1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 *  linux/fs/super.c
   4 *
   5 *  Copyright (C) 1991, 1992  Linus Torvalds
   6 *
   7 *  super.c contains code to handle: - mount structures
   8 *                                   - super-block tables
   9 *                                   - filesystem drivers list
  10 *                                   - mount system call
  11 *                                   - umount system call
  12 *                                   - ustat system call
  13 *
  14 * GK 2/5/95  -  Changed to support mounting the root fs via NFS
  15 *
  16 *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
  17 *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
  18 *  Added options to /proc/mounts:
  19 *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
  20 *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
  21 *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
  22 */
  23
  24#include <linux/export.h>
  25#include <linux/slab.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 <linux/fscrypt.h>
  36#include <linux/fsnotify.h>
  37#include <linux/lockdep.h>
  38#include <linux/user_namespace.h>
  39#include <linux/fs_context.h>
  40#include <uapi/linux/mount.h>
  41#include "internal.h"
  42
  43static int thaw_super_locked(struct super_block *sb);
  44
  45static LIST_HEAD(super_blocks);
  46static DEFINE_SPINLOCK(sb_lock);
  47
  48static char *sb_writers_name[SB_FREEZE_LEVELS] = {
  49	"sb_writers",
  50	"sb_pagefaults",
  51	"sb_internal",
  52};
  53
  54/*
  55 * One thing we have to be careful of with a per-sb shrinker is that we don't
  56 * drop the last active reference to the superblock from within the shrinker.
  57 * If that happens we could trigger unregistering the shrinker from within the
  58 * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
  59 * take a passive reference to the superblock to avoid this from occurring.
  60 */
  61static unsigned long super_cache_scan(struct shrinker *shrink,
  62				      struct shrink_control *sc)
  63{
  64	struct super_block *sb;
  65	long	fs_objects = 0;
  66	long	total_objects;
  67	long	freed = 0;
  68	long	dentries;
  69	long	inodes;
  70
  71	sb = container_of(shrink, struct super_block, s_shrink);
  72
  73	/*
  74	 * Deadlock avoidance.  We may hold various FS locks, and we don't want
  75	 * to recurse into the FS that called us in clear_inode() and friends..
  76	 */
  77	if (!(sc->gfp_mask & __GFP_FS))
  78		return SHRINK_STOP;
  79
  80	if (!trylock_super(sb))
  81		return SHRINK_STOP;
  82
  83	if (sb->s_op->nr_cached_objects)
  84		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
  85
  86	inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
  87	dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc);
  88	total_objects = dentries + inodes + fs_objects + 1;
  89	if (!total_objects)
  90		total_objects = 1;
  91
  92	/* proportion the scan between the caches */
  93	dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);
  94	inodes = mult_frac(sc->nr_to_scan, inodes, total_objects);
  95	fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
  96
  97	/*
  98	 * prune the dcache first as the icache is pinned by it, then
  99	 * prune the icache, followed by the filesystem specific caches
 100	 *
 101	 * Ensure that we always scan at least one object - memcg kmem
 102	 * accounting uses this to fully empty the caches.
 103	 */
 104	sc->nr_to_scan = dentries + 1;
 105	freed = prune_dcache_sb(sb, sc);
 106	sc->nr_to_scan = inodes + 1;
 107	freed += prune_icache_sb(sb, sc);
 108
 109	if (fs_objects) {
 110		sc->nr_to_scan = fs_objects + 1;
 111		freed += sb->s_op->free_cached_objects(sb, sc);
 112	}
 113
 114	up_read(&sb->s_umount);
 115	return freed;
 116}
 117
 118static unsigned long super_cache_count(struct shrinker *shrink,
 119				       struct shrink_control *sc)
 120{
 121	struct super_block *sb;
 122	long	total_objects = 0;
 123
 124	sb = container_of(shrink, struct super_block, s_shrink);
 125
 126	/*
 127	 * We don't call trylock_super() here as it is a scalability bottleneck,
 128	 * so we're exposed to partial setup state. The shrinker rwsem does not
 129	 * protect filesystem operations backing list_lru_shrink_count() or
 130	 * s_op->nr_cached_objects(). Counts can change between
 131	 * super_cache_count and super_cache_scan, so we really don't need locks
 132	 * here.
 133	 *
 134	 * However, if we are currently mounting the superblock, the underlying
 135	 * filesystem might be in a state of partial construction and hence it
 136	 * is dangerous to access it.  trylock_super() uses a SB_BORN check to
 137	 * avoid this situation, so do the same here. The memory barrier is
 138	 * matched with the one in mount_fs() as we don't hold locks here.
 139	 */
 140	if (!(sb->s_flags & SB_BORN))
 141		return 0;
 142	smp_rmb();
 143
 144	if (sb->s_op && sb->s_op->nr_cached_objects)
 145		total_objects = sb->s_op->nr_cached_objects(sb, sc);
 146
 147	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);
 148	total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
 149
 150	if (!total_objects)
 151		return SHRINK_EMPTY;
 152
 153	total_objects = vfs_pressure_ratio(total_objects);
 154	return total_objects;
 155}
 156
 157static void destroy_super_work(struct work_struct *work)
 158{
 159	struct super_block *s = container_of(work, struct super_block,
 160							destroy_work);
 161	int i;
 162
 163	for (i = 0; i < SB_FREEZE_LEVELS; i++)
 164		percpu_free_rwsem(&s->s_writers.rw_sem[i]);
 165	kfree(s);
 166}
 167
 168static void destroy_super_rcu(struct rcu_head *head)
 169{
 170	struct super_block *s = container_of(head, struct super_block, rcu);
 171	INIT_WORK(&s->destroy_work, destroy_super_work);
 172	schedule_work(&s->destroy_work);
 173}
 174
 175/* Free a superblock that has never been seen by anyone */
 176static void destroy_unused_super(struct super_block *s)
 177{
 178	if (!s)
 179		return;
 180	up_write(&s->s_umount);
 181	list_lru_destroy(&s->s_dentry_lru);
 182	list_lru_destroy(&s->s_inode_lru);
 183	security_sb_free(s);
 184	put_user_ns(s->s_user_ns);
 185	kfree(s->s_subtype);
 186	free_prealloced_shrinker(&s->s_shrink);
 187	/* no delays needed */
 188	destroy_super_work(&s->destroy_work);
 189}
 190
 191/**
 192 *	alloc_super	-	create new superblock
 193 *	@type:	filesystem type superblock should belong to
 194 *	@flags: the mount flags
 195 *	@user_ns: User namespace for the super_block
 196 *
 197 *	Allocates and initializes a new &struct super_block.  alloc_super()
 198 *	returns a pointer new superblock or %NULL if allocation had failed.
 199 */
 200static struct super_block *alloc_super(struct file_system_type *type, int flags,
 201				       struct user_namespace *user_ns)
 202{
 203	struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
 204	static const struct super_operations default_op;
 205	int i;
 206
 207	if (!s)
 208		return NULL;
 209
 210	INIT_LIST_HEAD(&s->s_mounts);
 211	s->s_user_ns = get_user_ns(user_ns);
 212	init_rwsem(&s->s_umount);
 213	lockdep_set_class(&s->s_umount, &type->s_umount_key);
 214	/*
 215	 * sget() can have s_umount recursion.
 216	 *
 217	 * When it cannot find a suitable sb, it allocates a new
 218	 * one (this one), and tries again to find a suitable old
 219	 * one.
 220	 *
 221	 * In case that succeeds, it will acquire the s_umount
 222	 * lock of the old one. Since these are clearly distrinct
 223	 * locks, and this object isn't exposed yet, there's no
 224	 * risk of deadlocks.
 225	 *
 226	 * Annotate this by putting this lock in a different
 227	 * subclass.
 228	 */
 229	down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
 230
 231	if (security_sb_alloc(s))
 232		goto fail;
 233
 234	for (i = 0; i < SB_FREEZE_LEVELS; i++) {
 235		if (__percpu_init_rwsem(&s->s_writers.rw_sem[i],
 236					sb_writers_name[i],
 237					&type->s_writers_key[i]))
 238			goto fail;
 239	}
 240	init_waitqueue_head(&s->s_writers.wait_unfrozen);
 241	s->s_bdi = &noop_backing_dev_info;
 242	s->s_flags = flags;
 243	if (s->s_user_ns != &init_user_ns)
 244		s->s_iflags |= SB_I_NODEV;
 245	INIT_HLIST_NODE(&s->s_instances);
 246	INIT_HLIST_BL_HEAD(&s->s_roots);
 247	mutex_init(&s->s_sync_lock);
 248	INIT_LIST_HEAD(&s->s_inodes);
 249	spin_lock_init(&s->s_inode_list_lock);
 250	INIT_LIST_HEAD(&s->s_inodes_wb);
 251	spin_lock_init(&s->s_inode_wblist_lock);
 252
 253	s->s_count = 1;
 254	atomic_set(&s->s_active, 1);
 255	mutex_init(&s->s_vfs_rename_mutex);
 256	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
 257	init_rwsem(&s->s_dquot.dqio_sem);
 258	s->s_maxbytes = MAX_NON_LFS;
 259	s->s_op = &default_op;
 260	s->s_time_gran = 1000000000;
 261	s->s_time_min = TIME64_MIN;
 262	s->s_time_max = TIME64_MAX;
 263	s->cleancache_poolid = CLEANCACHE_NO_POOL;
 264
 265	s->s_shrink.seeks = DEFAULT_SEEKS;
 266	s->s_shrink.scan_objects = super_cache_scan;
 267	s->s_shrink.count_objects = super_cache_count;
 268	s->s_shrink.batch = 1024;
 269	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
 270	if (prealloc_shrinker(&s->s_shrink))
 271		goto fail;
 272	if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
 273		goto fail;
 274	if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
 275		goto fail;
 276	return s;
 277
 278fail:
 279	destroy_unused_super(s);
 280	return NULL;
 281}
 282
 283/* Superblock refcounting  */
 284
 285/*
 286 * Drop a superblock's refcount.  The caller must hold sb_lock.
 287 */
 288static void __put_super(struct super_block *s)
 289{
 290	if (!--s->s_count) {
 291		list_del_init(&s->s_list);
 292		WARN_ON(s->s_dentry_lru.node);
 293		WARN_ON(s->s_inode_lru.node);
 294		WARN_ON(!list_empty(&s->s_mounts));
 295		security_sb_free(s);
 296		fscrypt_sb_free(s);
 297		put_user_ns(s->s_user_ns);
 298		kfree(s->s_subtype);
 299		call_rcu(&s->rcu, destroy_super_rcu);
 300	}
 301}
 302
 303/**
 304 *	put_super	-	drop a temporary reference to superblock
 305 *	@sb: superblock in question
 306 *
 307 *	Drops a temporary reference, frees superblock if there's no
 308 *	references left.
 309 */
 310static void put_super(struct super_block *sb)
 311{
 312	spin_lock(&sb_lock);
 313	__put_super(sb);
 314	spin_unlock(&sb_lock);
 315}
 316
 317
 318/**
 319 *	deactivate_locked_super	-	drop an active reference to superblock
 320 *	@s: superblock to deactivate
 321 *
 322 *	Drops an active reference to superblock, converting it into a temporary
 323 *	one if there is no other active references left.  In that case we
 324 *	tell fs driver to shut it down and drop the temporary reference we
 325 *	had just acquired.
 326 *
 327 *	Caller holds exclusive lock on superblock; that lock is released.
 328 */
 329void deactivate_locked_super(struct super_block *s)
 330{
 331	struct file_system_type *fs = s->s_type;
 332	if (atomic_dec_and_test(&s->s_active)) {
 333		cleancache_invalidate_fs(s);
 334		unregister_shrinker(&s->s_shrink);
 335		fs->kill_sb(s);
 336
 337		/*
 338		 * Since list_lru_destroy() may sleep, we cannot call it from
 339		 * put_super(), where we hold the sb_lock. Therefore we destroy
 340		 * the lru lists right now.
 341		 */
 342		list_lru_destroy(&s->s_dentry_lru);
 343		list_lru_destroy(&s->s_inode_lru);
 344
 345		put_filesystem(fs);
 346		put_super(s);
 347	} else {
 348		up_write(&s->s_umount);
 349	}
 350}
 351
 352EXPORT_SYMBOL(deactivate_locked_super);
 353
 354/**
 355 *	deactivate_super	-	drop an active reference to superblock
 356 *	@s: superblock to deactivate
 357 *
 358 *	Variant of deactivate_locked_super(), except that superblock is *not*
 359 *	locked by caller.  If we are going to drop the final active reference,
 360 *	lock will be acquired prior to that.
 361 */
 362void deactivate_super(struct super_block *s)
 363{
 364        if (!atomic_add_unless(&s->s_active, -1, 1)) {
 365		down_write(&s->s_umount);
 366		deactivate_locked_super(s);
 367	}
 368}
 369
 370EXPORT_SYMBOL(deactivate_super);
 371
 372/**
 373 *	grab_super - acquire an active reference
 374 *	@s: reference we are trying to make active
 375 *
 376 *	Tries to acquire an active reference.  grab_super() is used when we
 377 * 	had just found a superblock in super_blocks or fs_type->fs_supers
 378 *	and want to turn it into a full-blown active reference.  grab_super()
 379 *	is called with sb_lock held and drops it.  Returns 1 in case of
 380 *	success, 0 if we had failed (superblock contents was already dead or
 381 *	dying when grab_super() had been called).  Note that this is only
 382 *	called for superblocks not in rundown mode (== ones still on ->fs_supers
 383 *	of their type), so increment of ->s_count is OK here.
 384 */
 385static int grab_super(struct super_block *s) __releases(sb_lock)
 386{
 387	s->s_count++;
 388	spin_unlock(&sb_lock);
 389	down_write(&s->s_umount);
 390	if ((s->s_flags & SB_BORN) && atomic_inc_not_zero(&s->s_active)) {
 391		put_super(s);
 392		return 1;
 393	}
 394	up_write(&s->s_umount);
 395	put_super(s);
 396	return 0;
 397}
 398
 399/*
 400 *	trylock_super - try to grab ->s_umount shared
 401 *	@sb: reference we are trying to grab
 402 *
 403 *	Try to prevent fs shutdown.  This is used in places where we
 404 *	cannot take an active reference but we need to ensure that the
 405 *	filesystem is not shut down while we are working on it. It returns
 406 *	false if we cannot acquire s_umount or if we lose the race and
 407 *	filesystem already got into shutdown, and returns true with the s_umount
 408 *	lock held in read mode in case of success. On successful return,
 409 *	the caller must drop the s_umount lock when done.
 410 *
 411 *	Note that unlike get_super() et.al. this one does *not* bump ->s_count.
 412 *	The reason why it's safe is that we are OK with doing trylock instead
 413 *	of down_read().  There's a couple of places that are OK with that, but
 414 *	it's very much not a general-purpose interface.
 415 */
 416bool trylock_super(struct super_block *sb)
 417{
 418	if (down_read_trylock(&sb->s_umount)) {
 419		if (!hlist_unhashed(&sb->s_instances) &&
 420		    sb->s_root && (sb->s_flags & SB_BORN))
 421			return true;
 422		up_read(&sb->s_umount);
 423	}
 424
 425	return false;
 426}
 427
 428/**
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 429 *	generic_shutdown_super	-	common helper for ->kill_sb()
 430 *	@sb: superblock to kill
 431 *
 432 *	generic_shutdown_super() does all fs-independent work on superblock
 433 *	shutdown.  Typical ->kill_sb() should pick all fs-specific objects
 434 *	that need destruction out of superblock, call generic_shutdown_super()
 435 *	and release aforementioned objects.  Note: dentries and inodes _are_
 436 *	taken care of and do not need specific handling.
 437 *
 438 *	Upon calling this function, the filesystem may no longer alter or
 439 *	rearrange the set of dentries belonging to this super_block, nor may it
 440 *	change the attachments of dentries to inodes.
 441 */
 442void generic_shutdown_super(struct super_block *sb)
 443{
 444	const struct super_operations *sop = sb->s_op;
 445
 446	if (sb->s_root) {
 447		shrink_dcache_for_umount(sb);
 448		sync_filesystem(sb);
 449		sb->s_flags &= ~SB_ACTIVE;
 450
 451		fsnotify_sb_delete(sb);
 452		cgroup_writeback_umount();
 453
 
 454		evict_inodes(sb);
 
 
 
 
 455
 456		if (sb->s_dio_done_wq) {
 457			destroy_workqueue(sb->s_dio_done_wq);
 458			sb->s_dio_done_wq = NULL;
 459		}
 460
 461		if (sop->put_super)
 462			sop->put_super(sb);
 463
 464		if (!list_empty(&sb->s_inodes)) {
 465			printk("VFS: Busy inodes after unmount of %s. "
 466			   "Self-destruct in 5 seconds.  Have a nice day...\n",
 467			   sb->s_id);
 468		}
 469	}
 470	spin_lock(&sb_lock);
 471	/* should be initialized for __put_super_and_need_restart() */
 472	hlist_del_init(&sb->s_instances);
 473	spin_unlock(&sb_lock);
 474	up_write(&sb->s_umount);
 475	if (sb->s_bdi != &noop_backing_dev_info) {
 
 
 476		bdi_put(sb->s_bdi);
 477		sb->s_bdi = &noop_backing_dev_info;
 478	}
 479}
 480
 481EXPORT_SYMBOL(generic_shutdown_super);
 482
 483bool mount_capable(struct fs_context *fc)
 484{
 485	if (!(fc->fs_type->fs_flags & FS_USERNS_MOUNT))
 486		return capable(CAP_SYS_ADMIN);
 487	else
 488		return ns_capable(fc->user_ns, CAP_SYS_ADMIN);
 489}
 490
 491/**
 492 * sget_fc - Find or create a superblock
 493 * @fc:	Filesystem context.
 494 * @test: Comparison callback
 495 * @set: Setup callback
 496 *
 497 * Find or create a superblock using the parameters stored in the filesystem
 498 * context and the two callback functions.
 499 *
 500 * If an extant superblock is matched, then that will be returned with an
 501 * elevated reference count that the caller must transfer or discard.
 502 *
 503 * If no match is made, a new superblock will be allocated and basic
 504 * initialisation will be performed (s_type, s_fs_info and s_id will be set and
 505 * the set() callback will be invoked), the superblock will be published and it
 506 * will be returned in a partially constructed state with SB_BORN and SB_ACTIVE
 507 * as yet unset.
 508 */
 509struct super_block *sget_fc(struct fs_context *fc,
 510			    int (*test)(struct super_block *, struct fs_context *),
 511			    int (*set)(struct super_block *, struct fs_context *))
 512{
 513	struct super_block *s = NULL;
 514	struct super_block *old;
 515	struct user_namespace *user_ns = fc->global ? &init_user_ns : fc->user_ns;
 516	int err;
 517
 518retry:
 519	spin_lock(&sb_lock);
 520	if (test) {
 521		hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) {
 522			if (test(old, fc))
 523				goto share_extant_sb;
 524		}
 525	}
 526	if (!s) {
 527		spin_unlock(&sb_lock);
 528		s = alloc_super(fc->fs_type, fc->sb_flags, user_ns);
 529		if (!s)
 530			return ERR_PTR(-ENOMEM);
 531		goto retry;
 532	}
 533
 534	s->s_fs_info = fc->s_fs_info;
 535	err = set(s, fc);
 536	if (err) {
 537		s->s_fs_info = NULL;
 538		spin_unlock(&sb_lock);
 539		destroy_unused_super(s);
 540		return ERR_PTR(err);
 541	}
 542	fc->s_fs_info = NULL;
 543	s->s_type = fc->fs_type;
 544	s->s_iflags |= fc->s_iflags;
 545	strlcpy(s->s_id, s->s_type->name, sizeof(s->s_id));
 546	list_add_tail(&s->s_list, &super_blocks);
 547	hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
 548	spin_unlock(&sb_lock);
 549	get_filesystem(s->s_type);
 550	register_shrinker_prepared(&s->s_shrink);
 551	return s;
 552
 553share_extant_sb:
 554	if (user_ns != old->s_user_ns) {
 555		spin_unlock(&sb_lock);
 556		destroy_unused_super(s);
 557		return ERR_PTR(-EBUSY);
 558	}
 559	if (!grab_super(old))
 560		goto retry;
 561	destroy_unused_super(s);
 562	return old;
 563}
 564EXPORT_SYMBOL(sget_fc);
 565
 566/**
 567 *	sget	-	find or create a superblock
 568 *	@type:	  filesystem type superblock should belong to
 569 *	@test:	  comparison callback
 570 *	@set:	  setup callback
 571 *	@flags:	  mount flags
 572 *	@data:	  argument to each of them
 573 */
 574struct super_block *sget(struct file_system_type *type,
 575			int (*test)(struct super_block *,void *),
 576			int (*set)(struct super_block *,void *),
 577			int flags,
 578			void *data)
 579{
 580	struct user_namespace *user_ns = current_user_ns();
 581	struct super_block *s = NULL;
 582	struct super_block *old;
 583	int err;
 584
 585	/* We don't yet pass the user namespace of the parent
 586	 * mount through to here so always use &init_user_ns
 587	 * until that changes.
 588	 */
 589	if (flags & SB_SUBMOUNT)
 590		user_ns = &init_user_ns;
 591
 592retry:
 593	spin_lock(&sb_lock);
 594	if (test) {
 595		hlist_for_each_entry(old, &type->fs_supers, s_instances) {
 596			if (!test(old, data))
 597				continue;
 598			if (user_ns != old->s_user_ns) {
 599				spin_unlock(&sb_lock);
 600				destroy_unused_super(s);
 601				return ERR_PTR(-EBUSY);
 602			}
 603			if (!grab_super(old))
 604				goto retry;
 605			destroy_unused_super(s);
 606			return old;
 607		}
 608	}
 609	if (!s) {
 610		spin_unlock(&sb_lock);
 611		s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
 612		if (!s)
 613			return ERR_PTR(-ENOMEM);
 614		goto retry;
 615	}
 616
 617	err = set(s, data);
 618	if (err) {
 619		spin_unlock(&sb_lock);
 620		destroy_unused_super(s);
 621		return ERR_PTR(err);
 622	}
 623	s->s_type = type;
 624	strlcpy(s->s_id, type->name, sizeof(s->s_id));
 625	list_add_tail(&s->s_list, &super_blocks);
 626	hlist_add_head(&s->s_instances, &type->fs_supers);
 627	spin_unlock(&sb_lock);
 628	get_filesystem(type);
 629	register_shrinker_prepared(&s->s_shrink);
 630	return s;
 631}
 632EXPORT_SYMBOL(sget);
 633
 634void drop_super(struct super_block *sb)
 635{
 636	up_read(&sb->s_umount);
 637	put_super(sb);
 638}
 639
 640EXPORT_SYMBOL(drop_super);
 641
 642void drop_super_exclusive(struct super_block *sb)
 643{
 644	up_write(&sb->s_umount);
 645	put_super(sb);
 646}
 647EXPORT_SYMBOL(drop_super_exclusive);
 648
 649static void __iterate_supers(void (*f)(struct super_block *))
 650{
 651	struct super_block *sb, *p = NULL;
 652
 653	spin_lock(&sb_lock);
 654	list_for_each_entry(sb, &super_blocks, s_list) {
 655		if (hlist_unhashed(&sb->s_instances))
 656			continue;
 657		sb->s_count++;
 658		spin_unlock(&sb_lock);
 659
 660		f(sb);
 661
 662		spin_lock(&sb_lock);
 663		if (p)
 664			__put_super(p);
 665		p = sb;
 666	}
 667	if (p)
 668		__put_super(p);
 669	spin_unlock(&sb_lock);
 670}
 671/**
 672 *	iterate_supers - call function for all active superblocks
 673 *	@f: function to call
 674 *	@arg: argument to pass to it
 675 *
 676 *	Scans the superblock list and calls given function, passing it
 677 *	locked superblock and given argument.
 678 */
 679void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 680{
 681	struct super_block *sb, *p = NULL;
 682
 683	spin_lock(&sb_lock);
 684	list_for_each_entry(sb, &super_blocks, s_list) {
 685		if (hlist_unhashed(&sb->s_instances))
 686			continue;
 687		sb->s_count++;
 688		spin_unlock(&sb_lock);
 689
 690		down_read(&sb->s_umount);
 691		if (sb->s_root && (sb->s_flags & SB_BORN))
 692			f(sb, arg);
 693		up_read(&sb->s_umount);
 694
 695		spin_lock(&sb_lock);
 696		if (p)
 697			__put_super(p);
 698		p = sb;
 699	}
 700	if (p)
 701		__put_super(p);
 702	spin_unlock(&sb_lock);
 703}
 704
 705/**
 706 *	iterate_supers_type - call function for superblocks of given type
 707 *	@type: fs type
 708 *	@f: function to call
 709 *	@arg: argument to pass to it
 710 *
 711 *	Scans the superblock list and calls given function, passing it
 712 *	locked superblock and given argument.
 713 */
 714void iterate_supers_type(struct file_system_type *type,
 715	void (*f)(struct super_block *, void *), void *arg)
 716{
 717	struct super_block *sb, *p = NULL;
 718
 719	spin_lock(&sb_lock);
 720	hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
 721		sb->s_count++;
 722		spin_unlock(&sb_lock);
 723
 724		down_read(&sb->s_umount);
 725		if (sb->s_root && (sb->s_flags & SB_BORN))
 726			f(sb, arg);
 727		up_read(&sb->s_umount);
 728
 729		spin_lock(&sb_lock);
 730		if (p)
 731			__put_super(p);
 732		p = sb;
 733	}
 734	if (p)
 735		__put_super(p);
 736	spin_unlock(&sb_lock);
 737}
 738
 739EXPORT_SYMBOL(iterate_supers_type);
 740
 741static struct super_block *__get_super(struct block_device *bdev, bool excl)
 
 
 
 
 
 
 
 742{
 743	struct super_block *sb;
 744
 745	if (!bdev)
 746		return NULL;
 747
 748	spin_lock(&sb_lock);
 749rescan:
 750	list_for_each_entry(sb, &super_blocks, s_list) {
 751		if (hlist_unhashed(&sb->s_instances))
 752			continue;
 753		if (sb->s_bdev == bdev) {
 754			sb->s_count++;
 755			spin_unlock(&sb_lock);
 756			if (!excl)
 757				down_read(&sb->s_umount);
 758			else
 759				down_write(&sb->s_umount);
 760			/* still alive? */
 761			if (sb->s_root && (sb->s_flags & SB_BORN))
 762				return sb;
 763			if (!excl)
 764				up_read(&sb->s_umount);
 765			else
 766				up_write(&sb->s_umount);
 767			/* nope, got unmounted */
 768			spin_lock(&sb_lock);
 769			__put_super(sb);
 770			goto rescan;
 771		}
 772	}
 773	spin_unlock(&sb_lock);
 774	return NULL;
 775}
 776
 777/**
 778 *	get_super - get the superblock of a device
 779 *	@bdev: device to get the superblock for
 780 *
 781 *	Scans the superblock list and finds the superblock of the file system
 782 *	mounted on the device given. %NULL is returned if no match is found.
 783 */
 784struct super_block *get_super(struct block_device *bdev)
 785{
 786	return __get_super(bdev, false);
 787}
 788EXPORT_SYMBOL(get_super);
 789
 790static struct super_block *__get_super_thawed(struct block_device *bdev,
 791					      bool excl)
 792{
 793	while (1) {
 794		struct super_block *s = __get_super(bdev, excl);
 795		if (!s || s->s_writers.frozen == SB_UNFROZEN)
 796			return s;
 797		if (!excl)
 798			up_read(&s->s_umount);
 799		else
 800			up_write(&s->s_umount);
 801		wait_event(s->s_writers.wait_unfrozen,
 802			   s->s_writers.frozen == SB_UNFROZEN);
 803		put_super(s);
 804	}
 805}
 806
 807/**
 808 *	get_super_thawed - get thawed superblock of a device
 809 *	@bdev: device to get the superblock for
 810 *
 811 *	Scans the superblock list and finds the superblock of the file system
 812 *	mounted on the device. The superblock is returned once it is thawed
 813 *	(or immediately if it was not frozen). %NULL is returned if no match
 814 *	is found.
 815 */
 816struct super_block *get_super_thawed(struct block_device *bdev)
 817{
 818	return __get_super_thawed(bdev, false);
 819}
 820EXPORT_SYMBOL(get_super_thawed);
 821
 822/**
 823 *	get_super_exclusive_thawed - get thawed superblock of a device
 824 *	@bdev: device to get the superblock for
 825 *
 826 *	Scans the superblock list and finds the superblock of the file system
 827 *	mounted on the device. The superblock is returned once it is thawed
 828 *	(or immediately if it was not frozen) and s_umount semaphore is held
 829 *	in exclusive mode. %NULL is returned if no match is found.
 830 */
 831struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
 832{
 833	return __get_super_thawed(bdev, true);
 834}
 835EXPORT_SYMBOL(get_super_exclusive_thawed);
 836
 837/**
 838 * get_active_super - get an active reference to the superblock of a device
 839 * @bdev: device to get the superblock for
 840 *
 841 * Scans the superblock list and finds the superblock of the file system
 842 * mounted on the device given.  Returns the superblock with an active
 843 * reference or %NULL if none was found.
 844 */
 845struct super_block *get_active_super(struct block_device *bdev)
 846{
 847	struct super_block *sb;
 848
 849	if (!bdev)
 850		return NULL;
 851
 852restart:
 853	spin_lock(&sb_lock);
 854	list_for_each_entry(sb, &super_blocks, s_list) {
 855		if (hlist_unhashed(&sb->s_instances))
 856			continue;
 857		if (sb->s_bdev == bdev) {
 858			if (!grab_super(sb))
 859				goto restart;
 860			up_write(&sb->s_umount);
 861			return sb;
 862		}
 863	}
 864	spin_unlock(&sb_lock);
 865	return NULL;
 866}
 867
 868struct super_block *user_get_super(dev_t dev)
 869{
 870	struct super_block *sb;
 871
 872	spin_lock(&sb_lock);
 873rescan:
 874	list_for_each_entry(sb, &super_blocks, s_list) {
 875		if (hlist_unhashed(&sb->s_instances))
 876			continue;
 877		if (sb->s_dev ==  dev) {
 878			sb->s_count++;
 879			spin_unlock(&sb_lock);
 880			down_read(&sb->s_umount);
 
 
 
 881			/* still alive? */
 882			if (sb->s_root && (sb->s_flags & SB_BORN))
 883				return sb;
 884			up_read(&sb->s_umount);
 
 
 
 885			/* nope, got unmounted */
 886			spin_lock(&sb_lock);
 887			__put_super(sb);
 888			goto rescan;
 889		}
 890	}
 891	spin_unlock(&sb_lock);
 892	return NULL;
 893}
 894
 895/**
 896 * reconfigure_super - asks filesystem to change superblock parameters
 897 * @fc: The superblock and configuration
 898 *
 899 * Alters the configuration parameters of a live superblock.
 900 */
 901int reconfigure_super(struct fs_context *fc)
 902{
 903	struct super_block *sb = fc->root->d_sb;
 904	int retval;
 905	bool remount_ro = false;
 906	bool force = fc->sb_flags & SB_FORCE;
 907
 908	if (fc->sb_flags_mask & ~MS_RMT_MASK)
 909		return -EINVAL;
 910	if (sb->s_writers.frozen != SB_UNFROZEN)
 911		return -EBUSY;
 912
 913	retval = security_sb_remount(sb, fc->security);
 914	if (retval)
 915		return retval;
 916
 917	if (fc->sb_flags_mask & SB_RDONLY) {
 918#ifdef CONFIG_BLOCK
 919		if (!(fc->sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))
 
 920			return -EACCES;
 921#endif
 922
 923		remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb);
 924	}
 925
 926	if (remount_ro) {
 927		if (!hlist_empty(&sb->s_pins)) {
 928			up_write(&sb->s_umount);
 929			group_pin_kill(&sb->s_pins);
 930			down_write(&sb->s_umount);
 931			if (!sb->s_root)
 932				return 0;
 933			if (sb->s_writers.frozen != SB_UNFROZEN)
 934				return -EBUSY;
 935			remount_ro = !sb_rdonly(sb);
 936		}
 937	}
 938	shrink_dcache_sb(sb);
 939
 940	/* If we are reconfiguring to RDONLY and current sb is read/write,
 941	 * make sure there are no files open for writing.
 942	 */
 943	if (remount_ro) {
 944		if (force) {
 945			sb->s_readonly_remount = 1;
 946			smp_wmb();
 947		} else {
 948			retval = sb_prepare_remount_readonly(sb);
 949			if (retval)
 950				return retval;
 951		}
 952	}
 953
 954	if (fc->ops->reconfigure) {
 955		retval = fc->ops->reconfigure(fc);
 956		if (retval) {
 957			if (!force)
 958				goto cancel_readonly;
 959			/* If forced remount, go ahead despite any errors */
 960			WARN(1, "forced remount of a %s fs returned %i\n",
 961			     sb->s_type->name, retval);
 962		}
 963	}
 964
 965	WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |
 966				 (fc->sb_flags & fc->sb_flags_mask)));
 967	/* Needs to be ordered wrt mnt_is_readonly() */
 968	smp_wmb();
 969	sb->s_readonly_remount = 0;
 970
 971	/*
 972	 * Some filesystems modify their metadata via some other path than the
 973	 * bdev buffer cache (eg. use a private mapping, or directories in
 974	 * pagecache, etc). Also file data modifications go via their own
 975	 * mappings. So If we try to mount readonly then copy the filesystem
 976	 * from bdev, we could get stale data, so invalidate it to give a best
 977	 * effort at coherency.
 978	 */
 979	if (remount_ro && sb->s_bdev)
 980		invalidate_bdev(sb->s_bdev);
 981	return 0;
 982
 983cancel_readonly:
 984	sb->s_readonly_remount = 0;
 985	return retval;
 986}
 987
 988static void do_emergency_remount_callback(struct super_block *sb)
 989{
 990	down_write(&sb->s_umount);
 991	if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
 992	    !sb_rdonly(sb)) {
 993		struct fs_context *fc;
 994
 995		fc = fs_context_for_reconfigure(sb->s_root,
 996					SB_RDONLY | SB_FORCE, SB_RDONLY);
 997		if (!IS_ERR(fc)) {
 998			if (parse_monolithic_mount_data(fc, NULL) == 0)
 999				(void)reconfigure_super(fc);
1000			put_fs_context(fc);
1001		}
1002	}
1003	up_write(&sb->s_umount);
1004}
1005
1006static void do_emergency_remount(struct work_struct *work)
1007{
1008	__iterate_supers(do_emergency_remount_callback);
1009	kfree(work);
1010	printk("Emergency Remount complete\n");
1011}
1012
1013void emergency_remount(void)
1014{
1015	struct work_struct *work;
1016
1017	work = kmalloc(sizeof(*work), GFP_ATOMIC);
1018	if (work) {
1019		INIT_WORK(work, do_emergency_remount);
1020		schedule_work(work);
1021	}
1022}
1023
1024static void do_thaw_all_callback(struct super_block *sb)
1025{
1026	down_write(&sb->s_umount);
1027	if (sb->s_root && sb->s_flags & SB_BORN) {
1028		emergency_thaw_bdev(sb);
1029		thaw_super_locked(sb);
1030	} else {
1031		up_write(&sb->s_umount);
1032	}
1033}
1034
1035static void do_thaw_all(struct work_struct *work)
1036{
1037	__iterate_supers(do_thaw_all_callback);
1038	kfree(work);
1039	printk(KERN_WARNING "Emergency Thaw complete\n");
1040}
1041
1042/**
1043 * emergency_thaw_all -- forcibly thaw every frozen filesystem
1044 *
1045 * Used for emergency unfreeze of all filesystems via SysRq
1046 */
1047void emergency_thaw_all(void)
1048{
1049	struct work_struct *work;
1050
1051	work = kmalloc(sizeof(*work), GFP_ATOMIC);
1052	if (work) {
1053		INIT_WORK(work, do_thaw_all);
1054		schedule_work(work);
1055	}
1056}
1057
1058static DEFINE_IDA(unnamed_dev_ida);
1059
1060/**
1061 * get_anon_bdev - Allocate a block device for filesystems which don't have one.
1062 * @p: Pointer to a dev_t.
1063 *
1064 * Filesystems which don't use real block devices can call this function
1065 * to allocate a virtual block device.
1066 *
1067 * Context: Any context.  Frequently called while holding sb_lock.
1068 * Return: 0 on success, -EMFILE if there are no anonymous bdevs left
1069 * or -ENOMEM if memory allocation failed.
1070 */
1071int get_anon_bdev(dev_t *p)
1072{
1073	int dev;
1074
1075	/*
1076	 * Many userspace utilities consider an FSID of 0 invalid.
1077	 * Always return at least 1 from get_anon_bdev.
1078	 */
1079	dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1,
1080			GFP_ATOMIC);
1081	if (dev == -ENOSPC)
1082		dev = -EMFILE;
1083	if (dev < 0)
1084		return dev;
1085
1086	*p = MKDEV(0, dev);
1087	return 0;
1088}
1089EXPORT_SYMBOL(get_anon_bdev);
1090
1091void free_anon_bdev(dev_t dev)
1092{
1093	ida_free(&unnamed_dev_ida, MINOR(dev));
1094}
1095EXPORT_SYMBOL(free_anon_bdev);
1096
1097int set_anon_super(struct super_block *s, void *data)
1098{
1099	return get_anon_bdev(&s->s_dev);
1100}
1101EXPORT_SYMBOL(set_anon_super);
1102
1103void kill_anon_super(struct super_block *sb)
1104{
1105	dev_t dev = sb->s_dev;
1106	generic_shutdown_super(sb);
1107	free_anon_bdev(dev);
1108}
1109EXPORT_SYMBOL(kill_anon_super);
1110
1111void kill_litter_super(struct super_block *sb)
1112{
1113	if (sb->s_root)
1114		d_genocide(sb->s_root);
1115	kill_anon_super(sb);
1116}
1117EXPORT_SYMBOL(kill_litter_super);
1118
1119int set_anon_super_fc(struct super_block *sb, struct fs_context *fc)
1120{
1121	return set_anon_super(sb, NULL);
1122}
1123EXPORT_SYMBOL(set_anon_super_fc);
1124
1125static int test_keyed_super(struct super_block *sb, struct fs_context *fc)
1126{
1127	return sb->s_fs_info == fc->s_fs_info;
1128}
1129
1130static int test_single_super(struct super_block *s, struct fs_context *fc)
1131{
1132	return 1;
1133}
1134
1135/**
1136 * vfs_get_super - Get a superblock with a search key set in s_fs_info.
1137 * @fc: The filesystem context holding the parameters
1138 * @keying: How to distinguish superblocks
1139 * @fill_super: Helper to initialise a new superblock
1140 *
1141 * Search for a superblock and create a new one if not found.  The search
1142 * criterion is controlled by @keying.  If the search fails, a new superblock
1143 * is created and @fill_super() is called to initialise it.
1144 *
1145 * @keying can take one of a number of values:
1146 *
1147 * (1) vfs_get_single_super - Only one superblock of this type may exist on the
1148 *     system.  This is typically used for special system filesystems.
1149 *
1150 * (2) vfs_get_keyed_super - Multiple superblocks may exist, but they must have
1151 *     distinct keys (where the key is in s_fs_info).  Searching for the same
1152 *     key again will turn up the superblock for that key.
1153 *
1154 * (3) vfs_get_independent_super - Multiple superblocks may exist and are
1155 *     unkeyed.  Each call will get a new superblock.
1156 *
1157 * A permissions check is made by sget_fc() unless we're getting a superblock
1158 * for a kernel-internal mount or a submount.
1159 */
1160int vfs_get_super(struct fs_context *fc,
1161		  enum vfs_get_super_keying keying,
1162		  int (*fill_super)(struct super_block *sb,
1163				    struct fs_context *fc))
1164{
1165	int (*test)(struct super_block *, struct fs_context *);
1166	struct super_block *sb;
1167	int err;
1168
1169	switch (keying) {
1170	case vfs_get_single_super:
1171	case vfs_get_single_reconf_super:
1172		test = test_single_super;
1173		break;
1174	case vfs_get_keyed_super:
1175		test = test_keyed_super;
1176		break;
1177	case vfs_get_independent_super:
1178		test = NULL;
1179		break;
1180	default:
1181		BUG();
1182	}
1183
1184	sb = sget_fc(fc, test, set_anon_super_fc);
1185	if (IS_ERR(sb))
1186		return PTR_ERR(sb);
1187
1188	if (!sb->s_root) {
1189		err = fill_super(sb, fc);
1190		if (err)
1191			goto error;
1192
1193		sb->s_flags |= SB_ACTIVE;
1194		fc->root = dget(sb->s_root);
1195	} else {
1196		fc->root = dget(sb->s_root);
1197		if (keying == vfs_get_single_reconf_super) {
1198			err = reconfigure_super(fc);
1199			if (err < 0) {
1200				dput(fc->root);
1201				fc->root = NULL;
1202				goto error;
1203			}
1204		}
1205	}
1206
1207	return 0;
1208
1209error:
1210	deactivate_locked_super(sb);
1211	return err;
1212}
1213EXPORT_SYMBOL(vfs_get_super);
1214
1215int get_tree_nodev(struct fs_context *fc,
1216		  int (*fill_super)(struct super_block *sb,
1217				    struct fs_context *fc))
1218{
1219	return vfs_get_super(fc, vfs_get_independent_super, fill_super);
1220}
1221EXPORT_SYMBOL(get_tree_nodev);
1222
1223int get_tree_single(struct fs_context *fc,
1224		  int (*fill_super)(struct super_block *sb,
1225				    struct fs_context *fc))
1226{
1227	return vfs_get_super(fc, vfs_get_single_super, fill_super);
1228}
1229EXPORT_SYMBOL(get_tree_single);
1230
1231int get_tree_single_reconf(struct fs_context *fc,
1232		  int (*fill_super)(struct super_block *sb,
1233				    struct fs_context *fc))
1234{
1235	return vfs_get_super(fc, vfs_get_single_reconf_super, fill_super);
1236}
1237EXPORT_SYMBOL(get_tree_single_reconf);
1238
1239int get_tree_keyed(struct fs_context *fc,
1240		  int (*fill_super)(struct super_block *sb,
1241				    struct fs_context *fc),
1242		void *key)
1243{
1244	fc->s_fs_info = key;
1245	return vfs_get_super(fc, vfs_get_keyed_super, fill_super);
1246}
1247EXPORT_SYMBOL(get_tree_keyed);
1248
1249#ifdef CONFIG_BLOCK
1250
1251static int set_bdev_super(struct super_block *s, void *data)
1252{
1253	s->s_bdev = data;
1254	s->s_dev = s->s_bdev->bd_dev;
1255	s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
1256
 
 
1257	return 0;
1258}
1259
1260static int set_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1261{
1262	return set_bdev_super(s, fc->sget_key);
1263}
1264
1265static int test_bdev_super_fc(struct super_block *s, struct fs_context *fc)
1266{
1267	return s->s_bdev == fc->sget_key;
1268}
1269
1270/**
1271 * get_tree_bdev - Get a superblock based on a single block device
1272 * @fc: The filesystem context holding the parameters
1273 * @fill_super: Helper to initialise a new superblock
1274 */
1275int get_tree_bdev(struct fs_context *fc,
1276		int (*fill_super)(struct super_block *,
1277				  struct fs_context *))
1278{
1279	struct block_device *bdev;
1280	struct super_block *s;
1281	fmode_t mode = FMODE_READ | FMODE_EXCL;
1282	int error = 0;
1283
1284	if (!(fc->sb_flags & SB_RDONLY))
1285		mode |= FMODE_WRITE;
1286
1287	if (!fc->source)
1288		return invalf(fc, "No source specified");
1289
1290	bdev = blkdev_get_by_path(fc->source, mode, fc->fs_type);
1291	if (IS_ERR(bdev)) {
1292		errorf(fc, "%s: Can't open blockdev", fc->source);
1293		return PTR_ERR(bdev);
1294	}
1295
1296	/* Once the superblock is inserted into the list by sget_fc(), s_umount
1297	 * will protect the lockfs code from trying to start a snapshot while
1298	 * we are mounting
1299	 */
1300	mutex_lock(&bdev->bd_fsfreeze_mutex);
1301	if (bdev->bd_fsfreeze_count > 0) {
1302		mutex_unlock(&bdev->bd_fsfreeze_mutex);
1303		blkdev_put(bdev, mode);
1304		warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
 
1305		return -EBUSY;
1306	}
1307
1308	fc->sb_flags |= SB_NOSEC;
1309	fc->sget_key = bdev;
1310	s = sget_fc(fc, test_bdev_super_fc, set_bdev_super_fc);
1311	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1312	if (IS_ERR(s)) {
1313		blkdev_put(bdev, mode);
1314		return PTR_ERR(s);
1315	}
1316
1317	if (s->s_root) {
1318		/* Don't summarily change the RO/RW state. */
1319		if ((fc->sb_flags ^ s->s_flags) & SB_RDONLY) {
1320			warnf(fc, "%pg: Can't mount, would change RO state", bdev);
1321			deactivate_locked_super(s);
1322			blkdev_put(bdev, mode);
1323			return -EBUSY;
1324		}
1325
1326		/*
1327		 * s_umount nests inside bd_mutex during
1328		 * __invalidate_device().  blkdev_put() acquires
1329		 * bd_mutex and can't be called under s_umount.  Drop
1330		 * s_umount temporarily.  This is safe as we're
1331		 * holding an active reference.
1332		 */
1333		up_write(&s->s_umount);
1334		blkdev_put(bdev, mode);
1335		down_write(&s->s_umount);
1336	} else {
1337		s->s_mode = mode;
1338		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
 
 
1339		sb_set_blocksize(s, block_size(bdev));
1340		error = fill_super(s, fc);
1341		if (error) {
1342			deactivate_locked_super(s);
1343			return error;
1344		}
1345
1346		s->s_flags |= SB_ACTIVE;
1347		bdev->bd_super = s;
1348	}
1349
1350	BUG_ON(fc->root);
1351	fc->root = dget(s->s_root);
1352	return 0;
1353}
1354EXPORT_SYMBOL(get_tree_bdev);
1355
1356static int test_bdev_super(struct super_block *s, void *data)
1357{
1358	return (void *)s->s_bdev == data;
1359}
1360
1361struct dentry *mount_bdev(struct file_system_type *fs_type,
1362	int flags, const char *dev_name, void *data,
1363	int (*fill_super)(struct super_block *, void *, int))
1364{
1365	struct block_device *bdev;
1366	struct super_block *s;
1367	fmode_t mode = FMODE_READ | FMODE_EXCL;
1368	int error = 0;
1369
1370	if (!(flags & SB_RDONLY))
1371		mode |= FMODE_WRITE;
1372
1373	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
1374	if (IS_ERR(bdev))
1375		return ERR_CAST(bdev);
1376
1377	/*
1378	 * once the super is inserted into the list by sget, s_umount
1379	 * will protect the lockfs code from trying to start a snapshot
1380	 * while we are mounting
1381	 */
1382	mutex_lock(&bdev->bd_fsfreeze_mutex);
1383	if (bdev->bd_fsfreeze_count > 0) {
1384		mutex_unlock(&bdev->bd_fsfreeze_mutex);
1385		error = -EBUSY;
1386		goto error_bdev;
1387	}
1388	s = sget(fs_type, test_bdev_super, set_bdev_super, flags | SB_NOSEC,
1389		 bdev);
1390	mutex_unlock(&bdev->bd_fsfreeze_mutex);
1391	if (IS_ERR(s))
1392		goto error_s;
1393
1394	if (s->s_root) {
1395		if ((flags ^ s->s_flags) & SB_RDONLY) {
1396			deactivate_locked_super(s);
1397			error = -EBUSY;
1398			goto error_bdev;
1399		}
1400
1401		/*
1402		 * s_umount nests inside bd_mutex during
1403		 * __invalidate_device().  blkdev_put() acquires
1404		 * bd_mutex and can't be called under s_umount.  Drop
1405		 * s_umount temporarily.  This is safe as we're
1406		 * holding an active reference.
1407		 */
1408		up_write(&s->s_umount);
1409		blkdev_put(bdev, mode);
1410		down_write(&s->s_umount);
1411	} else {
1412		s->s_mode = mode;
1413		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
 
 
1414		sb_set_blocksize(s, block_size(bdev));
1415		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1416		if (error) {
1417			deactivate_locked_super(s);
1418			goto error;
1419		}
1420
1421		s->s_flags |= SB_ACTIVE;
1422		bdev->bd_super = s;
1423	}
1424
1425	return dget(s->s_root);
1426
1427error_s:
1428	error = PTR_ERR(s);
1429error_bdev:
1430	blkdev_put(bdev, mode);
1431error:
1432	return ERR_PTR(error);
1433}
1434EXPORT_SYMBOL(mount_bdev);
1435
1436void kill_block_super(struct super_block *sb)
1437{
1438	struct block_device *bdev = sb->s_bdev;
1439	fmode_t mode = sb->s_mode;
1440
1441	bdev->bd_super = NULL;
1442	generic_shutdown_super(sb);
1443	sync_blockdev(bdev);
1444	WARN_ON_ONCE(!(mode & FMODE_EXCL));
1445	blkdev_put(bdev, mode | FMODE_EXCL);
1446}
1447
1448EXPORT_SYMBOL(kill_block_super);
1449#endif
1450
1451struct dentry *mount_nodev(struct file_system_type *fs_type,
1452	int flags, void *data,
1453	int (*fill_super)(struct super_block *, void *, int))
1454{
1455	int error;
1456	struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1457
1458	if (IS_ERR(s))
1459		return ERR_CAST(s);
1460
1461	error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1462	if (error) {
1463		deactivate_locked_super(s);
1464		return ERR_PTR(error);
1465	}
1466	s->s_flags |= SB_ACTIVE;
1467	return dget(s->s_root);
1468}
1469EXPORT_SYMBOL(mount_nodev);
1470
1471static int reconfigure_single(struct super_block *s,
1472			      int flags, void *data)
1473{
1474	struct fs_context *fc;
1475	int ret;
1476
1477	/* The caller really need to be passing fc down into mount_single(),
1478	 * then a chunk of this can be removed.  [Bollocks -- AV]
1479	 * Better yet, reconfiguration shouldn't happen, but rather the second
1480	 * mount should be rejected if the parameters are not compatible.
1481	 */
1482	fc = fs_context_for_reconfigure(s->s_root, flags, MS_RMT_MASK);
1483	if (IS_ERR(fc))
1484		return PTR_ERR(fc);
1485
1486	ret = parse_monolithic_mount_data(fc, data);
1487	if (ret < 0)
1488		goto out;
1489
1490	ret = reconfigure_super(fc);
1491out:
1492	put_fs_context(fc);
1493	return ret;
1494}
1495
1496static int compare_single(struct super_block *s, void *p)
1497{
1498	return 1;
1499}
1500
1501struct dentry *mount_single(struct file_system_type *fs_type,
1502	int flags, void *data,
1503	int (*fill_super)(struct super_block *, void *, int))
1504{
1505	struct super_block *s;
1506	int error;
1507
1508	s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1509	if (IS_ERR(s))
1510		return ERR_CAST(s);
1511	if (!s->s_root) {
1512		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
1513		if (!error)
1514			s->s_flags |= SB_ACTIVE;
1515	} else {
1516		error = reconfigure_single(s, flags, data);
1517	}
1518	if (unlikely(error)) {
1519		deactivate_locked_super(s);
1520		return ERR_PTR(error);
1521	}
1522	return dget(s->s_root);
1523}
1524EXPORT_SYMBOL(mount_single);
1525
1526/**
1527 * vfs_get_tree - Get the mountable root
1528 * @fc: The superblock configuration context.
1529 *
1530 * The filesystem is invoked to get or create a superblock which can then later
1531 * be used for mounting.  The filesystem places a pointer to the root to be
1532 * used for mounting in @fc->root.
1533 */
1534int vfs_get_tree(struct fs_context *fc)
1535{
1536	struct super_block *sb;
1537	int error;
1538
1539	if (fc->root)
1540		return -EBUSY;
1541
1542	/* Get the mountable root in fc->root, with a ref on the root and a ref
1543	 * on the superblock.
1544	 */
1545	error = fc->ops->get_tree(fc);
1546	if (error < 0)
1547		return error;
1548
1549	if (!fc->root) {
1550		pr_err("Filesystem %s get_tree() didn't set fc->root\n",
1551		       fc->fs_type->name);
1552		/* We don't know what the locking state of the superblock is -
1553		 * if there is a superblock.
1554		 */
1555		BUG();
1556	}
1557
1558	sb = fc->root->d_sb;
1559	WARN_ON(!sb->s_bdi);
1560
1561	/*
1562	 * Write barrier is for super_cache_count(). We place it before setting
1563	 * SB_BORN as the data dependency between the two functions is the
1564	 * superblock structure contents that we just set up, not the SB_BORN
1565	 * flag.
1566	 */
1567	smp_wmb();
1568	sb->s_flags |= SB_BORN;
1569
1570	error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
1571	if (unlikely(error)) {
1572		fc_drop_locked(fc);
1573		return error;
1574	}
1575
1576	/*
1577	 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1578	 * but s_maxbytes was an unsigned long long for many releases. Throw
1579	 * this warning for a little while to try and catch filesystems that
1580	 * violate this rule.
1581	 */
1582	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1583		"negative value (%lld)\n", fc->fs_type->name, sb->s_maxbytes);
1584
1585	return 0;
1586}
1587EXPORT_SYMBOL(vfs_get_tree);
1588
1589/*
1590 * Setup private BDI for given superblock. It gets automatically cleaned up
1591 * in generic_shutdown_super().
1592 */
1593int super_setup_bdi_name(struct super_block *sb, char *fmt, ...)
1594{
1595	struct backing_dev_info *bdi;
1596	int err;
1597	va_list args;
1598
1599	bdi = bdi_alloc(GFP_KERNEL);
1600	if (!bdi)
1601		return -ENOMEM;
1602
1603	bdi->name = sb->s_type->name;
1604
1605	va_start(args, fmt);
1606	err = bdi_register_va(bdi, fmt, args);
1607	va_end(args);
1608	if (err) {
1609		bdi_put(bdi);
1610		return err;
1611	}
1612	WARN_ON(sb->s_bdi != &noop_backing_dev_info);
1613	sb->s_bdi = bdi;
 
1614
1615	return 0;
1616}
1617EXPORT_SYMBOL(super_setup_bdi_name);
1618
1619/*
1620 * Setup private BDI for given superblock. I gets automatically cleaned up
1621 * in generic_shutdown_super().
1622 */
1623int super_setup_bdi(struct super_block *sb)
1624{
1625	static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
1626
1627	return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name,
1628				    atomic_long_inc_return(&bdi_seq));
1629}
1630EXPORT_SYMBOL(super_setup_bdi);
1631
1632/*
1633 * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1634 * instead.
1635 */
1636void __sb_end_write(struct super_block *sb, int level)
1637{
1638	percpu_up_read(sb->s_writers.rw_sem + level-1);
1639}
1640EXPORT_SYMBOL(__sb_end_write);
1641
1642/*
1643 * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1644 * instead.
1645 */
1646int __sb_start_write(struct super_block *sb, int level, bool wait)
1647{
1648	bool force_trylock = false;
1649	int ret = 1;
1650
1651#ifdef CONFIG_LOCKDEP
1652	/*
1653	 * We want lockdep to tell us about possible deadlocks with freezing
1654	 * but it's it bit tricky to properly instrument it. Getting a freeze
1655	 * protection works as getting a read lock but there are subtle
1656	 * problems. XFS for example gets freeze protection on internal level
1657	 * twice in some cases, which is OK only because we already hold a
1658	 * freeze protection also on higher level. Due to these cases we have
1659	 * to use wait == F (trylock mode) which must not fail.
1660	 */
1661	if (wait) {
1662		int i;
1663
1664		for (i = 0; i < level - 1; i++)
1665			if (percpu_rwsem_is_held(sb->s_writers.rw_sem + i)) {
1666				force_trylock = true;
1667				break;
1668			}
1669	}
1670#endif
1671	if (wait && !force_trylock)
1672		percpu_down_read(sb->s_writers.rw_sem + level-1);
1673	else
1674		ret = percpu_down_read_trylock(sb->s_writers.rw_sem + level-1);
1675
1676	WARN_ON(force_trylock && !ret);
1677	return ret;
1678}
1679EXPORT_SYMBOL(__sb_start_write);
1680
1681/**
1682 * sb_wait_write - wait until all writers to given file system finish
1683 * @sb: the super for which we wait
1684 * @level: type of writers we wait for (normal vs page fault)
1685 *
1686 * This function waits until there are no writers of given type to given file
1687 * system.
1688 */
1689static void sb_wait_write(struct super_block *sb, int level)
1690{
1691	percpu_down_write(sb->s_writers.rw_sem + level-1);
1692}
1693
1694/*
1695 * We are going to return to userspace and forget about these locks, the
1696 * ownership goes to the caller of thaw_super() which does unlock().
1697 */
1698static void lockdep_sb_freeze_release(struct super_block *sb)
1699{
1700	int level;
1701
1702	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1703		percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1704}
1705
1706/*
1707 * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).
1708 */
1709static void lockdep_sb_freeze_acquire(struct super_block *sb)
1710{
1711	int level;
1712
1713	for (level = 0; level < SB_FREEZE_LEVELS; ++level)
1714		percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
1715}
1716
1717static void sb_freeze_unlock(struct super_block *sb)
1718{
1719	int level;
1720
1721	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
1722		percpu_up_write(sb->s_writers.rw_sem + level);
1723}
1724
1725/**
1726 * freeze_super - lock the filesystem and force it into a consistent state
1727 * @sb: the super to lock
1728 *
1729 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1730 * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1731 * -EBUSY.
1732 *
1733 * During this function, sb->s_writers.frozen goes through these values:
1734 *
1735 * SB_UNFROZEN: File system is normal, all writes progress as usual.
1736 *
1737 * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1738 * writes should be blocked, though page faults are still allowed. We wait for
1739 * all writes to complete and then proceed to the next stage.
1740 *
1741 * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1742 * but internal fs threads can still modify the filesystem (although they
1743 * should not dirty new pages or inodes), writeback can run etc. After waiting
1744 * for all running page faults we sync the filesystem which will clean all
1745 * dirty pages and inodes (no new dirty pages or inodes can be created when
1746 * sync is running).
1747 *
1748 * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1749 * modification are blocked (e.g. XFS preallocation truncation on inode
1750 * reclaim). This is usually implemented by blocking new transactions for
1751 * filesystems that have them and need this additional guard. After all
1752 * internal writers are finished we call ->freeze_fs() to finish filesystem
1753 * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1754 * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1755 *
1756 * sb->s_writers.frozen is protected by sb->s_umount.
1757 */
1758int freeze_super(struct super_block *sb)
1759{
1760	int ret;
1761
1762	atomic_inc(&sb->s_active);
1763	down_write(&sb->s_umount);
1764	if (sb->s_writers.frozen != SB_UNFROZEN) {
1765		deactivate_locked_super(sb);
1766		return -EBUSY;
1767	}
1768
1769	if (!(sb->s_flags & SB_BORN)) {
1770		up_write(&sb->s_umount);
1771		return 0;	/* sic - it's "nothing to do" */
1772	}
1773
1774	if (sb_rdonly(sb)) {
1775		/* Nothing to do really... */
1776		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1777		up_write(&sb->s_umount);
1778		return 0;
1779	}
1780
1781	sb->s_writers.frozen = SB_FREEZE_WRITE;
1782	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
1783	up_write(&sb->s_umount);
1784	sb_wait_write(sb, SB_FREEZE_WRITE);
1785	down_write(&sb->s_umount);
1786
1787	/* Now we go and block page faults... */
1788	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1789	sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1790
1791	/* All writers are done so after syncing there won't be dirty data */
1792	sync_filesystem(sb);
 
 
 
 
 
 
 
1793
1794	/* Now wait for internal filesystem counter */
1795	sb->s_writers.frozen = SB_FREEZE_FS;
1796	sb_wait_write(sb, SB_FREEZE_FS);
1797
1798	if (sb->s_op->freeze_fs) {
1799		ret = sb->s_op->freeze_fs(sb);
1800		if (ret) {
1801			printk(KERN_ERR
1802				"VFS:Filesystem freeze failed\n");
1803			sb->s_writers.frozen = SB_UNFROZEN;
1804			sb_freeze_unlock(sb);
1805			wake_up(&sb->s_writers.wait_unfrozen);
1806			deactivate_locked_super(sb);
1807			return ret;
1808		}
1809	}
1810	/*
1811	 * For debugging purposes so that fs can warn if it sees write activity
1812	 * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
1813	 */
1814	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1815	lockdep_sb_freeze_release(sb);
1816	up_write(&sb->s_umount);
1817	return 0;
1818}
1819EXPORT_SYMBOL(freeze_super);
1820
1821/**
1822 * thaw_super -- unlock filesystem
1823 * @sb: the super to thaw
1824 *
1825 * Unlocks the filesystem and marks it writeable again after freeze_super().
1826 */
1827static int thaw_super_locked(struct super_block *sb)
1828{
1829	int error;
1830
1831	if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
1832		up_write(&sb->s_umount);
1833		return -EINVAL;
1834	}
1835
1836	if (sb_rdonly(sb)) {
1837		sb->s_writers.frozen = SB_UNFROZEN;
1838		goto out;
1839	}
1840
1841	lockdep_sb_freeze_acquire(sb);
1842
1843	if (sb->s_op->unfreeze_fs) {
1844		error = sb->s_op->unfreeze_fs(sb);
1845		if (error) {
1846			printk(KERN_ERR
1847				"VFS:Filesystem thaw failed\n");
1848			lockdep_sb_freeze_release(sb);
1849			up_write(&sb->s_umount);
1850			return error;
1851		}
1852	}
1853
1854	sb->s_writers.frozen = SB_UNFROZEN;
1855	sb_freeze_unlock(sb);
1856out:
1857	wake_up(&sb->s_writers.wait_unfrozen);
1858	deactivate_locked_super(sb);
1859	return 0;
1860}
1861
 
 
 
 
 
 
1862int thaw_super(struct super_block *sb)
1863{
1864	down_write(&sb->s_umount);
1865	return thaw_super_locked(sb);
1866}
1867EXPORT_SYMBOL(thaw_super);