+		close(dev_null);
+		return err;
+	}
+	close(dev_null);
+#endif
+	return 0;
+}
+
 _PUBLIC_ void close_low_fds(bool stdin_too, bool stdout_too, bool stderr_too)
 {
 #ifndef VALGRIND
diff --git a/lib/util/samba_util.h b/lib/util/samba_util.h
index 2ffe028959b..b31ee1f8f0a 100644
--- a/lib/util/samba_util.h
+++ b/lib/util/samba_util.h
@@ -839,6 +839,11 @@ _PUBLIC_ int idr_remove(struct idr_context *idp, int id);
 /* The following definitions come from lib/util/become_daemon.c  */
 
 /**
+ Close a fd and open dev/null in its place
+**/
+_PUBLIC_ int close_low_fd(int fd);
+
+/**
  Close the low 3 fd's and open dev/null in their place
 **/
 _PUBLIC_ void close_low_fds(bool stdin_too, bool stdout_too, bool stderr_too);