fs/debugfs/inode.c

   1 /*
   2  *  inode.c - part of debugfs, a tiny little debug file system
   3  *
   4  *  Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
   5  *  Copyright (C) 2004 IBM Inc.
   6  *
   7  *      This program is free software; you can redistribute it and/or
   8  *      modify it under the terms of the GNU General Public License version
   9  *      2 as published by the Free Software Foundation.
  10  *
  11  *  debugfs is for people to use instead of /proc or /sys.
  12  *  See Documentation/DocBook/kernel-api for more details.
  13  *
  14  */
  15
  16 #include <linux/module.h>
  17 #include <linux/fs.h>
  18 #include <linux/mount.h>
  19 #include <linux/pagemap.h>
  20 #include <linux/init.h>
  21 #include <linux/kobject.h>
  22 #include <linux/namei.h>
  23 #include <linux/debugfs.h>
  24 #include <linux/fsnotify.h>
  25 #include <linux/string.h>
  26 #include <linux/seq_file.h>
  27 #include <linux/parser.h>
  28 #include <linux/magic.h>
  29 #include <linux/slab.h>
  30
  31 #define DEBUGFS_DEFAULT_MODE    0700
  32
  33 static struct vfsmount *debugfs_mount;
  34 static int debugfs_mount_count;
  35 static bool debugfs_registered;
  36
  37 static struct inode *debugfs_get_inode(struct super_block *sb)
  38 {
  39         struct inode *inode = new_inode(sb);
  40         if (inode) {
  41                 inode->i_ino = get_next_ino();
  42                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  43         }
  44         return inode;
  45 }
  46
  47 struct debugfs_mount_opts {
  48         kuid_t uid;
  49         kgid_t gid;
  50         umode_t mode;
  51 };
  52
  53 enum {
  54         Opt_uid,
  55         Opt_gid,
  56         Opt_mode,
  57         Opt_err
  58 };
  59
  60 static const match_table_t tokens = {
  61         {Opt_uid, "uid=%u"},
  62         {Opt_gid, "gid=%u"},
  63         {Opt_mode, "mode=%o"},
  64         {Opt_err, NULL}
  65 };
  66
  67 struct debugfs_fs_info {
  68         struct debugfs_mount_opts mount_opts;
  69 };
  70
  71 static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
  72 {
  73         substring_t args[MAX_OPT_ARGS];
  74         int option;
  75         int token;
  76         kuid_t uid;
  77         kgid_t gid;
  78         char *p;
  79
  80         opts->mode = DEBUGFS_DEFAULT_MODE;
  81
  82         while ((p = strsep(&data, ",")) != NULL) {
  83                 if (!*p)
  84                         continue;
  85
  86                 token = match_token(p, tokens, args);
  87                 switch (token) {
  88                 case Opt_uid:
  89                         if (match_int(&args[0], &option))
  90                                 return -EINVAL;
  91                         uid = make_kuid(current_user_ns(), option);
  92                         if (!uid_valid(uid))
  93                                 return -EINVAL;
  94                         opts->uid = uid;
  95                         break;
  96                 case Opt_gid:
  97                         if (match_int(&args[0], &option))
  98                                 return -EINVAL;
  99                         gid = make_kgid(current_user_ns(), option);
 100                         if (!gid_valid(gid))
 101                                 return -EINVAL;
 102                         opts->gid = gid;
 103                         break;
 104                 case Opt_mode:
 105                         if (match_octal(&args[0], &option))
 106                                 return -EINVAL;
 107                         opts->mode = option & S_IALLUGO;
 108                         break;
 109                 /*
 110                  * We might like to report bad mount options here;
 111                  * but traditionally debugfs has ignored all mount options
 112                  */
 113                 }
 114         }
 115
 116         return 0;
 117 }
 118
 119 static int debugfs_apply_options(struct super_block *sb)
 120 {
 121         struct debugfs_fs_info *fsi = sb->s_fs_info;
 122         struct inode *inode = d_inode(sb->s_root);
 123         struct debugfs_mount_opts *opts = &fsi->mount_opts;
 124
 125         inode->i_mode &= ~S_IALLUGO;
 126         inode->i_mode |= opts->mode;
 127
 128         inode->i_uid = opts->uid;
 129         inode->i_gid = opts->gid;
 130
 131         return 0;
 132 }
 133
 134 static int debugfs_remount(struct super_block *sb, int *flags, char *data)
 135 {
 136         int err;
 137         struct debugfs_fs_info *fsi = sb->s_fs_info;
 138
 139         sync_filesystem(sb);
 140         err = debugfs_parse_options(data, &fsi->mount_opts);
 141         if (err)
 142                 goto fail;
 143
 144         debugfs_apply_options(sb);
 145
 146 fail:
 147         return err;
 148 }
 149
 150 static int debugfs_show_options(struct seq_file *m, struct dentry *root)
 151 {
 152         struct debugfs_fs_info *fsi = root->d_sb->s_fs_info;
 153         struct debugfs_mount_opts *opts = &fsi->mount_opts;
 154
 155         if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
 156                 seq_printf(m, ",uid=%u",
 157                            from_kuid_munged(&init_user_ns, opts->uid));
 158         if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
 159                 seq_printf(m, ",gid=%u",
 160                            from_kgid_munged(&init_user_ns, opts->gid));
 161         if (opts->mode != DEBUGFS_DEFAULT_MODE)
 162                 seq_printf(m, ",mode=%o", opts->mode);
 163
 164         return 0;
 165 }
 166
 167 static void debugfs_evict_inode(struct inode *inode)
 168 {
 169         truncate_inode_pages_final(&inode->i_data);
 170         clear_inode(inode);
 171         if (S_ISLNK(inode->i_mode))
 172                 kfree(inode->i_link);
 173 }
 174
 175 static const struct super_operations debugfs_super_operations = {
 176         .statfs         = simple_statfs,
 177         .remount_fs     = debugfs_remount,
 178         .show_options   = debugfs_show_options,
 179         .evict_inode    = debugfs_evict_inode,
 180 };
 181
 182 static struct vfsmount *debugfs_automount(struct path *path)
 183 {
 184         struct vfsmount *(*f)(void *);
 185         f = (struct vfsmount *(*)(void *))path->dentry->d_fsdata;
 186         return f(d_inode(path->dentry)->i_private);
 187 }
 188
 189 static const struct dentry_operations debugfs_dops = {
 190         .d_delete = always_delete_dentry,
 191         .d_automount = debugfs_automount,
 192 };
 193
 194 static int debug_fill_super(struct super_block *sb, void *data, int silent)
 195 {
 196         static struct tree_descr debug_files[] = {{""}};
 197         struct debugfs_fs_info *fsi;
 198         int err;
 199
 200         save_mount_options(sb, data);
 201
 202         fsi = kzalloc(sizeof(struct debugfs_fs_info), GFP_KERNEL);
 203         sb->s_fs_info = fsi;
 204         if (!fsi) {
 205                 err = -ENOMEM;
 206                 goto fail;
 207         }
 208
 209         err = debugfs_parse_options(data, &fsi->mount_opts);
 210         if (err)
 211                 goto fail;
 212
 213         err  =  simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
 214         if (err)
 215                 goto fail;
 216
 217         sb->s_op = &debugfs_super_operations;
 218         sb->s_d_op = &debugfs_dops;
 219
 220         debugfs_apply_options(sb);
 221
 222         return 0;
 223
 224 fail:
 225         kfree(fsi);
 226         sb->s_fs_info = NULL;
 227         return err;
 228 }
 229
 230 static struct dentry *debug_mount(struct file_system_type *fs_type,
 231                         int flags, const char *dev_name,
 232                         void *data)
 233 {
 234         return mount_single(fs_type, flags, data, debug_fill_super);
 235 }
 236
 237 static struct file_system_type debug_fs_type = {
 238         .owner =        THIS_MODULE,
 239         .name =         "debugfs",
 240         .mount =        debug_mount,
 241         .kill_sb =      kill_litter_super,
 242 };
 243 MODULE_ALIAS_FS("debugfs");
 244
 245 static struct dentry *start_creating(const char *name, struct dentry *parent)
 246 {
 247         struct dentry *dentry;
 248         int error;
 249
 250         pr_debug("debugfs: creating file '%s'\n",name);
 251
 252         if (IS_ERR(parent))
 253                 return parent;
 254
 255         error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
 256                               &debugfs_mount_count);
 257         if (error)
 258                 return ERR_PTR(error);
 259
 260         /* If the parent is not specified, we create it in the root.
 261          * We need the root dentry to do this, which is in the super
 262          * block. A pointer to that is in the struct vfsmount that we
 263          * have around.
 264          */
 265         if (!parent)
 266                 parent = debugfs_mount->mnt_root;
 267
 268         inode_lock(d_inode(parent));
 269         dentry = lookup_one_len(name, parent, strlen(name));
 270         if (!IS_ERR(dentry) && d_really_is_positive(dentry)) {
 271                 dput(dentry);
 272                 dentry = ERR_PTR(-EEXIST);
 273         }
 274
 275         if (IS_ERR(dentry)) {
 276                 inode_unlock(d_inode(parent));
 277                 simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 278         }
 279
 280         return dentry;
 281 }
 282
 283 static struct dentry *failed_creating(struct dentry *dentry)
 284 {
 285         inode_unlock(d_inode(dentry->d_parent));
 286         dput(dentry);
 287         simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 288         return NULL;
 289 }
 290
 291 static struct dentry *end_creating(struct dentry *dentry)
 292 {
 293         inode_unlock(d_inode(dentry->d_parent));
 294         return dentry;
 295 }
 296
 297 /**
 298  * debugfs_create_file - create a file in the debugfs filesystem
 299  * @name: a pointer to a string containing the name of the file to create.
 300  * @mode: the permission that the file should have.
 301  * @parent: a pointer to the parent dentry for this file.  This should be a
 302  *          directory dentry if set.  If this parameter is NULL, then the
 303  *          file will be created in the root of the debugfs filesystem.
 304  * @data: a pointer to something that the caller will want to get to later
 305  *        on.  The inode.i_private pointer will point to this value on
 306  *        the open() call.
 307  * @fops: a pointer to a struct file_operations that should be used for
 308  *        this file.
 309  *
 310  * This is the basic "create a file" function for debugfs.  It allows for a
 311  * wide range of flexibility in creating a file, or a directory (if you want
 312  * to create a directory, the debugfs_create_dir() function is
 313  * recommended to be used instead.)
 314  *
 315  * This function will return a pointer to a dentry if it succeeds.  This
 316  * pointer must be passed to the debugfs_remove() function when the file is
 317  * to be removed (no automatic cleanup happens if your module is unloaded,
 318  * you are responsible here.)  If an error occurs, %NULL will be returned.
 319  *
 320  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 321  * returned.
 322  */
 323 struct dentry *debugfs_create_file(const char *name, umode_t mode,
 324                                    struct dentry *parent, void *data,
 325                                    const struct file_operations *fops)
 326 {
 327         struct dentry *dentry;
 328         struct inode *inode;
 329
 330         if (!(mode & S_IFMT))
 331                 mode |= S_IFREG;
 332         BUG_ON(!S_ISREG(mode));
 333         dentry = start_creating(name, parent);
 334
 335         if (IS_ERR(dentry))
 336                 return NULL;
 337
 338         inode = debugfs_get_inode(dentry->d_sb);
 339         if (unlikely(!inode))
 340                 return failed_creating(dentry);
 341
 342         inode->i_mode = mode;
 343         inode->i_fop = fops ? fops : &debugfs_file_operations;
 344         inode->i_private = data;
 345         d_instantiate(dentry, inode);
 346         fsnotify_create(d_inode(dentry->d_parent), dentry);
 347         return end_creating(dentry);
 348 }
 349 EXPORT_SYMBOL_GPL(debugfs_create_file);
 350
 351 /**
 352  * debugfs_create_file_size - create a file in the debugfs filesystem
 353  * @name: a pointer to a string containing the name of the file to create.
 354  * @mode: the permission that the file should have.
 355  * @parent: a pointer to the parent dentry for this file.  This should be a
 356  *          directory dentry if set.  If this parameter is NULL, then the
 357  *          file will be created in the root of the debugfs filesystem.
 358  * @data: a pointer to something that the caller will want to get to later
 359  *        on.  The inode.i_private pointer will point to this value on
 360  *        the open() call.
 361  * @fops: a pointer to a struct file_operations that should be used for
 362  *        this file.
 363  * @file_size: initial file size
 364  *
 365  * This is the basic "create a file" function for debugfs.  It allows for a
 366  * wide range of flexibility in creating a file, or a directory (if you want
 367  * to create a directory, the debugfs_create_dir() function is
 368  * recommended to be used instead.)
 369  *
 370  * This function will return a pointer to a dentry if it succeeds.  This
 371  * pointer must be passed to the debugfs_remove() function when the file is
 372  * to be removed (no automatic cleanup happens if your module is unloaded,
 373  * you are responsible here.)  If an error occurs, %NULL will be returned.
 374  *
 375  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 376  * returned.
 377  */
 378 struct dentry *debugfs_create_file_size(const char *name, umode_t mode,
 379                                         struct dentry *parent, void *data,
 380                                         const struct file_operations *fops,
 381                                         loff_t file_size)
 382 {
 383         struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);
 384
 385         if (de)
 386                 d_inode(de)->i_size = file_size;
 387         return de;
 388 }
 389 EXPORT_SYMBOL_GPL(debugfs_create_file_size);
 390
 391 /**
 392  * debugfs_create_dir - create a directory in the debugfs filesystem
 393  * @name: a pointer to a string containing the name of the directory to
 394  *        create.
 395  * @parent: a pointer to the parent dentry for this file.  This should be a
 396  *          directory dentry if set.  If this parameter is NULL, then the
 397  *          directory will be created in the root of the debugfs filesystem.
 398  *
 399  * This function creates a directory in debugfs with the given name.
 400  *
 401  * This function will return a pointer to a dentry if it succeeds.  This
 402  * pointer must be passed to the debugfs_remove() function when the file is
 403  * to be removed (no automatic cleanup happens if your module is unloaded,
 404  * you are responsible here.)  If an error occurs, %NULL will be returned.
 405  *
 406  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 407  * returned.
 408  */
 409 struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
 410 {
 411         struct dentry *dentry = start_creating(name, parent);
 412         struct inode *inode;
 413
 414         if (IS_ERR(dentry))
 415                 return NULL;
 416
 417         inode = debugfs_get_inode(dentry->d_sb);
 418         if (unlikely(!inode))
 419                 return failed_creating(dentry);
 420
 421         inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
 422         inode->i_op = &simple_dir_inode_operations;
 423         inode->i_fop = &simple_dir_operations;
 424
 425         /* directory inodes start off with i_nlink == 2 (for "." entry) */
 426         inc_nlink(inode);
 427         d_instantiate(dentry, inode);
 428         inc_nlink(d_inode(dentry->d_parent));
 429         fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
 430         return end_creating(dentry);
 431 }
 432 EXPORT_SYMBOL_GPL(debugfs_create_dir);
 433
 434 /**
 435  * debugfs_create_automount - create automount point in the debugfs filesystem
 436  * @name: a pointer to a string containing the name of the file to create.
 437  * @parent: a pointer to the parent dentry for this file.  This should be a
 438  *          directory dentry if set.  If this parameter is NULL, then the
 439  *          file will be created in the root of the debugfs filesystem.
 440  * @f: function to be called when pathname resolution steps on that one.
 441  * @data: opaque argument to pass to f().
 442  *
 443  * @f should return what ->d_automount() would.
 444  */
 445 struct dentry *debugfs_create_automount(const char *name,
 446                                         struct dentry *parent,
 447                                         struct vfsmount *(*f)(void *),
 448                                         void *data)
 449 {
 450         struct dentry *dentry = start_creating(name, parent);
 451         struct inode *inode;
 452
 453         if (IS_ERR(dentry))
 454                 return NULL;
 455
 456         inode = debugfs_get_inode(dentry->d_sb);
 457         if (unlikely(!inode))
 458                 return failed_creating(dentry);
 459
 460         make_empty_dir_inode(inode);
 461         inode->i_flags |= S_AUTOMOUNT;
 462         inode->i_private = data;
 463         dentry->d_fsdata = (void *)f;
 464         d_instantiate(dentry, inode);
 465         return end_creating(dentry);
 466 }
 467 EXPORT_SYMBOL(debugfs_create_automount);
 468
 469 /**
 470  * debugfs_create_symlink- create a symbolic link in the debugfs filesystem
 471  * @name: a pointer to a string containing the name of the symbolic link to
 472  *        create.
 473  * @parent: a pointer to the parent dentry for this symbolic link.  This
 474  *          should be a directory dentry if set.  If this parameter is NULL,
 475  *          then the symbolic link will be created in the root of the debugfs
 476  *          filesystem.
 477  * @target: a pointer to a string containing the path to the target of the
 478  *          symbolic link.
 479  *
 480  * This function creates a symbolic link with the given name in debugfs that
 481  * links to the given target path.
 482  *
 483  * This function will return a pointer to a dentry if it succeeds.  This
 484  * pointer must be passed to the debugfs_remove() function when the symbolic
 485  * link is to be removed (no automatic cleanup happens if your module is
 486  * unloaded, you are responsible here.)  If an error occurs, %NULL will be
 487  * returned.
 488  *
 489  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 490  * returned.
 491  */
 492 struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
 493                                       const char *target)
 494 {
 495         struct dentry *dentry;
 496         struct inode *inode;
 497         char *link = kstrdup(target, GFP_KERNEL);
 498         if (!link)
 499                 return NULL;
 500
 501         dentry = start_creating(name, parent);
 502         if (IS_ERR(dentry)) {
 503                 kfree(link);
 504                 return NULL;
 505         }
 506
 507         inode = debugfs_get_inode(dentry->d_sb);
 508         if (unlikely(!inode)) {
 509                 kfree(link);
 510                 return failed_creating(dentry);
 511         }
 512         inode->i_mode = S_IFLNK | S_IRWXUGO;
 513         inode->i_op = &simple_symlink_inode_operations;
 514         inode->i_link = link;
 515         d_instantiate(dentry, inode);
 516         return end_creating(dentry);
 517 }
 518 EXPORT_SYMBOL_GPL(debugfs_create_symlink);
 519
 520 static int __debugfs_remove(struct dentry *dentry, struct dentry *parent)
 521 {
 522         int ret = 0;
 523
 524         if (simple_positive(dentry)) {
 525                 dget(dentry);
 526                 if (d_is_dir(dentry))
 527                         ret = simple_rmdir(d_inode(parent), dentry);
 528                 else
 529                         simple_unlink(d_inode(parent), dentry);
 530                 if (!ret)
 531                         d_delete(dentry);
 532                 dput(dentry);
 533         }
 534         return ret;
 535 }
 536
 537 /**
 538  * debugfs_remove - removes a file or directory from the debugfs filesystem
 539  * @dentry: a pointer to a the dentry of the file or directory to be
 540  *          removed.  If this parameter is NULL or an error value, nothing
 541  *          will be done.
 542  *
 543  * This function removes a file or directory in debugfs that was previously
 544  * created with a call to another debugfs function (like
 545  * debugfs_create_file() or variants thereof.)
 546  *
 547  * This function is required to be called in order for the file to be
 548  * removed, no automatic cleanup of files will happen when a module is
 549  * removed, you are responsible here.
 550  */
 551 void debugfs_remove(struct dentry *dentry)
 552 {
 553         struct dentry *parent;
 554         int ret;
 555
 556         if (IS_ERR_OR_NULL(dentry))
 557                 return;
 558
 559         parent = dentry->d_parent;
 560         if (!parent || d_really_is_negative(parent))
 561                 return;
 562
 563         inode_lock(d_inode(parent));
 564         ret = __debugfs_remove(dentry, parent);
 565         inode_unlock(d_inode(parent));
 566         if (!ret)
 567                 simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 568 }
 569 EXPORT_SYMBOL_GPL(debugfs_remove);
 570
 571 /**
 572  * debugfs_remove_recursive - recursively removes a directory
 573  * @dentry: a pointer to a the dentry of the directory to be removed.  If this
 574  *          parameter is NULL or an error value, nothing will be done.
 575  *
 576  * This function recursively removes a directory tree in debugfs that
 577  * was previously created with a call to another debugfs function
 578  * (like debugfs_create_file() or variants thereof.)
 579  *
 580  * This function is required to be called in order for the file to be
 581  * removed, no automatic cleanup of files will happen when a module is
 582  * removed, you are responsible here.
 583  */
 584 void debugfs_remove_recursive(struct dentry *dentry)
 585 {
 586         struct dentry *child, *parent;
 587
 588         if (IS_ERR_OR_NULL(dentry))
 589                 return;
 590
 591         parent = dentry->d_parent;
 592         if (!parent || d_really_is_negative(parent))
 593                 return;
 594
 595         parent = dentry;
 596  down:
 597         inode_lock(d_inode(parent));
 598  loop:
 599         /*
 600          * The parent->d_subdirs is protected by the d_lock. Outside that
 601          * lock, the child can be unlinked and set to be freed which can
 602          * use the d_u.d_child as the rcu head and corrupt this list.
 603          */
 604         spin_lock(&parent->d_lock);
 605         list_for_each_entry(child, &parent->d_subdirs, d_child) {
 606                 if (!simple_positive(child))
 607                         continue;
 608
 609                 /* perhaps simple_empty(child) makes more sense */
 610                 if (!list_empty(&child->d_subdirs)) {
 611                         spin_unlock(&parent->d_lock);
 612                         inode_unlock(d_inode(parent));
 613                         parent = child;
 614                         goto down;
 615                 }
 616
 617                 spin_unlock(&parent->d_lock);
 618
 619                 if (!__debugfs_remove(child, parent))
 620                         simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 621
 622                 /*
 623                  * The parent->d_lock protects agaist child from unlinking
 624                  * from d_subdirs. When releasing the parent->d_lock we can
 625                  * no longer trust that the next pointer is valid.
 626                  * Restart the loop. We'll skip this one with the
 627                  * simple_positive() check.
 628                  */
 629                 goto loop;
 630         }
 631         spin_unlock(&parent->d_lock);
 632
 633         inode_unlock(d_inode(parent));
 634         child = parent;
 635         parent = parent->d_parent;
 636         inode_lock(d_inode(parent));
 637
 638         if (child != dentry)
 639                 /* go up */
 640                 goto loop;
 641
 642         if (!__debugfs_remove(child, parent))
 643                 simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 644         inode_unlock(d_inode(parent));
 645 }
 646 EXPORT_SYMBOL_GPL(debugfs_remove_recursive);
 647
 648 /**
 649  * debugfs_rename - rename a file/directory in the debugfs filesystem
 650  * @old_dir: a pointer to the parent dentry for the renamed object. This
 651  *          should be a directory dentry.
 652  * @old_dentry: dentry of an object to be renamed.
 653  * @new_dir: a pointer to the parent dentry where the object should be
 654  *          moved. This should be a directory dentry.
 655  * @new_name: a pointer to a string containing the target name.
 656  *
 657  * This function renames a file/directory in debugfs.  The target must not
 658  * exist for rename to succeed.
 659  *
 660  * This function will return a pointer to old_dentry (which is updated to
 661  * reflect renaming) if it succeeds. If an error occurs, %NULL will be
 662  * returned.
 663  *
 664  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 665  * returned.
 666  */
 667 struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
 668                 struct dentry *new_dir, const char *new_name)
 669 {
 670         int error;
 671         struct dentry *dentry = NULL, *trap;
 672         const char *old_name;
 673
 674         trap = lock_rename(new_dir, old_dir);
 675         /* Source or destination directories don't exist? */
 676         if (d_really_is_negative(old_dir) || d_really_is_negative(new_dir))
 677                 goto exit;
 678         /* Source does not exist, cyclic rename, or mountpoint? */
 679         if (d_really_is_negative(old_dentry) || old_dentry == trap ||
 680             d_mountpoint(old_dentry))
 681                 goto exit;
 682         dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
 683         /* Lookup failed, cyclic rename or target exists? */
 684         if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
 685                 goto exit;
 686
 687         old_name = fsnotify_oldname_init(old_dentry->d_name.name);
 688
 689         error = simple_rename(d_inode(old_dir), old_dentry, d_inode(new_dir),
 690                 dentry);
 691         if (error) {
 692                 fsnotify_oldname_free(old_name);
 693                 goto exit;
 694         }
 695         d_move(old_dentry, dentry);
 696         fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name,
 697                 d_is_dir(old_dentry),
 698                 NULL, old_dentry);
 699         fsnotify_oldname_free(old_name);
 700         unlock_rename(new_dir, old_dir);
 701         dput(dentry);
 702         return old_dentry;
 703 exit:
 704         if (dentry && !IS_ERR(dentry))
 705                 dput(dentry);
 706         unlock_rename(new_dir, old_dir);
 707         return NULL;
 708 }
 709 EXPORT_SYMBOL_GPL(debugfs_rename);
 710
 711 /**
 712  * debugfs_initialized - Tells whether debugfs has been registered
 713  */
 714 bool debugfs_initialized(void)
 715 {
 716         return debugfs_registered;
 717 }
 718 EXPORT_SYMBOL_GPL(debugfs_initialized);
 719
 720 static int __init debugfs_init(void)
 721 {
 722         int retval;
 723
 724         retval = sysfs_create_mount_point(kernel_kobj, "debug");
 725         if (retval)
 726                 return retval;
 727
 728         retval = register_filesystem(&debug_fs_type);
 729         if (retval)
 730                 sysfs_remove_mount_point(kernel_kobj, "debug");
 731         else
 732                 debugfs_registered = true;
 733
 734         return retval;
 735 }
 736 core_initcall(debugfs_init);
 737