fs/hostfs/hostfs_kern.c

   1 /*
   2  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   3  * Licensed under the GPL
   4  *
   5  * Ported the filesystem routines to 2.5.
   6  * 2003-02-10 Petr Baudis <pasky@ucw.cz>
   7  */
   8
   9 #include <linux/fs.h>
  10 #include <linux/magic.h>
  11 #include <linux/module.h>
  12 #include <linux/mm.h>
  13 #include <linux/pagemap.h>
  14 #include <linux/statfs.h>
  15 #include <linux/slab.h>
  16 #include <linux/seq_file.h>
  17 #include <linux/mount.h>
  18 #include <linux/namei.h>
  19 #include "hostfs.h"
  20 #include <init.h>
  21 #include <kern.h>
  22
  23 struct hostfs_inode_info {
  24         int fd;
  25         fmode_t mode;
  26         struct inode vfs_inode;
  27         struct mutex open_mutex;
  28 };
  29
  30 static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode)
  31 {
  32         return list_entry(inode, struct hostfs_inode_info, vfs_inode);
  33 }
  34
  35 #define FILE_HOSTFS_I(file) HOSTFS_I(file_inode(file))
  36
  37 /* Changed in hostfs_args before the kernel starts running */
  38 static char *root_ino = "";
  39 static int append = 0;
  40
  41 static const struct inode_operations hostfs_iops;
  42 static const struct inode_operations hostfs_dir_iops;
  43 static const struct inode_operations hostfs_link_iops;
  44
  45 #ifndef MODULE
  46 static int __init hostfs_args(char *options, int *add)
  47 {
  48         char *ptr;
  49
  50         ptr = strchr(options, ',');
  51         if (ptr != NULL)
  52                 *ptr++ = '\0';
  53         if (*options != '\0')
  54                 root_ino = options;
  55
  56         options = ptr;
  57         while (options) {
  58                 ptr = strchr(options, ',');
  59                 if (ptr != NULL)
  60                         *ptr++ = '\0';
  61                 if (*options != '\0') {
  62                         if (!strcmp(options, "append"))
  63                                 append = 1;
  64                         else printf("hostfs_args - unsupported option - %s\n",
  65                                     options);
  66                 }
  67                 options = ptr;
  68         }
  69         return 0;
  70 }
  71
  72 __uml_setup("hostfs=", hostfs_args,
  73 "hostfs=<root dir>,<flags>,...\n"
  74 "    This is used to set hostfs parameters.  The root directory argument\n"
  75 "    is used to confine all hostfs mounts to within the specified directory\n"
  76 "    tree on the host.  If this isn't specified, then a user inside UML can\n"
  77 "    mount anything on the host that's accessible to the user that's running\n"
  78 "    it.\n"
  79 "    The only flag currently supported is 'append', which specifies that all\n"
  80 "    files opened by hostfs will be opened in append mode.\n\n"
  81 );
  82 #endif
  83
  84 static char *__dentry_name(struct dentry *dentry, char *name)
  85 {
  86         char *p = dentry_path_raw(dentry, name, PATH_MAX);
  87         char *root;
  88         size_t len;
  89
  90         root = dentry->d_sb->s_fs_info;
  91         len = strlen(root);
  92         if (IS_ERR(p)) {
  93                 __putname(name);
  94                 return NULL;
  95         }
  96
  97         /*
  98          * This function relies on the fact that dentry_path_raw() will place
  99          * the path name at the end of the provided buffer.
 100          */
 101         BUG_ON(p + strlen(p) + 1 != name + PATH_MAX);
 102
 103         strlcpy(name, root, PATH_MAX);
 104         if (len > p - name) {
 105                 __putname(name);
 106                 return NULL;
 107         }
 108
 109         if (p > name + len)
 110                 strcpy(name + len, p);
 111
 112         return name;
 113 }
 114
 115 static char *dentry_name(struct dentry *dentry)
 116 {
 117         char *name = __getname();
 118         if (!name)
 119                 return NULL;
 120
 121         return __dentry_name(dentry, name);
 122 }
 123
 124 static char *inode_name(struct inode *ino)
 125 {
 126         struct dentry *dentry;
 127         char *name;
 128
 129         dentry = d_find_alias(ino);
 130         if (!dentry)
 131                 return NULL;
 132
 133         name = dentry_name(dentry);
 134
 135         dput(dentry);
 136
 137         return name;
 138 }
 139
 140 static char *follow_link(char *link)
 141 {
 142         int len, n;
 143         char *name, *resolved, *end;
 144
 145         name = __getname();
 146         if (!name) {
 147                 n = -ENOMEM;
 148                 goto out_free;
 149         }
 150
 151         n = hostfs_do_readlink(link, name, PATH_MAX);
 152         if (n < 0)
 153                 goto out_free;
 154         else if (n == PATH_MAX) {
 155                 n = -E2BIG;
 156                 goto out_free;
 157         }
 158
 159         if (*name == '/')
 160                 return name;
 161
 162         end = strrchr(link, '/');
 163         if (end == NULL)
 164                 return name;
 165
 166         *(end + 1) = '\0';
 167         len = strlen(link) + strlen(name) + 1;
 168
 169         resolved = kmalloc(len, GFP_KERNEL);
 170         if (resolved == NULL) {
 171                 n = -ENOMEM;
 172                 goto out_free;
 173         }
 174
 175         sprintf(resolved, "%s%s", link, name);
 176         __putname(name);
 177         kfree(link);
 178         return resolved;
 179
 180  out_free:
 181         __putname(name);
 182         return ERR_PTR(n);
 183 }
 184
 185 static struct inode *hostfs_iget(struct super_block *sb)
 186 {
 187         struct inode *inode = new_inode(sb);
 188         if (!inode)
 189                 return ERR_PTR(-ENOMEM);
 190         return inode;
 191 }
 192
 193 static int hostfs_statfs(struct dentry *dentry, struct kstatfs *sf)
 194 {
 195         /*
 196          * do_statfs uses struct statfs64 internally, but the linux kernel
 197          * struct statfs still has 32-bit versions for most of these fields,
 198          * so we convert them here
 199          */
 200         int err;
 201         long long f_blocks;
 202         long long f_bfree;
 203         long long f_bavail;
 204         long long f_files;
 205         long long f_ffree;
 206
 207         err = do_statfs(dentry->d_sb->s_fs_info,
 208                         &sf->f_bsize, &f_blocks, &f_bfree, &f_bavail, &f_files,
 209                         &f_ffree, &sf->f_fsid, sizeof(sf->f_fsid),
 210                         &sf->f_namelen);
 211         if (err)
 212                 return err;
 213         sf->f_blocks = f_blocks;
 214         sf->f_bfree = f_bfree;
 215         sf->f_bavail = f_bavail;
 216         sf->f_files = f_files;
 217         sf->f_ffree = f_ffree;
 218         sf->f_type = HOSTFS_SUPER_MAGIC;
 219         return 0;
 220 }
 221
 222 static struct inode *hostfs_alloc_inode(struct super_block *sb)
 223 {
 224         struct hostfs_inode_info *hi;
 225
 226         hi = kmalloc(sizeof(*hi), GFP_KERNEL);
 227         if (hi == NULL)
 228                 return NULL;
 229         hi->fd = -1;
 230         hi->mode = 0;
 231         inode_init_once(&hi->vfs_inode);
 232         mutex_init(&hi->open_mutex);
 233         return &hi->vfs_inode;
 234 }
 235
 236 static void hostfs_evict_inode(struct inode *inode)
 237 {
 238         truncate_inode_pages_final(&inode->i_data);
 239         clear_inode(inode);
 240         if (HOSTFS_I(inode)->fd != -1) {
 241                 close_file(&HOSTFS_I(inode)->fd);
 242                 HOSTFS_I(inode)->fd = -1;
 243         }
 244 }
 245
 246 static void hostfs_i_callback(struct rcu_head *head)
 247 {
 248         struct inode *inode = container_of(head, struct inode, i_rcu);
 249         kfree(HOSTFS_I(inode));
 250 }
 251
 252 static void hostfs_destroy_inode(struct inode *inode)
 253 {
 254         call_rcu(&inode->i_rcu, hostfs_i_callback);
 255 }
 256
 257 static int hostfs_show_options(struct seq_file *seq, struct dentry *root)
 258 {
 259         const char *root_path = root->d_sb->s_fs_info;
 260         size_t offset = strlen(root_ino) + 1;
 261
 262         if (strlen(root_path) > offset)
 263                 seq_show_option(seq, root_path + offset, NULL);
 264
 265         if (append)
 266                 seq_puts(seq, ",append");
 267
 268         return 0;
 269 }
 270
 271 static const struct super_operations hostfs_sbops = {
 272         .alloc_inode    = hostfs_alloc_inode,
 273         .destroy_inode  = hostfs_destroy_inode,
 274         .evict_inode    = hostfs_evict_inode,
 275         .statfs         = hostfs_statfs,
 276         .show_options   = hostfs_show_options,
 277 };
 278
 279 static int hostfs_readdir(struct file *file, struct dir_context *ctx)
 280 {
 281         void *dir;
 282         char *name;
 283         unsigned long long next, ino;
 284         int error, len;
 285         unsigned int type;
 286
 287         name = dentry_name(file->f_path.dentry);
 288         if (name == NULL)
 289                 return -ENOMEM;
 290         dir = open_dir(name, &error);
 291         __putname(name);
 292         if (dir == NULL)
 293                 return -error;
 294         next = ctx->pos;
 295         seek_dir(dir, next);
 296         while ((name = read_dir(dir, &next, &ino, &len, &type)) != NULL) {
 297                 if (!dir_emit(ctx, name, len, ino, type))
 298                         break;
 299                 ctx->pos = next;
 300         }
 301         close_dir(dir);
 302         return 0;
 303 }
 304
 305 static int hostfs_open(struct inode *ino, struct file *file)
 306 {
 307         char *name;
 308         fmode_t mode;
 309         int err;
 310         int r, w, fd;
 311
 312         mode = file->f_mode & (FMODE_READ | FMODE_WRITE);
 313         if ((mode & HOSTFS_I(ino)->mode) == mode)
 314                 return 0;
 315
 316         mode |= HOSTFS_I(ino)->mode;
 317
 318 retry:
 319         r = w = 0;
 320
 321         if (mode & FMODE_READ)
 322                 r = 1;
 323         if (mode & FMODE_WRITE)
 324                 r = w = 1;
 325
 326         name = dentry_name(file->f_path.dentry);
 327         if (name == NULL)
 328                 return -ENOMEM;
 329
 330         fd = open_file(name, r, w, append);
 331         __putname(name);
 332         if (fd < 0)
 333                 return fd;
 334
 335         mutex_lock(&HOSTFS_I(ino)->open_mutex);
 336         /* somebody else had handled it first? */
 337         if ((mode & HOSTFS_I(ino)->mode) == mode) {
 338                 mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 339                 close_file(&fd);
 340                 return 0;
 341         }
 342         if ((mode | HOSTFS_I(ino)->mode) != mode) {
 343                 mode |= HOSTFS_I(ino)->mode;
 344                 mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 345                 close_file(&fd);
 346                 goto retry;
 347         }
 348         if (HOSTFS_I(ino)->fd == -1) {
 349                 HOSTFS_I(ino)->fd = fd;
 350         } else {
 351                 err = replace_file(fd, HOSTFS_I(ino)->fd);
 352                 close_file(&fd);
 353                 if (err < 0) {
 354                         mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 355                         return err;
 356                 }
 357         }
 358         HOSTFS_I(ino)->mode = mode;
 359         mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 360
 361         return 0;
 362 }
 363
 364 static int hostfs_file_release(struct inode *inode, struct file *file)
 365 {
 366         filemap_write_and_wait(inode->i_mapping);
 367
 368         return 0;
 369 }
 370
 371 static int hostfs_fsync(struct file *file, loff_t start, loff_t end,
 372                         int datasync)
 373 {
 374         struct inode *inode = file->f_mapping->host;
 375         int ret;
 376
 377         ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
 378         if (ret)
 379                 return ret;
 380
 381         mutex_lock(&inode->i_mutex);
 382         ret = fsync_file(HOSTFS_I(inode)->fd, datasync);
 383         mutex_unlock(&inode->i_mutex);
 384
 385         return ret;
 386 }
 387
 388 static const struct file_operations hostfs_file_fops = {
 389         .llseek         = generic_file_llseek,
 390         .splice_read    = generic_file_splice_read,
 391         .read_iter      = generic_file_read_iter,
 392         .write_iter     = generic_file_write_iter,
 393         .mmap           = generic_file_mmap,
 394         .open           = hostfs_open,
 395         .release        = hostfs_file_release,
 396         .fsync          = hostfs_fsync,
 397 };
 398
 399 static const struct file_operations hostfs_dir_fops = {
 400         .llseek         = generic_file_llseek,
 401         .iterate        = hostfs_readdir,
 402         .read           = generic_read_dir,
 403         .open           = hostfs_open,
 404         .fsync          = hostfs_fsync,
 405 };
 406
 407 static int hostfs_writepage(struct page *page, struct writeback_control *wbc)
 408 {
 409         struct address_space *mapping = page->mapping;
 410         struct inode *inode = mapping->host;
 411         char *buffer;
 412         loff_t base = page_offset(page);
 413         int count = PAGE_CACHE_SIZE;
 414         int end_index = inode->i_size >> PAGE_CACHE_SHIFT;
 415         int err;
 416
 417         if (page->index >= end_index)
 418                 count = inode->i_size & (PAGE_CACHE_SIZE-1);
 419
 420         buffer = kmap(page);
 421
 422         err = write_file(HOSTFS_I(inode)->fd, &base, buffer, count);
 423         if (err != count) {
 424                 ClearPageUptodate(page);
 425                 goto out;
 426         }
 427
 428         if (base > inode->i_size)
 429                 inode->i_size = base;
 430
 431         if (PageError(page))
 432                 ClearPageError(page);
 433         err = 0;
 434
 435  out:
 436         kunmap(page);
 437
 438         unlock_page(page);
 439         return err;
 440 }
 441
 442 static int hostfs_readpage(struct file *file, struct page *page)
 443 {
 444         char *buffer;
 445         loff_t start = page_offset(page);
 446         int bytes_read, ret = 0;
 447
 448         buffer = kmap(page);
 449         bytes_read = read_file(FILE_HOSTFS_I(file)->fd, &start, buffer,
 450                         PAGE_CACHE_SIZE);
 451         if (bytes_read < 0) {
 452                 ClearPageUptodate(page);
 453                 SetPageError(page);
 454                 ret = bytes_read;
 455                 goto out;
 456         }
 457
 458         memset(buffer + bytes_read, 0, PAGE_CACHE_SIZE - bytes_read);
 459
 460         ClearPageError(page);
 461         SetPageUptodate(page);
 462
 463  out:
 464         flush_dcache_page(page);
 465         kunmap(page);
 466         unlock_page(page);
 467         return ret;
 468 }
 469
 470 static int hostfs_write_begin(struct file *file, struct address_space *mapping,
 471                               loff_t pos, unsigned len, unsigned flags,
 472                               struct page **pagep, void **fsdata)
 473 {
 474         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 475
 476         *pagep = grab_cache_page_write_begin(mapping, index, flags);
 477         if (!*pagep)
 478                 return -ENOMEM;
 479         return 0;
 480 }
 481
 482 static int hostfs_write_end(struct file *file, struct address_space *mapping,
 483                             loff_t pos, unsigned len, unsigned copied,
 484                             struct page *page, void *fsdata)
 485 {
 486         struct inode *inode = mapping->host;
 487         void *buffer;
 488         unsigned from = pos & (PAGE_CACHE_SIZE - 1);
 489         int err;
 490
 491         buffer = kmap(page);
 492         err = write_file(FILE_HOSTFS_I(file)->fd, &pos, buffer + from, copied);
 493         kunmap(page);
 494
 495         if (!PageUptodate(page) && err == PAGE_CACHE_SIZE)
 496                 SetPageUptodate(page);
 497
 498         /*
 499          * If err > 0, write_file has added err to pos, so we are comparing
 500          * i_size against the last byte written.
 501          */
 502         if (err > 0 && (pos > inode->i_size))
 503                 inode->i_size = pos;
 504         unlock_page(page);
 505         page_cache_release(page);
 506
 507         return err;
 508 }
 509
 510 static const struct address_space_operations hostfs_aops = {
 511         .writepage      = hostfs_writepage,
 512         .readpage       = hostfs_readpage,
 513         .set_page_dirty = __set_page_dirty_nobuffers,
 514         .write_begin    = hostfs_write_begin,
 515         .write_end      = hostfs_write_end,
 516 };
 517
 518 static int read_name(struct inode *ino, char *name)
 519 {
 520         dev_t rdev;
 521         struct hostfs_stat st;
 522         int err = stat_file(name, &st, -1);
 523         if (err)
 524                 return err;
 525
 526         /* Reencode maj and min with the kernel encoding.*/
 527         rdev = MKDEV(st.maj, st.min);
 528
 529         switch (st.mode & S_IFMT) {
 530         case S_IFLNK:
 531                 ino->i_op = &hostfs_link_iops;
 532                 break;
 533         case S_IFDIR:
 534                 ino->i_op = &hostfs_dir_iops;
 535                 ino->i_fop = &hostfs_dir_fops;
 536                 break;
 537         case S_IFCHR:
 538         case S_IFBLK:
 539         case S_IFIFO:
 540         case S_IFSOCK:
 541                 init_special_inode(ino, st.mode & S_IFMT, rdev);
 542                 ino->i_op = &hostfs_iops;
 543                 break;
 544         case S_IFREG:
 545                 ino->i_op = &hostfs_iops;
 546                 ino->i_fop = &hostfs_file_fops;
 547                 ino->i_mapping->a_ops = &hostfs_aops;
 548                 break;
 549         default:
 550                 return -EIO;
 551         }
 552
 553         ino->i_ino = st.ino;
 554         ino->i_mode = st.mode;
 555         set_nlink(ino, st.nlink);
 556         i_uid_write(ino, st.uid);
 557         i_gid_write(ino, st.gid);
 558         ino->i_atime = st.atime;
 559         ino->i_mtime = st.mtime;
 560         ino->i_ctime = st.ctime;
 561         ino->i_size = st.size;
 562         ino->i_blocks = st.blocks;
 563         return 0;
 564 }
 565
 566 static int hostfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
 567                          bool excl)
 568 {
 569         struct inode *inode;
 570         char *name;
 571         int error, fd;
 572
 573         inode = hostfs_iget(dir->i_sb);
 574         if (IS_ERR(inode)) {
 575                 error = PTR_ERR(inode);
 576                 goto out;
 577         }
 578
 579         error = -ENOMEM;
 580         name = dentry_name(dentry);
 581         if (name == NULL)
 582                 goto out_put;
 583
 584         fd = file_create(name, mode & 0777);
 585         if (fd < 0)
 586                 error = fd;
 587         else
 588                 error = read_name(inode, name);
 589
 590         __putname(name);
 591         if (error)
 592                 goto out_put;
 593
 594         HOSTFS_I(inode)->fd = fd;
 595         HOSTFS_I(inode)->mode = FMODE_READ | FMODE_WRITE;
 596         d_instantiate(dentry, inode);
 597         return 0;
 598
 599  out_put:
 600         iput(inode);
 601  out:
 602         return error;
 603 }
 604
 605 static struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry,
 606                                     unsigned int flags)
 607 {
 608         struct inode *inode;
 609         char *name;
 610         int err;
 611
 612         inode = hostfs_iget(ino->i_sb);
 613         if (IS_ERR(inode)) {
 614                 err = PTR_ERR(inode);
 615                 goto out;
 616         }
 617
 618         err = -ENOMEM;
 619         name = dentry_name(dentry);
 620         if (name == NULL)
 621                 goto out_put;
 622
 623         err = read_name(inode, name);
 624
 625         __putname(name);
 626         if (err == -ENOENT) {
 627                 iput(inode);
 628                 inode = NULL;
 629         }
 630         else if (err)
 631                 goto out_put;
 632
 633         d_add(dentry, inode);
 634         return NULL;
 635
 636  out_put:
 637         iput(inode);
 638  out:
 639         return ERR_PTR(err);
 640 }
 641
 642 static int hostfs_link(struct dentry *to, struct inode *ino,
 643                        struct dentry *from)
 644 {
 645         char *from_name, *to_name;
 646         int err;
 647
 648         if ((from_name = dentry_name(from)) == NULL)
 649                 return -ENOMEM;
 650         to_name = dentry_name(to);
 651         if (to_name == NULL) {
 652                 __putname(from_name);
 653                 return -ENOMEM;
 654         }
 655         err = link_file(to_name, from_name);
 656         __putname(from_name);
 657         __putname(to_name);
 658         return err;
 659 }
 660
 661 static int hostfs_unlink(struct inode *ino, struct dentry *dentry)
 662 {
 663         char *file;
 664         int err;
 665
 666         if (append)
 667                 return -EPERM;
 668
 669         if ((file = dentry_name(dentry)) == NULL)
 670                 return -ENOMEM;
 671
 672         err = unlink_file(file);
 673         __putname(file);
 674         return err;
 675 }
 676
 677 static int hostfs_symlink(struct inode *ino, struct dentry *dentry,
 678                           const char *to)
 679 {
 680         char *file;
 681         int err;
 682
 683         if ((file = dentry_name(dentry)) == NULL)
 684                 return -ENOMEM;
 685         err = make_symlink(file, to);
 686         __putname(file);
 687         return err;
 688 }
 689
 690 static int hostfs_mkdir(struct inode *ino, struct dentry *dentry, umode_t mode)
 691 {
 692         char *file;
 693         int err;
 694
 695         if ((file = dentry_name(dentry)) == NULL)
 696                 return -ENOMEM;
 697         err = do_mkdir(file, mode);
 698         __putname(file);
 699         return err;
 700 }
 701
 702 static int hostfs_rmdir(struct inode *ino, struct dentry *dentry)
 703 {
 704         char *file;
 705         int err;
 706
 707         if ((file = dentry_name(dentry)) == NULL)
 708                 return -ENOMEM;
 709         err = do_rmdir(file);
 710         __putname(file);
 711         return err;
 712 }
 713
 714 static int hostfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
 715 {
 716         struct inode *inode;
 717         char *name;
 718         int err;
 719
 720         inode = hostfs_iget(dir->i_sb);
 721         if (IS_ERR(inode)) {
 722                 err = PTR_ERR(inode);
 723                 goto out;
 724         }
 725
 726         err = -ENOMEM;
 727         name = dentry_name(dentry);
 728         if (name == NULL)
 729                 goto out_put;
 730
 731         init_special_inode(inode, mode, dev);
 732         err = do_mknod(name, mode, MAJOR(dev), MINOR(dev));
 733         if (!err)
 734                 goto out_free;
 735
 736         err = read_name(inode, name);
 737         __putname(name);
 738         if (err)
 739                 goto out_put;
 740         if (err)
 741                 goto out_put;
 742
 743         d_instantiate(dentry, inode);
 744         return 0;
 745
 746  out_free:
 747         __putname(name);
 748  out_put:
 749         iput(inode);
 750  out:
 751         return err;
 752 }
 753
 754 static int hostfs_rename2(struct inode *old_dir, struct dentry *old_dentry,
 755                           struct inode *new_dir, struct dentry *new_dentry,
 756                           unsigned int flags)
 757 {
 758         char *old_name, *new_name;
 759         int err;
 760
 761         if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
 762                 return -EINVAL;
 763
 764         old_name = dentry_name(old_dentry);
 765         if (old_name == NULL)
 766                 return -ENOMEM;
 767         new_name = dentry_name(new_dentry);
 768         if (new_name == NULL) {
 769                 __putname(old_name);
 770                 return -ENOMEM;
 771         }
 772         if (!flags)
 773                 err = rename_file(old_name, new_name);
 774         else
 775                 err = rename2_file(old_name, new_name, flags);
 776
 777         __putname(old_name);
 778         __putname(new_name);
 779         return err;
 780 }
 781
 782 static int hostfs_permission(struct inode *ino, int desired)
 783 {
 784         char *name;
 785         int r = 0, w = 0, x = 0, err;
 786
 787         if (desired & MAY_NOT_BLOCK)
 788                 return -ECHILD;
 789
 790         if (desired & MAY_READ) r = 1;
 791         if (desired & MAY_WRITE) w = 1;
 792         if (desired & MAY_EXEC) x = 1;
 793         name = inode_name(ino);
 794         if (name == NULL)
 795                 return -ENOMEM;
 796
 797         if (S_ISCHR(ino->i_mode) || S_ISBLK(ino->i_mode) ||
 798             S_ISFIFO(ino->i_mode) || S_ISSOCK(ino->i_mode))
 799                 err = 0;
 800         else
 801                 err = access_file(name, r, w, x);
 802         __putname(name);
 803         if (!err)
 804                 err = generic_permission(ino, desired);
 805         return err;
 806 }
 807
 808 static int hostfs_setattr(struct dentry *dentry, struct iattr *attr)
 809 {
 810         struct inode *inode = d_inode(dentry);
 811         struct hostfs_iattr attrs;
 812         char *name;
 813         int err;
 814
 815         int fd = HOSTFS_I(inode)->fd;
 816
 817         err = inode_change_ok(inode, attr);
 818         if (err)
 819                 return err;
 820
 821         if (append)
 822                 attr->ia_valid &= ~ATTR_SIZE;
 823
 824         attrs.ia_valid = 0;
 825         if (attr->ia_valid & ATTR_MODE) {
 826                 attrs.ia_valid |= HOSTFS_ATTR_MODE;
 827                 attrs.ia_mode = attr->ia_mode;
 828         }
 829         if (attr->ia_valid & ATTR_UID) {
 830                 attrs.ia_valid |= HOSTFS_ATTR_UID;
 831                 attrs.ia_uid = from_kuid(&init_user_ns, attr->ia_uid);
 832         }
 833         if (attr->ia_valid & ATTR_GID) {
 834                 attrs.ia_valid |= HOSTFS_ATTR_GID;
 835                 attrs.ia_gid = from_kgid(&init_user_ns, attr->ia_gid);
 836         }
 837         if (attr->ia_valid & ATTR_SIZE) {
 838                 attrs.ia_valid |= HOSTFS_ATTR_SIZE;
 839                 attrs.ia_size = attr->ia_size;
 840         }
 841         if (attr->ia_valid & ATTR_ATIME) {
 842                 attrs.ia_valid |= HOSTFS_ATTR_ATIME;
 843                 attrs.ia_atime = attr->ia_atime;
 844         }
 845         if (attr->ia_valid & ATTR_MTIME) {
 846                 attrs.ia_valid |= HOSTFS_ATTR_MTIME;
 847                 attrs.ia_mtime = attr->ia_mtime;
 848         }
 849         if (attr->ia_valid & ATTR_CTIME) {
 850                 attrs.ia_valid |= HOSTFS_ATTR_CTIME;
 851                 attrs.ia_ctime = attr->ia_ctime;
 852         }
 853         if (attr->ia_valid & ATTR_ATIME_SET) {
 854                 attrs.ia_valid |= HOSTFS_ATTR_ATIME_SET;
 855         }
 856         if (attr->ia_valid & ATTR_MTIME_SET) {
 857                 attrs.ia_valid |= HOSTFS_ATTR_MTIME_SET;
 858         }
 859         name = dentry_name(dentry);
 860         if (name == NULL)
 861                 return -ENOMEM;
 862         err = set_attr(name, &attrs, fd);
 863         __putname(name);
 864         if (err)
 865                 return err;
 866
 867         if ((attr->ia_valid & ATTR_SIZE) &&
 868             attr->ia_size != i_size_read(inode))
 869                 truncate_setsize(inode, attr->ia_size);
 870
 871         setattr_copy(inode, attr);
 872         mark_inode_dirty(inode);
 873         return 0;
 874 }
 875
 876 static const struct inode_operations hostfs_iops = {
 877         .permission     = hostfs_permission,
 878         .setattr        = hostfs_setattr,
 879 };
 880
 881 static const struct inode_operations hostfs_dir_iops = {
 882         .create         = hostfs_create,
 883         .lookup         = hostfs_lookup,
 884         .link           = hostfs_link,
 885         .unlink         = hostfs_unlink,
 886         .symlink        = hostfs_symlink,
 887         .mkdir          = hostfs_mkdir,
 888         .rmdir          = hostfs_rmdir,
 889         .mknod          = hostfs_mknod,
 890         .rename2        = hostfs_rename2,
 891         .permission     = hostfs_permission,
 892         .setattr        = hostfs_setattr,
 893 };
 894
 895 static void *hostfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 896 {
 897         char *link = __getname();
 898         if (link) {
 899                 char *path = dentry_name(dentry);
 900                 int err = -ENOMEM;
 901                 if (path) {
 902                         err = hostfs_do_readlink(path, link, PATH_MAX);
 903                         if (err == PATH_MAX)
 904                                 err = -E2BIG;
 905                         __putname(path);
 906                 }
 907                 if (err < 0) {
 908                         __putname(link);
 909                         link = ERR_PTR(err);
 910                 }
 911         } else {
 912                 link = ERR_PTR(-ENOMEM);
 913         }
 914
 915         nd_set_link(nd, link);
 916         return NULL;
 917 }
 918
 919 static void hostfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 920 {
 921         char *s = nd_get_link(nd);
 922         if (!IS_ERR(s))
 923                 __putname(s);
 924 }
 925
 926 static const struct inode_operations hostfs_link_iops = {
 927         .readlink       = generic_readlink,
 928         .follow_link    = hostfs_follow_link,
 929         .put_link       = hostfs_put_link,
 930 };
 931
 932 static int hostfs_fill_sb_common(struct super_block *sb, void *d, int silent)
 933 {
 934         struct inode *root_inode;
 935         char *host_root_path, *req_root = d;
 936         int err;
 937
 938         sb->s_blocksize = 1024;
 939         sb->s_blocksize_bits = 10;
 940         sb->s_magic = HOSTFS_SUPER_MAGIC;
 941         sb->s_op = &hostfs_sbops;
 942         sb->s_d_op = &simple_dentry_operations;
 943         sb->s_maxbytes = MAX_LFS_FILESIZE;
 944
 945         /* NULL is printed as <NULL> by sprintf: avoid that. */
 946         if (req_root == NULL)
 947                 req_root = "";
 948
 949         err = -ENOMEM;
 950         sb->s_fs_info = host_root_path =
 951                 kmalloc(strlen(root_ino) + strlen(req_root) + 2, GFP_KERNEL);
 952         if (host_root_path == NULL)
 953                 goto out;
 954
 955         sprintf(host_root_path, "%s/%s", root_ino, req_root);
 956
 957         root_inode = new_inode(sb);
 958         if (!root_inode)
 959                 goto out;
 960
 961         err = read_name(root_inode, host_root_path);
 962         if (err)
 963                 goto out_put;
 964
 965         if (S_ISLNK(root_inode->i_mode)) {
 966                 char *name = follow_link(host_root_path);
 967                 if (IS_ERR(name))
 968                         err = PTR_ERR(name);
 969                 else
 970                         err = read_name(root_inode, name);
 971                 kfree(name);
 972                 if (err)
 973                         goto out_put;
 974         }
 975
 976         err = -ENOMEM;
 977         sb->s_root = d_make_root(root_inode);
 978         if (sb->s_root == NULL)
 979                 goto out;
 980
 981         return 0;
 982
 983 out_put:
 984         iput(root_inode);
 985 out:
 986         return err;
 987 }
 988
 989 static struct dentry *hostfs_read_sb(struct file_system_type *type,
 990                           int flags, const char *dev_name,
 991                           void *data)
 992 {
 993         return mount_nodev(type, flags, data, hostfs_fill_sb_common);
 994 }
 995
 996 static void hostfs_kill_sb(struct super_block *s)
 997 {
 998         kill_anon_super(s);
 999         kfree(s->s_fs_info);
1000 }
1001
1002 static struct file_system_type hostfs_type = {
1003         .owner          = THIS_MODULE,
1004         .name           = "hostfs",
1005         .mount          = hostfs_read_sb,
1006         .kill_sb        = hostfs_kill_sb,
1007         .fs_flags       = 0,
1008 };
1009 MODULE_ALIAS_FS("hostfs");
1010
1011 static int __init init_hostfs(void)
1012 {
1013         return register_filesystem(&hostfs_type);
1014 }
1015
1016 static void __exit exit_hostfs(void)
1017 {
1018         unregister_filesystem(&hostfs_type);
1019 }
1020
1021 module_init(init_hostfs)
1022 module_exit(exit_hostfs)
1023 MODULE_LICENSE("GPL");