fs/exportfs/expfs.c

   1
   2 #include <linux/fs.h>
   3 #include <linux/file.h>
   4 #include <linux/module.h>
   5 #include <linux/smp_lock.h>
   6 #include <linux/namei.h>
   7
   8 struct export_operations export_op_default;
   9
  10 #define CALL(ops,fun) ((ops->fun)?(ops->fun):export_op_default.fun)
  11
  12 #define dprintk(fmt, args...) do{}while(0)
  13
  14 static struct dentry *
  15 find_acceptable_alias(struct dentry *result,
  16                 int (*acceptable)(void *context, struct dentry *dentry),
  17                 void *context)
  18 {
  19         struct dentry *dentry, *toput = NULL;
  20
  21         spin_lock(&dcache_lock);
  22         list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) {
  23                 dget_locked(dentry);
  24                 spin_unlock(&dcache_lock);
  25                 if (toput)
  26                         dput(toput);
  27                 if (dentry != result && acceptable(context, dentry)) {
  28                         dput(result);
  29                         return dentry;
  30                 }
  31                 spin_lock(&dcache_lock);
  32                 toput = dentry;
  33         }
  34         spin_unlock(&dcache_lock);
  35
  36         if (toput)
  37                 dput(toput);
  38         return NULL;
  39 }
  40
  41 /**
  42  * find_exported_dentry - helper routine to implement export_operations->decode_fh
  43  * @sb:         The &super_block identifying the filesystem
  44  * @obj:        An opaque identifier of the object to be found - passed to
  45  *              get_inode
  46  * @parent:     An optional opqaue identifier of the parent of the object.
  47  * @acceptable: A function used to test possible &dentries to see if they are
  48  *              acceptable
  49  * @context:    A parameter to @acceptable so that it knows on what basis to
  50  *              judge.
  51  *
  52  * find_exported_dentry is the central helper routine to enable file systems
  53  * to provide the decode_fh() export_operation.  It's main task is to take
  54  * an &inode, find or create an appropriate &dentry structure, and possibly
  55  * splice this into the dcache in the correct place.
  56  *
  57  * The decode_fh() operation provided by the filesystem should call
  58  * find_exported_dentry() with the same parameters that it received except
  59  * that instead of the file handle fragment, pointers to opaque identifiers
  60  * for the object and optionally its parent are passed.  The default decode_fh
  61  * routine passes one pointer to the start of the filehandle fragment, and
  62  * one 8 bytes into the fragment.  It is expected that most filesystems will
  63  * take this approach, though the offset to the parent identifier may well be
  64  * different.
  65  *
  66  * find_exported_dentry() will call get_dentry to get an dentry pointer from
  67  * the file system.  If any &dentry in the d_alias list is acceptable, it will
  68  * be returned.  Otherwise find_exported_dentry() will attempt to splice a new
  69  * &dentry into the dcache using get_name() and get_parent() to find the
  70  * appropriate place.
  71  */
  72
  73 struct dentry *
  74 find_exported_dentry(struct super_block *sb, void *obj, void *parent,
  75                      int (*acceptable)(void *context, struct dentry *de),
  76                      void *context)
  77 {
  78         struct dentry *result = NULL;
  79         struct dentry *target_dir;
  80         int err;
  81         struct export_operations *nops = sb->s_export_op;
  82         struct dentry *alias;
  83         int noprogress;
  84         char nbuf[NAME_MAX+1];
  85
  86         /*
  87          * Attempt to find the inode.
  88          */
  89         result = CALL(sb->s_export_op,get_dentry)(sb,obj);
  90         err = -ESTALE;
  91         if (result == NULL)
  92                 goto err_out;
  93         if (IS_ERR(result)) {
  94                 err = PTR_ERR(result);
  95                 goto err_out;
  96         }
  97         if (S_ISDIR(result->d_inode->i_mode) &&
  98             (result->d_flags & DCACHE_DISCONNECTED)) {
  99                 /* it is an unconnected directory, we must connect it */
 100                 ;
 101         } else {
 102                 if (acceptable(context, result))
 103                         return result;
 104                 if (S_ISDIR(result->d_inode->i_mode)) {
 105                         err = -EACCES;
 106                         goto err_result;
 107                 }
 108
 109                 alias = find_acceptable_alias(result, acceptable, context);
 110                 if (alias)
 111                         return alias;
 112         }
 113
 114         /* It's a directory, or we are required to confirm the file's
 115          * location in the tree based on the parent information
 116          */
 117         dprintk("find_exported_dentry: need to look harder for %s/%d\n",sb->s_id,*(int*)obj);
 118         if (S_ISDIR(result->d_inode->i_mode))
 119                 target_dir = dget(result);
 120         else {
 121                 if (parent == NULL)
 122                         goto err_result;
 123
 124                 target_dir = CALL(sb->s_export_op,get_dentry)(sb,parent);
 125                 if (IS_ERR(target_dir))
 126                         err = PTR_ERR(target_dir);
 127                 if (target_dir == NULL || IS_ERR(target_dir))
 128                         goto err_result;
 129         }
 130         /*
 131          * Now we need to make sure that target_dir is properly connected.
 132          * It may already be, as the flag isn't always updated when connection
 133          * happens.
 134          * So, we walk up parent links until we find a connected directory,
 135          * or we run out of directories.  Then we find the parent, find
 136          * the name of the child in that parent, and do a lookup.
 137          * This should connect the child into the parent
 138          * We then repeat.
 139          */
 140
 141         /* it is possible that a confused file system might not let us complete
 142          * the path to the root.  For example, if get_parent returns a directory
 143          * in which we cannot find a name for the child.  While this implies a
 144          * very sick filesystem we don't want it to cause knfsd to spin.  Hence
 145          * the noprogress counter.  If we go through the loop 10 times (2 is
 146          * probably enough) without getting anywhere, we just give up
 147          */
 148         noprogress= 0;
 149         while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
 150                 struct dentry *pd = target_dir;
 151
 152                 dget(pd);
 153                 spin_lock(&pd->d_lock);
 154                 while (!IS_ROOT(pd) &&
 155                                 (pd->d_parent->d_flags&DCACHE_DISCONNECTED)) {
 156                         struct dentry *parent = pd->d_parent;
 157
 158                         dget(parent);
 159                         spin_unlock(&pd->d_lock);
 160                         dput(pd);
 161                         pd = parent;
 162                         spin_lock(&pd->d_lock);
 163                 }
 164                 spin_unlock(&pd->d_lock);
 165
 166                 if (!IS_ROOT(pd)) {
 167                         /* must have found a connected parent - great */
 168                         spin_lock(&pd->d_lock);
 169                         pd->d_flags &= ~DCACHE_DISCONNECTED;
 170                         spin_unlock(&pd->d_lock);
 171                         noprogress = 0;
 172                 } else if (pd == sb->s_root) {
 173                         printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
 174                         spin_lock(&pd->d_lock);
 175                         pd->d_flags &= ~DCACHE_DISCONNECTED;
 176                         spin_unlock(&pd->d_lock);
 177                         noprogress = 0;
 178                 } else {
 179                         /* we have hit the top of a disconnected path.  Try
 180                          * to find parent and connect
 181                          * note: racing with some other process renaming a
 182                          * directory isn't much of a problem here.  If someone
 183                          * renames the directory, it will end up properly
 184                          * connected, which is what we want
 185                          */
 186                         struct dentry *ppd;
 187                         struct dentry *npd;
 188
 189                         mutex_lock(&pd->d_inode->i_mutex);
 190                         ppd = CALL(nops,get_parent)(pd);
 191                         mutex_unlock(&pd->d_inode->i_mutex);
 192
 193                         if (IS_ERR(ppd)) {
 194                                 err = PTR_ERR(ppd);
 195                                 dprintk("find_exported_dentry: get_parent of %ld failed, err %d\n",
 196                                         pd->d_inode->i_ino, err);
 197                                 dput(pd);
 198                                 break;
 199                         }
 200                         dprintk("find_exported_dentry: find name of %lu in %lu\n", pd->d_inode->i_ino, ppd->d_inode->i_ino);
 201                         err = CALL(nops,get_name)(ppd, nbuf, pd);
 202                         if (err) {
 203                                 dput(ppd);
 204                                 dput(pd);
 205                                 if (err == -ENOENT)
 206                                         /* some race between get_parent and
 207                                          * get_name?  just try again
 208                                          */
 209                                         continue;
 210                                 break;
 211                         }
 212                         dprintk("find_exported_dentry: found name: %s\n", nbuf);
 213                         mutex_lock(&ppd->d_inode->i_mutex);
 214                         npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
 215                         mutex_unlock(&ppd->d_inode->i_mutex);
 216                         if (IS_ERR(npd)) {
 217                                 err = PTR_ERR(npd);
 218                                 dprintk("find_exported_dentry: lookup failed: %d\n", err);
 219                                 dput(ppd);
 220                                 dput(pd);
 221                                 break;
 222                         }
 223                         /* we didn't really want npd, we really wanted
 224                          * a side-effect of the lookup.
 225                          * hopefully, npd == pd, though it isn't really
 226                          * a problem if it isn't
 227                          */
 228                         if (npd == pd)
 229                                 noprogress = 0;
 230                         else
 231                                 printk("find_exported_dentry: npd != pd\n");
 232                         dput(npd);
 233                         dput(ppd);
 234                         if (IS_ROOT(pd)) {
 235                                 /* something went wrong, we have to give up */
 236                                 dput(pd);
 237                                 break;
 238                         }
 239                 }
 240                 dput(pd);
 241         }
 242
 243         if (target_dir->d_flags & DCACHE_DISCONNECTED) {
 244                 /* something went wrong - oh-well */
 245                 if (!err)
 246                         err = -ESTALE;
 247                 goto err_target;
 248         }
 249         /* if we weren't after a directory, have one more step to go */
 250         if (result != target_dir) {
 251                 struct dentry *nresult;
 252                 err = CALL(nops,get_name)(target_dir, nbuf, result);
 253                 if (!err) {
 254                         mutex_lock(&target_dir->d_inode->i_mutex);
 255                         nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
 256                         mutex_unlock(&target_dir->d_inode->i_mutex);
 257                         if (!IS_ERR(nresult)) {
 258                                 if (nresult->d_inode) {
 259                                         dput(result);
 260                                         result = nresult;
 261                                 } else
 262                                         dput(nresult);
 263                         }
 264                 }
 265         }
 266         dput(target_dir);
 267         /* now result is properly connected, it is our best bet */
 268         if (acceptable(context, result))
 269                 return result;
 270
 271         alias = find_acceptable_alias(result, acceptable, context);
 272         if (alias)
 273                 return alias;
 274
 275         /* drat - I just cannot find anything acceptable */
 276         dput(result);
 277         /* It might be justifiable to return ESTALE here,
 278          * but the filehandle at-least looks reasonable good
 279          * and it just be a permission problem, so returning
 280          * -EACCESS is safer
 281          */
 282         return ERR_PTR(-EACCES);
 283
 284  err_target:
 285         dput(target_dir);
 286  err_result:
 287         dput(result);
 288  err_out:
 289         return ERR_PTR(err);
 290 }
 291
 292
 293
 294 static struct dentry *get_parent(struct dentry *child)
 295 {
 296         /* get_parent cannot be supported generically, the locking
 297          * is too icky.
 298          * instead, we just return EACCES.  If server reboots or inodes
 299          * get flushed, you lose
 300          */
 301         return ERR_PTR(-EACCES);
 302 }
 303
 304
 305 struct getdents_callback {
 306         char *name;             /* name that was found. It already points to a
 307                                    buffer NAME_MAX+1 is size */
 308         unsigned long ino;      /* the inum we are looking for */
 309         int found;              /* inode matched? */
 310         int sequence;           /* sequence counter */
 311 };
 312
 313 /*
 314  * A rather strange filldir function to capture
 315  * the name matching the specified inode number.
 316  */
 317 static int filldir_one(void * __buf, const char * name, int len,
 318                         loff_t pos, u64 ino, unsigned int d_type)
 319 {
 320         struct getdents_callback *buf = __buf;
 321         int result = 0;
 322
 323         buf->sequence++;
 324         if (buf->ino == ino) {
 325                 memcpy(buf->name, name, len);
 326                 buf->name[len] = '\0';
 327                 buf->found = 1;
 328                 result = -1;
 329         }
 330         return result;
 331 }
 332
 333 /**
 334  * get_name - default export_operations->get_name function
 335  * @dentry: the directory in which to find a name
 336  * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
 337  * @child:  the dentry for the child directory.
 338  *
 339  * calls readdir on the parent until it finds an entry with
 340  * the same inode number as the child, and returns that.
 341  */
 342 static int get_name(struct dentry *dentry, char *name,
 343                         struct dentry *child)
 344 {
 345         struct inode *dir = dentry->d_inode;
 346         int error;
 347         struct file *file;
 348         struct getdents_callback buffer;
 349
 350         error = -ENOTDIR;
 351         if (!dir || !S_ISDIR(dir->i_mode))
 352                 goto out;
 353         error = -EINVAL;
 354         if (!dir->i_fop)
 355                 goto out;
 356         /*
 357          * Open the directory ...
 358          */
 359         file = dentry_open(dget(dentry), NULL, O_RDONLY);
 360         error = PTR_ERR(file);
 361         if (IS_ERR(file))
 362                 goto out;
 363
 364         error = -EINVAL;
 365         if (!file->f_op->readdir)
 366                 goto out_close;
 367
 368         buffer.name = name;
 369         buffer.ino = child->d_inode->i_ino;
 370         buffer.found = 0;
 371         buffer.sequence = 0;
 372         while (1) {
 373                 int old_seq = buffer.sequence;
 374
 375                 error = vfs_readdir(file, filldir_one, &buffer);
 376
 377                 if (error < 0)
 378                         break;
 379
 380                 error = 0;
 381                 if (buffer.found)
 382                         break;
 383                 error = -ENOENT;
 384                 if (old_seq == buffer.sequence)
 385                         break;
 386         }
 387
 388 out_close:
 389         fput(file);
 390 out:
 391         return error;
 392 }
 393
 394
 395 static struct dentry *export_iget(struct super_block *sb, unsigned long ino, __u32 generation)
 396 {
 397
 398         /* iget isn't really right if the inode is currently unallocated!!
 399          * This should really all be done inside each filesystem
 400          *
 401          * ext2fs' read_inode has been strengthed to return a bad_inode if
 402          * the inode had been deleted.
 403          *
 404          * Currently we don't know the generation for parent directory, so
 405          * a generation of 0 means "accept any"
 406          */
 407         struct inode *inode;
 408         struct dentry *result;
 409         if (ino == 0)
 410                 return ERR_PTR(-ESTALE);
 411         inode = iget(sb, ino);
 412         if (inode == NULL)
 413                 return ERR_PTR(-ENOMEM);
 414         if (is_bad_inode(inode)
 415             || (generation && inode->i_generation != generation)
 416                 ) {
 417                 /* we didn't find the right inode.. */
 418                 dprintk("fh_verify: Inode %lu, Bad count: %d %d or version  %u %u\n",
 419                         inode->i_ino,
 420                         inode->i_nlink, atomic_read(&inode->i_count),
 421                         inode->i_generation,
 422                         generation);
 423
 424                 iput(inode);
 425                 return ERR_PTR(-ESTALE);
 426         }
 427         /* now to find a dentry.
 428          * If possible, get a well-connected one
 429          */
 430         result = d_alloc_anon(inode);
 431         if (!result) {
 432                 iput(inode);
 433                 return ERR_PTR(-ENOMEM);
 434         }
 435         return result;
 436 }
 437
 438
 439 static struct dentry *get_object(struct super_block *sb, void *vobjp)
 440 {
 441         __u32 *objp = vobjp;
 442         unsigned long ino = objp[0];
 443         __u32 generation = objp[1];
 444
 445         return export_iget(sb, ino, generation);
 446 }
 447
 448
 449 /**
 450  * export_encode_fh - default export_operations->encode_fh function
 451  * @dentry:  the dentry to encode
 452  * @fh:      where to store the file handle fragment
 453  * @max_len: maximum length to store there
 454  * @connectable: whether to store parent information
 455  *
 456  * This default encode_fh function assumes that the 32 inode number
 457  * is suitable for locating an inode, and that the generation number
 458  * can be used to check that it is still valid.  It places them in the
 459  * filehandle fragment where export_decode_fh expects to find them.
 460  */
 461 static int export_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
 462                    int connectable)
 463 {
 464         struct inode * inode = dentry->d_inode;
 465         int len = *max_len;
 466         int type = 1;
 467
 468         if (len < 2 || (connectable && len < 4))
 469                 return 255;
 470
 471         len = 2;
 472         fh[0] = inode->i_ino;
 473         fh[1] = inode->i_generation;
 474         if (connectable && !S_ISDIR(inode->i_mode)) {
 475                 struct inode *parent;
 476
 477                 spin_lock(&dentry->d_lock);
 478                 parent = dentry->d_parent->d_inode;
 479                 fh[2] = parent->i_ino;
 480                 fh[3] = parent->i_generation;
 481                 spin_unlock(&dentry->d_lock);
 482                 len = 4;
 483                 type = 2;
 484         }
 485         *max_len = len;
 486         return type;
 487 }
 488
 489
 490 /**
 491  * export_decode_fh - default export_operations->decode_fh function
 492  * @sb:  The superblock
 493  * @fh:  pointer to the file handle fragment
 494  * @fh_len: length of file handle fragment
 495  * @acceptable: function for testing acceptability of dentrys
 496  * @context:   context for @acceptable
 497  *
 498  * This is the default decode_fh() function.
 499  * a fileid_type of 1 indicates that the filehandlefragment
 500  * just contains an object identifier understood by  get_dentry.
 501  * a fileid_type of 2 says that there is also a directory
 502  * identifier 8 bytes in to the filehandlefragement.
 503  */
 504 static struct dentry *export_decode_fh(struct super_block *sb, __u32 *fh, int fh_len,
 505                               int fileid_type,
 506                          int (*acceptable)(void *context, struct dentry *de),
 507                          void *context)
 508 {
 509         __u32 parent[2];
 510         parent[0] = parent[1] = 0;
 511         if (fh_len < 2 || fileid_type > 2)
 512                 return NULL;
 513         if (fileid_type == 2) {
 514                 if (fh_len > 2) parent[0] = fh[2];
 515                 if (fh_len > 3) parent[1] = fh[3];
 516         }
 517         return find_exported_dentry(sb, fh, parent,
 518                                    acceptable, context);
 519 }
 520
 521 struct export_operations export_op_default = {
 522         .decode_fh      = export_decode_fh,
 523         .encode_fh      = export_encode_fh,
 524
 525         .get_name       = get_name,
 526         .get_parent     = get_parent,
 527         .get_dentry     = get_object,
 528 };
 529
 530 EXPORT_SYMBOL(export_op_default);
 531 EXPORT_SYMBOL(find_exported_dentry);
 532
 533 MODULE_LICENSE("GPL");