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