writeback: split writeback_inodes_wb

[linux-2.6/next.git] / kernel / gcov / fs.c

/*
 *  This code exports profiling data as debugfs files to userspace.
 *
 *    Copyright IBM Corp. 2009
 *    Author(s): Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
 *
 *    Uses gcc-internal data definitions.
 *    Based on the gcov-kernel patch by:
 *               Hubertus Franke <frankeh@us.ibm.com>
 *               Nigel Hinds <nhinds@us.ibm.com>
 *               Rajan Ravindran <rajancr@us.ibm.com>
 *               Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
 *               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 - represents a debugfs entry
 * @list: list head for child node list
 * @children: child nodes
 * @all: list head for list of all nodes
 * @parent: parent node
 * @info: associated profiling data structure if not a directory
 * @ghost: when an object file containing profiling data is unloaded we keep a
 *         copy of the profiling data here to allow collecting coverage data
 *         for cleanup code. Such a node is called a "ghost".
 * @dentry: main debugfs entry, either a directory or data file
 * @links: associated symbolic links
 * @name: data file basename
 *
 * struct gcov_node represents an entity within the gcov/ subdirectory
 * of debugfs. There are directory and data file nodes. The latter represent
 * the actual synthesized data file plus any associated symbolic links which
 * are needed by the gcov tool to work correctly.
 */
struct gcov_node {
        struct list_head list;
        struct list_head children;
        struct list_head all;
        struct gcov_node *parent;
        struct gcov_info *info;
        struct gcov_info *ghost;
        struct dentry *dentry;
        struct dentry **links;
        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 the profiling data set for a given node. This can either be the
 * original profiling data structure or a duplicate (also called "ghost")
 * in case the associated object file has been unloaded.
 */
static struct gcov_info *get_node_info(struct gcov_node *node)
{
        if (node->info)
                return node->info;

        return node->ghost;
}

/*
 * 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.
         */
        info = gcov_info_dup(get_node_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;
}

static void remove_node(struct gcov_node *node);

/*
 * write() implementation for gcov data files. Reset profiling data for the
 * associated file. If the object file has been unloaded (i.e. this is
 * a "ghost" node), 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->ghost)
                        remove_node(node);
                else
                        gcov_info_reset(node->info);
        }
        /* 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);
        node->info = info;
        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) {
                pr_warning("out of memory\n");
                return NULL;
        }
        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;
}

/* 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);
        if (node->ghost)
                gcov_info_free(node->ghost);
        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 ghost nodes.
 */
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->info)
                        gcov_info_reset(node->info);
                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,
};

/*
 * 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;
}

/*
 * The profiling data set associated with this node is being unloaded. Store a
 * copy of the profiling data and turn this node into a "ghost".
 */
static int ghost_node(struct gcov_node *node)
{
        node->ghost = gcov_info_dup(node->info);
        if (!node->ghost) {
                pr_warning("could not save data for '%s' (out of memory)\n",
                           node->info->filename);
                return -ENOMEM;
        }
        node->info = NULL;

        return 0;
}

/*
 * Profiling data for this node has been loaded again. Add profiling data
 * from previous instantiation and turn this node into a regular node.
 */
static void revive_node(struct gcov_node *node, struct gcov_info *info)
{
        if (gcov_info_is_compatible(node->ghost, info))
                gcov_info_add(info, node->ghost);
        else {
                pr_warning("discarding saved data for '%s' (version changed)\n",
                           info->filename);
        }
        gcov_info_free(node->ghost);
        node->ghost = NULL;
        node->info = info;
}

/*
 * 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:
                /* Add new node or revive ghost. */
                if (!node) {
                        add_node(info);
                        break;
                }
                if (gcov_persist)
                        revive_node(node, info);
                else {
                        pr_warning("could not add '%s' (already exists)\n",
                                   info->filename);
                }
                break;
        case GCOV_REMOVE:
                /* Remove node or turn into ghost. */
                if (!node) {
                        pr_warning("could not remove '%s' (not found)\n",
                                   info->filename);
                        break;
                }
                if (gcov_persist) {
                        if (!ghost_node(node))
                                break;
                }
                remove_node(node);
                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);