[RFC PATCH 12/16] rv/reactors: Add the printk reactor

[Daniel Bristot de Oliveira <bristot@redhat.com>]

Sample reactor that printks the reaction message.

Note: do not use this reactor with rq_lock taken, it will lock the
system until printk can handle that.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Gabriele Paoloni <gabriele.paoloni@intel.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
---
 kernel/trace/rv/Kconfig           |  8 ++++++
 kernel/trace/rv/Makefile          |  3 ++-
 kernel/trace/rv/reactors/printk.c | 43 +++++++++++++++++++++++++++++++
 3 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100644 kernel/trace/rv/reactors/printk.c

diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index 612b36b97663..6cbfb0f9cf76 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -38,4 +38,12 @@ config RV_REACTORS
 	  tracing reactions, printing the monitor output via tracepoints,
 	  but other reactions can be added (on-demand) via this interface.
 
+config RV_REACT_PRINTK
+	tristate "Printk reactor"
+	depends on RV_REACTORS
+	default y if RV_REACTORS
+	help
+	  Enables the printk reactor. The printk reactor emmits a printk()
+	  message if an exception is found.
+
 endif # RV
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index af0ff9a46418..a57cb3c3d410 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_RV) += rv.o
-obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
 obj-$(CONFIG_RV_MON_WIP) += monitors/wip/wip.o
 obj-$(CONFIG_RV_MON_WWNR) += monitors/wwnr/wwnr.o
+obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
+obj-$(CONFIG_RV_REACT_PRINTK) += reactors/printk.o
diff --git a/kernel/trace/rv/reactors/printk.c b/kernel/trace/rv/reactors/printk.c
new file mode 100644
index 000000000000..f929eead6000
--- /dev/null
+++ b/kernel/trace/rv/reactors/printk.c
@@ -0,0 +1,43 @@
+/*
+ * Printk RV reactor:
+ *   Prints the exception msg to the kernel message log.
+ *
+ * Copyright (C) 2019-2021 Daniel Bristot de Oliveira <bristot@redhat.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0
+ */
+#include <linux/ftrace.h>
+#include <linux/tracepoint.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/rv.h>
+
+static void rv_printk_reaction(char *msg)
+{
+	printk(msg);
+}
+
+struct rv_reactor rv_printk = {
+	.name = "printk",
+	.description = "prints the exception msg to the kernel message log",
+	.react = rv_printk_reaction
+};
+
+int register_react_printk(void)
+{
+	rv_register_reactor(&rv_printk);
+	return 0;
+}
+
+void unregister_react_printk(void)
+{
+	rv_unregister_reactor(&rv_printk);
+}
+
+module_init(register_react_printk);
+module_exit(unregister_react_printk);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Daniel Bristot de Oliveira");
+MODULE_DESCRIPTION("printk rv reactor: printk if an exception is hit");
-- 
2.26.2