fs.c

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/*
 *  This code exports profiling data as debugfs files to userspace.
 *
 *    Copyright IBM Corp. 2009
 *    Author(s): Peter Oberparleiter <[email protected]>
 *
 *    Uses gcc-internal data definitions.
 *    Based on the gcov-kernel patch by:
 *       Hubertus Franke <[email protected]>
 *       Nigel Hinds <[email protected]>
 *       Rajan Ravindran <[email protected]>
 *       Peter Oberparleiter <[email protected]>
 *       Paul Larson
 *       Yi CDL Yang
 */

#define pr_fmt(fmt) "gcov: " fmt

#include <linux/init.h>
#include <linux/module.h>
#include <linux/debugfs.h>
#include <linux/fs.h>
#include <linux/list.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/seq_file.h>
#include "gcov.h"

struct gcov_node {
    struct list_head list;
    struct list_head children;
    struct list_head all;
    struct gcov_node *parent;
    struct gcov_info **loaded_info;
    struct gcov_info *unloaded_info;
    struct dentry *dentry;
    struct dentry **links;
    int num_loaded;
    char name[0];
};

static const char objtree[] = OBJTREE;
static const char srctree[] = SRCTREE;
static struct gcov_node root_node;
static struct dentry *reset_dentry;
static LIST_HEAD(all_head);
static DEFINE_MUTEX(node_lock);

/* If non-zero, keep copies of profiling data for unloaded modules. */
static int gcov_persist = 1;

static int __init gcov_persist_setup(char *str)
{
    unsigned long val;

    if (strict_strtoul(str, 0, &val)) {
        pr_warning("invalid gcov_persist parameter '%s'\n", str);
        return 0;
    }
    gcov_persist = val;
    pr_info("setting gcov_persist to %d\n", gcov_persist);

    return 1;
}
__setup("gcov_persist=", gcov_persist_setup);

/*
 * seq_file.start() implementation for gcov data files. Note that the
 * gcov_iterator interface is designed to be more restrictive than seq_file
 * (no start from arbitrary position, etc.), to simplify the iterator
 * implementation.
 */
static void *gcov_seq_start(struct seq_file *seq, loff_t *pos)
{
    loff_t i;

    gcov_iter_start(seq->private);
    for (i = 0; i < *pos; i++) {
        if (gcov_iter_next(seq->private))
            return NULL;
    }
    return seq->private;
}

/* seq_file.next() implementation for gcov data files. */
static void *gcov_seq_next(struct seq_file *seq, void *data, loff_t *pos)
{
    struct gcov_iterator *iter = data;

    if (gcov_iter_next(iter))
        return NULL;
    (*pos)++;

    return iter;
}

/* seq_file.show() implementation for gcov data files. */
static int gcov_seq_show(struct seq_file *seq, void *data)
{
    struct gcov_iterator *iter = data;

    if (gcov_iter_write(iter, seq))
        return -EINVAL;
    return 0;
}

static void gcov_seq_stop(struct seq_file *seq, void *data)
{
    /* Unused. */
}

static const struct seq_operations gcov_seq_ops = {
    .start  = gcov_seq_start,
    .next   = gcov_seq_next,
    .show   = gcov_seq_show,
    .stop   = gcov_seq_stop,
};

/*
 * Return a profiling data set associated with the given node. This is
 * either a data set for a loaded object file or a data set copy in case
 * all associated object files have been unloaded.
 */
static struct gcov_info *get_node_info(struct gcov_node *node)
{
    if (node->num_loaded > 0)
        return node->loaded_info[0];

    return node->unloaded_info;
}

/*
 * Return a newly allocated profiling data set which contains the sum of
 * all profiling data associated with the given node.
 */
static struct gcov_info *get_accumulated_info(struct gcov_node *node)
{
    struct gcov_info *info;
    int i = 0;

    if (node->unloaded_info)
        info = gcov_info_dup(node->unloaded_info);
    else
        info = gcov_info_dup(node->loaded_info[i++]);
    if (!info)
        return NULL;
    for (; i < node->num_loaded; i++)
        gcov_info_add(info, node->loaded_info[i]);

    return info;
}

/*
 * open() implementation for gcov data files. Create a copy of the profiling
 * data set and initialize the iterator and seq_file interface.
 */
static int gcov_seq_open(struct inode *inode, struct file *file)
{
    struct gcov_node *node = inode->i_private;
    struct gcov_iterator *iter;
    struct seq_file *seq;
    struct gcov_info *info;
    int rc = -ENOMEM;

    mutex_lock(&node_lock);
    /*
     * Read from a profiling data copy to minimize reference tracking
     * complexity and concurrent access and to keep accumulating multiple
     * profiling data sets associated with one node simple.
     */
    info = get_accumulated_info(node);
    if (!info)
        goto out_unlock;
    iter = gcov_iter_new(info);
    if (!iter)
        goto err_free_info;
    rc = seq_open(file, &gcov_seq_ops);
    if (rc)
        goto err_free_iter_info;
    seq = file->private_data;
    seq->private = iter;
out_unlock:
    mutex_unlock(&node_lock);
    return rc;

err_free_iter_info:
    gcov_iter_free(iter);
err_free_info:
    gcov_info_free(info);
    goto out_unlock;
}

/*
 * release() implementation for gcov data files. Release resources allocated
 * by open().
 */
static int gcov_seq_release(struct inode *inode, struct file *file)
{
    struct gcov_iterator *iter;
    struct gcov_info *info;
    struct seq_file *seq;

    seq = file->private_data;
    iter = seq->private;
    info = gcov_iter_get_info(iter);
    gcov_iter_free(iter);
    gcov_info_free(info);
    seq_release(inode, file);

    return 0;
}

/*
 * Find a node by the associated data file name. Needs to be called with
 * node_lock held.
 */
static struct gcov_node *get_node_by_name(const char *name)
{
    struct gcov_node *node;
    struct gcov_info *info;

    list_for_each_entry(node, &all_head, all) {
        info = get_node_info(node);
        if (info && (strcmp(info->filename, name) == 0))
            return node;
    }

    return NULL;
}

/*
 * Reset all profiling data associated with the specified node.
 */
static void reset_node(struct gcov_node *node)
{
    int i;

    if (node->unloaded_info)
        gcov_info_reset(node->unloaded_info);
    for (i = 0; i < node->num_loaded; i++)
        gcov_info_reset(node->loaded_info[i]);
}

static void remove_node(struct gcov_node *node);

/*
 * write() implementation for gcov data files. Reset profiling data for the
 * corresponding file. If all associated object files have been unloaded,
 * remove the debug fs node as well.
 */
static ssize_t gcov_seq_write(struct file *file, const char __user *addr,
                  size_t len, loff_t *pos)
{
    struct seq_file *seq;
    struct gcov_info *info;
    struct gcov_node *node;

    seq = file->private_data;
    info = gcov_iter_get_info(seq->private);
    mutex_lock(&node_lock);
    node = get_node_by_name(info->filename);
    if (node) {
        /* Reset counts or remove node for unloaded modules. */
        if (node->num_loaded == 0)
            remove_node(node);
        else
            reset_node(node);
    }
    /* Reset counts for open file. */
    gcov_info_reset(info);
    mutex_unlock(&node_lock);

    return len;
}

/*
 * Given a string <path> representing a file path of format:
 *   path/to/file.gcda
 * construct and return a new string:
 *   <dir/>path/to/file.<ext>
 */
static char *link_target(const char *dir, const char *path, const char *ext)
{
    char *target;
    char *old_ext;
    char *copy;

    copy = kstrdup(path, GFP_KERNEL);
    if (!copy)
        return NULL;
    old_ext = strrchr(copy, '.');
    if (old_ext)
        *old_ext = '\0';
    if (dir)
        target = kasprintf(GFP_KERNEL, "%s/%s.%s", dir, copy, ext);
    else
        target = kasprintf(GFP_KERNEL, "%s.%s", copy, ext);
    kfree(copy);

    return target;
}

/*
 * Construct a string representing the symbolic link target for the given
 * gcov data file name and link type. Depending on the link type and the
 * location of the data file, the link target can either point to a
 * subdirectory of srctree, objtree or in an external location.
 */
static char *get_link_target(const char *filename, const struct gcov_link *ext)
{
    const char *rel;
    char *result;

    if (strncmp(filename, objtree, strlen(objtree)) == 0) {
        rel = filename + strlen(objtree) + 1;
        if (ext->dir == SRC_TREE)
            result = link_target(srctree, rel, ext->ext);
        else
            result = link_target(objtree, rel, ext->ext);
    } else {
        /* External compilation. */
        result = link_target(NULL, filename, ext->ext);
    }

    return result;
}

#define SKEW_PREFIX ".tmp_"

/*
 * For a filename .tmp_filename.ext return filename.ext. Needed to compensate
 * for filename skewing caused by the mod-versioning mechanism.
 */
static const char *deskew(const char *basename)
{
    if (strncmp(basename, SKEW_PREFIX, sizeof(SKEW_PREFIX) - 1) == 0)
        return basename + sizeof(SKEW_PREFIX) - 1;
    return basename;
}

/*
 * Create links to additional files (usually .c and .gcno files) which the
 * gcov tool expects to find in the same directory as the gcov data file.
 */
static void add_links(struct gcov_node *node, struct dentry *parent)
{
    char *basename;
    char *target;
    int num;
    int i;

    for (num = 0; gcov_link[num].ext; num++)
        /* Nothing. */;
    node->links = kcalloc(num, sizeof(struct dentry *), GFP_KERNEL);
    if (!node->links)
        return;
    for (i = 0; i < num; i++) {
        target = get_link_target(get_node_info(node)->filename,
                     &gcov_link[i]);
        if (!target)
            goto out_err;
        basename = strrchr(target, '/');
        if (!basename)
            goto out_err;
        basename++;
        node->links[i] = debugfs_create_symlink(deskew(basename),
                            parent, target);
        if (!node->links[i])
            goto out_err;
        kfree(target);
    }

    return;
out_err:
    kfree(target);
    while (i-- > 0)
        debugfs_remove(node->links[i]);
    kfree(node->links);
    node->links = NULL;
}

static const struct file_operations gcov_data_fops = {
    .open       = gcov_seq_open,
    .release    = gcov_seq_release,
    .read       = seq_read,
    .llseek     = seq_lseek,
    .write      = gcov_seq_write,
};

/* Basic initialization of a new node. */
static void init_node(struct gcov_node *node, struct gcov_info *info,
              const char *name, struct gcov_node *parent)
{
    INIT_LIST_HEAD(&node->list);
    INIT_LIST_HEAD(&node->children);
    INIT_LIST_HEAD(&node->all);
    if (node->loaded_info) {
        node->loaded_info[0] = info;
        node->num_loaded = 1;
    }
    node->parent = parent;
    if (name)
        strcpy(node->name, name);
}

/*
 * Create a new node and associated debugfs entry. Needs to be called with
 * node_lock held.
 */
static struct gcov_node *new_node(struct gcov_node *parent,
                  struct gcov_info *info, const char *name)
{
    struct gcov_node *node;

    node = kzalloc(sizeof(struct gcov_node) + strlen(name) + 1, GFP_KERNEL);
    if (!node)
        goto err_nomem;
    if (info) {
        node->loaded_info = kcalloc(1, sizeof(struct gcov_info *),
                       GFP_KERNEL);
        if (!node->loaded_info)
            goto err_nomem;
    }
    init_node(node, info, name, parent);
    /* Differentiate between gcov data file nodes and directory nodes. */
    if (info) {
        node->dentry = debugfs_create_file(deskew(node->name), 0600,
                    parent->dentry, node, &gcov_data_fops);
    } else
        node->dentry = debugfs_create_dir(node->name, parent->dentry);
    if (!node->dentry) {
        pr_warning("could not create file\n");
        kfree(node);
        return NULL;
    }
    if (info)
        add_links(node, parent->dentry);
    list_add(&node->list, &parent->children);
    list_add(&node->all, &all_head);

    return node;

err_nomem:
    kfree(node);
    pr_warning("out of memory\n");
    return NULL;
}

/* Remove symbolic links associated with node. */
static void remove_links(struct gcov_node *node)
{
    int i;

    if (!node->links)
        return;
    for (i = 0; gcov_link[i].ext; i++)
        debugfs_remove(node->links[i]);
    kfree(node->links);
    node->links = NULL;
}

/*
 * Remove node from all lists and debugfs and release associated resources.
 * Needs to be called with node_lock held.
 */
static void release_node(struct gcov_node *node)
{
    list_del(&node->list);
    list_del(&node->all);
    debugfs_remove(node->dentry);
    remove_links(node);
    kfree(node->loaded_info);
    if (node->unloaded_info)
        gcov_info_free(node->unloaded_info);
    kfree(node);
}

/* Release node and empty parents. Needs to be called with node_lock held. */
static void remove_node(struct gcov_node *node)
{
    struct gcov_node *parent;

    while ((node != &root_node) && list_empty(&node->children)) {
        parent = node->parent;
        release_node(node);
        node = parent;
    }
}

/*
 * Find child node with given basename. Needs to be called with node_lock
 * held.
 */
static struct gcov_node *get_child_by_name(struct gcov_node *parent,
                       const char *name)
{
    struct gcov_node *node;

    list_for_each_entry(node, &parent->children, list) {
        if (strcmp(node->name, name) == 0)
            return node;
    }

    return NULL;
}

/*
 * write() implementation for reset file. Reset all profiling data to zero
 * and remove nodes for which all associated object files are unloaded.
 */
static ssize_t reset_write(struct file *file, const char __user *addr,
               size_t len, loff_t *pos)
{
    struct gcov_node *node;

    mutex_lock(&node_lock);
restart:
    list_for_each_entry(node, &all_head, all) {
        if (node->num_loaded > 0)
            reset_node(node);
        else if (list_empty(&node->children)) {
            remove_node(node);
            /* Several nodes may have gone - restart loop. */
            goto restart;
        }
    }
    mutex_unlock(&node_lock);

    return len;
}

/* read() implementation for reset file. Unused. */
static ssize_t reset_read(struct file *file, char __user *addr, size_t len,
              loff_t *pos)
{
    /* Allow read operation so that a recursive copy won't fail. */
    return 0;
}

static const struct file_operations gcov_reset_fops = {
    .write  = reset_write,
    .read   = reset_read,
    .llseek = noop_llseek,
};

/*
 * Create a node for a given profiling data set and add it to all lists and
 * debugfs. Needs to be called with node_lock held.
 */
static void add_node(struct gcov_info *info)
{
    char *filename;
    char *curr;
    char *next;
    struct gcov_node *parent;
    struct gcov_node *node;

    filename = kstrdup(info->filename, GFP_KERNEL);
    if (!filename)
        return;
    parent = &root_node;
    /* Create directory nodes along the path. */
    for (curr = filename; (next = strchr(curr, '/')); curr = next + 1) {
        if (curr == next)
            continue;
        *next = 0;
        if (strcmp(curr, ".") == 0)
            continue;
        if (strcmp(curr, "..") == 0) {
            if (!parent->parent)
                goto err_remove;
            parent = parent->parent;
            continue;
        }
        node = get_child_by_name(parent, curr);
        if (!node) {
            node = new_node(parent, NULL, curr);
            if (!node)
                goto err_remove;
        }
        parent = node;
    }
    /* Create file node. */
    node = new_node(parent, info, curr);
    if (!node)
        goto err_remove;
out:
    kfree(filename);
    return;

err_remove:
    remove_node(parent);
    goto out;
}

/*
 * Associate a profiling data set with an existing node. Needs to be called
 * with node_lock held.
 */
static void add_info(struct gcov_node *node, struct gcov_info *info)
{
    struct gcov_info **loaded_info;
    int num = node->num_loaded;

    /*
     * Prepare new array. This is done first to simplify cleanup in
     * case the new data set is incompatible, the node only contains
     * unloaded data sets and there's not enough memory for the array.
     */
    loaded_info = kcalloc(num + 1, sizeof(struct gcov_info *), GFP_KERNEL);
    if (!loaded_info) {
        pr_warning("could not add '%s' (out of memory)\n",
               info->filename);
        return;
    }
    memcpy(loaded_info, node->loaded_info,
           num * sizeof(struct gcov_info *));
    loaded_info[num] = info;
    /* Check if the new data set is compatible. */
    if (num == 0) {
        /*
         * A module was unloaded, modified and reloaded. The new
         * data set replaces the copy of the last one.
         */
        if (!gcov_info_is_compatible(node->unloaded_info, info)) {
            pr_warning("discarding saved data for %s "
                   "(incompatible version)\n", info->filename);
            gcov_info_free(node->unloaded_info);
            node->unloaded_info = NULL;
        }
    } else {
        /*
         * Two different versions of the same object file are loaded.
         * The initial one takes precedence.
         */
        if (!gcov_info_is_compatible(node->loaded_info[0], info)) {
            pr_warning("could not add '%s' (incompatible "
                   "version)\n", info->filename);
            kfree(loaded_info);
            return;
        }
    }
    /* Overwrite previous array. */
    kfree(node->loaded_info);
    node->loaded_info = loaded_info;
    node->num_loaded = num + 1;
}

/*
 * Return the index of a profiling data set associated with a node.
 */
static int get_info_index(struct gcov_node *node, struct gcov_info *info)
{
    int i;

    for (i = 0; i < node->num_loaded; i++) {
        if (node->loaded_info[i] == info)
            return i;
    }
    return -ENOENT;
}

/*
 * Save the data of a profiling data set which is being unloaded.
 */
static void save_info(struct gcov_node *node, struct gcov_info *info)
{
    if (node->unloaded_info)
        gcov_info_add(node->unloaded_info, info);
    else {
        node->unloaded_info = gcov_info_dup(info);
        if (!node->unloaded_info) {
            pr_warning("could not save data for '%s' "
                   "(out of memory)\n", info->filename);
        }
    }
}

/*
 * Disassociate a profiling data set from a node. Needs to be called with
 * node_lock held.
 */
static void remove_info(struct gcov_node *node, struct gcov_info *info)
{
    int i;

    i = get_info_index(node, info);
    if (i < 0) {
        pr_warning("could not remove '%s' (not found)\n",
               info->filename);
        return;
    }
    if (gcov_persist)
        save_info(node, info);
    /* Shrink array. */
    node->loaded_info[i] = node->loaded_info[node->num_loaded - 1];
    node->num_loaded--;
    if (node->num_loaded > 0)
        return;
    /* Last loaded data set was removed. */
    kfree(node->loaded_info);
    node->loaded_info = NULL;
    node->num_loaded = 0;
    if (!node->unloaded_info)
        remove_node(node);
}

/*
 * Callback to create/remove profiling files when code compiled with
 * -fprofile-arcs is loaded/unloaded.
 */
void gcov_event(enum gcov_action action, struct gcov_info *info)
{
    struct gcov_node *node;

    mutex_lock(&node_lock);
    node = get_node_by_name(info->filename);
    switch (action) {
    case GCOV_ADD:
        if (node)
            add_info(node, info);
        else
            add_node(info);
        break;
    case GCOV_REMOVE:
        if (node)
            remove_info(node, info);
        else {
            pr_warning("could not remove '%s' (not found)\n",
                   info->filename);
        }
        break;
    }
    mutex_unlock(&node_lock);
}

/* Create debugfs entries. */
static __init int gcov_fs_init(void)
{
    int rc = -EIO;

    init_node(&root_node, NULL, NULL, NULL);
    /*
     * /sys/kernel/debug/gcov will be parent for the reset control file
     * and all profiling files.
     */
    root_node.dentry = debugfs_create_dir("gcov", NULL);
    if (!root_node.dentry)
        goto err_remove;
    /*
     * Create reset file which resets all profiling counts when written
     * to.
     */
    reset_dentry = debugfs_create_file("reset", 0600, root_node.dentry,
                       NULL, &gcov_reset_fops);
    if (!reset_dentry)
        goto err_remove;
    /* Replay previous events to get our fs hierarchy up-to-date. */
    gcov_enable_events();
    return 0;

err_remove:
    pr_err("init failed\n");
    if (root_node.dentry)
        debugfs_remove(root_node.dentry);

    return rc;
}
device_initcall(gcov_fs_init);