rv: Add runtime reactors interface

A runtime monitor can cause a reaction to the detection of an
exception on the model's execution. By default, the monitors have
tracing reactions, printing the monitor output via tracepoints.
But other reactions can be added (on-demand) via this interface.

The user interface resembles the kernel tracing interface and
presents these files:

"available_reactors"
  - Reading shows the available reactors, one per line.

   For example:
   [root@f32 rv]# cat available_reactors
   nop
   panic
   printk

 "reacting_on"
   - It is an on/off general switch for reactors, disabling
   all reactions.

 "monitors/MONITOR/reactors"
   - List available reactors, with the select reaction for the given
   MONITOR inside []. The default one is the nop (no operation)
   reactor.
   - Writing the name of a reactor enables it to the given
   MONITOR.

   For example:
   [root@f32 rv]# cat monitors/wip/reactors
   [nop]
   panic
   printk
   [root@f32 rv]# echo panic > monitors/wip/reactors
   [root@f32 rv]# cat monitors/wip/reactors
   nop
   [panic]
   printk

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
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: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Gabriele Paoloni <gpaoloni@redhat.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
Cc: linux-trace-devel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>

include/linux/rv.h

@@ -6,6 +6,11 @@
  *
  * Copyright (C) 2019-2022 Daniel Bristot de Oliveira <bristot@kernel.org>
  */
+struct rv_reactor {
+	char			*name;
+	char			*description;
+	void			(*react)(char *);
+};
 
 struct rv_monitor {
 	const char		*name;
@@ -14,8 +19,13 @@ struct rv_monitor {
 	int			(*start)(void);
 	void			(*stop)(void);
 	void			(*reset)(void);
+	void			(*react)(char *);
 };
 
 extern bool monitoring_on;
 int rv_unregister_monitor(struct rv_monitor *monitor);
 int rv_register_monitor(struct rv_monitor *monitor);
+
+extern bool reacting_on;
+int rv_unregister_reactor(struct rv_reactor *reactor);
+int rv_register_reactor(struct rv_reactor *reactor);

kernel/trace/rv/Kconfig

@@ -10,3 +10,17 @@ menuconfig RV
 	  theorem proving). RV works by analyzing the trace of the system's
 	  actual execution, comparing it against a formal specification of
 	  the system behavior.
+
+if RV
+
+config RV_REACTORS
+	bool "Runtime verification reactors"
+	default y if RV
+	help
+	  Enables the online runtime verification reactors. A runtime
+	  monitor can cause a reaction to the detection of an exception
+	  on the model's execution. By default, the monitors have
+	  tracing reactions, printing the monitor output via tracepoints,
+	  but other reactions can be added (on-demand) via this interface.
+
+endif # RV

kernel/trace/rv/Makefile

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_RV) += rv.o
+obj-$(CONFIG_RV_REACTORS) += rv_reactors.o

kernel/trace/rv/rv.c

@@ -312,8 +312,13 @@ static int create_monitor_dir(struct rv_monitor_def *mdef)
 		retval = -ENOMEM;
 		goto out_remove_root;
 	}
+#ifdef CONFIG_RV_REACTORS
+	retval = reactor_create_monitor_files(mdef);
+	if (retval)
+		goto out_remove_root;
+#endif
 
-	return retval;
+	return 0;
 
 out_remove_root:
 	rv_remove(mdef->root_d);
@@ -621,7 +626,11 @@ int rv_register_monitor(struct rv_monitor *monitor)
 
 	r->monitor = monitor;
 
-	create_monitor_dir(r);
+	retval = create_monitor_dir(r);
+	if (retval) {
+		kfree(r);
+		goto out_unlock;
+	}
 
 	list_add_tail(&r->list, &rv_monitors_list);
 
@@ -681,6 +690,10 @@ int __init rv_init_interface(void)
 	rv_create_file("monitoring_on", 0600, rv_root.root_dir, NULL,
 		       &monitoring_on_fops);
 
+#ifdef CONFIG_RV_REACTORS
+	init_rv_reactors(rv_root.root_dir);
+	reacting_on=true;
+#endif
 	monitoring_on=true;
 
 	return 0;

kernel/trace/rv/rv.h

@@ -14,12 +14,25 @@ struct rv_interface {
 #define rv_remove		tracefs_remove
 
 #define MAX_RV_MONITOR_NAME_SIZE	100
+#define MAX_RV_REACTOR_NAME_SIZE	100
 
 extern struct mutex rv_interface_lock;
 
+#ifdef CONFIG_RV_REACTORS
+struct rv_reactor_def {
+	struct list_head list;
+	struct rv_reactor *reactor;
+	/* protected by the monitor interface lock */
+	int counter;
+};
+#endif
+
 struct rv_monitor_def {
 	struct list_head list;
 	struct rv_monitor *monitor;
+#ifdef CONFIG_RV_REACTORS
+	struct rv_reactor_def *rdef;
+#endif
 	struct dentry *root_d;
 	bool enabled;
 	bool reacting;
@@ -29,3 +42,9 @@ extern bool monitoring_on;
 struct dentry *get_monitors_root(void);
 void reset_all_monitors(void);
 int init_rv_monitors(struct dentry *root_dir);
+
+#ifdef CONFIG_RV_REACTORS
+extern bool reacting_on;
+int reactor_create_monitor_files(struct rv_monitor_def *mdef);
+int init_rv_reactors(struct dentry *root_dir);
+#endif