sysfs: Only take active references on attributes.

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / fs / sysfs / dir.c

/*
 * fs/sysfs/dir.c - sysfs core and dir operation implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
 *
 * This file is released under the GPLv2.
 *
 * Please see Documentation/filesystems/sysfs.txt for more information.
 */

#undef DEBUG

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/idr.h>
#include <linux/completion.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/security.h>
#include "sysfs.h"

DEFINE_MUTEX(sysfs_mutex);
DEFINE_SPINLOCK(sysfs_assoc_lock);

static DEFINE_SPINLOCK(sysfs_ino_lock);
static DEFINE_IDA(sysfs_ino_ida);

/**
 *      sysfs_link_sibling - link sysfs_dirent into sibling list
 *      @sd: sysfs_dirent of interest
 *
 *      Link @sd into its sibling list which starts from
 *      sd->s_parent->s_dir.children.
 *
 *      Locking:
 *      mutex_lock(sysfs_mutex)
 */
static void sysfs_link_sibling(struct sysfs_dirent *sd)
{
        struct sysfs_dirent *parent_sd = sd->s_parent;
        struct sysfs_dirent **pos;

        BUG_ON(sd->s_sibling);

        /* Store directory entries in order by ino.  This allows
         * readdir to properly restart without having to add a
         * cursor into the s_dir.children list.
         */
        for (pos = &parent_sd->s_dir.children; *pos; pos = &(*pos)->s_sibling) {
                if (sd->s_ino < (*pos)->s_ino)
                        break;
        }
        sd->s_sibling = *pos;
        *pos = sd;
}

/**
 *      sysfs_unlink_sibling - unlink sysfs_dirent from sibling list
 *      @sd: sysfs_dirent of interest
 *
 *      Unlink @sd from its sibling list which starts from
 *      sd->s_parent->s_dir.children.
 *
 *      Locking:
 *      mutex_lock(sysfs_mutex)
 */
static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
{
        struct sysfs_dirent **pos;

        for (pos = &sd->s_parent->s_dir.children; *pos;
             pos = &(*pos)->s_sibling) {
                if (*pos == sd) {
                        *pos = sd->s_sibling;
                        sd->s_sibling = NULL;
                        break;
                }
        }
}

/**
 *      sysfs_get_active - get an active reference to sysfs_dirent
 *      @sd: sysfs_dirent to get an active reference to
 *
 *      Get an active reference of @sd.  This function is noop if @sd
 *      is NULL.
 *
 *      RETURNS:
 *      Pointer to @sd on success, NULL on failure.
 */
struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
{
        if (unlikely(!sd))
                return NULL;

        while (1) {
                int v, t;

                v = atomic_read(&sd->s_active);
                if (unlikely(v < 0))
                        return NULL;

                t = atomic_cmpxchg(&sd->s_active, v, v + 1);
                if (likely(t == v)) {
                        rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_);
                        return sd;
                }
                if (t < 0)
                        return NULL;

                cpu_relax();
        }
}

/**
 *      sysfs_put_active - put an active reference to sysfs_dirent
 *      @sd: sysfs_dirent to put an active reference to
 *
 *      Put an active reference to @sd.  This function is noop if @sd
 *      is NULL.
 */
void sysfs_put_active(struct sysfs_dirent *sd)
{
        struct completion *cmpl;
        int v;

        if (unlikely(!sd))
                return;

        rwsem_release(&sd->dep_map, 1, _RET_IP_);
        v = atomic_dec_return(&sd->s_active);
        if (likely(v != SD_DEACTIVATED_BIAS))
                return;

        /* atomic_dec_return() is a mb(), we'll always see the updated
         * sd->s_sibling.
         */
        cmpl = (void *)sd->s_sibling;
        complete(cmpl);
}

/**
 *      sysfs_deactivate - deactivate sysfs_dirent
 *      @sd: sysfs_dirent to deactivate
 *
 *      Deny new active references and drain existing ones.
 */
static void sysfs_deactivate(struct sysfs_dirent *sd)
{
        DECLARE_COMPLETION_ONSTACK(wait);
        int v;

        BUG_ON(sd->s_sibling || !(sd->s_flags & SYSFS_FLAG_REMOVED));

        if (!(sysfs_type(sd) & SYSFS_ACTIVE_REF))
                return;

        sd->s_sibling = (void *)&wait;

        rwsem_acquire(&sd->dep_map, 0, 0, _RET_IP_);
        /* atomic_add_return() is a mb(), put_active() will always see
         * the updated sd->s_sibling.
         */
        v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);

        if (v != SD_DEACTIVATED_BIAS) {
                lock_contended(&sd->dep_map, _RET_IP_);
                wait_for_completion(&wait);
        }

        sd->s_sibling = NULL;

        lock_acquired(&sd->dep_map, _RET_IP_);
        rwsem_release(&sd->dep_map, 1, _RET_IP_);
}

static int sysfs_alloc_ino(ino_t *pino)
{
        int ino, rc;

 retry:
        spin_lock(&sysfs_ino_lock);
        rc = ida_get_new_above(&sysfs_ino_ida, 2, &ino);
        spin_unlock(&sysfs_ino_lock);

        if (rc == -EAGAIN) {
                if (ida_pre_get(&sysfs_ino_ida, GFP_KERNEL))
                        goto retry;
                rc = -ENOMEM;
        }

        *pino = ino;
        return rc;
}

static void sysfs_free_ino(ino_t ino)
{
        spin_lock(&sysfs_ino_lock);
        ida_remove(&sysfs_ino_ida, ino);
        spin_unlock(&sysfs_ino_lock);
}

void release_sysfs_dirent(struct sysfs_dirent * sd)
{
        struct sysfs_dirent *parent_sd;

 repeat:
        /* Moving/renaming is always done while holding reference.
         * sd->s_parent won't change beneath us.
         */
        parent_sd = sd->s_parent;

        if (sysfs_type(sd) == SYSFS_KOBJ_LINK)
                sysfs_put(sd->s_symlink.target_sd);
        if (sysfs_type(sd) & SYSFS_COPY_NAME)
                kfree(sd->s_name);
        if (sd->s_iattr && sd->s_iattr->ia_secdata)
                security_release_secctx(sd->s_iattr->ia_secdata,
                                        sd->s_iattr->ia_secdata_len);
        kfree(sd->s_iattr);
        sysfs_free_ino(sd->s_ino);
        kmem_cache_free(sysfs_dir_cachep, sd);

        sd = parent_sd;
        if (sd && atomic_dec_and_test(&sd->s_count))
                goto repeat;
}

static int sysfs_dentry_delete(struct dentry *dentry)
{
        struct sysfs_dirent *sd = dentry->d_fsdata;
        return !!(sd->s_flags & SYSFS_FLAG_REMOVED);
}

static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
{
        struct sysfs_dirent *sd = dentry->d_fsdata;
        int is_dir;

        mutex_lock(&sysfs_mutex);

        /* The sysfs dirent has been deleted */
        if (sd->s_flags & SYSFS_FLAG_REMOVED)
                goto out_bad;

        /* The sysfs dirent has been moved? */
        if (dentry->d_parent->d_fsdata != sd->s_parent)
                goto out_bad;

        /* The sysfs dirent has been renamed */
        if (strcmp(dentry->d_name.name, sd->s_name) != 0)
                goto out_bad;

        mutex_unlock(&sysfs_mutex);
out_valid:
        return 1;
out_bad:
        /* Remove the dentry from the dcache hashes.
         * If this is a deleted dentry we use d_drop instead of d_delete
         * so sysfs doesn't need to cope with negative dentries.
         *
         * If this is a dentry that has simply been renamed we
         * use d_drop to remove it from the dcache lookup on its
         * old parent.  If this dentry persists later when a lookup
         * is performed at its new name the dentry will be readded
         * to the dcache hashes.
         */
        is_dir = (sysfs_type(sd) == SYSFS_DIR);
        mutex_unlock(&sysfs_mutex);
        if (is_dir) {
                /* If we have submounts we must allow the vfs caches
                 * to lie about the state of the filesystem to prevent
                 * leaks and other nasty things.
                 */
                if (have_submounts(dentry))
                        goto out_valid;
                shrink_dcache_parent(dentry);
        }
        d_drop(dentry);
        return 0;
}

static void sysfs_dentry_iput(struct dentry *dentry, struct inode *inode)
{
        struct sysfs_dirent * sd = dentry->d_fsdata;

        sysfs_put(sd);
        iput(inode);
}

static const struct dentry_operations sysfs_dentry_ops = {
        .d_revalidate   = sysfs_dentry_revalidate,
        .d_delete       = sysfs_dentry_delete,
        .d_iput         = sysfs_dentry_iput,
};

struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
{
        char *dup_name = NULL;
        struct sysfs_dirent *sd;

        if (type & SYSFS_COPY_NAME) {
                name = dup_name = kstrdup(name, GFP_KERNEL);
                if (!name)
                        return NULL;
        }

        sd = kmem_cache_zalloc(sysfs_dir_cachep, GFP_KERNEL);
        if (!sd)
                goto err_out1;

        if (sysfs_alloc_ino(&sd->s_ino))
                goto err_out2;

        atomic_set(&sd->s_count, 1);
        atomic_set(&sd->s_active, 0);

        sd->s_name = name;
        sd->s_mode = mode;
        sd->s_flags = type;

        return sd;

 err_out2:
        kmem_cache_free(sysfs_dir_cachep, sd);
 err_out1:
        kfree(dup_name);
        return NULL;
}

/**
 *      sysfs_addrm_start - prepare for sysfs_dirent add/remove
 *      @acxt: pointer to sysfs_addrm_cxt to be used
 *      @parent_sd: parent sysfs_dirent
 *
 *      This function is called when the caller is about to add or
 *      remove sysfs_dirent under @parent_sd.  This function acquires
 *      sysfs_mutex.  @acxt is used to keep and pass context to
 *      other addrm functions.
 *
 *      LOCKING:
 *      Kernel thread context (may sleep).  sysfs_mutex is locked on
 *      return.
 */
void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
                       struct sysfs_dirent *parent_sd)
{
        memset(acxt, 0, sizeof(*acxt));
        acxt->parent_sd = parent_sd;

        mutex_lock(&sysfs_mutex);
}

/**
 *      __sysfs_add_one - add sysfs_dirent to parent without warning
 *      @acxt: addrm context to use
 *      @sd: sysfs_dirent to be added
 *
 *      Get @acxt->parent_sd and set sd->s_parent to it and increment
 *      nlink of parent inode if @sd is a directory and link into the
 *      children list of the parent.
 *
 *      This function should be called between calls to
 *      sysfs_addrm_start() and sysfs_addrm_finish() and should be
 *      passed the same @acxt as passed to sysfs_addrm_start().
 *
 *      LOCKING:
 *      Determined by sysfs_addrm_start().
 *
 *      RETURNS:
 *      0 on success, -EEXIST if entry with the given name already
 *      exists.
 */
int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
{
        struct sysfs_inode_attrs *ps_iattr;

        if (sysfs_find_dirent(acxt->parent_sd, sd->s_name))
                return -EEXIST;

        sd->s_parent = sysfs_get(acxt->parent_sd);

        sysfs_link_sibling(sd);

        /* Update timestamps on the parent */
        ps_iattr = acxt->parent_sd->s_iattr;
        if (ps_iattr) {
                struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
                ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
        }

        return 0;
}

/**
 *      sysfs_pathname - return full path to sysfs dirent
 *      @sd: sysfs_dirent whose path we want
 *      @path: caller allocated buffer
 *
 *      Gives the name "/" to the sysfs_root entry; any path returned
 *      is relative to wherever sysfs is mounted.
 *
 *      XXX: does no error checking on @path size
 */
static char *sysfs_pathname(struct sysfs_dirent *sd, char *path)
{
        if (sd->s_parent) {
                sysfs_pathname(sd->s_parent, path);
                strcat(path, "/");
        }
        strcat(path, sd->s_name);
        return path;
}

/**
 *      sysfs_add_one - add sysfs_dirent to parent
 *      @acxt: addrm context to use
 *      @sd: sysfs_dirent to be added
 *
 *      Get @acxt->parent_sd and set sd->s_parent to it and increment
 *      nlink of parent inode if @sd is a directory and link into the
 *      children list of the parent.
 *
 *      This function should be called between calls to
 *      sysfs_addrm_start() and sysfs_addrm_finish() and should be
 *      passed the same @acxt as passed to sysfs_addrm_start().
 *
 *      LOCKING:
 *      Determined by sysfs_addrm_start().
 *
 *      RETURNS:
 *      0 on success, -EEXIST if entry with the given name already
 *      exists.
 */
int sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
{
        int ret;

        ret = __sysfs_add_one(acxt, sd);
        if (ret == -EEXIST) {
                char *path = kzalloc(PATH_MAX, GFP_KERNEL);
                WARN(1, KERN_WARNING
                     "sysfs: cannot create duplicate filename '%s'\n",
                     (path == NULL) ? sd->s_name :
                     strcat(strcat(sysfs_pathname(acxt->parent_sd, path), "/"),
                            sd->s_name));
                kfree(path);
        }

        return ret;
}

/**
 *      sysfs_remove_one - remove sysfs_dirent from parent
 *      @acxt: addrm context to use
 *      @sd: sysfs_dirent to be removed
 *
 *      Mark @sd removed and drop nlink of parent inode if @sd is a
 *      directory.  @sd is unlinked from the children list.
 *
 *      This function should be called between calls to
 *      sysfs_addrm_start() and sysfs_addrm_finish() and should be
 *      passed the same @acxt as passed to sysfs_addrm_start().
 *
 *      LOCKING:
 *      Determined by sysfs_addrm_start().
 */
void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
{
        struct sysfs_inode_attrs *ps_iattr;

        BUG_ON(sd->s_flags & SYSFS_FLAG_REMOVED);

        sysfs_unlink_sibling(sd);

        /* Update timestamps on the parent */
        ps_iattr = acxt->parent_sd->s_iattr;
        if (ps_iattr) {
                struct iattr *ps_iattrs = &ps_iattr->ia_iattr;
                ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
        }

        sd->s_flags |= SYSFS_FLAG_REMOVED;
        sd->s_sibling = acxt->removed;
        acxt->removed = sd;
}

/**
 *      sysfs_addrm_finish - finish up sysfs_dirent add/remove
 *      @acxt: addrm context to finish up
 *
 *      Finish up sysfs_dirent add/remove.  Resources acquired by
 *      sysfs_addrm_start() are released and removed sysfs_dirents are
 *      cleaned up.
 *
 *      LOCKING:
 *      sysfs_mutex is released.
 */
void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
{
        /* release resources acquired by sysfs_addrm_start() */
        mutex_unlock(&sysfs_mutex);

        /* kill removed sysfs_dirents */
        while (acxt->removed) {
                struct sysfs_dirent *sd = acxt->removed;

                acxt->removed = sd->s_sibling;
                sd->s_sibling = NULL;

                sysfs_deactivate(sd);
                unmap_bin_file(sd);
                sysfs_put(sd);
        }
}

/**
 *      sysfs_find_dirent - find sysfs_dirent with the given name
 *      @parent_sd: sysfs_dirent to search under
 *      @name: name to look for
 *
 *      Look for sysfs_dirent with name @name under @parent_sd.
 *
 *      LOCKING:
 *      mutex_lock(sysfs_mutex)
 *
 *      RETURNS:
 *      Pointer to sysfs_dirent if found, NULL if not.
 */
struct sysfs_dirent *sysfs_find_dirent(struct sysfs_dirent *parent_sd,
                                       const unsigned char *name)
{
        struct sysfs_dirent *sd;

        for (sd = parent_sd->s_dir.children; sd; sd = sd->s_sibling)
                if (!strcmp(sd->s_name, name))
                        return sd;
        return NULL;
}

/**
 *      sysfs_get_dirent - find and get sysfs_dirent with the given name
 *      @parent_sd: sysfs_dirent to search under
 *      @name: name to look for
 *
 *      Look for sysfs_dirent with name @name under @parent_sd and get
 *      it if found.
 *
 *      LOCKING:
 *      Kernel thread context (may sleep).  Grabs sysfs_mutex.
 *
 *      RETURNS:
 *      Pointer to sysfs_dirent if found, NULL if not.
 */
struct sysfs_dirent *sysfs_get_dirent(struct sysfs_dirent *parent_sd,
                                      const unsigned char *name)
{
        struct sysfs_dirent *sd;

        mutex_lock(&sysfs_mutex);
        sd = sysfs_find_dirent(parent_sd, name);
        sysfs_get(sd);
        mutex_unlock(&sysfs_mutex);

        return sd;
}
EXPORT_SYMBOL_GPL(sysfs_get_dirent);

static int create_dir(struct kobject *kobj, struct sysfs_dirent *parent_sd,
                      const char *name, struct sysfs_dirent **p_sd)
{
        umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
        struct sysfs_addrm_cxt acxt;
        struct sysfs_dirent *sd;
        int rc;

        /* allocate */
        sd = sysfs_new_dirent(name, mode, SYSFS_DIR);
        if (!sd)
                return -ENOMEM;
        sd->s_dir.kobj = kobj;

        /* link in */
        sysfs_addrm_start(&acxt, parent_sd);
        rc = sysfs_add_one(&acxt, sd);
        sysfs_addrm_finish(&acxt);

        if (rc == 0)
                *p_sd = sd;
        else
                sysfs_put(sd);

        return rc;
}

int sysfs_create_subdir(struct kobject *kobj, const char *name,
                        struct sysfs_dirent **p_sd)
{
        return create_dir(kobj, kobj->sd, name, p_sd);
}

/**
 *      sysfs_create_dir - create a directory for an object.
 *      @kobj:          object we're creating directory for. 
 */
int sysfs_create_dir(struct kobject * kobj)
{
        struct sysfs_dirent *parent_sd, *sd;
        int error = 0;

        BUG_ON(!kobj);

        if (kobj->parent)
                parent_sd = kobj->parent->sd;
        else
                parent_sd = &sysfs_root;

        error = create_dir(kobj, parent_sd, kobject_name(kobj), &sd);
        if (!error)
                kobj->sd = sd;
        return error;
}

static struct dentry * sysfs_lookup(struct inode *dir, struct dentry *dentry,
                                struct nameidata *nd)
{
        struct dentry *ret = NULL;
        struct sysfs_dirent *parent_sd = dentry->d_parent->d_fsdata;
        struct sysfs_dirent *sd;
        struct inode *inode;

        mutex_lock(&sysfs_mutex);

        sd = sysfs_find_dirent(parent_sd, dentry->d_name.name);

        /* no such entry */
        if (!sd) {
                ret = ERR_PTR(-ENOENT);
                goto out_unlock;
        }

        /* attach dentry and inode */
        inode = sysfs_get_inode(sd);
        if (!inode) {
                ret = ERR_PTR(-ENOMEM);
                goto out_unlock;
        }

        /* instantiate and hash dentry */
        ret = d_find_alias(inode);
        if (!ret) {
                dentry->d_op = &sysfs_dentry_ops;
                dentry->d_fsdata = sysfs_get(sd);
                d_add(dentry, inode);
        } else {
                d_move(ret, dentry);
                iput(inode);
        }

 out_unlock:
        mutex_unlock(&sysfs_mutex);
        return ret;
}

const struct inode_operations sysfs_dir_inode_operations = {
        .lookup         = sysfs_lookup,
        .permission     = sysfs_permission,
        .setattr        = sysfs_setattr,
        .getattr        = sysfs_getattr,
        .setxattr       = sysfs_setxattr,
};

static void remove_dir(struct sysfs_dirent *sd)
{
        struct sysfs_addrm_cxt acxt;

        sysfs_addrm_start(&acxt, sd->s_parent);
        sysfs_remove_one(&acxt, sd);
        sysfs_addrm_finish(&acxt);
}

void sysfs_remove_subdir(struct sysfs_dirent *sd)
{
        remove_dir(sd);
}


static void __sysfs_remove_dir(struct sysfs_dirent *dir_sd)
{
        struct sysfs_addrm_cxt acxt;
        struct sysfs_dirent **pos;

        if (!dir_sd)
                return;

        pr_debug("sysfs %s: removing dir\n", dir_sd->s_name);
        sysfs_addrm_start(&acxt, dir_sd);
        pos = &dir_sd->s_dir.children;
        while (*pos) {
                struct sysfs_dirent *sd = *pos;

                if (sysfs_type(sd) != SYSFS_DIR)
                        sysfs_remove_one(&acxt, sd);
                else
                        pos = &(*pos)->s_sibling;
        }
        sysfs_addrm_finish(&acxt);

        remove_dir(dir_sd);
}

/**
 *      sysfs_remove_dir - remove an object's directory.
 *      @kobj:  object.
 *
 *      The only thing special about this is that we remove any files in
 *      the directory before we remove the directory, and we've inlined
 *      what used to be sysfs_rmdir() below, instead of calling separately.
 */

void sysfs_remove_dir(struct kobject * kobj)
{
        struct sysfs_dirent *sd = kobj->sd;

        spin_lock(&sysfs_assoc_lock);
        kobj->sd = NULL;
        spin_unlock(&sysfs_assoc_lock);

        __sysfs_remove_dir(sd);
}

int sysfs_rename(struct sysfs_dirent *sd,
        struct sysfs_dirent *new_parent_sd, const char *new_name)
{
        const char *dup_name = NULL;
        int error;

        mutex_lock(&sysfs_mutex);

        error = 0;
        if ((sd->s_parent == new_parent_sd) &&
            (strcmp(sd->s_name, new_name) == 0))
                goto out;       /* nothing to rename */

        error = -EEXIST;
        if (sysfs_find_dirent(new_parent_sd, new_name))
                goto out;

        /* rename sysfs_dirent */
        if (strcmp(sd->s_name, new_name) != 0) {
                error = -ENOMEM;
                new_name = dup_name = kstrdup(new_name, GFP_KERNEL);
                if (!new_name)
                        goto out;

                dup_name = sd->s_name;
                sd->s_name = new_name;
        }

        /* Remove from old parent's list and insert into new parent's list. */
        if (sd->s_parent != new_parent_sd) {
                sysfs_unlink_sibling(sd);
                sysfs_get(new_parent_sd);
                sysfs_put(sd->s_parent);
                sd->s_parent = new_parent_sd;
                sysfs_link_sibling(sd);
        }

        error = 0;
 out:
        mutex_unlock(&sysfs_mutex);
        kfree(dup_name);
        return error;
}

int sysfs_rename_dir(struct kobject *kobj, const char *new_name)
{
        return sysfs_rename(kobj->sd, kobj->sd->s_parent, new_name);
}

int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
{
        struct sysfs_dirent *sd = kobj->sd;
        struct sysfs_dirent *new_parent_sd;

        BUG_ON(!sd->s_parent);
        new_parent_sd = new_parent_kobj && new_parent_kobj->sd ?
                new_parent_kobj->sd : &sysfs_root;

        return sysfs_rename(sd, new_parent_sd, sd->s_name);
}

/* Relationship between s_mode and the DT_xxx types */
static inline unsigned char dt_type(struct sysfs_dirent *sd)
{
        return (sd->s_mode >> 12) & 15;
}

static int sysfs_dir_release(struct inode *inode, struct file *filp)
{
        sysfs_put(filp->private_data);
        return 0;
}

static struct sysfs_dirent *sysfs_dir_pos(struct sysfs_dirent *parent_sd,
        ino_t ino, struct sysfs_dirent *pos)
{
        if (pos) {
                int valid = !(pos->s_flags & SYSFS_FLAG_REMOVED) &&
                        pos->s_parent == parent_sd &&
                        ino == pos->s_ino;
                sysfs_put(pos);
                if (valid)
                        return pos;
        }
        pos = NULL;
        if ((ino > 1) && (ino < INT_MAX)) {
                pos = parent_sd->s_dir.children;
                while (pos && (ino > pos->s_ino))
                        pos = pos->s_sibling;
        }
        return pos;
}

static struct sysfs_dirent *sysfs_dir_next_pos(struct sysfs_dirent *parent_sd,
        ino_t ino, struct sysfs_dirent *pos)
{
        pos = sysfs_dir_pos(parent_sd, ino, pos);
        if (pos)
                pos = pos->s_sibling;
        return pos;
}

static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
        struct dentry *dentry = filp->f_path.dentry;
        struct sysfs_dirent * parent_sd = dentry->d_fsdata;
        struct sysfs_dirent *pos = filp->private_data;
        ino_t ino;

        if (filp->f_pos == 0) {
                ino = parent_sd->s_ino;
                if (filldir(dirent, ".", 1, filp->f_pos, ino, DT_DIR) == 0)
                        filp->f_pos++;
        }
        if (filp->f_pos == 1) {
                if (parent_sd->s_parent)
                        ino = parent_sd->s_parent->s_ino;
                else
                        ino = parent_sd->s_ino;
                if (filldir(dirent, "..", 2, filp->f_pos, ino, DT_DIR) == 0)
                        filp->f_pos++;
        }
        mutex_lock(&sysfs_mutex);
        for (pos = sysfs_dir_pos(parent_sd, filp->f_pos, pos);
             pos;
             pos = sysfs_dir_next_pos(parent_sd, filp->f_pos, pos)) {
                const char * name;
                unsigned int type;
                int len, ret;

                name = pos->s_name;
                len = strlen(name);
                ino = pos->s_ino;
                type = dt_type(pos);
                filp->f_pos = ino;
                filp->private_data = sysfs_get(pos);

                mutex_unlock(&sysfs_mutex);
                ret = filldir(dirent, name, len, filp->f_pos, ino, type);
                mutex_lock(&sysfs_mutex);
                if (ret < 0)
                        break;
        }
        mutex_unlock(&sysfs_mutex);
        if ((filp->f_pos > 1) && !pos) { /* EOF */
                filp->f_pos = INT_MAX;
                filp->private_data = NULL;
        }
        return 0;
}


const struct file_operations sysfs_dir_operations = {
        .read           = generic_read_dir,
        .readdir        = sysfs_readdir,
        .release        = sysfs_dir_release,
        .llseek         = generic_file_llseek,
};