linux/fs/super.c
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   1/*
   2 *  linux/fs/super.c
   3 *
   4 *  Copyright (C) 1991, 1992  Linus Torvalds
   5 *
   6 *  super.c contains code to handle: - mount structures
   7 *                                   - super-block tables
   8 *                                   - filesystem drivers list
   9 *                                   - mount system call
  10 *                                   - umount system call
  11 *                                   - ustat system call
  12 *
  13 * GK 2/5/95  -  Changed to support mounting the root fs via NFS
  14 *
  15 *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
  16 *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
  17 *  Added options to /proc/mounts:
  18 *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
  19 *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
  20 *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
  21 */
  22
  23#include <linux/module.h>
  24#include <linux/slab.h>
  25#include <linux/acct.h>
  26#include <linux/blkdev.h>
  27#include <linux/mount.h>
  28#include <linux/security.h>
  29#include <linux/writeback.h>            /* for the emergency remount stuff */
  30#include <linux/idr.h>
  31#include <linux/mutex.h>
  32#include <linux/backing-dev.h>
  33#include <linux/rculist_bl.h>
  34#include <linux/cleancache.h>
  35#include "internal.h"
  36
  37
  38LIST_HEAD(super_blocks);
  39DEFINE_SPINLOCK(sb_lock);
  40
  41/*
  42 * One thing we have to be careful of with a per-sb shrinker is that we don't
  43 * drop the last active reference to the superblock from within the shrinker.
  44 * If that happens we could trigger unregistering the shrinker from within the
  45 * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
  46 * take a passive reference to the superblock to avoid this from occurring.
  47 */
  48static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
  49{
  50        struct super_block *sb;
  51        int     fs_objects = 0;
  52        int     total_objects;
  53
  54        sb = container_of(shrink, struct super_block, s_shrink);
  55
  56        /*
  57         * Deadlock avoidance.  We may hold various FS locks, and we don't want
  58         * to recurse into the FS that called us in clear_inode() and friends..
  59         */
  60        if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
  61                return -1;
  62
  63        if (!grab_super_passive(sb))
  64                return !sc->nr_to_scan ? 0 : -1;
  65
  66        if (sb->s_op && sb->s_op->nr_cached_objects)
  67                fs_objects = sb->s_op->nr_cached_objects(sb);
  68
  69        total_objects = sb->s_nr_dentry_unused +
  70                        sb->s_nr_inodes_unused + fs_objects + 1;
  71
  72        if (sc->nr_to_scan) {
  73                int     dentries;
  74                int     inodes;
  75
  76                /* proportion the scan between the caches */
  77                dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
  78                                                        total_objects;
  79                inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
  80                                                        total_objects;
  81                if (fs_objects)
  82                        fs_objects = (sc->nr_to_scan * fs_objects) /
  83                                                        total_objects;
  84                /*
  85                 * prune the dcache first as the icache is pinned by it, then
  86                 * prune the icache, followed by the filesystem specific caches
  87                 */
  88                prune_dcache_sb(sb, dentries);
  89                prune_icache_sb(sb, inodes);
  90
  91                if (fs_objects && sb->s_op->free_cached_objects) {
  92                        sb->s_op->free_cached_objects(sb, fs_objects);
  93                        fs_objects = sb->s_op->nr_cached_objects(sb);
  94                }
  95                total_objects = sb->s_nr_dentry_unused +
  96                                sb->s_nr_inodes_unused + fs_objects;
  97        }
  98
  99        total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure;
 100        drop_super(sb);
 101        return total_objects;
 102}
 103
 104/**
 105 *      alloc_super     -       create new superblock
 106 *      @type:  filesystem type superblock should belong to
 107 *
 108 *      Allocates and initializes a new &struct super_block.  alloc_super()
 109 *      returns a pointer new superblock or %NULL if allocation had failed.
 110 */
 111static struct super_block *alloc_super(struct file_system_type *type)
 112{
 113        struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
 114        static const struct super_operations default_op;
 115
 116        if (s) {
 117                if (security_sb_alloc(s)) {
 118                        kfree(s);
 119                        s = NULL;
 120                        goto out;
 121                }
 122#ifdef CONFIG_SMP
 123                s->s_files = alloc_percpu(struct list_head);
 124                if (!s->s_files) {
 125                        security_sb_free(s);
 126                        kfree(s);
 127                        s = NULL;
 128                        goto out;
 129                } else {
 130                        int i;
 131
 132                        for_each_possible_cpu(i)
 133                                INIT_LIST_HEAD(per_cpu_ptr(s->s_files, i));
 134                }
 135#else
 136                INIT_LIST_HEAD(&s->s_files);
 137#endif
 138                s->s_bdi = &default_backing_dev_info;
 139                INIT_LIST_HEAD(&s->s_instances);
 140                INIT_HLIST_BL_HEAD(&s->s_anon);
 141                INIT_LIST_HEAD(&s->s_inodes);
 142                INIT_LIST_HEAD(&s->s_dentry_lru);
 143                INIT_LIST_HEAD(&s->s_inode_lru);
 144                spin_lock_init(&s->s_inode_lru_lock);
 145                init_rwsem(&s->s_umount);
 146                mutex_init(&s->s_lock);
 147                lockdep_set_class(&s->s_umount, &type->s_umount_key);
 148                /*
 149                 * The locking rules for s_lock are up to the
 150                 * filesystem. For example ext3fs has different
 151                 * lock ordering than usbfs:
 152                 */
 153                lockdep_set_class(&s->s_lock, &type->s_lock_key);
 154                /*
 155                 * sget() can have s_umount recursion.
 156                 *
 157                 * When it cannot find a suitable sb, it allocates a new
 158                 * one (this one), and tries again to find a suitable old
 159                 * one.
 160                 *
 161                 * In case that succeeds, it will acquire the s_umount
 162                 * lock of the old one. Since these are clearly distrinct
 163                 * locks, and this object isn't exposed yet, there's no
 164                 * risk of deadlocks.
 165                 *
 166                 * Annotate this by putting this lock in a different
 167                 * subclass.
 168                 */
 169                down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
 170                s->s_count = 1;
 171                atomic_set(&s->s_active, 1);
 172                mutex_init(&s->s_vfs_rename_mutex);
 173                lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
 174                mutex_init(&s->s_dquot.dqio_mutex);
 175                mutex_init(&s->s_dquot.dqonoff_mutex);
 176                init_rwsem(&s->s_dquot.dqptr_sem);
 177                init_waitqueue_head(&s->s_wait_unfrozen);
 178                s->s_maxbytes = MAX_NON_LFS;
 179                s->s_op = &default_op;
 180                s->s_time_gran = 1000000000;
 181                s->cleancache_poolid = -1;
 182
 183                s->s_shrink.seeks = DEFAULT_SEEKS;
 184                s->s_shrink.shrink = prune_super;
 185                s->s_shrink.batch = 1024;
 186        }
 187out:
 188        return s;
 189}
 190
 191/**
 192 *      destroy_super   -       frees a superblock
 193 *      @s: superblock to free
 194 *
 195 *      Frees a superblock.
 196 */
 197static inline void destroy_super(struct super_block *s)
 198{
 199#ifdef CONFIG_SMP
 200        free_percpu(s->s_files);
 201#endif
 202        security_sb_free(s);
 203        kfree(s->s_subtype);
 204        kfree(s->s_options);
 205        kfree(s);
 206}
 207
 208/* Superblock refcounting  */
 209
 210/*
 211 * Drop a superblock's refcount.  The caller must hold sb_lock.
 212 */
 213void __put_super(struct super_block *sb)
 214{
 215        if (!--sb->s_count) {
 216                list_del_init(&sb->s_list);
 217                destroy_super(sb);
 218        }
 219}
 220
 221/**
 222 *      put_super       -       drop a temporary reference to superblock
 223 *      @sb: superblock in question
 224 *
 225 *      Drops a temporary reference, frees superblock if there's no
 226 *      references left.
 227 */
 228void put_super(struct super_block *sb)
 229{
 230        spin_lock(&sb_lock);
 231        __put_super(sb);
 232        spin_unlock(&sb_lock);
 233}
 234
 235
 236/**
 237 *      deactivate_locked_super -       drop an active reference to superblock
 238 *      @s: superblock to deactivate
 239 *
 240 *      Drops an active reference to superblock, converting it into a temprory
 241 *      one if there is no other active references left.  In that case we
 242 *      tell fs driver to shut it down and drop the temporary reference we
 243 *      had just acquired.
 244 *
 245 *      Caller holds exclusive lock on superblock; that lock is released.
 246 */
 247void deactivate_locked_super(struct super_block *s)
 248{
 249        struct file_system_type *fs = s->s_type;
 250        if (atomic_dec_and_test(&s->s_active)) {
 251                cleancache_flush_fs(s);
 252                fs->kill_sb(s);
 253
 254                /* caches are now gone, we can safely kill the shrinker now */
 255                unregister_shrinker(&s->s_shrink);
 256
 257                /*
 258                 * We need to call rcu_barrier so all the delayed rcu free
 259                 * inodes are flushed before we release the fs module.
 260                 */
 261                rcu_barrier();
 262                put_filesystem(fs);
 263                put_super(s);
 264        } else {
 265                up_write(&s->s_umount);
 266        }
 267}
 268
 269EXPORT_SYMBOL(deactivate_locked_super);
 270
 271/**
 272 *      deactivate_super        -       drop an active reference to superblock
 273 *      @s: superblock to deactivate
 274 *
 275 *      Variant of deactivate_locked_super(), except that superblock is *not*
 276 *      locked by caller.  If we are going to drop the final active reference,
 277 *      lock will be acquired prior to that.
 278 */
 279void deactivate_super(struct super_block *s)
 280{
 281        if (!atomic_add_unless(&s->s_active, -1, 1)) {
 282                down_write(&s->s_umount);
 283                deactivate_locked_super(s);
 284        }
 285}
 286
 287EXPORT_SYMBOL(deactivate_super);
 288
 289/**
 290 *      grab_super - acquire an active reference
 291 *      @s: reference we are trying to make active
 292 *
 293 *      Tries to acquire an active reference.  grab_super() is used when we
 294 *      had just found a superblock in super_blocks or fs_type->fs_supers
 295 *      and want to turn it into a full-blown active reference.  grab_super()
 296 *      is called with sb_lock held and drops it.  Returns 1 in case of
 297 *      success, 0 if we had failed (superblock contents was already dead or
 298 *      dying when grab_super() had been called).
 299 */
 300static int grab_super(struct super_block *s) __releases(sb_lock)
 301{
 302        if (atomic_inc_not_zero(&s->s_active)) {
 303                spin_unlock(&sb_lock);
 304                return 1;
 305        }
 306        /* it's going away */
 307        s->s_count++;
 308        spin_unlock(&sb_lock);
 309        /* wait for it to die */
 310        down_write(&s->s_umount);
 311        up_write(&s->s_umount);
 312        put_super(s);
 313        return 0;
 314}
 315
 316/*
 317 *      grab_super_passive - acquire a passive reference
 318 *      @s: reference we are trying to grab
 319 *
 320 *      Tries to acquire a passive reference. This is used in places where we
 321 *      cannot take an active reference but we need to ensure that the
 322 *      superblock does not go away while we are working on it. It returns
 323 *      false if a reference was not gained, and returns true with the s_umount
 324 *      lock held in read mode if a reference is gained. On successful return,
 325 *      the caller must drop the s_umount lock and the passive reference when
 326 *      done.
 327 */
 328bool grab_super_passive(struct super_block *sb)
 329{
 330        spin_lock(&sb_lock);
 331        if (list_empty(&sb->s_instances)) {
 332                spin_unlock(&sb_lock);
 333                return false;
 334        }
 335
 336        sb->s_count++;
 337        spin_unlock(&sb_lock);
 338
 339        if (down_read_trylock(&sb->s_umount)) {
 340                if (sb->s_root)
 341                        return true;
 342                up_read(&sb->s_umount);
 343        }
 344
 345        put_super(sb);
 346        return false;
 347}
 348
 349/*
 350 * Superblock locking.  We really ought to get rid of these two.
 351 */
 352void lock_super(struct super_block * sb)
 353{
 354        mutex_lock(&sb->s_lock);
 355}
 356
 357void unlock_super(struct super_block * sb)
 358{
 359        mutex_unlock(&sb->s_lock);
 360}
 361
 362EXPORT_SYMBOL(lock_super);
 363EXPORT_SYMBOL(unlock_super);
 364
 365/**
 366 *      generic_shutdown_super  -       common helper for ->kill_sb()
 367 *      @sb: superblock to kill
 368 *
 369 *      generic_shutdown_super() does all fs-independent work on superblock
 370 *      shutdown.  Typical ->kill_sb() should pick all fs-specific objects
 371 *      that need destruction out of superblock, call generic_shutdown_super()
 372 *      and release aforementioned objects.  Note: dentries and inodes _are_
 373 *      taken care of and do not need specific handling.
 374 *
 375 *      Upon calling this function, the filesystem may no longer alter or
 376 *      rearrange the set of dentries belonging to this super_block, nor may it
 377 *      change the attachments of dentries to inodes.
 378 */
 379void generic_shutdown_super(struct super_block *sb)
 380{
 381        const struct super_operations *sop = sb->s_op;
 382
 383        if (sb->s_root) {
 384                shrink_dcache_for_umount(sb);
 385                sync_filesystem(sb);
 386                sb->s_flags &= ~MS_ACTIVE;
 387
 388                fsnotify_unmount_inodes(&sb->s_inodes);
 389
 390                evict_inodes(sb);
 391
 392                if (sop->put_super)
 393                        sop->put_super(sb);
 394
 395                if (!list_empty(&sb->s_inodes)) {
 396                        printk("VFS: Busy inodes after unmount of %s. "
 397                           "Self-destruct in 5 seconds.  Have a nice day...\n",
 398                           sb->s_id);
 399                }
 400        }
 401        spin_lock(&sb_lock);
 402        /* should be initialized for __put_super_and_need_restart() */
 403        list_del_init(&sb->s_instances);
 404        spin_unlock(&sb_lock);
 405        up_write(&sb->s_umount);
 406}
 407
 408EXPORT_SYMBOL(generic_shutdown_super);
 409
 410/**
 411 *      sget    -       find or create a superblock
 412 *      @type:  filesystem type superblock should belong to
 413 *      @test:  comparison callback
 414 *      @set:   setup callback
 415 *      @data:  argument to each of them
 416 */
 417struct super_block *sget(struct file_system_type *type,
 418                        int (*test)(struct super_block *,void *),
 419                        int (*set)(struct super_block *,void *),
 420                        void *data)
 421{
 422        struct super_block *s = NULL;
 423        struct super_block *old;
 424        int err;
 425
 426retry:
 427        spin_lock(&sb_lock);
 428        if (test) {
 429                list_for_each_entry(old, &type->fs_supers, s_instances) {
 430                        if (!test(old, data))
 431                                continue;
 432                        if (!grab_super(old))
 433                                goto retry;
 434                        if (s) {
 435                                up_write(&s->s_umount);
 436                                destroy_super(s);
 437                                s = NULL;
 438                        }
 439                        down_write(&old->s_umount);
 440                        if (unlikely(!(old->s_flags & MS_BORN))) {
 441                                deactivate_locked_super(old);
 442                                goto retry;
 443                        }
 444                        return old;
 445                }
 446        }
 447        if (!s) {
 448                spin_unlock(&sb_lock);
 449                s = alloc_super(type);
 450                if (!s)
 451                        return ERR_PTR(-ENOMEM);
 452                goto retry;
 453        }
 454                
 455        err = set(s, data);
 456        if (err) {
 457                spin_unlock(&sb_lock);
 458                up_write(&s->s_umount);
 459                destroy_super(s);
 460                return ERR_PTR(err);
 461        }
 462        s->s_type = type;
 463        strlcpy(s->s_id, type->name, sizeof(s->s_id));
 464        list_add_tail(&s->s_list, &super_blocks);
 465        list_add(&s->s_instances, &type->fs_supers);
 466        spin_unlock(&sb_lock);
 467        get_filesystem(type);
 468        register_shrinker(&s->s_shrink);
 469        return s;
 470}
 471
 472EXPORT_SYMBOL(sget);
 473
 474void drop_super(struct super_block *sb)
 475{
 476        up_read(&sb->s_umount);
 477        put_super(sb);
 478}
 479
 480EXPORT_SYMBOL(drop_super);
 481
 482/**
 483 * sync_supers - helper for periodic superblock writeback
 484 *
 485 * Call the write_super method if present on all dirty superblocks in
 486 * the system.  This is for the periodic writeback used by most older
 487 * filesystems.  For data integrity superblock writeback use
 488 * sync_filesystems() instead.
 489 *
 490 * Note: check the dirty flag before waiting, so we don't
 491 * hold up the sync while mounting a device. (The newly
 492 * mounted device won't need syncing.)
 493 */
 494void sync_supers(void)
 495{
 496        struct super_block *sb, *p = NULL;
 497
 498        spin_lock(&sb_lock);
 499        list_for_each_entry(sb, &super_blocks, s_list) {
 500                if (list_empty(&sb->s_instances))
 501                        continue;
 502                if (sb->s_op->write_super && sb->s_dirt) {
 503                        sb->s_count++;
 504                        spin_unlock(&sb_lock);
 505
 506                        down_read(&sb->s_umount);
 507                        if (sb->s_root && sb->s_dirt)
 508                                sb->s_op->write_super(sb);
 509                        up_read(&sb->s_umount);
 510
 511                        spin_lock(&sb_lock);
 512                        if (p)
 513                                __put_super(p);
 514                        p = sb;
 515                }
 516        }
 517        if (p)
 518                __put_super(p);
 519        spin_unlock(&sb_lock);
 520}
 521
 522/**
 523 *      iterate_supers - call function for all active superblocks
 524 *      @f: function to call
 525 *      @arg: argument to pass to it
 526 *
 527 *      Scans the superblock list and calls given function, passing it
 528 *      locked superblock and given argument.
 529 */
 530void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 531{
 532        struct super_block *sb, *p = NULL;
 533
 534        spin_lock(&sb_lock);
 535        list_for_each_entry(sb, &super_blocks, s_list) {
 536                if (list_empty(&sb->s_instances))
 537                        continue;
 538                sb->s_count++;
 539                spin_unlock(&sb_lock);
 540
 541                down_read(&sb->s_umount);
 542                if (sb->s_root)
 543                        f(sb, arg);
 544                up_read(&sb->s_umount);
 545
 546                spin_lock(&sb_lock);
 547                if (p)
 548                        __put_super(p);
 549                p = sb;
 550        }
 551        if (p)
 552                __put_super(p);
 553        spin_unlock(&sb_lock);
 554}
 555
 556/**
 557 *      iterate_supers_type - call function for superblocks of given type
 558 *      @type: fs type
 559 *      @f: function to call
 560 *      @arg: argument to pass to it
 561 *
 562 *      Scans the superblock list and calls given function, passing it
 563 *      locked superblock and given argument.
 564 */
 565void iterate_supers_type(struct file_system_type *type,
 566        void (*f)(struct super_block *, void *), void *arg)
 567{
 568        struct super_block *sb, *p = NULL;
 569
 570        spin_lock(&sb_lock);
 571        list_for_each_entry(sb, &type->fs_supers, s_instances) {
 572                sb->s_count++;
 573                spin_unlock(&sb_lock);
 574
 575                down_read(&sb->s_umount);
 576                if (sb->s_root)
 577                        f(sb, arg);
 578                up_read(&sb->s_umount);
 579
 580                spin_lock(&sb_lock);
 581                if (p)
 582                        __put_super(p);
 583                p = sb;
 584        }
 585        if (p)
 586                __put_super(p);
 587        spin_unlock(&sb_lock);
 588}
 589
 590EXPORT_SYMBOL(iterate_supers_type);
 591
 592/**
 593 *      get_super - get the superblock of a device
 594 *      @bdev: device to get the superblock for
 595 *      
 596 *      Scans the superblock list and finds the superblock of the file system
 597 *      mounted on the device given. %NULL is returned if no match is found.
 598 */
 599
 600struct super_block *get_super(struct block_device *bdev)
 601{
 602        struct super_block *sb;
 603
 604        if (!bdev)
 605                return NULL;
 606
 607        spin_lock(&sb_lock);
 608rescan:
 609        list_for_each_entry(sb, &super_blocks, s_list) {
 610                if (list_empty(&sb->s_instances))
 611                        continue;
 612                if (sb->s_bdev == bdev) {
 613                        sb->s_count++;
 614                        spin_unlock(&sb_lock);
 615                        down_read(&sb->s_umount);
 616                        /* still alive? */
 617                        if (sb->s_root)
 618                                return sb;
 619                        up_read(&sb->s_umount);
 620                        /* nope, got unmounted */
 621                        spin_lock(&sb_lock);
 622                        __put_super(sb);
 623                        goto rescan;
 624                }
 625        }
 626        spin_unlock(&sb_lock);
 627        return NULL;
 628}
 629
 630EXPORT_SYMBOL(get_super);
 631
 632/**
 633 * get_active_super - get an active reference to the superblock of a device
 634 * @bdev: device to get the superblock for
 635 *
 636 * Scans the superblock list and finds the superblock of the file system
 637 * mounted on the device given.  Returns the superblock with an active
 638 * reference or %NULL if none was found.
 639 */
 640struct super_block *get_active_super(struct block_device *bdev)
 641{
 642        struct super_block *sb;
 643
 644        if (!bdev)
 645                return NULL;
 646
 647restart:
 648        spin_lock(&sb_lock);
 649        list_for_each_entry(sb, &super_blocks, s_list) {
 650                if (list_empty(&sb->s_instances))
 651                        continue;
 652                if (sb->s_bdev == bdev) {
 653                        if (grab_super(sb)) /* drops sb_lock */
 654                                return sb;
 655                        else
 656                                goto restart;
 657                }
 658        }
 659        spin_unlock(&sb_lock);
 660        return NULL;
 661}
 662 
 663struct super_block *user_get_super(dev_t dev)
 664{
 665        struct super_block *sb;
 666
 667        spin_lock(&sb_lock);
 668rescan:
 669        list_for_each_entry(sb, &super_blocks, s_list) {
 670                if (list_empty(&sb->s_instances))
 671                        continue;
 672                if (sb->s_dev ==  dev) {
 673                        sb->s_count++;
 674                        spin_unlock(&sb_lock);
 675                        down_read(&sb->s_umount);
 676                        /* still alive? */
 677                        if (sb->s_root)
 678                                return sb;
 679                        up_read(&sb->s_umount);
 680                        /* nope, got unmounted */
 681                        spin_lock(&sb_lock);
 682                        __put_super(sb);
 683                        goto rescan;
 684                }
 685        }
 686        spin_unlock(&sb_lock);
 687        return NULL;
 688}
 689
 690/**
 691 *      do_remount_sb - asks filesystem to change mount options.
 692 *      @sb:    superblock in question
 693 *      @flags: numeric part of options
 694 *      @data:  the rest of options
 695 *      @force: whether or not to force the change
 696 *
 697 *      Alters the mount options of a mounted file system.
 698 */
 699int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 700{
 701        int retval;
 702        int remount_ro;
 703
 704        if (sb->s_frozen != SB_UNFROZEN)
 705                return -EBUSY;
 706
 707#ifdef CONFIG_BLOCK
 708        if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
 709                return -EACCES;
 710#endif
 711
 712        if (flags & MS_RDONLY)
 713                acct_auto_close(sb);
 714        shrink_dcache_sb(sb);
 715        sync_filesystem(sb);
 716
 717        remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
 718
 719        /* If we are remounting RDONLY and current sb is read/write,
 720           make sure there are no rw files opened */
 721        if (remount_ro) {
 722                if (force)
 723                        mark_files_ro(sb);
 724                else if (!fs_may_remount_ro(sb))
 725                        return -EBUSY;
 726        }
 727
 728        if (sb->s_op->remount_fs) {
 729                retval = sb->s_op->remount_fs(sb, &flags, data);
 730                if (retval)
 731                        return retval;
 732        }
 733        sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
 734
 735        /*
 736         * Some filesystems modify their metadata via some other path than the
 737         * bdev buffer cache (eg. use a private mapping, or directories in
 738         * pagecache, etc). Also file data modifications go via their own
 739         * mappings. So If we try to mount readonly then copy the filesystem
 740         * from bdev, we could get stale data, so invalidate it to give a best
 741         * effort at coherency.
 742         */
 743        if (remount_ro && sb->s_bdev)
 744                invalidate_bdev(sb->s_bdev);
 745        return 0;
 746}
 747
 748static void do_emergency_remount(struct work_struct *work)
 749{
 750        struct super_block *sb, *p = NULL;
 751
 752        spin_lock(&sb_lock);
 753        list_for_each_entry(sb, &super_blocks, s_list) {
 754                if (list_empty(&sb->s_instances))
 755                        continue;
 756                sb->s_count++;
 757                spin_unlock(&sb_lock);
 758                down_write(&sb->s_umount);
 759                if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
 760                        /*
 761                         * What lock protects sb->s_flags??
 762                         */
 763                        do_remount_sb(sb, MS_RDONLY, NULL, 1);
 764                }
 765                up_write(&sb->s_umount);
 766                spin_lock(&sb_lock);
 767                if (p)
 768                        __put_super(p);
 769                p = sb;
 770        }
 771        if (p)
 772                __put_super(p);
 773        spin_unlock(&sb_lock);
 774        kfree(work);
 775        printk("Emergency Remount complete\n");
 776}
 777
 778void emergency_remount(void)
 779{
 780        struct work_struct *work;
 781
 782        work = kmalloc(sizeof(*work), GFP_ATOMIC);
 783        if (work) {
 784                INIT_WORK(work, do_emergency_remount);
 785                schedule_work(work);
 786        }
 787}
 788
 789/*
 790 * Unnamed block devices are dummy devices used by virtual
 791 * filesystems which don't use real block-devices.  -- jrs
 792 */
 793
 794static DEFINE_IDA(unnamed_dev_ida);
 795static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
 796static int unnamed_dev_start = 0; /* don't bother trying below it */
 797
 798int get_anon_bdev(dev_t *p)
 799{
 800        int dev;
 801        int error;
 802
 803 retry:
 804        if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
 805                return -ENOMEM;
 806        spin_lock(&unnamed_dev_lock);
 807        error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
 808        if (!error)
 809                unnamed_dev_start = dev + 1;
 810        spin_unlock(&unnamed_dev_lock);
 811        if (error == -EAGAIN)
 812                /* We raced and lost with another CPU. */
 813                goto retry;
 814        else if (error)
 815                return -EAGAIN;
 816
 817        if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) {
 818                spin_lock(&unnamed_dev_lock);
 819                ida_remove(&unnamed_dev_ida, dev);
 820                if (unnamed_dev_start > dev)
 821                        unnamed_dev_start = dev;
 822                spin_unlock(&unnamed_dev_lock);
 823                return -EMFILE;
 824        }
 825        *p = MKDEV(0, dev & MINORMASK);
 826        return 0;
 827}
 828EXPORT_SYMBOL(get_anon_bdev);
 829
 830void free_anon_bdev(dev_t dev)
 831{
 832        int slot = MINOR(dev);
 833        spin_lock(&unnamed_dev_lock);
 834        ida_remove(&unnamed_dev_ida, slot);
 835        if (slot < unnamed_dev_start)
 836                unnamed_dev_start = slot;
 837        spin_unlock(&unnamed_dev_lock);
 838}
 839EXPORT_SYMBOL(free_anon_bdev);
 840
 841int set_anon_super(struct super_block *s, void *data)
 842{
 843        int error = get_anon_bdev(&s->s_dev);
 844        if (!error)
 845                s->s_bdi = &noop_backing_dev_info;
 846        return error;
 847}
 848
 849EXPORT_SYMBOL(set_anon_super);
 850
 851void kill_anon_super(struct super_block *sb)
 852{
 853        dev_t dev = sb->s_dev;
 854        generic_shutdown_super(sb);
 855        free_anon_bdev(dev);
 856}
 857
 858EXPORT_SYMBOL(kill_anon_super);
 859
 860void kill_litter_super(struct super_block *sb)
 861{
 862        if (sb->s_root)
 863                d_genocide(sb->s_root);
 864        kill_anon_super(sb);
 865}
 866
 867EXPORT_SYMBOL(kill_litter_super);
 868
 869static int ns_test_super(struct super_block *sb, void *data)
 870{
 871        return sb->s_fs_info == data;
 872}
 873
 874static int ns_set_super(struct super_block *sb, void *data)
 875{
 876        sb->s_fs_info = data;
 877        return set_anon_super(sb, NULL);
 878}
 879
 880struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
 881        void *data, int (*fill_super)(struct super_block *, void *, int))
 882{
 883        struct super_block *sb;
 884
 885        sb = sget(fs_type, ns_test_super, ns_set_super, data);
 886        if (IS_ERR(sb))
 887                return ERR_CAST(sb);
 888
 889        if (!sb->s_root) {
 890                int err;
 891                sb->s_flags = flags;
 892                err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
 893                if (err) {
 894                        deactivate_locked_super(sb);
 895                        return ERR_PTR(err);
 896                }
 897
 898                sb->s_flags |= MS_ACTIVE;
 899        }
 900
 901        return dget(sb->s_root);
 902}
 903
 904EXPORT_SYMBOL(mount_ns);
 905
 906#ifdef CONFIG_BLOCK
 907static int set_bdev_super(struct super_block *s, void *data)
 908{
 909        s->s_bdev = data;
 910        s->s_dev = s->s_bdev->bd_dev;
 911
 912        /*
 913         * We set the bdi here to the queue backing, file systems can
 914         * overwrite this in ->fill_super()
 915         */
 916        s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
 917        return 0;
 918}
 919
 920static int test_bdev_super(struct super_block *s, void *data)
 921{
 922        return (void *)s->s_bdev == data;
 923}
 924
 925struct dentry *mount_bdev(struct file_system_type *fs_type,
 926        int flags, const char *dev_name, void *data,
 927        int (*fill_super)(struct super_block *, void *, int))
 928{
 929        struct block_device *bdev;
 930        struct super_block *s;
 931        fmode_t mode = FMODE_READ | FMODE_EXCL;
 932        int error = 0;
 933
 934        if (!(flags & MS_RDONLY))
 935                mode |= FMODE_WRITE;
 936
 937        bdev = blkdev_get_by_path(dev_name, mode, fs_type);
 938        if (IS_ERR(bdev))
 939                return ERR_CAST(bdev);
 940
 941        /*
 942         * once the super is inserted into the list by sget, s_umount
 943         * will protect the lockfs code from trying to start a snapshot
 944         * while we are mounting
 945         */
 946        mutex_lock(&bdev->bd_fsfreeze_mutex);
 947        if (bdev->bd_fsfreeze_count > 0) {
 948                mutex_unlock(&bdev->bd_fsfreeze_mutex);
 949                error = -EBUSY;
 950                goto error_bdev;
 951        }
 952        s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
 953        mutex_unlock(&bdev->bd_fsfreeze_mutex);
 954        if (IS_ERR(s))
 955                goto error_s;
 956
 957        if (s->s_root) {
 958                if ((flags ^ s->s_flags) & MS_RDONLY) {
 959                        deactivate_locked_super(s);
 960                        error = -EBUSY;
 961                        goto error_bdev;
 962                }
 963
 964                /*
 965                 * s_umount nests inside bd_mutex during
 966                 * __invalidate_device().  blkdev_put() acquires
 967                 * bd_mutex and can't be called under s_umount.  Drop
 968                 * s_umount temporarily.  This is safe as we're
 969                 * holding an active reference.
 970                 */
 971                up_write(&s->s_umount);
 972                blkdev_put(bdev, mode);
 973                down_write(&s->s_umount);
 974        } else {
 975                char b[BDEVNAME_SIZE];
 976
 977                s->s_flags = flags | MS_NOSEC;
 978                s->s_mode = mode;
 979                strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
 980                sb_set_blocksize(s, block_size(bdev));
 981                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
 982                if (error) {
 983                        deactivate_locked_super(s);
 984                        goto error;
 985                }
 986
 987                s->s_flags |= MS_ACTIVE;
 988                bdev->bd_super = s;
 989        }
 990
 991        return dget(s->s_root);
 992
 993error_s:
 994        error = PTR_ERR(s);
 995error_bdev:
 996        blkdev_put(bdev, mode);
 997error:
 998        return ERR_PTR(error);
 999}
1000EXPORT_SYMBOL(mount_bdev);
1001
1002void kill_block_super(struct super_block *sb)
1003{
1004        struct block_device *bdev = sb->s_bdev;
1005        fmode_t mode = sb->s_mode;
1006
1007        bdev->bd_super = NULL;
1008        generic_shutdown_super(sb);
1009        sync_blockdev(bdev);
1010        WARN_ON_ONCE(!(mode & FMODE_EXCL));
1011        blkdev_put(bdev, mode | FMODE_EXCL);
1012}
1013
1014EXPORT_SYMBOL(kill_block_super);
1015#endif
1016
1017struct dentry *mount_nodev(struct file_system_type *fs_type,
1018        int flags, void *data,
1019        int (*fill_super)(struct super_block *, void *, int))
1020{
1021        int error;
1022        struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
1023
1024        if (IS_ERR(s))
1025                return ERR_CAST(s);
1026
1027        s->s_flags = flags;
1028
1029        error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1030        if (error) {
1031                deactivate_locked_super(s);
1032                return ERR_PTR(error);
1033        }
1034        s->s_flags |= MS_ACTIVE;
1035        return dget(s->s_root);
1036}
1037EXPORT_SYMBOL(mount_nodev);
1038
1039static int compare_single(struct super_block *s, void *p)
1040{
1041        return 1;
1042}
1043
1044struct dentry *mount_single(struct file_system_type *fs_type,
1045        int flags, void *data,
1046        int (*fill_super)(struct super_block *, void *, int))
1047{
1048        struct super_block *s;
1049        int error;
1050
1051        s = sget(fs_type, compare_single, set_anon_super, NULL);
1052        if (IS_ERR(s))
1053                return ERR_CAST(s);
1054        if (!s->s_root) {
1055                s->s_flags = flags;
1056                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1057                if (error) {
1058                        deactivate_locked_super(s);
1059                        return ERR_PTR(error);
1060                }
1061                s->s_flags |= MS_ACTIVE;
1062        } else {
1063                do_remount_sb(s, flags, data, 0);
1064        }
1065        return dget(s->s_root);
1066}
1067EXPORT_SYMBOL(mount_single);
1068
1069struct dentry *
1070mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
1071{
1072        struct dentry *root;
1073        struct super_block *sb;
1074        char *secdata = NULL;
1075        int error = -ENOMEM;
1076
1077        if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1078                secdata = alloc_secdata();
1079                if (!secdata)
1080                        goto out;
1081
1082                error = security_sb_copy_data(data, secdata);
1083                if (error)
1084                        goto out_free_secdata;
1085        }
1086
1087        root = type->mount(type, flags, name, data);
1088        if (IS_ERR(root)) {
1089                error = PTR_ERR(root);
1090                goto out_free_secdata;
1091        }
1092        sb = root->d_sb;
1093        BUG_ON(!sb);
1094        WARN_ON(!sb->s_bdi);
1095        WARN_ON(sb->s_bdi == &default_backing_dev_info);
1096        sb->s_flags |= MS_BORN;
1097
1098        error = security_sb_kern_mount(sb, flags, secdata);
1099        if (error)
1100                goto out_sb;
1101
1102        /*
1103         * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1104         * but s_maxbytes was an unsigned long long for many releases. Throw
1105         * this warning for a little while to try and catch filesystems that
1106         * violate this rule.
1107         */
1108        WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1109                "negative value (%lld)\n", type->name, sb->s_maxbytes);
1110
1111        up_write(&sb->s_umount);
1112        free_secdata(secdata);
1113        return root;
1114out_sb:
1115        dput(root);
1116        deactivate_locked_super(sb);
1117out_free_secdata:
1118        free_secdata(secdata);
1119out:
1120        return ERR_PTR(error);
1121}
1122
1123/**
1124 * freeze_super - lock the filesystem and force it into a consistent state
1125 * @sb: the super to lock
1126 *
1127 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1128 * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1129 * -EBUSY.
1130 */
1131int freeze_super(struct super_block *sb)
1132{
1133        int ret;
1134
1135        atomic_inc(&sb->s_active);
1136        down_write(&sb->s_umount);
1137        if (sb->s_frozen) {
1138                deactivate_locked_super(sb);
1139                return -EBUSY;
1140        }
1141
1142        if (sb->s_flags & MS_RDONLY) {
1143                sb->s_frozen = SB_FREEZE_TRANS;
1144                smp_wmb();
1145                up_write(&sb->s_umount);
1146                return 0;
1147        }
1148
1149        sb->s_frozen = SB_FREEZE_WRITE;
1150        smp_wmb();
1151
1152        sync_filesystem(sb);
1153
1154        sb->s_frozen = SB_FREEZE_TRANS;
1155        smp_wmb();
1156
1157        sync_blockdev(sb->s_bdev);
1158        if (sb->s_op->freeze_fs) {
1159                ret = sb->s_op->freeze_fs(sb);
1160                if (ret) {
1161                        printk(KERN_ERR
1162                                "VFS:Filesystem freeze failed\n");
1163                        sb->s_frozen = SB_UNFROZEN;
1164                        deactivate_locked_super(sb);
1165                        return ret;
1166                }
1167        }
1168        up_write(&sb->s_umount);
1169        return 0;
1170}
1171EXPORT_SYMBOL(freeze_super);
1172
1173/**
1174 * thaw_super -- unlock filesystem
1175 * @sb: the super to thaw
1176 *
1177 * Unlocks the filesystem and marks it writeable again after freeze_super().
1178 */
1179int thaw_super(struct super_block *sb)
1180{
1181        int error;
1182
1183        down_write(&sb->s_umount);
1184        if (sb->s_frozen == SB_UNFROZEN) {
1185                up_write(&sb->s_umount);
1186                return -EINVAL;
1187        }
1188
1189        if (sb->s_flags & MS_RDONLY)
1190                goto out;
1191
1192        if (sb->s_op->unfreeze_fs) {
1193                error = sb->s_op->unfreeze_fs(sb);
1194                if (error) {
1195                        printk(KERN_ERR
1196                                "VFS:Filesystem thaw failed\n");
1197                        sb->s_frozen = SB_FREEZE_TRANS;
1198                        up_write(&sb->s_umount);
1199                        return error;
1200                }
1201        }
1202
1203out:
1204        sb->s_frozen = SB_UNFROZEN;
1205        smp_wmb();
1206        wake_up(&sb->s_wait_unfrozen);
1207        deactivate_locked_super(sb);
1208
1209        return 0;
1210}
1211EXPORT_SYMBOL(thaw_super);
1212
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