fs/debugfs/inode.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  inode.c - part of debugfs, a tiny little debug file system
   4  *
   5  *  Copyright (C) 2004,2019 Greg Kroah-Hartman <greg@kroah.com>
   6  *  Copyright (C) 2004 IBM Inc.
   7  *  Copyright (C) 2019 Linux Foundation <gregkh@linuxfoundation.org>
   8  *
   9  *  debugfs is for people to use instead of /proc or /sys.
  10  *  See ./Documentation/core-api/kernel-api.rst for more details.
  11  */
  12
  13 #define pr_fmt(fmt)     "debugfs: " fmt
  14
  15 #include <linux/module.h>
  16 #include <linux/fs.h>
  17 #include <linux/mount.h>
  18 #include <linux/pagemap.h>
  19 #include <linux/init.h>
  20 #include <linux/kobject.h>
  21 #include <linux/namei.h>
  22 #include <linux/debugfs.h>
  23 #include <linux/fsnotify.h>
  24 #include <linux/string.h>
  25 #include <linux/seq_file.h>
  26 #include <linux/parser.h>
  27 #include <linux/magic.h>
  28 #include <linux/slab.h>
  29 #include <linux/security.h>
  30
  31 #include "internal.h"
  32
  33 #define DEBUGFS_DEFAULT_MODE    0700
  34
  35 static struct vfsmount *debugfs_mount;
  36 static int debugfs_mount_count;
  37 static bool debugfs_registered;
  38 static unsigned int debugfs_allow __ro_after_init = DEFAULT_DEBUGFS_ALLOW_BITS;
  39
  40 /*
  41  * Don't allow access attributes to be changed whilst the kernel is locked down
  42  * so that we can use the file mode as part of a heuristic to determine whether
  43  * to lock down individual files.
  44  */
  45 static int debugfs_setattr(struct user_namespace *mnt_userns,
  46                            struct dentry *dentry, struct iattr *ia)
  47 {
  48         int ret;
  49
  50         if (ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) {
  51                 ret = security_locked_down(LOCKDOWN_DEBUGFS);
  52                 if (ret)
  53                         return ret;
  54         }
  55         return simple_setattr(&init_user_ns, dentry, ia);
  56 }
  57
  58 static const struct inode_operations debugfs_file_inode_operations = {
  59         .setattr        = debugfs_setattr,
  60 };
  61 static const struct inode_operations debugfs_dir_inode_operations = {
  62         .lookup         = simple_lookup,
  63         .setattr        = debugfs_setattr,
  64 };
  65 static const struct inode_operations debugfs_symlink_inode_operations = {
  66         .get_link       = simple_get_link,
  67         .setattr        = debugfs_setattr,
  68 };
  69
  70 static struct inode *debugfs_get_inode(struct super_block *sb)
  71 {
  72         struct inode *inode = new_inode(sb);
  73         if (inode) {
  74                 inode->i_ino = get_next_ino();
  75                 inode->i_atime = inode->i_mtime =
  76                         inode->i_ctime = current_time(inode);
  77         }
  78         return inode;
  79 }
  80
  81 struct debugfs_mount_opts {
  82         kuid_t uid;
  83         kgid_t gid;
  84         umode_t mode;
  85 };
  86
  87 enum {
  88         Opt_uid,
  89         Opt_gid,
  90         Opt_mode,
  91         Opt_err
  92 };
  93
  94 static const match_table_t tokens = {
  95         {Opt_uid, "uid=%u"},
  96         {Opt_gid, "gid=%u"},
  97         {Opt_mode, "mode=%o"},
  98         {Opt_err, NULL}
  99 };
 100
 101 struct debugfs_fs_info {
 102         struct debugfs_mount_opts mount_opts;
 103 };
 104
 105 static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
 106 {
 107         substring_t args[MAX_OPT_ARGS];
 108         int option;
 109         int token;
 110         kuid_t uid;
 111         kgid_t gid;
 112         char *p;
 113
 114         opts->mode = DEBUGFS_DEFAULT_MODE;
 115
 116         while ((p = strsep(&data, ",")) != NULL) {
 117                 if (!*p)
 118                         continue;
 119
 120                 token = match_token(p, tokens, args);
 121                 switch (token) {
 122                 case Opt_uid:
 123                         if (match_int(&args[0], &option))
 124                                 return -EINVAL;
 125                         uid = make_kuid(current_user_ns(), option);
 126                         if (!uid_valid(uid))
 127                                 return -EINVAL;
 128                         opts->uid = uid;
 129                         break;
 130                 case Opt_gid:
 131                         if (match_int(&args[0], &option))
 132                                 return -EINVAL;
 133                         gid = make_kgid(current_user_ns(), option);
 134                         if (!gid_valid(gid))
 135                                 return -EINVAL;
 136                         opts->gid = gid;
 137                         break;
 138                 case Opt_mode:
 139                         if (match_octal(&args[0], &option))
 140                                 return -EINVAL;
 141                         opts->mode = option & S_IALLUGO;
 142                         break;
 143                 /*
 144                  * We might like to report bad mount options here;
 145                  * but traditionally debugfs has ignored all mount options
 146                  */
 147                 }
 148         }
 149
 150         return 0;
 151 }
 152
 153 static int debugfs_apply_options(struct super_block *sb)
 154 {
 155         struct debugfs_fs_info *fsi = sb->s_fs_info;
 156         struct inode *inode = d_inode(sb->s_root);
 157         struct debugfs_mount_opts *opts = &fsi->mount_opts;
 158
 159         inode->i_mode &= ~S_IALLUGO;
 160         inode->i_mode |= opts->mode;
 161
 162         inode->i_uid = opts->uid;
 163         inode->i_gid = opts->gid;
 164
 165         return 0;
 166 }
 167
 168 static int debugfs_remount(struct super_block *sb, int *flags, char *data)
 169 {
 170         int err;
 171         struct debugfs_fs_info *fsi = sb->s_fs_info;
 172
 173         sync_filesystem(sb);
 174         err = debugfs_parse_options(data, &fsi->mount_opts);
 175         if (err)
 176                 goto fail;
 177
 178         debugfs_apply_options(sb);
 179
 180 fail:
 181         return err;
 182 }
 183
 184 static int debugfs_show_options(struct seq_file *m, struct dentry *root)
 185 {
 186         struct debugfs_fs_info *fsi = root->d_sb->s_fs_info;
 187         struct debugfs_mount_opts *opts = &fsi->mount_opts;
 188
 189         if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
 190                 seq_printf(m, ",uid=%u",
 191                            from_kuid_munged(&init_user_ns, opts->uid));
 192         if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
 193                 seq_printf(m, ",gid=%u",
 194                            from_kgid_munged(&init_user_ns, opts->gid));
 195         if (opts->mode != DEBUGFS_DEFAULT_MODE)
 196                 seq_printf(m, ",mode=%o", opts->mode);
 197
 198         return 0;
 199 }
 200
 201 static void debugfs_free_inode(struct inode *inode)
 202 {
 203         if (S_ISLNK(inode->i_mode))
 204                 kfree(inode->i_link);
 205         free_inode_nonrcu(inode);
 206 }
 207
 208 static const struct super_operations debugfs_super_operations = {
 209         .statfs         = simple_statfs,
 210         .remount_fs     = debugfs_remount,
 211         .show_options   = debugfs_show_options,
 212         .free_inode     = debugfs_free_inode,
 213 };
 214
 215 static void debugfs_release_dentry(struct dentry *dentry)
 216 {
 217         void *fsd = dentry->d_fsdata;
 218
 219         if (!((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
 220                 kfree(dentry->d_fsdata);
 221 }
 222
 223 static struct vfsmount *debugfs_automount(struct path *path)
 224 {
 225         debugfs_automount_t f;
 226         f = (debugfs_automount_t)path->dentry->d_fsdata;
 227         return f(path->dentry, d_inode(path->dentry)->i_private);
 228 }
 229
 230 static const struct dentry_operations debugfs_dops = {
 231         .d_delete = always_delete_dentry,
 232         .d_release = debugfs_release_dentry,
 233         .d_automount = debugfs_automount,
 234 };
 235
 236 static int debug_fill_super(struct super_block *sb, void *data, int silent)
 237 {
 238         static const struct tree_descr debug_files[] = {{""}};
 239         struct debugfs_fs_info *fsi;
 240         int err;
 241
 242         fsi = kzalloc(sizeof(struct debugfs_fs_info), GFP_KERNEL);
 243         sb->s_fs_info = fsi;
 244         if (!fsi) {
 245                 err = -ENOMEM;
 246                 goto fail;
 247         }
 248
 249         err = debugfs_parse_options(data, &fsi->mount_opts);
 250         if (err)
 251                 goto fail;
 252
 253         err  =  simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
 254         if (err)
 255                 goto fail;
 256
 257         sb->s_op = &debugfs_super_operations;
 258         sb->s_d_op = &debugfs_dops;
 259
 260         debugfs_apply_options(sb);
 261
 262         return 0;
 263
 264 fail:
 265         kfree(fsi);
 266         sb->s_fs_info = NULL;
 267         return err;
 268 }
 269
 270 static struct dentry *debug_mount(struct file_system_type *fs_type,
 271                         int flags, const char *dev_name,
 272                         void *data)
 273 {
 274         if (!(debugfs_allow & DEBUGFS_ALLOW_API))
 275                 return ERR_PTR(-EPERM);
 276
 277         return mount_single(fs_type, flags, data, debug_fill_super);
 278 }
 279
 280 static struct file_system_type debug_fs_type = {
 281         .owner =        THIS_MODULE,
 282         .name =         "debugfs",
 283         .mount =        debug_mount,
 284         .kill_sb =      kill_litter_super,
 285 };
 286 MODULE_ALIAS_FS("debugfs");
 287
 288 /**
 289  * debugfs_lookup() - look up an existing debugfs file
 290  * @name: a pointer to a string containing the name of the file to look up.
 291  * @parent: a pointer to the parent dentry of the file.
 292  *
 293  * This function will return a pointer to a dentry if it succeeds.  If the file
 294  * doesn't exist or an error occurs, %NULL will be returned.  The returned
 295  * dentry must be passed to dput() when it is no longer needed.
 296  *
 297  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 298  * returned.
 299  */
 300 struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
 301 {
 302         struct dentry *dentry;
 303
 304         if (!debugfs_initialized() || IS_ERR_OR_NULL(name) || IS_ERR(parent))
 305                 return NULL;
 306
 307         if (!parent)
 308                 parent = debugfs_mount->mnt_root;
 309
 310         dentry = lookup_positive_unlocked(name, parent, strlen(name));
 311         if (IS_ERR(dentry))
 312                 return NULL;
 313         return dentry;
 314 }
 315 EXPORT_SYMBOL_GPL(debugfs_lookup);
 316
 317 static struct dentry *start_creating(const char *name, struct dentry *parent)
 318 {
 319         struct dentry *dentry;
 320         int error;
 321
 322         if (!(debugfs_allow & DEBUGFS_ALLOW_API))
 323                 return ERR_PTR(-EPERM);
 324
 325         if (!debugfs_initialized())
 326                 return ERR_PTR(-ENOENT);
 327
 328         pr_debug("creating file '%s'\n", name);
 329
 330         if (IS_ERR(parent))
 331                 return parent;
 332
 333         error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
 334                               &debugfs_mount_count);
 335         if (error) {
 336                 pr_err("Unable to pin filesystem for file '%s'\n", name);
 337                 return ERR_PTR(error);
 338         }
 339
 340         /* If the parent is not specified, we create it in the root.
 341          * We need the root dentry to do this, which is in the super
 342          * block. A pointer to that is in the struct vfsmount that we
 343          * have around.
 344          */
 345         if (!parent)
 346                 parent = debugfs_mount->mnt_root;
 347
 348         inode_lock(d_inode(parent));
 349         if (unlikely(IS_DEADDIR(d_inode(parent))))
 350                 dentry = ERR_PTR(-ENOENT);
 351         else
 352                 dentry = lookup_one_len(name, parent, strlen(name));
 353         if (!IS_ERR(dentry) && d_really_is_positive(dentry)) {
 354                 if (d_is_dir(dentry))
 355                         pr_err("Directory '%s' with parent '%s' already present!\n",
 356                                name, parent->d_name.name);
 357                 else
 358                         pr_err("File '%s' in directory '%s' already present!\n",
 359                                name, parent->d_name.name);
 360                 dput(dentry);
 361                 dentry = ERR_PTR(-EEXIST);
 362         }
 363
 364         if (IS_ERR(dentry)) {
 365                 inode_unlock(d_inode(parent));
 366                 simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 367         }
 368
 369         return dentry;
 370 }
 371
 372 static struct dentry *failed_creating(struct dentry *dentry)
 373 {
 374         inode_unlock(d_inode(dentry->d_parent));
 375         dput(dentry);
 376         simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 377         return ERR_PTR(-ENOMEM);
 378 }
 379
 380 static struct dentry *end_creating(struct dentry *dentry)
 381 {
 382         inode_unlock(d_inode(dentry->d_parent));
 383         return dentry;
 384 }
 385
 386 static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
 387                                 struct dentry *parent, void *data,
 388                                 const struct file_operations *proxy_fops,
 389                                 const struct file_operations *real_fops)
 390 {
 391         struct dentry *dentry;
 392         struct inode *inode;
 393
 394         if (!(mode & S_IFMT))
 395                 mode |= S_IFREG;
 396         BUG_ON(!S_ISREG(mode));
 397         dentry = start_creating(name, parent);
 398
 399         if (IS_ERR(dentry))
 400                 return dentry;
 401
 402         if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
 403                 failed_creating(dentry);
 404                 return ERR_PTR(-EPERM);
 405         }
 406
 407         inode = debugfs_get_inode(dentry->d_sb);
 408         if (unlikely(!inode)) {
 409                 pr_err("out of free dentries, can not create file '%s'\n",
 410                        name);
 411                 return failed_creating(dentry);
 412         }
 413
 414         inode->i_mode = mode;
 415         inode->i_private = data;
 416
 417         inode->i_op = &debugfs_file_inode_operations;
 418         inode->i_fop = proxy_fops;
 419         dentry->d_fsdata = (void *)((unsigned long)real_fops |
 420                                 DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
 421
 422         d_instantiate(dentry, inode);
 423         fsnotify_create(d_inode(dentry->d_parent), dentry);
 424         return end_creating(dentry);
 425 }
 426
 427 /**
 428  * debugfs_create_file - create a file in the debugfs filesystem
 429  * @name: a pointer to a string containing the name of the file to create.
 430  * @mode: the permission that the file should have.
 431  * @parent: a pointer to the parent dentry for this file.  This should be a
 432  *          directory dentry if set.  If this parameter is NULL, then the
 433  *          file will be created in the root of the debugfs filesystem.
 434  * @data: a pointer to something that the caller will want to get to later
 435  *        on.  The inode.i_private pointer will point to this value on
 436  *        the open() call.
 437  * @fops: a pointer to a struct file_operations that should be used for
 438  *        this file.
 439  *
 440  * This is the basic "create a file" function for debugfs.  It allows for a
 441  * wide range of flexibility in creating a file, or a directory (if you want
 442  * to create a directory, the debugfs_create_dir() function is
 443  * recommended to be used instead.)
 444  *
 445  * This function will return a pointer to a dentry if it succeeds.  This
 446  * pointer must be passed to the debugfs_remove() function when the file is
 447  * to be removed (no automatic cleanup happens if your module is unloaded,
 448  * you are responsible here.)  If an error occurs, ERR_PTR(-ERROR) will be
 449  * returned.
 450  *
 451  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 452  * returned.
 453  *
 454  * NOTE: it's expected that most callers should _ignore_ the errors returned
 455  * by this function. Other debugfs functions handle the fact that the "dentry"
 456  * passed to them could be an error and they don't crash in that case.
 457  * Drivers should generally work fine even if debugfs fails to init anyway.
 458  */
 459 struct dentry *debugfs_create_file(const char *name, umode_t mode,
 460                                    struct dentry *parent, void *data,
 461                                    const struct file_operations *fops)
 462 {
 463
 464         return __debugfs_create_file(name, mode, parent, data,
 465                                 fops ? &debugfs_full_proxy_file_operations :
 466                                         &debugfs_noop_file_operations,
 467                                 fops);
 468 }
 469 EXPORT_SYMBOL_GPL(debugfs_create_file);
 470
 471 /**
 472  * debugfs_create_file_unsafe - create a file in the debugfs filesystem
 473  * @name: a pointer to a string containing the name of the file to create.
 474  * @mode: the permission that the file should have.
 475  * @parent: a pointer to the parent dentry for this file.  This should be a
 476  *          directory dentry if set.  If this parameter is NULL, then the
 477  *          file will be created in the root of the debugfs filesystem.
 478  * @data: a pointer to something that the caller will want to get to later
 479  *        on.  The inode.i_private pointer will point to this value on
 480  *        the open() call.
 481  * @fops: a pointer to a struct file_operations that should be used for
 482  *        this file.
 483  *
 484  * debugfs_create_file_unsafe() is completely analogous to
 485  * debugfs_create_file(), the only difference being that the fops
 486  * handed it will not get protected against file removals by the
 487  * debugfs core.
 488  *
 489  * It is your responsibility to protect your struct file_operation
 490  * methods against file removals by means of debugfs_file_get()
 491  * and debugfs_file_put(). ->open() is still protected by
 492  * debugfs though.
 493  *
 494  * Any struct file_operations defined by means of
 495  * DEFINE_DEBUGFS_ATTRIBUTE() is protected against file removals and
 496  * thus, may be used here.
 497  */
 498 struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
 499                                    struct dentry *parent, void *data,
 500                                    const struct file_operations *fops)
 501 {
 502
 503         return __debugfs_create_file(name, mode, parent, data,
 504                                 fops ? &debugfs_open_proxy_file_operations :
 505                                         &debugfs_noop_file_operations,
 506                                 fops);
 507 }
 508 EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe);
 509
 510 /**
 511  * debugfs_create_file_size - create a file in the debugfs filesystem
 512  * @name: a pointer to a string containing the name of the file to create.
 513  * @mode: the permission that the file should have.
 514  * @parent: a pointer to the parent dentry for this file.  This should be a
 515  *          directory dentry if set.  If this parameter is NULL, then the
 516  *          file will be created in the root of the debugfs filesystem.
 517  * @data: a pointer to something that the caller will want to get to later
 518  *        on.  The inode.i_private pointer will point to this value on
 519  *        the open() call.
 520  * @fops: a pointer to a struct file_operations that should be used for
 521  *        this file.
 522  * @file_size: initial file size
 523  *
 524  * This is the basic "create a file" function for debugfs.  It allows for a
 525  * wide range of flexibility in creating a file, or a directory (if you want
 526  * to create a directory, the debugfs_create_dir() function is
 527  * recommended to be used instead.)
 528  */
 529 void debugfs_create_file_size(const char *name, umode_t mode,
 530                               struct dentry *parent, void *data,
 531                               const struct file_operations *fops,
 532                               loff_t file_size)
 533 {
 534         struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);
 535
 536         if (!IS_ERR(de))
 537                 d_inode(de)->i_size = file_size;
 538 }
 539 EXPORT_SYMBOL_GPL(debugfs_create_file_size);
 540
 541 /**
 542  * debugfs_create_dir - create a directory in the debugfs filesystem
 543  * @name: a pointer to a string containing the name of the directory to
 544  *        create.
 545  * @parent: a pointer to the parent dentry for this file.  This should be a
 546  *          directory dentry if set.  If this parameter is NULL, then the
 547  *          directory will be created in the root of the debugfs filesystem.
 548  *
 549  * This function creates a directory in debugfs with the given name.
 550  *
 551  * This function will return a pointer to a dentry if it succeeds.  This
 552  * pointer must be passed to the debugfs_remove() function when the file is
 553  * to be removed (no automatic cleanup happens if your module is unloaded,
 554  * you are responsible here.)  If an error occurs, ERR_PTR(-ERROR) will be
 555  * returned.
 556  *
 557  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 558  * returned.
 559  *
 560  * NOTE: it's expected that most callers should _ignore_ the errors returned
 561  * by this function. Other debugfs functions handle the fact that the "dentry"
 562  * passed to them could be an error and they don't crash in that case.
 563  * Drivers should generally work fine even if debugfs fails to init anyway.
 564  */
 565 struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
 566 {
 567         struct dentry *dentry = start_creating(name, parent);
 568         struct inode *inode;
 569
 570         if (IS_ERR(dentry))
 571                 return dentry;
 572
 573         if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
 574                 failed_creating(dentry);
 575                 return ERR_PTR(-EPERM);
 576         }
 577
 578         inode = debugfs_get_inode(dentry->d_sb);
 579         if (unlikely(!inode)) {
 580                 pr_err("out of free dentries, can not create directory '%s'\n",
 581                        name);
 582                 return failed_creating(dentry);
 583         }
 584
 585         inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
 586         inode->i_op = &debugfs_dir_inode_operations;
 587         inode->i_fop = &simple_dir_operations;
 588
 589         /* directory inodes start off with i_nlink == 2 (for "." entry) */
 590         inc_nlink(inode);
 591         d_instantiate(dentry, inode);
 592         inc_nlink(d_inode(dentry->d_parent));
 593         fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
 594         return end_creating(dentry);
 595 }
 596 EXPORT_SYMBOL_GPL(debugfs_create_dir);
 597
 598 /**
 599  * debugfs_create_automount - create automount point in the debugfs filesystem
 600  * @name: a pointer to a string containing the name of the file to create.
 601  * @parent: a pointer to the parent dentry for this file.  This should be a
 602  *          directory dentry if set.  If this parameter is NULL, then the
 603  *          file will be created in the root of the debugfs filesystem.
 604  * @f: function to be called when pathname resolution steps on that one.
 605  * @data: opaque argument to pass to f().
 606  *
 607  * @f should return what ->d_automount() would.
 608  */
 609 struct dentry *debugfs_create_automount(const char *name,
 610                                         struct dentry *parent,
 611                                         debugfs_automount_t f,
 612                                         void *data)
 613 {
 614         struct dentry *dentry = start_creating(name, parent);
 615         struct inode *inode;
 616
 617         if (IS_ERR(dentry))
 618                 return dentry;
 619
 620         if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
 621                 failed_creating(dentry);
 622                 return ERR_PTR(-EPERM);
 623         }
 624
 625         inode = debugfs_get_inode(dentry->d_sb);
 626         if (unlikely(!inode)) {
 627                 pr_err("out of free dentries, can not create automount '%s'\n",
 628                        name);
 629                 return failed_creating(dentry);
 630         }
 631
 632         make_empty_dir_inode(inode);
 633         inode->i_flags |= S_AUTOMOUNT;
 634         inode->i_private = data;
 635         dentry->d_fsdata = (void *)f;
 636         /* directory inodes start off with i_nlink == 2 (for "." entry) */
 637         inc_nlink(inode);
 638         d_instantiate(dentry, inode);
 639         inc_nlink(d_inode(dentry->d_parent));
 640         fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
 641         return end_creating(dentry);
 642 }
 643 EXPORT_SYMBOL(debugfs_create_automount);
 644
 645 /**
 646  * debugfs_create_symlink- create a symbolic link in the debugfs filesystem
 647  * @name: a pointer to a string containing the name of the symbolic link to
 648  *        create.
 649  * @parent: a pointer to the parent dentry for this symbolic link.  This
 650  *          should be a directory dentry if set.  If this parameter is NULL,
 651  *          then the symbolic link will be created in the root of the debugfs
 652  *          filesystem.
 653  * @target: a pointer to a string containing the path to the target of the
 654  *          symbolic link.
 655  *
 656  * This function creates a symbolic link with the given name in debugfs that
 657  * links to the given target path.
 658  *
 659  * This function will return a pointer to a dentry if it succeeds.  This
 660  * pointer must be passed to the debugfs_remove() function when the symbolic
 661  * link is to be removed (no automatic cleanup happens if your module is
 662  * unloaded, you are responsible here.)  If an error occurs, ERR_PTR(-ERROR)
 663  * will be returned.
 664  *
 665  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 666  * returned.
 667  */
 668 struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
 669                                       const char *target)
 670 {
 671         struct dentry *dentry;
 672         struct inode *inode;
 673         char *link = kstrdup(target, GFP_KERNEL);
 674         if (!link)
 675                 return ERR_PTR(-ENOMEM);
 676
 677         dentry = start_creating(name, parent);
 678         if (IS_ERR(dentry)) {
 679                 kfree(link);
 680                 return dentry;
 681         }
 682
 683         inode = debugfs_get_inode(dentry->d_sb);
 684         if (unlikely(!inode)) {
 685                 pr_err("out of free dentries, can not create symlink '%s'\n",
 686                        name);
 687                 kfree(link);
 688                 return failed_creating(dentry);
 689         }
 690         inode->i_mode = S_IFLNK | S_IRWXUGO;
 691         inode->i_op = &debugfs_symlink_inode_operations;
 692         inode->i_link = link;
 693         d_instantiate(dentry, inode);
 694         return end_creating(dentry);
 695 }
 696 EXPORT_SYMBOL_GPL(debugfs_create_symlink);
 697
 698 static void __debugfs_file_removed(struct dentry *dentry)
 699 {
 700         struct debugfs_fsdata *fsd;
 701
 702         /*
 703          * Paired with the closing smp_mb() implied by a successful
 704          * cmpxchg() in debugfs_file_get(): either
 705          * debugfs_file_get() must see a dead dentry or we must see a
 706          * debugfs_fsdata instance at ->d_fsdata here (or both).
 707          */
 708         smp_mb();
 709         fsd = READ_ONCE(dentry->d_fsdata);
 710         if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
 711                 return;
 712         if (!refcount_dec_and_test(&fsd->active_users))
 713                 wait_for_completion(&fsd->active_users_drained);
 714 }
 715
 716 static void remove_one(struct dentry *victim)
 717 {
 718         if (d_is_reg(victim))
 719                 __debugfs_file_removed(victim);
 720         simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 721 }
 722
 723 /**
 724  * debugfs_remove - recursively removes a directory
 725  * @dentry: a pointer to a the dentry of the directory to be removed.  If this
 726  *          parameter is NULL or an error value, nothing will be done.
 727  *
 728  * This function recursively removes a directory tree in debugfs that
 729  * was previously created with a call to another debugfs function
 730  * (like debugfs_create_file() or variants thereof.)
 731  *
 732  * This function is required to be called in order for the file to be
 733  * removed, no automatic cleanup of files will happen when a module is
 734  * removed, you are responsible here.
 735  */
 736 void debugfs_remove(struct dentry *dentry)
 737 {
 738         if (IS_ERR_OR_NULL(dentry))
 739                 return;
 740
 741         simple_pin_fs(&debug_fs_type, &debugfs_mount, &debugfs_mount_count);
 742         simple_recursive_removal(dentry, remove_one);
 743         simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 744 }
 745 EXPORT_SYMBOL_GPL(debugfs_remove);
 746
 747 /**
 748  * debugfs_lookup_and_remove - lookup a directory or file and recursively remove it
 749  * @name: a pointer to a string containing the name of the item to look up.
 750  * @parent: a pointer to the parent dentry of the item.
 751  *
 752  * This is the equlivant of doing something like
 753  * debugfs_remove(debugfs_lookup(..)) but with the proper reference counting
 754  * handled for the directory being looked up.
 755  */
 756 void debugfs_lookup_and_remove(const char *name, struct dentry *parent)
 757 {
 758         struct dentry *dentry;
 759
 760         dentry = debugfs_lookup(name, parent);
 761         if (!dentry)
 762                 return;
 763
 764         debugfs_remove(dentry);
 765         dput(dentry);
 766 }
 767 EXPORT_SYMBOL_GPL(debugfs_lookup_and_remove);
 768
 769 /**
 770  * debugfs_rename - rename a file/directory in the debugfs filesystem
 771  * @old_dir: a pointer to the parent dentry for the renamed object. This
 772  *          should be a directory dentry.
 773  * @old_dentry: dentry of an object to be renamed.
 774  * @new_dir: a pointer to the parent dentry where the object should be
 775  *          moved. This should be a directory dentry.
 776  * @new_name: a pointer to a string containing the target name.
 777  *
 778  * This function renames a file/directory in debugfs.  The target must not
 779  * exist for rename to succeed.
 780  *
 781  * This function will return a pointer to old_dentry (which is updated to
 782  * reflect renaming) if it succeeds. If an error occurs, %NULL will be
 783  * returned.
 784  *
 785  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 786  * returned.
 787  */
 788 struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
 789                 struct dentry *new_dir, const char *new_name)
 790 {
 791         int error;
 792         struct dentry *dentry = NULL, *trap;
 793         struct name_snapshot old_name;
 794
 795         if (IS_ERR(old_dir))
 796                 return old_dir;
 797         if (IS_ERR(new_dir))
 798                 return new_dir;
 799         if (IS_ERR_OR_NULL(old_dentry))
 800                 return old_dentry;
 801
 802         trap = lock_rename(new_dir, old_dir);
 803         /* Source or destination directories don't exist? */
 804         if (d_really_is_negative(old_dir) || d_really_is_negative(new_dir))
 805                 goto exit;
 806         /* Source does not exist, cyclic rename, or mountpoint? */
 807         if (d_really_is_negative(old_dentry) || old_dentry == trap ||
 808             d_mountpoint(old_dentry))
 809                 goto exit;
 810         dentry = lookup_one_len(new_name, new_dir, strlen(new_name));
 811         /* Lookup failed, cyclic rename or target exists? */
 812         if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
 813                 goto exit;
 814
 815         take_dentry_name_snapshot(&old_name, old_dentry);
 816
 817         error = simple_rename(&init_user_ns, d_inode(old_dir), old_dentry,
 818                               d_inode(new_dir), dentry, 0);
 819         if (error) {
 820                 release_dentry_name_snapshot(&old_name);
 821                 goto exit;
 822         }
 823         d_move(old_dentry, dentry);
 824         fsnotify_move(d_inode(old_dir), d_inode(new_dir), &old_name.name,
 825                 d_is_dir(old_dentry),
 826                 NULL, old_dentry);
 827         release_dentry_name_snapshot(&old_name);
 828         unlock_rename(new_dir, old_dir);
 829         dput(dentry);
 830         return old_dentry;
 831 exit:
 832         if (dentry && !IS_ERR(dentry))
 833                 dput(dentry);
 834         unlock_rename(new_dir, old_dir);
 835         if (IS_ERR(dentry))
 836                 return dentry;
 837         return ERR_PTR(-EINVAL);
 838 }
 839 EXPORT_SYMBOL_GPL(debugfs_rename);
 840
 841 /**
 842  * debugfs_initialized - Tells whether debugfs has been registered
 843  */
 844 bool debugfs_initialized(void)
 845 {
 846         return debugfs_registered;
 847 }
 848 EXPORT_SYMBOL_GPL(debugfs_initialized);
 849
 850 static int __init debugfs_kernel(char *str)
 851 {
 852         if (str) {
 853                 if (!strcmp(str, "on"))
 854                         debugfs_allow = DEBUGFS_ALLOW_API | DEBUGFS_ALLOW_MOUNT;
 855                 else if (!strcmp(str, "no-mount"))
 856                         debugfs_allow = DEBUGFS_ALLOW_API;
 857                 else if (!strcmp(str, "off"))
 858                         debugfs_allow = 0;
 859         }
 860
 861         return 0;
 862 }
 863 early_param("debugfs", debugfs_kernel);
 864 static int __init debugfs_init(void)
 865 {
 866         int retval;
 867
 868         if (!(debugfs_allow & DEBUGFS_ALLOW_MOUNT))
 869                 return -EPERM;
 870
 871         retval = sysfs_create_mount_point(kernel_kobj, "debug");
 872         if (retval)
 873                 return retval;
 874
 875         retval = register_filesystem(&debug_fs_type);
 876         if (retval)
 877                 sysfs_remove_mount_point(kernel_kobj, "debug");
 878         else
 879                 debugfs_registered = true;
 880
 881         return retval;
 882 }
 883 core_initcall(debugfs_init);