sysfs: In sysfs_lookup don't open code sysfs_find_dirent

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

/*
 * dir.c - Operations for sysfs directories.
 */

#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 "sysfs.h"

DEFINE_MUTEX(sysfs_mutex);
spinlock_t sysfs_assoc_lock = SPIN_LOCK_UNLOCKED;

static spinlock_t sysfs_ino_lock = SPIN_LOCK_UNLOCKED;
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_children.
 *
 *      Locking:
 *      mutex_lock(sysfs_mutex)
 */
static void sysfs_link_sibling(struct sysfs_dirent *sd)
{
        struct sysfs_dirent *parent_sd = sd->s_parent;

        BUG_ON(sd->s_sibling);
        sd->s_sibling = parent_sd->s_children;
        parent_sd->s_children = 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_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_children; *pos; pos = &(*pos)->s_sibling) {
                if (*pos == sd) {
                        *pos = sd->s_sibling;
                        sd->s_sibling = NULL;
                        break;
                }
        }
}

/**
 *      sysfs_get_dentry - get dentry for the given sysfs_dirent
 *      @sd: sysfs_dirent of interest
 *
 *      Get dentry for @sd.  Dentry is looked up if currently not
 *      present.  This function climbs sysfs_dirent tree till it
 *      reaches a sysfs_dirent with valid dentry attached and descends
 *      down from there looking up dentry for each step.
 *
 *      LOCKING:
 *      Kernel thread context (may sleep)
 *
 *      RETURNS:
 *      Pointer to found dentry on success, ERR_PTR() value on error.
 */
struct dentry *sysfs_get_dentry(struct sysfs_dirent *sd)
{
        struct sysfs_dirent *cur;
        struct dentry *parent_dentry, *dentry;
        int i, depth;

        /* Find the first parent which has valid s_dentry and get the
         * dentry.
         */
        mutex_lock(&sysfs_mutex);
 restart0:
        spin_lock(&sysfs_assoc_lock);
 restart1:
        spin_lock(&dcache_lock);

        dentry = NULL;
        depth = 0;
        cur = sd;
        while (!cur->s_dentry || !cur->s_dentry->d_inode) {
                if (cur->s_flags & SYSFS_FLAG_REMOVED) {
                        dentry = ERR_PTR(-ENOENT);
                        depth = 0;
                        break;
                }
                cur = cur->s_parent;
                depth++;
        }
        if (!IS_ERR(dentry))
                dentry = dget_locked(cur->s_dentry);

        spin_unlock(&dcache_lock);
        spin_unlock(&sysfs_assoc_lock);

        /* from the found dentry, look up depth times */
        while (depth--) {
                /* find and get depth'th ancestor */
                for (cur = sd, i = 0; cur && i < depth; i++)
                        cur = cur->s_parent;

                /* This can happen if tree structure was modified due
                 * to move/rename.  Restart.
                 */
                if (i != depth) {
                        dput(dentry);
                        goto restart0;
                }

                sysfs_get(cur);

                mutex_unlock(&sysfs_mutex);

                /* look it up */
                parent_dentry = dentry;
                mutex_lock(&parent_dentry->d_inode->i_mutex);
                dentry = lookup_one_len_kern(cur->s_name, parent_dentry,
                                             strlen(cur->s_name));
                mutex_unlock(&parent_dentry->d_inode->i_mutex);
                dput(parent_dentry);

                if (IS_ERR(dentry)) {
                        sysfs_put(cur);
                        return dentry;
                }

                mutex_lock(&sysfs_mutex);
                spin_lock(&sysfs_assoc_lock);

                /* This, again, can happen if tree structure has
                 * changed and we looked up the wrong thing.  Restart.
                 */
                if (cur->s_dentry != dentry) {
                        dput(dentry);
                        sysfs_put(cur);
                        goto restart1;
                }

                spin_unlock(&sysfs_assoc_lock);

                sysfs_put(cur);
        }

        mutex_unlock(&sysfs_mutex);
        return dentry;
}

/**
 *      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))
                        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;

        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_get_active_two - get active references to sysfs_dirent and parent
 *      @sd: sysfs_dirent of interest
 *
 *      Get active reference to @sd and its parent.  Parent's active
 *      reference is grabbed first.  This function is noop if @sd is
 *      NULL.
 *
 *      RETURNS:
 *      Pointer to @sd on success, NULL on failure.
 */
struct sysfs_dirent *sysfs_get_active_two(struct sysfs_dirent *sd)
{
        if (sd) {
                if (sd->s_parent && unlikely(!sysfs_get_active(sd->s_parent)))
                        return NULL;
                if (unlikely(!sysfs_get_active(sd))) {
                        sysfs_put_active(sd->s_parent);
                        return NULL;
                }
        }
        return sd;
}

/**
 *      sysfs_put_active_two - put active references to sysfs_dirent and parent
 *      @sd: sysfs_dirent of interest
 *
 *      Put active references to @sd and its parent.  This function is
 *      noop if @sd is NULL.
 */
void sysfs_put_active_two(struct sysfs_dirent *sd)
{
        if (sd) {
                sysfs_put_active(sd);
                sysfs_put_active(sd->s_parent);
        }
}

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

        /* 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)
                wait_for_completion(&wait);

        sd->s_sibling = NULL;
}

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_elem.symlink.target_sd);
        if (sysfs_type(sd) & SYSFS_COPY_NAME)
                kfree(sd->s_name);
        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 void sysfs_d_iput(struct dentry * dentry, struct inode * inode)
{
        struct sysfs_dirent * sd = dentry->d_fsdata;

        if (sd) {
                /* sd->s_dentry is protected with sysfs_assoc_lock.
                 * This allows sysfs_drop_dentry() to dereference it.
                 */
                spin_lock(&sysfs_assoc_lock);

                /* The dentry might have been deleted or another
                 * lookup could have happened updating sd->s_dentry to
                 * point the new dentry.  Ignore if it isn't pointing
                 * to this dentry.
                 */
                if (sd->s_dentry == dentry)
                        sd->s_dentry = NULL;
                spin_unlock(&sysfs_assoc_lock);
                sysfs_put(sd);
        }
        iput(inode);
}

static struct dentry_operations sysfs_dentry_ops = {
        .d_iput         = sysfs_d_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);
        atomic_set(&sd->s_event, 1);

        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_attach_dentry - associate sysfs_dirent with dentry
 *      @sd: target sysfs_dirent
 *      @dentry: dentry to associate
 *
 *      Associate @sd with @dentry.  This is protected by
 *      sysfs_assoc_lock to avoid race with sysfs_d_iput().
 *
 *      LOCKING:
 *      mutex_lock(sysfs_mutex)
 */
static void sysfs_attach_dentry(struct sysfs_dirent *sd, struct dentry *dentry)
{
        dentry->d_op = &sysfs_dentry_ops;
        dentry->d_fsdata = sysfs_get(sd);

        /* protect sd->s_dentry against sysfs_d_iput */
        spin_lock(&sysfs_assoc_lock);
        sd->s_dentry = dentry;
        spin_unlock(&sysfs_assoc_lock);

        d_rehash(dentry);
}

static int sysfs_ilookup_test(struct inode *inode, void *arg)
{
        struct sysfs_dirent *sd = arg;
        return inode->i_ino == sd->s_ino;
}

/**
 *      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, grabs inode for @parent_sd if available and lock
 *      i_mutex of it.  @acxt is used to keep and pass context to
 *      other addrm functions.
 *
 *      LOCKING:
 *      Kernel thread context (may sleep).  sysfs_mutex is locked on
 *      return.  i_mutex of parent inode is locked on return if
 *      available.
 */
void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
                       struct sysfs_dirent *parent_sd)
{
        struct inode *inode;

        memset(acxt, 0, sizeof(*acxt));
        acxt->parent_sd = parent_sd;

        /* Lookup parent inode.  inode initialization and I_NEW
         * clearing are protected by sysfs_mutex.  By grabbing it and
         * looking up with _nowait variant, inode state can be
         * determined reliably.
         */
        mutex_lock(&sysfs_mutex);

        inode = ilookup5_nowait(sysfs_sb, parent_sd->s_ino, sysfs_ilookup_test,
                                parent_sd);

        if (inode && !(inode->i_state & I_NEW)) {
                /* parent inode available */
                acxt->parent_inode = inode;

                /* sysfs_mutex is below i_mutex in lock hierarchy.
                 * First, trylock i_mutex.  If fails, unlock
                 * sysfs_mutex and lock them in order.
                 */
                if (!mutex_trylock(&inode->i_mutex)) {
                        mutex_unlock(&sysfs_mutex);
                        mutex_lock(&inode->i_mutex);
                        mutex_lock(&sysfs_mutex);
                }
        } else
                iput(inode);
}

/**
 *      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.  @sd is NOT
 *      linked into the children list of the parent.  The caller
 *      should invoke sysfs_link_sibling() after this function
 *      completes if @sd needs to be on 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().
 *
 *      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)
{
        if (sysfs_find_dirent(acxt->parent_sd, sd->s_name))
                return -EEXIST;

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

        if (sysfs_type(sd) == SYSFS_DIR && acxt->parent_inode)
                inc_nlink(acxt->parent_inode);

        acxt->cnt++;

        sysfs_link_sibling(sd);

        return 0;
}

/**
 *      sysfs_remove_one - remove sysfs_dirent from parent
 *      @acxt: addrm context to use
 *      @sd: sysfs_dirent to be added
 *
 *      Mark @sd removed and drop nlink of parent inode if @sd is a
 *      directory.  @sd is NOT unlinked from the children list of the
 *      parent.  The caller is repsonsible for removing @sd from the
 *      children list before calling this function.
 *
 *      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)
{
        BUG_ON(sd->s_flags & SYSFS_FLAG_REMOVED);

        sysfs_unlink_sibling(sd);

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

        if (sysfs_type(sd) == SYSFS_DIR && acxt->parent_inode)
                drop_nlink(acxt->parent_inode);

        acxt->cnt++;
}

/**
 *      sysfs_drop_dentry - drop dentry for the specified sysfs_dirent
 *      @sd: target sysfs_dirent
 *
 *      Drop dentry for @sd.  @sd must have been unlinked from its
 *      parent on entry to this function such that it can't be looked
 *      up anymore.
 *
 *      @sd->s_dentry which is protected with sysfs_assoc_lock points
 *      to the currently associated dentry but we're not holding a
 *      reference to it and racing with dput().  Grab dcache_lock and
 *      verify dentry before dropping it.  If @sd->s_dentry is NULL or
 *      dput() beats us, no need to bother.
 */
static void sysfs_drop_dentry(struct sysfs_dirent *sd)
{
        struct dentry *dentry = NULL;
        struct inode *inode;

        /* We're not holding a reference to ->s_dentry dentry but the
         * field will stay valid as long as sysfs_assoc_lock is held.
         */
        spin_lock(&sysfs_assoc_lock);
        spin_lock(&dcache_lock);

        /* drop dentry if it's there and dput() didn't kill it yet */
        if (sd->s_dentry && sd->s_dentry->d_inode) {
                dentry = dget_locked(sd->s_dentry);
                spin_lock(&dentry->d_lock);
                __d_drop(dentry);
                spin_unlock(&dentry->d_lock);
        }

        spin_unlock(&dcache_lock);
        spin_unlock(&sysfs_assoc_lock);

        dput(dentry);

        /* adjust nlink and update timestamp */
        inode = ilookup(sysfs_sb, sd->s_ino);
        if (inode) {
                mutex_lock(&inode->i_mutex);

                inode->i_ctime = CURRENT_TIME;
                drop_nlink(inode);
                if (sysfs_type(sd) == SYSFS_DIR)
                        drop_nlink(inode);

                mutex_unlock(&inode->i_mutex);
                iput(inode);
        }
}

/**
 *      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.  Timestamps on the parent inode are updated.
 *
 *      LOCKING:
 *      All mutexes acquired by sysfs_addrm_start() are released.
 */
void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
{
        /* release resources acquired by sysfs_addrm_start() */
        mutex_unlock(&sysfs_mutex);
        if (acxt->parent_inode) {
                struct inode *inode = acxt->parent_inode;

                /* if added/removed, update timestamps on the parent */
                if (acxt->cnt)
                        inode->i_ctime = inode->i_mtime = CURRENT_TIME;

                mutex_unlock(&inode->i_mutex);
                iput(inode);
        }

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

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

                sysfs_drop_dentry(sd);
                sysfs_deactivate(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_children; sd; sd = sd->s_sibling)
                if (sysfs_type(sd) && !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;
}

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_elem.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)
                goto out_unlock;

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

        d_instantiate(dentry, inode);
        sysfs_attach_dentry(sd, dentry);

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

const struct inode_operations sysfs_dir_inode_operations = {
        .lookup         = sysfs_lookup,
        .setattr        = sysfs_setattr,
};

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_children;
        while (*pos) {
                struct sysfs_dirent *sd = *pos;

                if (sysfs_type(sd) && 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_dir(struct kobject * kobj, const char *new_name)
{
        struct sysfs_dirent *sd;
        struct dentry *parent = NULL;
        struct dentry *old_dentry = NULL, *new_dentry = NULL;
        const char *dup_name = NULL;
        int error;

        /* get the original dentry */
        sd = kobj->sd;
        old_dentry = sysfs_get_dentry(sd);
        if (IS_ERR(old_dentry)) {
                error = PTR_ERR(old_dentry);
                goto out_dput;
        }

        parent = old_dentry->d_parent;

        /* lock parent and get dentry for new name */
        mutex_lock(&parent->d_inode->i_mutex);

        new_dentry = lookup_one_len(new_name, parent, strlen(new_name));
        if (IS_ERR(new_dentry)) {
                error = PTR_ERR(new_dentry);
                goto out_unlock;
        }

        error = -EINVAL;
        if (old_dentry == new_dentry)
                goto out_unlock;

        error = -EEXIST;
        if (new_dentry->d_inode)
                goto out_unlock;

        /* rename kobject and sysfs_dirent */
        error = -ENOMEM;
        new_name = dup_name = kstrdup(new_name, GFP_KERNEL);
        if (!new_name)
                goto out_drop;

        error = kobject_set_name(kobj, "%s", new_name);
        if (error)
                goto out_drop;

        mutex_lock(&sysfs_mutex);
        dup_name = sd->s_name;
        sd->s_name = new_name;
        mutex_unlock(&sysfs_mutex);

        /* rename */
        d_add(new_dentry, NULL);
        d_move(sd->s_dentry, new_dentry);

        error = 0;
        goto out_unlock;

 out_drop:
        d_drop(new_dentry);
 out_unlock:
        mutex_unlock(&parent->d_inode->i_mutex);
 out_dput:
        kfree(dup_name);
        dput(old_dentry);
        dput(new_dentry);
        return error;
}

int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
{
        struct sysfs_dirent *sd = kobj->sd;
        struct sysfs_dirent *new_parent_sd;
        struct dentry *old_parent, *new_parent = NULL;
        struct dentry *old_dentry = NULL, *new_dentry = NULL;
        int error;

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

        /* get dentries */
        old_dentry = sysfs_get_dentry(sd);
        if (IS_ERR(old_dentry)) {
                error = PTR_ERR(old_dentry);
                goto out_dput;
        }
        old_parent = sd->s_parent->s_dentry;

        new_parent = sysfs_get_dentry(new_parent_sd);
        if (IS_ERR(new_parent)) {
                error = PTR_ERR(new_parent);
                goto out_dput;
        }

        if (old_parent->d_inode == new_parent->d_inode) {
                error = 0;
                goto out_dput;  /* nothing to move */
        }
again:
        mutex_lock(&old_parent->d_inode->i_mutex);
        if (!mutex_trylock(&new_parent->d_inode->i_mutex)) {
                mutex_unlock(&old_parent->d_inode->i_mutex);
                goto again;
        }

        new_dentry = lookup_one_len(kobject_name(kobj), new_parent, strlen(kobject_name(kobj)));
        if (IS_ERR(new_dentry)) {
                error = PTR_ERR(new_dentry);
                goto out_unlock;
        } else
                error = 0;
        d_add(new_dentry, NULL);
        d_move(sd->s_dentry, new_dentry);
        dput(new_dentry);

        /* Remove from old parent's list and insert into new parent's list. */
        mutex_lock(&sysfs_mutex);

        sysfs_unlink_sibling(sd);
        sysfs_get(new_parent_sd);
        sysfs_put(sd->s_parent);
        sd->s_parent = new_parent_sd;
        sysfs_link_sibling(sd);

        mutex_unlock(&sysfs_mutex);

 out_unlock:
        mutex_unlock(&new_parent->d_inode->i_mutex);
        mutex_unlock(&old_parent->d_inode->i_mutex);
 out_dput:
        dput(new_parent);
        dput(old_dentry);
        dput(new_dentry);
        return error;
}

static int sysfs_dir_open(struct inode *inode, struct file *file)
{
        struct dentry * dentry = file->f_path.dentry;
        struct sysfs_dirent * parent_sd = dentry->d_fsdata;
        struct sysfs_dirent * sd;

        sd = sysfs_new_dirent("_DIR_", 0, 0);
        if (sd) {
                mutex_lock(&sysfs_mutex);
                sd->s_parent = sysfs_get(parent_sd);
                sysfs_link_sibling(sd);
                mutex_unlock(&sysfs_mutex);
        }

        file->private_data = sd;
        return sd ? 0 : -ENOMEM;
}

static int sysfs_dir_close(struct inode *inode, struct file *file)
{
        struct sysfs_dirent * cursor = file->private_data;

        mutex_lock(&sysfs_mutex);
        sysfs_unlink_sibling(cursor);
        mutex_unlock(&sysfs_mutex);

        release_sysfs_dirent(cursor);

        return 0;
}

/* 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_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 *cursor = filp->private_data;
        struct sysfs_dirent **pos;
        ino_t ino;
        int i = filp->f_pos;

        switch (i) {
                case 0:
                        ino = parent_sd->s_ino;
                        if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
                                break;
                        filp->f_pos++;
                        i++;
                        /* fallthrough */
                case 1:
                        if (parent_sd->s_parent)
                                ino = parent_sd->s_parent->s_ino;
                        else
                                ino = parent_sd->s_ino;
                        if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
                                break;
                        filp->f_pos++;
                        i++;
                        /* fallthrough */
                default:
                        mutex_lock(&sysfs_mutex);

                        pos = &parent_sd->s_children;
                        while (*pos != cursor)
                                pos = &(*pos)->s_sibling;

                        /* unlink cursor */
                        *pos = cursor->s_sibling;

                        if (filp->f_pos == 2)
                                pos = &parent_sd->s_children;

                        for ( ; *pos; pos = &(*pos)->s_sibling) {
                                struct sysfs_dirent *next = *pos;
                                const char * name;
                                int len;

                                if (!sysfs_type(next))
                                        continue;

                                name = next->s_name;
                                len = strlen(name);
                                ino = next->s_ino;

                                if (filldir(dirent, name, len, filp->f_pos, ino,
                                                 dt_type(next)) < 0)
                                        break;

                                filp->f_pos++;
                        }

                        /* put cursor back in */
                        cursor->s_sibling = *pos;
                        *pos = cursor;

                        mutex_unlock(&sysfs_mutex);
        }
        return 0;
}

static loff_t sysfs_dir_lseek(struct file * file, loff_t offset, int origin)
{
        struct dentry * dentry = file->f_path.dentry;

        switch (origin) {
                case 1:
                        offset += file->f_pos;
                case 0:
                        if (offset >= 0)
                                break;
                default:
                        return -EINVAL;
        }
        if (offset != file->f_pos) {
                mutex_lock(&sysfs_mutex);

                file->f_pos = offset;
                if (file->f_pos >= 2) {
                        struct sysfs_dirent *sd = dentry->d_fsdata;
                        struct sysfs_dirent *cursor = file->private_data;
                        struct sysfs_dirent **pos;
                        loff_t n = file->f_pos - 2;

                        sysfs_unlink_sibling(cursor);

                        pos = &sd->s_children;
                        while (n && *pos) {
                                struct sysfs_dirent *next = *pos;
                                if (sysfs_type(next))
                                        n--;
                                pos = &(*pos)->s_sibling;
                        }

                        cursor->s_sibling = *pos;
                        *pos = cursor;
                }

                mutex_unlock(&sysfs_mutex);
        }

        return offset;
}

const struct file_operations sysfs_dir_operations = {
        .open           = sysfs_dir_open,
        .release        = sysfs_dir_close,
        .llseek         = sysfs_dir_lseek,
        .read           = generic_read_dir,
        .readdir        = sysfs_readdir,
};