[PATCH v7 08/10] libtracefs: Implement tracefs_kprobe_clear_probe()

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Add the function tracefs_kprobe_clear_probe() that will remove a single
kprobe. If the @force parameter is set, it will disable that probe in all
instances (including the top level instance) before removing it.

If the @event parameter is NULL, then it will clear all events that are
defined by the @system parameter. If the @system parameter is NULL,
then it will use the default "kprobes" group.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/tracefs.h     |   1 +
 src/tracefs-kprobes.c | 123 +++++++++++++++++++++++++++++++++---------
 2 files changed, 100 insertions(+), 24 deletions(-)

diff --git a/include/tracefs.h b/include/tracefs.h
index 198517f23eca..1c8703ae7e26 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -229,4 +229,5 @@ char **tracefs_get_kprobes(enum tracefs_kprobe_type type);
 enum tracefs_kprobe_type tracefs_kprobe_info(const char *group, const char *event,
 					     char **type, char **addr, char **format);
 int tracefs_kprobe_clear_all(bool force);
+int tracefs_kprobe_clear_probe(const char *system, const char *event, bool force);
 #endif /* _TRACE_FS_H */
diff --git a/src/tracefs-kprobes.c b/src/tracefs-kprobes.c
index bafc15a4ce5d..2bc589a82627 100644
--- a/src/tracefs-kprobes.c
+++ b/src/tracefs-kprobes.c
@@ -345,18 +345,17 @@ static void disable_events(const char *system, const char *event,
 	return;
 }
 
-/**
- * tracefs_kprobe_clear_all - clear kprobe events
- * @force: Will attempt to disable all kprobe events and clear them
- *
- * Will remove all defined kprobe events. If any of them are enabled,
- * and @force is not set, then it will error with -1 and errno to be
- * EBUSY. If @force is set, then it will attempt to disable all the kprobe
- * events in all instances, and try again.
- *
- * Returns zero on success, -1 otherwise.
- */
-int tracefs_kprobe_clear_all(bool force)
+static int clear_kprobe(const char *system, const char *event)
+{
+	/* '-' + ':' + '/' + '\n' + '\0' = 5 bytes */
+	int len = strlen(system) + strlen(event) + 5;
+	char content[len];
+
+	sprintf(content, "-:%s/%s", system, event);
+	return tracefs_instance_file_append(NULL, KPROBE_EVENTS, content);
+}
+
+static int kprobe_clear_probes(const char *group, bool force)
 {
 	char **instance_list;
 	char **kprobe_list;
@@ -367,13 +366,6 @@ int tracefs_kprobe_clear_all(bool force)
 	int ret;
 	int i;
 
-	ret = tracefs_instance_file_clear(NULL, KPROBE_EVENTS);
-	if (!ret)
-		return 0;
-
-	if (!force)
-		return -1;
-
 	kprobe_list = tracefs_get_kprobes(TRACEFS_ALL_KPROBES);
 	if (!kprobe_list)
 		return -1;
@@ -385,6 +377,13 @@ int tracefs_kprobe_clear_all(bool force)
 	 * top level.
 	 */
 
+	/*
+	 * If a system is defined, the default is to pass unless
+	 * an event fails to be removed. If a system is not defined,
+	 * the default is to fail, unless all are removed.
+	 */
+	ret = group ? 0 : -1;
+
 	for (i = 0; kprobe_list[i]; i++) {
 		kprobe = kprobe_list[i];
 
@@ -396,15 +395,91 @@ int tracefs_kprobe_clear_all(bool force)
 		if (!event)
 			goto out;
 
-		disable_events(system, event, instance_list);
+		/* Skip if this does not match a given system */
+		if (group && strcmp(system, group) != 0)
+			continue;
 
-		ret = tracefs_instance_file_clear(NULL, KPROBE_EVENTS);
-		/* On success stop the loop */
-		if (!ret)
-			goto out;
+		if (force)
+			disable_events(system, event, instance_list);
+
+		if (group) {
+			ret = clear_kprobe(system, event);
+			if (ret < 0)
+				goto out;
+		} else {
+			ret = tracefs_instance_file_clear(NULL, KPROBE_EVENTS);
+			/* On success stop the loop */
+			if (!ret)
+				goto out;
+		}
+
+		/* Set the default for whether a system is defined or not */
+		ret = group ? 0 : -1;
 	}
  out:
 	tracefs_list_free(instance_list);
 	tracefs_list_free(kprobe_list);
 	return ret;
 }
+
+/**
+ * tracefs_kprobe_clear_all - clear kprobe events
+ * @force: Will attempt to disable all kprobe events and clear them
+ *
+ * Will remove all defined kprobe events. If any of them are enabled,
+ * and @force is not set, then it will error with -1 and errno to be
+ * EBUSY. If @force is set, then it will attempt to disable all the kprobe
+ * events in all instances, and try again.
+ *
+ * Returns zero on success, -1 otherwise.
+ */
+int tracefs_kprobe_clear_all(bool force)
+{
+	if (tracefs_instance_file_clear(NULL, KPROBE_EVENTS) == 0)
+		return 0;
+
+	if (!force)
+		return -1;
+
+	/* Attempt to disable all kprobe events */
+	return kprobe_clear_probes(NULL, force);
+}
+
+/**
+ * tracefs_kprobe_clear_all - clear kprobe events
+ * @system: System to clear (NULL means default)
+ * @event: Name of probe to clear in system (NULL for all probes in system)
+ * @force: Will attempt to disable all kprobe events and clear them
+ *
+ * Will remove the kprobes that match the @system and @event. If @system
+ * is NULL, then "kprobes" is used and will ignore all other system
+ * groups of kprobes. The @event is NULL then all events under the given
+ * @system are removed, otherwise only the event that matches.
+ *
+ * Returns zero on success, -1 otherwise.
+ */
+int tracefs_kprobe_clear_probe(const char *system, const char *event, bool force)
+{
+	char **instance_list;
+	int ret;
+
+	if (!system)
+		system = "kprobes";
+
+	if (!event)
+		return kprobe_clear_probes(system, force);
+
+	/*
+	 * Since we know we are disabling a specific event, try
+	 * to disable it first before clearing it.
+	 */
+	if (force) {
+		instance_list = tracefs_instances(NULL);
+		disable_events(system, event, instance_list);
+		tracefs_list_free(instance_list);
+	}
+
+	ret = clear_kprobe(system, event);
+
+	return ret < 0 ? -1 : 0;
+}
-- 
2.30.2