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 /**
  15  * find_exported_dentry - helper routine to implement export_operations->decode_fh
  16  * @sb:         The &super_block identifying the filesystem
  17  * @obj:        An opaque identifier of the object to be found - passed to
  18  *              get_inode
  19  * @parent:     An optional opqaue identifier of the parent of the object.
  20  * @acceptable: A function used to test possible &dentries to see if they are
  21  *              acceptable
  22  * @context:    A parameter to @acceptable so that it knows on what basis to
  23  *              judge.
  24  *
  25  * find_exported_dentry is the central helper routine to enable file systems
  26  * to provide the decode_fh() export_operation.  It's main task is to take
  27  * an &inode, find or create an appropriate &dentry structure, and possibly
  28  * splice this into the dcache in the correct place.
  29  *
  30  * The decode_fh() operation provided by the filesystem should call
  31  * find_exported_dentry() with the same parameters that it received except
  32  * that instead of the file handle fragment, pointers to opaque identifiers
  33  * for the object and optionally its parent are passed.  The default decode_fh
  34  * routine passes one pointer to the start of the filehandle fragment, and
  35  * one 8 bytes into the fragment.  It is expected that most filesystems will
  36  * take this approach, though the offset to the parent identifier may well be
  37  * different.
  38  *
  39  * find_exported_dentry() will call get_dentry to get an dentry pointer from
  40  * the file system.  If any &dentry in the d_alias list is acceptable, it will
  41  * be returned.  Otherwise find_exported_dentry() will attempt to splice a new
  42  * &dentry into the dcache using get_name() and get_parent() to find the
  43  * appropriate place.
  44  */
  45
  46 struct dentry *
  47 find_exported_dentry(struct super_block *sb, void *obj, void *parent,
  48                      int (*acceptable)(void *context, struct dentry *de),
  49                      void *context)
  50 {
  51         struct dentry *result = NULL;
  52         struct dentry *target_dir;
  53         int err;
  54         struct export_operations *nops = sb->s_export_op;
  55         struct list_head *le, *head;
  56         struct dentry *toput = NULL;
  57         int noprogress;
  58         char nbuf[NAME_MAX+1];
  59
  60         /*
  61          * Attempt to find the inode.
  62          */
  63         result = CALL(sb->s_export_op,get_dentry)(sb,obj);
  64         err = -ESTALE;
  65         if (result == NULL)
  66                 goto err_out;
  67         if (IS_ERR(result)) {
  68                 err = PTR_ERR(result);
  69                 goto err_out;
  70         }
  71         if (S_ISDIR(result->d_inode->i_mode) &&
  72             (result->d_flags & DCACHE_DISCONNECTED)) {
  73                 /* it is an unconnected directory, we must connect it */
  74                 ;
  75         } else {
  76                 if (acceptable(context, result))
  77                         return result;
  78                 if (S_ISDIR(result->d_inode->i_mode)) {
  79                         /* there is no other dentry, so fail */
  80                         goto err_result;
  81                 }
  82                 /* try any other aliases */
  83                 spin_lock(&dcache_lock);
  84                 head = &result->d_inode->i_dentry;
  85                 list_for_each(le, head) {
  86                         struct dentry *dentry = list_entry(le, struct dentry, d_alias);
  87                         dget_locked(dentry);
  88                         spin_unlock(&dcache_lock);
  89                         if (toput)
  90                                 dput(toput);
  91                         toput = NULL;
  92                         if (dentry != result &&
  93                             acceptable(context, dentry)) {
  94                                 dput(result);
  95                                 return dentry;
  96                         }
  97                         spin_lock(&dcache_lock);
  98                         toput = dentry;
  99                 }
 100                 spin_unlock(&dcache_lock);
 101                 if (toput)
 102                         dput(toput);
 103         }
 104
 105         /* It's a directory, or we are required to confirm the file's
 106          * location in the tree based on the parent information
 107          */
 108         dprintk("find_exported_dentry: need to look harder for %s/%d\n",sb->s_id,*(int*)obj);
 109         if (S_ISDIR(result->d_inode->i_mode))
 110                 target_dir = dget(result);
 111         else {
 112                 if (parent == NULL)
 113                         goto err_result;
 114
 115                 target_dir = CALL(sb->s_export_op,get_dentry)(sb,parent);
 116                 if (IS_ERR(target_dir))
 117                         err = PTR_ERR(target_dir);
 118                 if (target_dir == NULL || IS_ERR(target_dir))
 119                         goto err_result;
 120         }
 121         /*
 122          * Now we need to make sure that target_dir is properly connected.
 123          * It may already be, as the flag isn't always updated when connection
 124          * happens.
 125          * So, we walk up parent links until we find a connected directory,
 126          * or we run out of directories.  Then we find the parent, find
 127          * the name of the child in that parent, and do a lookup.
 128          * This should connect the child into the parent
 129          * We then repeat.
 130          */
 131
 132         /* it is possible that a confused file system might not let us complete
 133          * the path to the root.  For example, if get_parent returns a directory
 134          * in which we cannot find a name for the child.  While this implies a
 135          * very sick filesystem we don't want it to cause knfsd to spin.  Hence
 136          * the noprogress counter.  If we go through the loop 10 times (2 is
 137          * probably enough) without getting anywhere, we just give up
 138          */
 139         noprogress= 0;
 140         while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
 141                 struct dentry *pd = target_dir;
 142
 143                 dget(pd);
 144                 spin_lock(&pd->d_lock);
 145                 while (!IS_ROOT(pd) &&
 146                                 (pd->d_parent->d_flags&DCACHE_DISCONNECTED)) {
 147                         struct dentry *parent = pd->d_parent;
 148
 149                         dget(parent);
 150                         spin_unlock(&pd->d_lock);
 151                         dput(pd);
 152                         pd = parent;
 153                         spin_lock(&pd->d_lock);
 154                 }
 155                 spin_unlock(&pd->d_lock);
 156
 157                 if (!IS_ROOT(pd)) {
 158                         /* must have found a connected parent - great */
 159                         spin_lock(&pd->d_lock);
 160                         pd->d_flags &= ~DCACHE_DISCONNECTED;
 161                         spin_unlock(&pd->d_lock);
 162                         noprogress = 0;
 163                 } else if (pd == sb->s_root) {
 164                         printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
 165                         spin_lock(&pd->d_lock);
 166                         pd->d_flags &= ~DCACHE_DISCONNECTED;
 167                         spin_unlock(&pd->d_lock);
 168                         noprogress = 0;
 169                 } else {
 170                         /* we have hit the top of a disconnected path.  Try
 171                          * to find parent and connect
 172                          * note: racing with some other process renaming a
 173                          * directory isn't much of a problem here.  If someone
 174                          * renames the directory, it will end up properly
 175                          * connected, which is what we want
 176                          */
 177                         struct dentry *ppd;
 178                         struct dentry *npd;
 179
 180                         down(&pd->d_inode->i_sem);
 181                         ppd = CALL(nops,get_parent)(pd);
 182                         up(&pd->d_inode->i_sem);
 183
 184                         if (IS_ERR(ppd)) {
 185                                 err = PTR_ERR(ppd);
 186                                 dprintk("find_exported_dentry: get_parent of %ld failed, err %d\n",
 187                                         pd->d_inode->i_ino, err);
 188                                 dput(pd);
 189                                 break;
 190                         }
 191                         dprintk("find_exported_dentry: find name of %lu in %lu\n", pd->d_inode->i_ino, ppd->d_inode->i_ino);
 192                         err = CALL(nops,get_name)(ppd, nbuf, pd);
 193                         if (err) {
 194                                 dput(ppd);
 195                                 dput(pd);
 196                                 if (err == -ENOENT)
 197                                         /* some race between get_parent and
 198                                          * get_name?  just try again
 199                                          */
 200                                         continue;
 201                                 break;
 202                         }
 203                         dprintk("find_exported_dentry: found name: %s\n", nbuf);
 204                         down(&ppd->d_inode->i_sem);
 205                         npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
 206                         up(&ppd->d_inode->i_sem);
 207                         if (IS_ERR(npd)) {
 208                                 err = PTR_ERR(npd);
 209                                 dprintk("find_exported_dentry: lookup failed: %d\n", err);
 210                                 dput(ppd);
 211                                 dput(pd);
 212                                 break;
 213                         }
 214                         /* we didn't really want npd, we really wanted
 215                          * a side-effect of the lookup.
 216                          * hopefully, npd == pd, though it isn't really
 217                          * a problem if it isn't
 218                          */
 219                         if (npd == pd)
 220                                 noprogress = 0;
 221                         else
 222                                 printk("find_exported_dentry: npd != pd\n");
 223                         dput(npd);
 224                         dput(ppd);
 225                         if (IS_ROOT(pd)) {
 226                                 /* something went wrong, we have to give up */
 227                                 dput(pd);
 228                                 break;
 229                         }
 230                 }
 231                 dput(pd);
 232         }
 233
 234         if (target_dir->d_flags & DCACHE_DISCONNECTED) {
 235                 /* something went wrong - oh-well */
 236                 if (!err)
 237                         err = -ESTALE;
 238                 goto err_target;
 239         }
 240         /* if we weren't after a directory, have one more step to go */
 241         if (result != target_dir) {
 242                 struct dentry *nresult;
 243                 err = CALL(nops,get_name)(target_dir, nbuf, result);
 244                 if (!err) {
 245                         down(&target_dir->d_inode->i_sem);
 246                         nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
 247                         up(&target_dir->d_inode->i_sem);
 248                         if (!IS_ERR(nresult)) {
 249                                 if (nresult->d_inode) {
 250                                         dput(result);
 251                                         result = nresult;
 252                                 } else
 253                                         dput(nresult);
 254                         }
 255                 }
 256         }
 257         dput(target_dir);
 258         /* now result is properly connected, it is our best bet */
 259         if (acceptable(context, result))
 260                 return result;
 261         /* one last try of the aliases.. */
 262         spin_lock(&dcache_lock);
 263         toput = NULL;
 264         head = &result->d_inode->i_dentry;
 265         list_for_each(le, head) {
 266                 struct dentry *dentry = list_entry(le, struct dentry, d_alias);
 267                 dget_locked(dentry);
 268                 spin_unlock(&dcache_lock);
 269                 if (toput) dput(toput);
 270                 if (dentry != result &&
 271                     acceptable(context, dentry)) {
 272                         dput(result);
 273                         return dentry;
 274                 }
 275                 spin_lock(&dcache_lock);
 276                 toput = dentry;
 277         }
 278         spin_unlock(&dcache_lock);
 279         if (toput)
 280                 dput(toput);
 281
 282         /* drat - I just cannot find anything acceptable */
 283         dput(result);
 284         /* It might be justifiable to return ESTALE here,
 285          * but the filehandle at-least looks reasonable good
 286          * and it just be a permission problem, so returning
 287          * -EACCESS is safer
 288          */
 289         return ERR_PTR(-EACCES);
 290
 291  err_target:
 292         dput(target_dir);
 293  err_result:
 294         dput(result);
 295  err_out:
 296         return ERR_PTR(err);
 297 }
 298
 299
 300
 301 static struct dentry *get_parent(struct dentry *child)
 302 {
 303         /* get_parent cannot be supported generically, the locking
 304          * is too icky.
 305          * instead, we just return EACCES.  If server reboots or inodes
 306          * get flushed, you lose
 307          */
 308         return ERR_PTR(-EACCES);
 309 }
 310
 311
 312 struct getdents_callback {
 313         char *name;             /* name that was found. It already points to a
 314                                    buffer NAME_MAX+1 is size */
 315         unsigned long ino;      /* the inum we are looking for */
 316         int found;              /* inode matched? */
 317         int sequence;           /* sequence counter */
 318 };
 319
 320 /*
 321  * A rather strange filldir function to capture
 322  * the name matching the specified inode number.
 323  */
 324 static int filldir_one(void * __buf, const char * name, int len,
 325                         loff_t pos, ino_t ino, unsigned int d_type)
 326 {
 327         struct getdents_callback *buf = __buf;
 328         int result = 0;
 329
 330         buf->sequence++;
 331         if (buf->ino == ino) {
 332                 memcpy(buf->name, name, len);
 333                 buf->name[len] = '\0';
 334                 buf->found = 1;
 335                 result = -1;
 336         }
 337         return result;
 338 }
 339
 340 /**
 341  * get_name - default export_operations->get_name function
 342  * @dentry: the directory in which to find a name
 343  * @name:   a pointer to a %NAME_MAX+1 char buffer to store the name
 344  * @child:  the dentry for the child directory.
 345  *
 346  * calls readdir on the parent until it finds an entry with
 347  * the same inode number as the child, and returns that.
 348  */
 349 static int get_name(struct dentry *dentry, char *name,
 350                         struct dentry *child)
 351 {
 352         struct inode *dir = dentry->d_inode;
 353         int error;
 354         struct file *file;
 355         struct getdents_callback buffer;
 356
 357         error = -ENOTDIR;
 358         if (!dir || !S_ISDIR(dir->i_mode))
 359                 goto out;
 360         error = -EINVAL;
 361         if (!dir->i_fop)
 362                 goto out;
 363         /*
 364          * Open the directory ...
 365          */
 366         file = dentry_open(dget(dentry), NULL, O_RDONLY);
 367         error = PTR_ERR(file);
 368         if (IS_ERR(file))
 369                 goto out;
 370
 371         error = -EINVAL;
 372         if (!file->f_op->readdir)
 373                 goto out_close;
 374
 375         buffer.name = name;
 376         buffer.ino = child->d_inode->i_ino;
 377         buffer.found = 0;
 378         buffer.sequence = 0;
 379         while (1) {
 380                 int old_seq = buffer.sequence;
 381
 382                 error = vfs_readdir(file, filldir_one, &buffer);
 383
 384                 if (error < 0)
 385                         break;
 386
 387                 error = 0;
 388                 if (buffer.found)
 389                         break;
 390                 error = -ENOENT;
 391                 if (old_seq == buffer.sequence)
 392                         break;
 393         }
 394
 395 out_close:
 396         fput(file);
 397 out:
 398         return error;
 399 }
 400
 401
 402 static struct dentry *export_iget(struct super_block *sb, unsigned long ino, __u32 generation)
 403 {
 404
 405         /* iget isn't really right if the inode is currently unallocated!!
 406          * This should really all be done inside each filesystem
 407          *
 408          * ext2fs' read_inode has been strengthed to return a bad_inode if
 409          * the inode had been deleted.
 410          *
 411          * Currently we don't know the generation for parent directory, so
 412          * a generation of 0 means "accept any"
 413          */
 414         struct inode *inode;
 415         struct dentry *result;
 416         if (ino == 0)
 417                 return ERR_PTR(-ESTALE);
 418         inode = iget(sb, ino);
 419         if (inode == NULL)
 420                 return ERR_PTR(-ENOMEM);
 421         if (is_bad_inode(inode)
 422             || (generation && inode->i_generation != generation)
 423                 ) {
 424                 /* we didn't find the right inode.. */
 425                 dprintk("fh_verify: Inode %lu, Bad count: %d %d or version  %u %u\n",
 426                         inode->i_ino,
 427                         inode->i_nlink, atomic_read(&inode->i_count),
 428                         inode->i_generation,
 429                         generation);
 430
 431                 iput(inode);
 432                 return ERR_PTR(-ESTALE);
 433         }
 434         /* now to find a dentry.
 435          * If possible, get a well-connected one
 436          */
 437         result = d_alloc_anon(inode);
 438         if (!result) {
 439                 iput(inode);
 440                 return ERR_PTR(-ENOMEM);
 441         }
 442         return result;
 443 }
 444
 445
 446 static struct dentry *get_object(struct super_block *sb, void *vobjp)
 447 {
 448         __u32 *objp = vobjp;
 449         unsigned long ino = objp[0];
 450         __u32 generation = objp[1];
 451
 452         return export_iget(sb, ino, generation);
 453 }
 454
 455
 456 /**
 457  * export_encode_fh - default export_operations->encode_fh function
 458  * @dentry:  the dentry to encode
 459  * @fh:      where to store the file handle fragment
 460  * @max_len: maximum length to store there
 461  * @connectable: whether to store parent information
 462  *
 463  * This default encode_fh function assumes that the 32 inode number
 464  * is suitable for locating an inode, and that the generation number
 465  * can be used to check that it is still valid.  It places them in the
 466  * filehandle fragment where export_decode_fh expects to find them.
 467  */
 468 static int export_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
 469                    int connectable)
 470 {
 471         struct inode * inode = dentry->d_inode;
 472         int len = *max_len;
 473         int type = 1;
 474
 475         if (len < 2 || (connectable && len < 4))
 476                 return 255;
 477
 478         len = 2;
 479         fh[0] = inode->i_ino;
 480         fh[1] = inode->i_generation;
 481         if (connectable && !S_ISDIR(inode->i_mode)) {
 482                 struct inode *parent;
 483
 484                 spin_lock(&dentry->d_lock);
 485                 parent = dentry->d_parent->d_inode;
 486                 fh[2] = parent->i_ino;
 487                 fh[3] = parent->i_generation;
 488                 spin_unlock(&dentry->d_lock);
 489                 len = 4;
 490                 type = 2;
 491         }
 492         *max_len = len;
 493         return type;
 494 }
 495
 496
 497 /**
 498  * export_decode_fh - default export_operations->decode_fh function
 499  * @sb:  The superblock
 500  * @fh:  pointer to the file handle fragment
 501  * @fh_len: length of file handle fragment
 502  * @acceptable: function for testing acceptability of dentrys
 503  * @context:   context for @acceptable
 504  *
 505  * This is the default decode_fh() function.
 506  * a fileid_type of 1 indicates that the filehandlefragment
 507  * just contains an object identifier understood by  get_dentry.
 508  * a fileid_type of 2 says that there is also a directory
 509  * identifier 8 bytes in to the filehandlefragement.
 510  */
 511 static struct dentry *export_decode_fh(struct super_block *sb, __u32 *fh, int fh_len,
 512                               int fileid_type,
 513                          int (*acceptable)(void *context, struct dentry *de),
 514                          void *context)
 515 {
 516         __u32 parent[2];
 517         parent[0] = parent[1] = 0;
 518         if (fh_len < 2 || fileid_type > 2)
 519                 return NULL;
 520         if (fileid_type == 2) {
 521                 if (fh_len > 2) parent[0] = fh[2];
 522                 if (fh_len > 3) parent[1] = fh[3];
 523         }
 524         return find_exported_dentry(sb, fh, parent,
 525                                    acceptable, context);
 526 }
 527
 528 struct export_operations export_op_default = {
 529         .decode_fh      = export_decode_fh,
 530         .encode_fh      = export_encode_fh,
 531
 532         .get_name       = get_name,
 533         .get_parent     = get_parent,
 534         .get_dentry     = get_object,
 535 };
 536
 537 EXPORT_SYMBOL(export_op_default);
 538 EXPORT_SYMBOL(find_exported_dentry);
 539
 540 MODULE_LICENSE("GPL");