[PATCH 1/2] tracing/ftrace: handle more than one stat file per tracer

[Frederic Weisbecker]

Impact: new API for tracers

Make the stat tracing API reentrant. And also provide the new directory
/debugfs/tracing/trace_stat which will contain all the stat files for the
current active tracer.

Now a tracer will, if desired, want to provide a zero terminated array of
tracer_stat structures.
Each one contains the callbacks necessary for one stat file.
It have to provide at least a name for its stat file, an iterator with
stat_start/start_next callback and an output callback for one stat entry.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 46677ea..b093f36 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -335,6 +335,25 @@ struct tracer_flags {
 #define TRACER_OPT(s, b)	.name = #s, .bit = b
 
 /*
+ * If you want to provide a stat file (one-shot statistics), fill
+ * an iterator with stat_start/stat_next and a stat_show callbacks.
+ * The others callbacks are optional.
+ */
+struct tracer_stat {
+	/* The name of your stat file */
+	const char		*name;
+	/* Iteration over statistic entries */
+	void			*(*stat_start)(void);
+	void			*(*stat_next)(void *prev, int idx);
+	/* Compare two entries for sorting (optional) for stats */
+	int			(*stat_cmp)(void *p1, void *p2);
+	/* Print a stat entry */
+	int			(*stat_show)(struct seq_file *s, void *p);
+	/* Print the headers of your stat entries */
+	int			(*stat_headers)(struct seq_file *s);
+};
+
+/*
  * A specific tracer, represented by methods that operate on a trace array:
  */
 struct tracer {
@@ -361,21 +380,7 @@ struct tracer {
 	struct tracer		*next;
 	int			print_max;
 	struct tracer_flags 	*flags;
-
-	/*
-	 * If you change one of the following on tracing runtime, recall
-	 * init_tracer_stat()
-	 */
-
-	/* Iteration over statistic entries */
-	void			*(*stat_start)(void);
-	void			*(*stat_next)(void *prev, int idx);
-	/* Compare two entries for sorting (optional) for stats */
-	int			(*stat_cmp)(void *p1, void *p2);
-	/* Print a stat entry */
-	int			(*stat_show)(struct seq_file *s, void *p);
-	/* Print the headers of your stat entries */
-	int			(*stat_headers)(struct seq_file *s);
+	struct tracer_stat	*stats;
 };
 
 struct trace_seq {
diff --git a/kernel/trace/trace_stat.c b/kernel/trace/trace_stat.c
index 6f194a3..293be1c 100644
--- a/kernel/trace/trace_stat.c
+++ b/kernel/trace/trace_stat.c
@@ -21,31 +21,29 @@ struct trace_stat_list {
 	void *stat;
 };
 
-static struct trace_stat_list stat_list;
+/* A stat session is the stats output in one file */
+struct tracer_stat_session {
+	struct tracer_stat *ts;
+	struct trace_stat_list	stat_list;
+	struct mutex stat_mutex;
+};
 
-/*
- * This is a copy of the current tracer to avoid racy
- * and dangerous output while the current tracer is
- * switched.
- */
-static struct tracer current_tracer;
-
-/*
- * Protect both the current tracer and the global
- * stat list.
- */
-static DEFINE_MUTEX(stat_list_mutex);
+/* All of the sessions currently in use. Each stat file embeed one session */
+static struct tracer_stat_session **all_stat_sessions;
+static int nb_sessions;
+static struct dentry *stat_dir, **stat_files;
 
 
-static void reset_stat_list(void)
+static void reset_stat_session(struct tracer_stat_session *session)
 {
+	struct trace_stat_list *root = &session->stat_list;
 	struct trace_stat_list *node;
 	struct list_head *next;
 
-	if (list_empty(&stat_list.list))
+	if (list_empty(&root->list))
 		return;
 
-	node = list_entry(stat_list.list.next, struct trace_stat_list, list);
+	node = list_entry(root->list.next, struct trace_stat_list, list);
 	next = node->list.next;
 
 	while (&node->list != next) {
@@ -54,14 +52,65 @@ static void reset_stat_list(void)
 	}
 	kfree(node);
 
-	INIT_LIST_HEAD(&stat_list.list);
+	INIT_LIST_HEAD(&root->list);
 }
 
-void init_tracer_stat(struct tracer *trace)
+/* Called when a tracer is initialized */
+static int init_all_sessions(int nb, struct tracer_stat *ts)
+{
+	int i, j;
+	struct tracer_stat_session *session;
+
+	if (all_stat_sessions) {
+		for (i = 0; i < nb_sessions; i++) {
+			session = all_stat_sessions[i];
+			reset_stat_session(session);
+			mutex_destroy(&session->stat_mutex);
+			kfree(session);
+		}
+	}
+	all_stat_sessions = kmalloc(sizeof(struct tracer_stat_session *) * nb,
+				    GFP_KERNEL);
+	if (!all_stat_sessions)
+		return -ENOMEM;
+
+	for (i = 0; i < nb; i++) {
+		session = kmalloc(sizeof(struct tracer_stat_session) * nb,
+				  GFP_KERNEL);
+		if (!session)
+			goto free_sessions;
+
+		INIT_LIST_HEAD(&session->stat_list.list);
+		mutex_init(&session->stat_mutex);
+		session->ts = &ts[i];
+		all_stat_sessions[i] = session;
+	}
+	nb_sessions = nb;
+	return 0;
+
+free_sessions:
+
+	for (j = 0; j < i; j++)
+		kfree(all_stat_sessions[i]);
+
+	kfree(all_stat_sessions);
+	all_stat_sessions = NULL;
+
+	return -ENOMEM;
+}
+
+static int basic_tracer_stat_checks(struct tracer_stat *ts)
 {
-	mutex_lock(&stat_list_mutex);
-	current_tracer = *trace;
-	mutex_unlock(&stat_list_mutex);
+	int i;
+
+	if (!ts)
+		return 0;
+
+	for (i = 0; ts[i].name; i++) {
+		if (!ts[i].stat_start || !ts[i].stat_next || !ts[i].stat_show)
+			return -EBUSY;
+	}
+	return i;
 }
 
 /*
@@ -79,22 +128,19 @@ static int dummy_cmp(void *p1, void *p2)
  * All of these copies and sorting are required on all opening
  * since the stats could have changed between two file sessions.
  */
-static int stat_seq_init(void)
+static int stat_seq_init(struct tracer_stat_session *session)
 {
-	struct trace_stat_list *iter_entry, *new_entry;
+	struct trace_stat_list *iter_entry, *new_entry, *root;
+	struct tracer_stat *ts = session->ts;
 	void *prev_stat;
 	int ret = 0;
 	int i;
 
-	mutex_lock(&stat_list_mutex);
-	reset_stat_list();
-
-	if (!current_tracer.stat_start || !current_tracer.stat_next ||
-					!current_tracer.stat_show)
-		goto exit;
+	mutex_lock(&session->stat_mutex);
+	reset_stat_session(session);
 
-	if (!current_tracer.stat_cmp)
-		current_tracer.stat_cmp = dummy_cmp;
+	if (!ts->stat_cmp)
+		ts->stat_cmp = dummy_cmp;
 
 	/*
 	 * The first entry. Actually this is the second, but the first
@@ -107,8 +153,9 @@ static int stat_seq_init(void)
 	}
 
 	INIT_LIST_HEAD(&new_entry->list);
-	list_add(&new_entry->list, &stat_list.list);
-	new_entry->stat = current_tracer.stat_start();
+	root = &session->stat_list;
+	list_add(&new_entry->list, &root->list);
+	new_entry->stat = ts->stat_start();
 
 	prev_stat = new_entry->stat;
 
@@ -124,15 +171,15 @@ static int stat_seq_init(void)
 		}
 
 		INIT_LIST_HEAD(&new_entry->list);
-		new_entry->stat = current_tracer.stat_next(prev_stat, i);
+		new_entry->stat = ts->stat_next(prev_stat, i);
 
 		/* End of insertion */
 		if (!new_entry->stat)
 			break;
 
-		list_for_each_entry(iter_entry, &stat_list.list, list) {
+		list_for_each_entry(iter_entry, &root->list, list) {
 			/* Insertion with a descendent sorting */
-			if (current_tracer.stat_cmp(new_entry->stat,
+			if (ts->stat_cmp(new_entry->stat,
 						iter_entry->stat) > 0) {
 
 				list_add_tail(&new_entry->list,
@@ -141,7 +188,7 @@ static int stat_seq_init(void)
 
 			/* The current smaller value */
 			} else if (list_is_last(&iter_entry->list,
-						&stat_list.list)) {
+						&root->list)) {
 				list_add(&new_entry->list, &iter_entry->list);
 				break;
 			}
@@ -150,46 +197,49 @@ static int stat_seq_init(void)
 		prev_stat = new_entry->stat;
 	}
 exit:
-	mutex_unlock(&stat_list_mutex);
+	mutex_unlock(&session->stat_mutex);
 	return ret;
 
 exit_free_list:
-	reset_stat_list();
-	mutex_unlock(&stat_list_mutex);
+	reset_stat_session(session);
+	mutex_unlock(&session->stat_mutex);
 	return ret;
 }
 
 
 static void *stat_seq_start(struct seq_file *s, loff_t *pos)
 {
-	struct trace_stat_list *l = (struct trace_stat_list *)s->private;
+	struct tracer_stat_session *session = s->private;
 
 	/* Prevent from tracer switch or stat_list modification */
-	mutex_lock(&stat_list_mutex);
+	mutex_lock(&session->stat_mutex);
 
 	/* If we are in the beginning of the file, print the headers */
-	if (!*pos && current_tracer.stat_headers)
-		current_tracer.stat_headers(s);
+	if (!*pos && session->ts->stat_headers)
+		session->ts->stat_headers(s);
 
-	return seq_list_start(&l->list, *pos);
+	return seq_list_start(&session->stat_list.list, *pos);
 }
 
 static void *stat_seq_next(struct seq_file *s, void *p, loff_t *pos)
 {
-	struct trace_stat_list *l = (struct trace_stat_list *)s->private;
+	struct tracer_stat_session *session = s->private;
 
-	return seq_list_next(p, &l->list, pos);
+	return seq_list_next(p, &session->stat_list.list, pos);
 }
 
-static void stat_seq_stop(struct seq_file *m, void *p)
+static void stat_seq_stop(struct seq_file *s, void *p)
 {
-	mutex_unlock(&stat_list_mutex);
+	struct tracer_stat_session *session = s->private;
+	mutex_unlock(&session->stat_mutex);
 }
 
 static int stat_seq_show(struct seq_file *s, void *v)
 {
+	struct tracer_stat_session *session = s->private;
 	struct trace_stat_list *l = list_entry(v, struct trace_stat_list, list);
-	return current_tracer.stat_show(s, l->stat);
+
+	return session->ts->stat_show(s, l->stat);
 }
 
 static const struct seq_operations trace_stat_seq_ops = {
@@ -199,15 +249,18 @@ static const struct seq_operations trace_stat_seq_ops = {
 	.show = stat_seq_show
 };
 
+/* The session stat is refilled and resorted at each stat file opening */
 static int tracing_stat_open(struct inode *inode, struct file *file)
 {
 	int ret;
 
+	struct tracer_stat_session *session = inode->i_private;
+
 	ret = seq_open(file, &trace_stat_seq_ops);
 	if (!ret) {
 		struct seq_file *m = file->private_data;
-		m->private = &stat_list;
-		ret = stat_seq_init();
+		m->private = session;
+		ret = stat_seq_init(session);
 	}
 
 	return ret;
@@ -219,9 +272,11 @@ static int tracing_stat_open(struct inode *inode, struct file *file)
  */
 static int tracing_stat_release(struct inode *i, struct file *f)
 {
-	mutex_lock(&stat_list_mutex);
-	reset_stat_list();
-	mutex_unlock(&stat_list_mutex);
+	struct tracer_stat_session *session = i->i_private;
+
+	mutex_lock(&session->stat_mutex);
+	reset_stat_session(session);
+	mutex_unlock(&session->stat_mutex);
 	return 0;
 }
 
@@ -232,18 +287,70 @@ static const struct file_operations tracing_stat_fops = {
 	.release	= tracing_stat_release
 };
 
+
+static void destroy_trace_stat_files(void)
+{
+	int i;
+
+	if (stat_files) {
+		for (i = 0; i < nb_sessions; i++)
+			debugfs_remove(stat_files[i]);
+		kfree(stat_files);
+		stat_files = NULL;
+	}
+}
+
+static void init_trace_stat_files(void)
+{
+	int i;
+
+	if (!stat_dir || !nb_sessions)
+		return;
+
+	stat_files = kmalloc(sizeof(struct dentry *) * nb_sessions, GFP_KERNEL);
+
+	if (!stat_files) {
+		pr_warning("trace stat: not enough memory\n");
+		return;
+	}
+
+	for (i = 0; i < nb_sessions; i++) {
+		struct tracer_stat_session *session = all_stat_sessions[i];
+		stat_files[i] = debugfs_create_file(session->ts->name, 0644,
+						stat_dir,
+						session, &tracing_stat_fops);
+		if (!stat_files[i])
+			pr_warning("cannot create %s entry\n",
+				   session->ts->name);
+	}
+}
+
+void init_tracer_stat(struct tracer *trace)
+{
+	int nb = basic_tracer_stat_checks(trace->stats);
+
+	destroy_trace_stat_files();
+
+	if (nb < 0) {
+		pr_warning("stat tracing: missing stat callback on %s\n",
+			   trace->name);
+		return;
+	}
+	if (!nb)
+		return;
+
+	init_all_sessions(nb, trace->stats);
+	init_trace_stat_files();
+}
+
 static int __init tracing_stat_init(void)
 {
 	struct dentry *d_tracing;
-	struct dentry *entry;
 
-	INIT_LIST_HEAD(&stat_list.list);
 	d_tracing = tracing_init_dentry();
 
-	entry = debugfs_create_file("trace_stat", 0444, d_tracing,
-					NULL,
-				    &tracing_stat_fops);
-	if (!entry)
+	stat_dir = debugfs_create_dir("trace_stat", d_tracing);
+	if (!stat_dir)
 		pr_warning("Could not create debugfs "
 			   "'trace_stat' entry\n");
 	return 0;
-- 
1.6.0.4


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