trace_stat.c

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/*
 * Infrastructure for statistic tracing (histogram output).
 *
 * Copyright (C) 2008-2009 Frederic Weisbecker <[email protected]>
 *
 * Based on the code from trace_branch.c which is
 * Copyright (C) 2008 Steven Rostedt <[email protected]>
 *
 */


#include <linux/list.h>
#include <linux/slab.h>
#include <linux/rbtree.h>
#include <linux/debugfs.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;

/*
 * Iterate through the rbtree using a post order traversal path
 * to release the next node.
 * It won't necessary release one at each iteration
 * but it will at least advance closer to the next one
 * to be released.
 */
static struct rb_node *release_next(struct tracer_stat *ts,
                    struct rb_node *node)
{
    struct stat_node *snode;
    struct rb_node *parent = rb_parent(node);

    if (node->rb_left)
        return node->rb_left;
    else if (node->rb_right)
        return node->rb_right;
    else {
        if (!parent)
            ;
        else if (parent->rb_left == node)
            parent->rb_left = NULL;
        else
            parent->rb_right = NULL;

        snode = container_of(node, struct stat_node, node);
        if (ts->stat_release)
            ts->stat_release(snode->stat);
        kfree(snode);

        return parent;
    }
}

static void __reset_stat_session(struct stat_session *session)
{
    struct rb_node *node = session->stat_root.rb_node;

    while (node)
        node = release_next(session->ts, node);

    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)
{
    debugfs_remove(session->file);
    __reset_stat_session(session);
    mutex_destroy(&session->stat_mutex);
    kfree(session);
}

typedef int (*cmp_stat_t)(void *, void *);

static int insert_stat(struct rb_root *root, void *stat, cmp_stat_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(void *p1, 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 = 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();

    stat_dir = debugfs_create_dir("trace_stat", d_tracing);
    if (!stat_dir)
        pr_warning("Could not create debugfs "
               "'trace_stat' entry\n");
    return 0;
}

static int init_stat_file(struct stat_session *session)
{
    if (!stat_dir && tracing_stat_init())
        return -ENODEV;

    session->file = debugfs_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;

    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) {
            mutex_unlock(&all_stat_sessions_mutex);
            return -EINVAL;
        }
    }
    mutex_unlock(&all_stat_sessions_mutex);

    /* Init the session */
    session = kzalloc(sizeof(*session), GFP_KERNEL);
    if (!session)
        return -ENOMEM;

    session->ts = trace;
    INIT_LIST_HEAD(&session->session_list);
    mutex_init(&session->stat_mutex);

    ret = init_stat_file(session);
    if (ret) {
        destroy_session(session);
        return ret;
    }

    /* Register */
    mutex_lock(&all_stat_sessions_mutex);
    list_add_tail(&session->session_list, &all_stat_sessions);
    mutex_unlock(&all_stat_sessions_mutex);

    return 0;
}

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);
}