text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Infrastructure for statistic tracing (histogram output).
   *
   * Copyright (C) 2008-2009 Frederic Weisbecker <fweisbec@gmail.com>
   *
   * Based on the code from trace_branch.c which is
   * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
   *
   */
  
  #include <linux/security.h>
  #include <linux/list.h>
  #include <linux/slab.h>
  #include <linux/rbtree.h>
  #include <linux/tracefs.h>
  #include "trace_stat.h"
  #include "trace.h"
  
  
  /*
   * List of stat red-black nodes from a tracer
   * We use a such tree to sort quickly the stat
   * entries from the tracer.
   */
  struct stat_node {
  	struct rb_node		node;
  	void			*stat;
  };
  
  /* A stat session is the stats output in one file */
  struct stat_session {
  	struct list_head	session_list;
  	struct tracer_stat	*ts;
  	struct rb_root		stat_root;
  	struct mutex		stat_mutex;
  	struct dentry		*file;
  };
  
  /* All of the sessions currently in use. Each stat file embed one session */
  static LIST_HEAD(all_stat_sessions);
  static DEFINE_MUTEX(all_stat_sessions_mutex);
  
  /* The root directory for all stat files */
  static struct dentry		*stat_dir;
  
  static void __reset_stat_session(struct stat_session *session)
  {
  	struct stat_node *snode, *n;
  
  	rbtree_postorder_for_each_entry_safe(snode, n, &session->stat_root, node) {
  		if (session->ts->stat_release)
  			session->ts->stat_release(snode->stat);
  		kfree(snode);
  	}
  
  	session->stat_root = RB_ROOT;
  }
  
  static void reset_stat_session(struct stat_session *session)
  {
  	mutex_lock(&session->stat_mutex);
  	__reset_stat_session(session);
  	mutex_unlock(&session->stat_mutex);
  }
  
  static void destroy_session(struct stat_session *session)
  {
  	tracefs_remove(session->file);
  	__reset_stat_session(session);
  	mutex_destroy(&session->stat_mutex);
  	kfree(session);
  }
  
  static int insert_stat(struct rb_root *root, void *stat, cmp_func_t cmp)
  {
  	struct rb_node **new = &(root->rb_node), *parent = NULL;
  	struct stat_node *data;
  
  	data = kzalloc(sizeof(*data), GFP_KERNEL);
  	if (!data)
  		return -ENOMEM;
  	data->stat = stat;
  
  	/*
  	 * Figure out where to put new node
  	 * This is a descendent sorting
  	 */
  	while (*new) {
  		struct stat_node *this;
  		int result;
  
  		this = container_of(*new, struct stat_node, node);
  		result = cmp(data->stat, this->stat);
  
  		parent = *new;
  		if (result >= 0)
  			new = &((*new)->rb_left);
  		else
  			new = &((*new)->rb_right);
  	}
  
  	rb_link_node(&data->node, parent, new);
  	rb_insert_color(&data->node, root);
  	return 0;
  }
  
  /*
   * For tracers that don't provide a stat_cmp callback.
   * This one will force an insertion as right-most node
   * in the rbtree.
   */
  static int dummy_cmp(const void *p1, const void *p2)
  {
  	return -1;
  }
  
  /*
   * Initialize the stat rbtree at each trace_stat file opening.
   * 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(struct stat_session *session)
  {
  	struct tracer_stat *ts = session->ts;
  	struct rb_root *root = &session->stat_root;
  	void *stat;
  	int ret = 0;
  	int i;
  
  	mutex_lock(&session->stat_mutex);
  	__reset_stat_session(session);
  
  	if (!ts->stat_cmp)
  		ts->stat_cmp = dummy_cmp;
  
  	stat = ts->stat_start(ts);
  	if (!stat)
  		goto exit;
  
  	ret = insert_stat(root, stat, ts->stat_cmp);
  	if (ret)
  		goto exit;
  
  	/*
  	 * Iterate over the tracer stat entries and store them in an rbtree.
  	 */
  	for (i = 1; ; i++) {
  		stat = ts->stat_next(stat, i);
  
  		/* End of insertion */
  		if (!stat)
  			break;
  
  		ret = insert_stat(root, stat, ts->stat_cmp);
  		if (ret)
  			goto exit_free_rbtree;
  	}
  
  exit:
  	mutex_unlock(&session->stat_mutex);
  	return ret;
  
  exit_free_rbtree:
  	__reset_stat_session(session);
  	mutex_unlock(&session->stat_mutex);
  	return ret;
  }
  
  
  static void *stat_seq_start(struct seq_file *s, loff_t *pos)
  {
  	struct stat_session *session = s->private;
  	struct rb_node *node;
  	int n = *pos;
  	int i;
  
  	/* Prevent from tracer switch or rbtree modification */
  	mutex_lock(&session->stat_mutex);
  
  	/* If we are in the beginning of the file, print the headers */
  	if (session->ts->stat_headers) {
  		if (n == 0)
  			return SEQ_START_TOKEN;
  		n--;
  	}
  
  	node = rb_first(&session->stat_root);
  	for (i = 0; node && i < n; i++)
  		node = rb_next(node);
  
  	return node;
  }
  
  static void *stat_seq_next(struct seq_file *s, void *p, loff_t *pos)
  {
  	struct stat_session *session = s->private;
  	struct rb_node *node = p;
  
  	(*pos)++;
  
  	if (p == SEQ_START_TOKEN)
  		return rb_first(&session->stat_root);
  
  	return rb_next(node);
  }
  
  static void stat_seq_stop(struct seq_file *s, void *p)
  {
  	struct stat_session *session = s->private;
  	mutex_unlock(&session->stat_mutex);
  }
  
  static int stat_seq_show(struct seq_file *s, void *v)
  {
  	struct stat_session *session = s->private;
  	struct stat_node *l = container_of(v, struct stat_node, node);
  
  	if (v == SEQ_START_TOKEN)
  		return session->ts->stat_headers(s);
  
  	return session->ts->stat_show(s, l->stat);
  }
  
  static const struct seq_operations trace_stat_seq_ops = {
  	.start		= stat_seq_start,
  	.next		= stat_seq_next,
  	.stop		= stat_seq_stop,
  	.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 seq_file *m;
  	struct stat_session *session = inode->i_private;
  
  	ret = security_locked_down(LOCKDOWN_TRACEFS);
  	if (ret)
  		return ret;
  
  	ret = stat_seq_init(session);
  	if (ret)
  		return ret;
  
  	ret = seq_open(file, &trace_stat_seq_ops);
  	if (ret) {
  		reset_stat_session(session);
  		return ret;
  	}
  
  	m = file->private_data;
  	m->private = session;
  	return ret;
  }
  
  /*
   * Avoid consuming memory with our now useless rbtree.
   */
  static int tracing_stat_release(struct inode *i, struct file *f)
  {
  	struct stat_session *session = i->i_private;
  
  	reset_stat_session(session);
  
  	return seq_release(i, f);
  }
  
  static const struct file_operations tracing_stat_fops = {
  	.open		= tracing_stat_open,
  	.read		= seq_read,
  	.llseek		= seq_lseek,
  	.release	= tracing_stat_release
  };
  
  static int tracing_stat_init(void)
  {
  	struct dentry *d_tracing;
  
  	d_tracing = tracing_init_dentry();
  	if (IS_ERR(d_tracing))
  		return -ENODEV;
  
  	stat_dir = tracefs_create_dir("trace_stat", d_tracing);
  	if (!stat_dir) {
  		pr_warn("Could not create tracefs 'trace_stat' entry\n");
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  static int init_stat_file(struct stat_session *session)
  {
  	int ret;
  
  	if (!stat_dir && (ret = tracing_stat_init()))
  		return ret;
  
  	session->file = tracefs_create_file(session->ts->name, 0644,
  					    stat_dir,
  					    session, &tracing_stat_fops);
  	if (!session->file)
  		return -ENOMEM;
  	return 0;
  }
  
  int register_stat_tracer(struct tracer_stat *trace)
  {
  	struct stat_session *session, *node;
  	int ret = -EINVAL;
  
  	if (!trace)
  		return -EINVAL;
  
  	if (!trace->stat_start || !trace->stat_next || !trace->stat_show)
  		return -EINVAL;
  
  	/* Already registered? */
  	mutex_lock(&all_stat_sessions_mutex);
  	list_for_each_entry(node, &all_stat_sessions, session_list) {
  		if (node->ts == trace)
  			goto out;
  	}
  
  	ret = -ENOMEM;
  	/* Init the session */
  	session = kzalloc(sizeof(*session), GFP_KERNEL);
  	if (!session)
  		goto out;
  
  	session->ts = trace;
  	INIT_LIST_HEAD(&session->session_list);
  	mutex_init(&session->stat_mutex);
  
  	ret = init_stat_file(session);
  	if (ret) {
  		destroy_session(session);
  		goto out;
  	}
  
  	ret = 0;
  	/* Register */
  	list_add_tail(&session->session_list, &all_stat_sessions);
   out:
  	mutex_unlock(&all_stat_sessions_mutex);
  
  	return ret;
  }
  
  void unregister_stat_tracer(struct tracer_stat *trace)
  {
  	struct stat_session *node, *tmp;
  
  	mutex_lock(&all_stat_sessions_mutex);
  	list_for_each_entry_safe(node, tmp, &all_stat_sessions, session_list) {
  		if (node->ts == trace) {
  			list_del(&node->session_list);
  			destroy_session(node);
  			break;
  		}
  	}
  	mutex_unlock(&all_stat_sessions_mutex);
  }
  