From 5e22c27b94232371a9dd58abc868439a9e050fec Mon Sep 17 00:00:00 2001
From: Michael Jeanson <mjeanson@efficios.com>
Date: Wed, 12 May 2021 16:21:50 -0400
Subject: [PATCH] Add experimental bitwise enum config option

Only generate the bitwise enumerations when
CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM is enabled, so the default build
does not generate traces which lead to warnings when viewed with
babeltrace 1.x and babeltrace 2 with default options.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Id54ae3df470b9cdbc0edc0a528fa79532493d1ad
---
 Kconfig        | 11 +++++++++++
 Makefile       | 24 +++++++++++++++++++++---
 README.md      | 15 +++++++++++++++
 lttng-events.c |  3 +++
 4 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/Kconfig b/Kconfig
index 0ea35092..abaa4120 100644
--- a/Kconfig
+++ b/Kconfig
@@ -14,4 +14,15 @@ config LTTNG
 
 	  If unsure, say N.
 
+config LTTNG_EXPERIMENTAL_BITWISE_ENUM
+	bool "LTTng experimental bitwise enum support"
+	default n
+	depends on LTTNG
+	help
+	  Enable experimental bitwise enumerations. The traces produced with
+	  this option enabled will generate warnings when read by trace
+	  viewers with default options.
+
+	  If unsure, say N.
+
 source "lttng/tests/Kconfig"
diff --git a/Makefile b/Makefile
index a9aff3f1..c6173690 100644
--- a/Makefile
+++ b/Makefile
@@ -147,18 +147,36 @@ KERNELDIR ?= /lib/modules/$(shell uname -r)/build
 PWD := $(shell pwd)
 CFLAGS = $(EXTCFLAGS)
 
+# Experimental bitwise enum defaults to disabled.
+CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM ?= n
+
+# Emulate Kconfig behavior of setting defines for config options.
+LKCPPFLAGS = $(KCPPFLAGS)
+ifeq ($(CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM),y)
+LKCPPFLAGS += -DCONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM=y
+endif
+
 default: modules
 
 modules:
-	$(MAKE) -C $(KERNELDIR) M=$(PWD) CONFIG_LTTNG=m CONFIG_LTTNG_CLOCK_PLUGIN_TEST=m modules
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) \
+		CONFIG_LTTNG=m CONFIG_LTTNG_CLOCK_PLUGIN_TEST=m \
+		KCPPFLAGS='$(LKCPPFLAGS)' \
+		modules
 
 modules_install:
-	$(MAKE) -C $(KERNELDIR) M=$(PWD) CONFIG_LTTNG=m CONFIG_LTTNG_CLOCK_PLUGIN_TEST=m modules_install
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) \
+		CONFIG_LTTNG=m CONFIG_LTTNG_CLOCK_PLUGIN_TEST=m \
+		KCPPFLAGS='$(LKCPPFLAGS)' \
+		modules_install
 
 clean:
 	$(MAKE) -C $(KERNELDIR) M=$(PWD) clean
 
 %.i: %.c
-	$(MAKE) -C $(KERNELDIR) M=$(PWD) CONFIG_LTTNG=m CONFIG_LTTNG_CLOCK_PLUGIN_TEST=m $@
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) \
+		CONFIG_LTTNG=m CONFIG_LTTNG_CLOCK_PLUGIN_TEST=m \
+		KCPPFLAGS='$(LKCPPFLAGS)' \
+		$@
 
 endif # KERNELRELEASE
diff --git a/README.md b/README.md
index 7b04cd83..fc083249 100644
--- a/README.md
+++ b/README.md
@@ -95,6 +95,21 @@ available from LTTng:
   - `CONFIG_KALLSYMS_ALL`: state dump of mapping between block device
     number and name
 
+### LTTng specific kernel config options
+
+The following kernel configuration options are provided by LTTng:
+
+  - `CONFIG_LTTNG`: Build LTTng (Defaults to 'm').
+  - `CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM`: Enable the experimental bitwise
+    enumerations (Defaults to 'n'). This can be enabled by building with:
+
+         make CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM=y
+
+  - `CONFIG_LTTNG_CLOCK_PLUGIN_TEST`: Build the test clock plugin (Defaults to
+    'm'). This plugin overrides the trace clock and should always be built as a
+    module for testing.
+
+
 Customization/Extension
 -----------------------
 
diff --git a/lttng-events.c b/lttng-events.c
index 3450fa40..dfd112ab 100644
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -3096,6 +3096,9 @@ static int __init lttng_events_init(void)
 #else
 		"");
 #endif
+#ifdef CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM
+	printk(KERN_NOTICE "LTTng: Experimental bitwise enum enabled.\n");
+#endif /* CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM */
 	return 0;
 
 error_hotplug:
-- 
2.34.1