Add console management

lib/CMakeLists.txt

@@ -80,6 +80,7 @@ set (LIB_HEADERS
     atomic-gssize.h
     block-ref-parser.h
     cache.h
+    console.h
     cfg.h
     cfg-lexer.h
     cfg-lexer-subst.h
@@ -179,6 +180,7 @@ set(LIB_SOURCES
     apphook.c
     block-ref-parser.c
     cache.c
+    console.c
     cfg.c
     cfg-args.c
     cfg-block.c

lib/Makefile.am

@@ -97,6 +97,7 @@ pkginclude_HEADERS			+= \
 	lib/atomic-gssize.h \
 	lib/block-ref-parser.h		\
 	lib/cache.h			\
+	lib/console.h			\
 	lib/cfg.h			\
 	lib/cfg-grammar.h		\
 	lib/cfg-grammar-internal.h	\
@@ -195,6 +196,7 @@ lib_libsyslog_ng_la_SOURCES		= \
 	lib/apphook.c			\
 	lib/block-ref-parser.c		\
 	lib/cache.c			\
+	lib/console.c			\
 	lib/cfg.c			\
 	lib/cfg-args.c			\
 	lib/cfg-block.c			\

lib/console.c

@@ -0,0 +1,168 @@
+/*
+ * Copyright (c) 2002-2012 Balabit
+ * Copyright (c) 1998-2012 Balázs Scheidler
+ * Copyright (c) 2024 Balázs Scheidler <[email protected]>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As an additional exemption you are allowed to compile & link against the
+ * OpenSSL libraries as published by the OpenSSL project. See the file
+ * COPYING for details.
+ *
+ */
+#include "console.h"
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <syslog.h>
+
+GMutex console_lock;
+gboolean console_present = TRUE;
+gboolean using_initial_console = TRUE;
+const gchar *console_prefix;
+
+/**
+ * console_printf:
+ * @fmt: format string
+ * @...: arguments to @fmt
+ *
+ * This function sends a message to the client preferring to use the stderr
+ * channel as long as it is available and switching to using syslog() if it
+ * isn't. Generally the stderr channell will be available in the startup
+ * process and in the beginning of the first startup in the
+ * supervisor/daemon processes. Later on the stderr fd will be closed and we
+ * have to fall back to using the system log.
+ **/
+void
+console_printf(const gchar *fmt, ...)
+{
+  gchar buf[2048];
+  va_list ap;
+
+  va_start(ap, fmt);
+  g_vsnprintf(buf, sizeof(buf), fmt, ap);
+  va_end(ap);
+  if (console_is_present())
+    fprintf(stderr, "%s: %s\n", console_prefix, buf);
+  else
+    {
+      openlog(console_prefix, LOG_PID, LOG_DAEMON);
+      syslog(LOG_CRIT, "%s\n", buf);
+      closelog();
+    }
+}
+
+
+/* NOTE: this is not synced with any changes and is just an indication whether we have a console */
+gboolean
+console_is_present(void)
+{
+  gboolean result;
+
+  /* the lock only serves a memory barrier but is not a real synchronization */
+  g_mutex_lock(&console_lock);
+  result = console_present;
+  g_mutex_unlock(&console_lock);
+  return result;
+}
+
+gboolean
+console_is_attached(void)
+{
+  gboolean result;
+  /* the lock only serves a memory barrier but is not a real synchronization */
+  g_mutex_lock(&console_lock);
+  if (using_initial_console)
+    result = FALSE;
+  else
+    result = console_present;
+  g_mutex_unlock(&console_lock);
+  return result;
+}
+
+/* re-acquire a console after startup using an array of fds */
+void
+console_acquire_from_fds(gint fds[3])
+{
+  const gchar *takeover_message_on_old_console = "[Console taken over, no further output here]\n";
+  g_assert(!console_is_attached());
+
+  if (using_initial_console)
+    {
+      (void) write(1, takeover_message_on_old_console, strlen(takeover_message_on_old_console));
+    }
+
+  g_mutex_lock(&console_lock);
+
+  dup2(fds[0], STDIN_FILENO);
+  dup2(fds[1], STDOUT_FILENO);
+  dup2(fds[2], STDERR_FILENO);
+
+  console_present = TRUE;
+  using_initial_console = FALSE;
+  g_mutex_unlock(&console_lock);
+}
+
+/**
+ * console_release:
+ *
+ * Use /dev/null as input/output/error. This function is idempotent, can be
+ * called any number of times without harm.
+ **/
+void
+console_release(void)
+{
+  gint devnull_fd;
+
+  g_mutex_lock(&console_lock);
+
+  if (!console_present)
+    goto exit;
+
+  devnull_fd = open("/dev/null", O_RDONLY);
+  if (devnull_fd >= 0)
+    {
+      dup2(devnull_fd, STDIN_FILENO);
+      close(devnull_fd);
+    }
+  devnull_fd = open("/dev/null", O_WRONLY);
+  if (devnull_fd >= 0)
+    {
+      dup2(devnull_fd, STDOUT_FILENO);
+      dup2(devnull_fd, STDERR_FILENO);
+      close(devnull_fd);
+    }
+  clearerr(stdin);
+  clearerr(stdout);
+  clearerr(stderr);
+  console_present = FALSE;
+  using_initial_console = FALSE;
+
+exit:
+  g_mutex_unlock(&console_lock);
+}
+
+void
+console_global_init(const gchar *console_prefix_)
+{
+  g_mutex_init(&console_lock);
+  console_prefix = console_prefix_;
+}
+
+void
+console_global_deinit(void)
+{
+  g_mutex_clear(&console_lock);
+}

lib/console.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2002-2012 Balabit
+ * Copyright (c) 1998-2012 Balázs Scheidler
+ * Copyright (c) 2024 Balázs Scheidler <[email protected]>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As an additional exemption you are allowed to compile & link against the
+ * OpenSSL libraries as published by the OpenSSL project. See the file
+ * COPYING for details.
+ *
+ */
+#ifndef SYSLOG_NG_CONSOLE_H_INCLUDED
+#define SYSLOG_NG_CONSOLE_H_INCLUDED
+
+#include "syslog-ng.h"
+
+void console_printf(const gchar *fmt, ...) __attribute__ ((format (printf, 1, 2)));
+
+gboolean console_is_present(void);
+gboolean console_is_attached(void);
+void console_acquire_from_fds(gint fds[3]);
+void console_acquire_from_stdio(void);
+void console_release(void);
+
+void console_global_init(const gchar *console_prefix);
+void console_global_deinit(void);
+
+#endif