1/*
   2 *  linux/fs/buffer.c
   3 *
   4 *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
   5 */
   6
   7/*
   8 * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
   9 *
  10 * Removed a lot of unnecessary code and simplified things now that
  11 * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
  12 *
  13 * Speed up hash, lru, and free list operations.  Use gfp() for allocating
  14 * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
  15 *
  16 * Added 32k buffer block sizes - these are required older ARM systems. - RMK
  17 *
  18 * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
  19 */
  20
  21#include <linux/kernel.h>
  22#include <linux/syscalls.h>
  23#include <linux/fs.h>
  24#include <linux/mm.h>
  25#include <linux/percpu.h>
  26#include <linux/slab.h>
  27#include <linux/capability.h>
  28#include <linux/blkdev.h>
  29#include <linux/file.h>
  30#include <linux/quotaops.h>
  31#include <linux/highmem.h>
  32#include <linux/export.h>
  33#include <linux/backing-dev.h>
  34#include <linux/writeback.h>
  35#include <linux/hash.h>
  36#include <linux/suspend.h>
  37#include <linux/buffer_head.h>
  38#include <linux/task_io_accounting_ops.h>
  39#include <linux/bio.h>
  40#include <linux/notifier.h>
  41#include <linux/cpu.h>
  42#include <linux/bitops.h>
  43#include <linux/mpage.h>
  44#include <linux/bit_spinlock.h>
  45#include <trace/events/block.h>
  46
  47static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
  48static int submit_bh_wbc(int rw, struct buffer_head *bh,
  49			 unsigned long bio_flags,
  50			 struct writeback_control *wbc);
  51
  52#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
  53
  54void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
 
  55{
  56	bh->b_end_io = handler;
  57	bh->b_private = private;
  58}
  59EXPORT_SYMBOL(init_buffer);
  60
  61inline void touch_buffer(struct buffer_head *bh)
  62{
  63	trace_block_touch_buffer(bh);
  64	mark_page_accessed(bh->b_page);
  65}
  66EXPORT_SYMBOL(touch_buffer);
  67
  68void __lock_buffer(struct buffer_head *bh)
  69{
  70	wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
 
  71}
  72EXPORT_SYMBOL(__lock_buffer);
  73
  74void unlock_buffer(struct buffer_head *bh)
  75{
  76	clear_bit_unlock(BH_Lock, &bh->b_state);
  77	smp_mb__after_atomic();
  78	wake_up_bit(&bh->b_state, BH_Lock);
  79}
  80EXPORT_SYMBOL(unlock_buffer);
  81
  82/*
  83 * Returns if the page has dirty or writeback buffers. If all the buffers
  84 * are unlocked and clean then the PageDirty information is stale. If
  85 * any of the pages are locked, it is assumed they are locked for IO.
  86 */
  87void buffer_check_dirty_writeback(struct page *page,
  88				     bool *dirty, bool *writeback)
  89{
  90	struct buffer_head *head, *bh;
  91	*dirty = false;
  92	*writeback = false;
  93
  94	BUG_ON(!PageLocked(page));
  95
  96	if (!page_has_buffers(page))
  97		return;
  98
  99	if (PageWriteback(page))
 100		*writeback = true;
 101
 102	head = page_buffers(page);
 103	bh = head;
 104	do {
 105		if (buffer_locked(bh))
 106			*writeback = true;
 107
 108		if (buffer_dirty(bh))
 109			*dirty = true;
 110
 111		bh = bh->b_this_page;
 112	} while (bh != head);
 113}
 114EXPORT_SYMBOL(buffer_check_dirty_writeback);
 115
 116/*
 117 * Block until a buffer comes unlocked.  This doesn't stop it
 118 * from becoming locked again - you have to lock it yourself
 119 * if you want to preserve its state.
 120 */
 121void __wait_on_buffer(struct buffer_head * bh)
 122{
 123	wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
 124}
 125EXPORT_SYMBOL(__wait_on_buffer);
 126
 127static void
 128__clear_page_buffers(struct page *page)
 129{
 130	ClearPagePrivate(page);
 131	set_page_private(page, 0);
 132	put_page(page);
 133}
 134
 135static void buffer_io_error(struct buffer_head *bh, char *msg)
 
 136{
 137	if (!test_bit(BH_Quiet, &bh->b_state))
 138		printk_ratelimited(KERN_ERR
 139			"Buffer I/O error on dev %pg, logical block %llu%s\n",
 140			bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
 
 
 
 
 
 
 
 
 141}
 142
 143/*
 144 * End-of-IO handler helper function which does not touch the bh after
 145 * unlocking it.
 146 * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
 147 * a race there is benign: unlock_buffer() only use the bh's address for
 148 * hashing after unlocking the buffer, so it doesn't actually touch the bh
 149 * itself.
 150 */
 151static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
 152{
 153	if (uptodate) {
 154		set_buffer_uptodate(bh);
 155	} else {
 156		/* This happens, due to failed READA attempts. */
 157		clear_buffer_uptodate(bh);
 158	}
 159	unlock_buffer(bh);
 160}
 161
 162/*
 163 * Default synchronous end-of-IO handler..  Just mark it up-to-date and
 164 * unlock the buffer. This is what ll_rw_block uses too.
 165 */
 166void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
 167{
 168	__end_buffer_read_notouch(bh, uptodate);
 169	put_bh(bh);
 170}
 171EXPORT_SYMBOL(end_buffer_read_sync);
 172
 173void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 174{
 
 
 175	if (uptodate) {
 176		set_buffer_uptodate(bh);
 177	} else {
 178		buffer_io_error(bh, ", lost sync page write");
 
 
 
 
 
 179		set_buffer_write_io_error(bh);
 180		clear_buffer_uptodate(bh);
 181	}
 182	unlock_buffer(bh);
 183	put_bh(bh);
 184}
 185EXPORT_SYMBOL(end_buffer_write_sync);
 186
 187/*
 188 * Various filesystems appear to want __find_get_block to be non-blocking.
 189 * But it's the page lock which protects the buffers.  To get around this,
 190 * we get exclusion from try_to_free_buffers with the blockdev mapping's
 191 * private_lock.
 192 *
 193 * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
 194 * may be quite high.  This code could TryLock the page, and if that
 195 * succeeds, there is no need to take private_lock. (But if
 196 * private_lock is contended then so is mapping->tree_lock).
 197 */
 198static struct buffer_head *
 199__find_get_block_slow(struct block_device *bdev, sector_t block)
 200{
 201	struct inode *bd_inode = bdev->bd_inode;
 202	struct address_space *bd_mapping = bd_inode->i_mapping;
 203	struct buffer_head *ret = NULL;
 204	pgoff_t index;
 205	struct buffer_head *bh;
 206	struct buffer_head *head;
 207	struct page *page;
 208	int all_mapped = 1;
 209
 210	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
 211	page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
 212	if (!page)
 213		goto out;
 214
 215	spin_lock(&bd_mapping->private_lock);
 216	if (!page_has_buffers(page))
 217		goto out_unlock;
 218	head = page_buffers(page);
 219	bh = head;
 220	do {
 221		if (!buffer_mapped(bh))
 222			all_mapped = 0;
 223		else if (bh->b_blocknr == block) {
 224			ret = bh;
 225			get_bh(bh);
 226			goto out_unlock;
 227		}
 228		bh = bh->b_this_page;
 229	} while (bh != head);
 230
 231	/* we might be here because some of the buffers on this page are
 232	 * not mapped.  This is due to various races between
 233	 * file io on the block device and getblk.  It gets dealt with
 234	 * elsewhere, don't buffer_error if we had some unmapped buffers
 235	 */
 236	if (all_mapped) {
 
 
 237		printk("__find_get_block_slow() failed. "
 238			"block=%llu, b_blocknr=%llu\n",
 239			(unsigned long long)block,
 240			(unsigned long long)bh->b_blocknr);
 241		printk("b_state=0x%08lx, b_size=%zu\n",
 242			bh->b_state, bh->b_size);
 243		printk("device %pg blocksize: %d\n", bdev,
 244			1 << bd_inode->i_blkbits);
 245	}
 246out_unlock:
 247	spin_unlock(&bd_mapping->private_lock);
 248	put_page(page);
 249out:
 250	return ret;
 251}
 252
 253/*
 254 * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
 255 */
 256static void free_more_memory(void)
 257{
 258	struct zone *zone;
 259	int nid;
 260
 261	wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
 262	yield();
 263
 264	for_each_online_node(nid) {
 265		(void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
 266						gfp_zone(GFP_NOFS), NULL,
 267						&zone);
 268		if (zone)
 269			try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
 270						GFP_NOFS, NULL);
 271	}
 272}
 273
 274/*
 275 * I/O completion handler for block_read_full_page() - pages
 276 * which come unlocked at the end of I/O.
 277 */
 278static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 279{
 280	unsigned long flags;
 281	struct buffer_head *first;
 282	struct buffer_head *tmp;
 283	struct page *page;
 284	int page_uptodate = 1;
 285
 286	BUG_ON(!buffer_async_read(bh));
 287
 288	page = bh->b_page;
 289	if (uptodate) {
 290		set_buffer_uptodate(bh);
 291	} else {
 292		clear_buffer_uptodate(bh);
 293		buffer_io_error(bh, ", async page read");
 
 294		SetPageError(page);
 295	}
 296
 297	/*
 298	 * Be _very_ careful from here on. Bad things can happen if
 299	 * two buffer heads end IO at almost the same time and both
 300	 * decide that the page is now completely done.
 301	 */
 302	first = page_buffers(page);
 303	local_irq_save(flags);
 304	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 305	clear_buffer_async_read(bh);
 306	unlock_buffer(bh);
 307	tmp = bh;
 308	do {
 309		if (!buffer_uptodate(tmp))
 310			page_uptodate = 0;
 311		if (buffer_async_read(tmp)) {
 312			BUG_ON(!buffer_locked(tmp));
 313			goto still_busy;
 314		}
 315		tmp = tmp->b_this_page;
 316	} while (tmp != bh);
 317	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 318	local_irq_restore(flags);
 319
 320	/*
 321	 * If none of the buffers had errors and they are all
 322	 * uptodate then we can set the page uptodate.
 323	 */
 324	if (page_uptodate && !PageError(page))
 325		SetPageUptodate(page);
 326	unlock_page(page);
 327	return;
 328
 329still_busy:
 330	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 331	local_irq_restore(flags);
 332	return;
 333}
 334
 335/*
 336 * Completion handler for block_write_full_page() - pages which are unlocked
 337 * during I/O, and which have PageWriteback cleared upon I/O completion.
 338 */
 339void end_buffer_async_write(struct buffer_head *bh, int uptodate)
 340{
 
 341	unsigned long flags;
 342	struct buffer_head *first;
 343	struct buffer_head *tmp;
 344	struct page *page;
 345
 346	BUG_ON(!buffer_async_write(bh));
 347
 348	page = bh->b_page;
 349	if (uptodate) {
 350		set_buffer_uptodate(bh);
 351	} else {
 352		buffer_io_error(bh, ", lost async page write");
 
 
 
 
 
 353		set_bit(AS_EIO, &page->mapping->flags);
 354		set_buffer_write_io_error(bh);
 355		clear_buffer_uptodate(bh);
 356		SetPageError(page);
 357	}
 358
 359	first = page_buffers(page);
 360	local_irq_save(flags);
 361	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 362
 363	clear_buffer_async_write(bh);
 364	unlock_buffer(bh);
 365	tmp = bh->b_this_page;
 366	while (tmp != bh) {
 367		if (buffer_async_write(tmp)) {
 368			BUG_ON(!buffer_locked(tmp));
 369			goto still_busy;
 370		}
 371		tmp = tmp->b_this_page;
 372	}
 373	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 374	local_irq_restore(flags);
 375	end_page_writeback(page);
 376	return;
 377
 378still_busy:
 379	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 380	local_irq_restore(flags);
 381	return;
 382}
 383EXPORT_SYMBOL(end_buffer_async_write);
 384
 385/*
 386 * If a page's buffers are under async readin (end_buffer_async_read
 387 * completion) then there is a possibility that another thread of
 388 * control could lock one of the buffers after it has completed
 389 * but while some of the other buffers have not completed.  This
 390 * locked buffer would confuse end_buffer_async_read() into not unlocking
 391 * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
 392 * that this buffer is not under async I/O.
 393 *
 394 * The page comes unlocked when it has no locked buffer_async buffers
 395 * left.
 396 *
 397 * PageLocked prevents anyone starting new async I/O reads any of
 398 * the buffers.
 399 *
 400 * PageWriteback is used to prevent simultaneous writeout of the same
 401 * page.
 402 *
 403 * PageLocked prevents anyone from starting writeback of a page which is
 404 * under read I/O (PageWriteback is only ever set against a locked page).
 405 */
 406static void mark_buffer_async_read(struct buffer_head *bh)
 407{
 408	bh->b_end_io = end_buffer_async_read;
 409	set_buffer_async_read(bh);
 410}
 411
 412static void mark_buffer_async_write_endio(struct buffer_head *bh,
 413					  bh_end_io_t *handler)
 414{
 415	bh->b_end_io = handler;
 416	set_buffer_async_write(bh);
 417}
 418
 419void mark_buffer_async_write(struct buffer_head *bh)
 420{
 421	mark_buffer_async_write_endio(bh, end_buffer_async_write);
 422}
 423EXPORT_SYMBOL(mark_buffer_async_write);
 424
 425
 426/*
 427 * fs/buffer.c contains helper functions for buffer-backed address space's
 428 * fsync functions.  A common requirement for buffer-based filesystems is
 429 * that certain data from the backing blockdev needs to be written out for
 430 * a successful fsync().  For example, ext2 indirect blocks need to be
 431 * written back and waited upon before fsync() returns.
 432 *
 433 * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
 434 * inode_has_buffers() and invalidate_inode_buffers() are provided for the
 435 * management of a list of dependent buffers at ->i_mapping->private_list.
 436 *
 437 * Locking is a little subtle: try_to_free_buffers() will remove buffers
 438 * from their controlling inode's queue when they are being freed.  But
 439 * try_to_free_buffers() will be operating against the *blockdev* mapping
 440 * at the time, not against the S_ISREG file which depends on those buffers.
 441 * So the locking for private_list is via the private_lock in the address_space
 442 * which backs the buffers.  Which is different from the address_space 
 443 * against which the buffers are listed.  So for a particular address_space,
 444 * mapping->private_lock does *not* protect mapping->private_list!  In fact,
 445 * mapping->private_list will always be protected by the backing blockdev's
 446 * ->private_lock.
 447 *
 448 * Which introduces a requirement: all buffers on an address_space's
 449 * ->private_list must be from the same address_space: the blockdev's.
 450 *
 451 * address_spaces which do not place buffers at ->private_list via these
 452 * utility functions are free to use private_lock and private_list for
 453 * whatever they want.  The only requirement is that list_empty(private_list)
 454 * be true at clear_inode() time.
 455 *
 456 * FIXME: clear_inode should not call invalidate_inode_buffers().  The
 457 * filesystems should do that.  invalidate_inode_buffers() should just go
 458 * BUG_ON(!list_empty).
 459 *
 460 * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
 461 * take an address_space, not an inode.  And it should be called
 462 * mark_buffer_dirty_fsync() to clearly define why those buffers are being
 463 * queued up.
 464 *
 465 * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
 466 * list if it is already on a list.  Because if the buffer is on a list,
 467 * it *must* already be on the right one.  If not, the filesystem is being
 468 * silly.  This will save a ton of locking.  But first we have to ensure
 469 * that buffers are taken *off* the old inode's list when they are freed
 470 * (presumably in truncate).  That requires careful auditing of all
 471 * filesystems (do it inside bforget()).  It could also be done by bringing
 472 * b_inode back.
 473 */
 474
 475/*
 476 * The buffer's backing address_space's private_lock must be held
 477 */
 478static void __remove_assoc_queue(struct buffer_head *bh)
 479{
 480	list_del_init(&bh->b_assoc_buffers);
 481	WARN_ON(!bh->b_assoc_map);
 482	if (buffer_write_io_error(bh))
 483		set_bit(AS_EIO, &bh->b_assoc_map->flags);
 484	bh->b_assoc_map = NULL;
 485}
 486
 487int inode_has_buffers(struct inode *inode)
 488{
 489	return !list_empty(&inode->i_data.private_list);
 490}
 491
 492/*
 493 * osync is designed to support O_SYNC io.  It waits synchronously for
 494 * all already-submitted IO to complete, but does not queue any new
 495 * writes to the disk.
 496 *
 497 * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
 498 * you dirty the buffers, and then use osync_inode_buffers to wait for
 499 * completion.  Any other dirty buffers which are not yet queued for
 500 * write will not be flushed to disk by the osync.
 501 */
 502static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 503{
 504	struct buffer_head *bh;
 505	struct list_head *p;
 506	int err = 0;
 507
 508	spin_lock(lock);
 509repeat:
 510	list_for_each_prev(p, list) {
 511		bh = BH_ENTRY(p);
 512		if (buffer_locked(bh)) {
 513			get_bh(bh);
 514			spin_unlock(lock);
 515			wait_on_buffer(bh);
 516			if (!buffer_uptodate(bh))
 517				err = -EIO;
 518			brelse(bh);
 519			spin_lock(lock);
 520			goto repeat;
 521		}
 522	}
 523	spin_unlock(lock);
 524	return err;
 525}
 526
 527static void do_thaw_one(struct super_block *sb, void *unused)
 528{
 
 529	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
 530		printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
 
 531}
 532
 533static void do_thaw_all(struct work_struct *work)
 534{
 535	iterate_supers(do_thaw_one, NULL);
 536	kfree(work);
 537	printk(KERN_WARNING "Emergency Thaw complete\n");
 538}
 539
 540/**
 541 * emergency_thaw_all -- forcibly thaw every frozen filesystem
 542 *
 543 * Used for emergency unfreeze of all filesystems via SysRq
 544 */
 545void emergency_thaw_all(void)
 546{
 547	struct work_struct *work;
 548
 549	work = kmalloc(sizeof(*work), GFP_ATOMIC);
 550	if (work) {
 551		INIT_WORK(work, do_thaw_all);
 552		schedule_work(work);
 553	}
 554}
 555
 556/**
 557 * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
 558 * @mapping: the mapping which wants those buffers written
 559 *
 560 * Starts I/O against the buffers at mapping->private_list, and waits upon
 561 * that I/O.
 562 *
 563 * Basically, this is a convenience function for fsync().
 564 * @mapping is a file or directory which needs those buffers to be written for
 565 * a successful fsync().
 566 */
 567int sync_mapping_buffers(struct address_space *mapping)
 568{
 569	struct address_space *buffer_mapping = mapping->private_data;
 570
 571	if (buffer_mapping == NULL || list_empty(&mapping->private_list))
 572		return 0;
 573
 574	return fsync_buffers_list(&buffer_mapping->private_lock,
 575					&mapping->private_list);
 576}
 577EXPORT_SYMBOL(sync_mapping_buffers);
 578
 579/*
 580 * Called when we've recently written block `bblock', and it is known that
 581 * `bblock' was for a buffer_boundary() buffer.  This means that the block at
 582 * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
 583 * dirty, schedule it for IO.  So that indirects merge nicely with their data.
 584 */
 585void write_boundary_block(struct block_device *bdev,
 586			sector_t bblock, unsigned blocksize)
 587{
 588	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
 589	if (bh) {
 590		if (buffer_dirty(bh))
 591			ll_rw_block(WRITE, 1, &bh);
 592		put_bh(bh);
 593	}
 594}
 595
 596void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 597{
 598	struct address_space *mapping = inode->i_mapping;
 599	struct address_space *buffer_mapping = bh->b_page->mapping;
 600
 601	mark_buffer_dirty(bh);
 602	if (!mapping->private_data) {
 603		mapping->private_data = buffer_mapping;
 604	} else {
 605		BUG_ON(mapping->private_data != buffer_mapping);
 606	}
 607	if (!bh->b_assoc_map) {
 608		spin_lock(&buffer_mapping->private_lock);
 609		list_move_tail(&bh->b_assoc_buffers,
 610				&mapping->private_list);
 611		bh->b_assoc_map = mapping;
 612		spin_unlock(&buffer_mapping->private_lock);
 613	}
 614}
 615EXPORT_SYMBOL(mark_buffer_dirty_inode);
 616
 617/*
 618 * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
 619 * dirty.
 620 *
 621 * If warn is true, then emit a warning if the page is not uptodate and has
 622 * not been truncated.
 623 *
 624 * The caller must hold lock_page_memcg().
 625 */
 626static void __set_page_dirty(struct page *page, struct address_space *mapping,
 627			     int warn)
 628{
 629	unsigned long flags;
 630
 631	spin_lock_irqsave(&mapping->tree_lock, flags);
 632	if (page->mapping) {	/* Race with truncate? */
 633		WARN_ON_ONCE(warn && !PageUptodate(page));
 634		account_page_dirtied(page, mapping);
 635		radix_tree_tag_set(&mapping->page_tree,
 636				page_index(page), PAGECACHE_TAG_DIRTY);
 637	}
 638	spin_unlock_irqrestore(&mapping->tree_lock, flags);
 
 639}
 640
 641/*
 642 * Add a page to the dirty page list.
 643 *
 644 * It is a sad fact of life that this function is called from several places
 645 * deeply under spinlocking.  It may not sleep.
 646 *
 647 * If the page has buffers, the uptodate buffers are set dirty, to preserve
 648 * dirty-state coherency between the page and the buffers.  It the page does
 649 * not have buffers then when they are later attached they will all be set
 650 * dirty.
 651 *
 652 * The buffers are dirtied before the page is dirtied.  There's a small race
 653 * window in which a writepage caller may see the page cleanness but not the
 654 * buffer dirtiness.  That's fine.  If this code were to set the page dirty
 655 * before the buffers, a concurrent writepage caller could clear the page dirty
 656 * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
 657 * page on the dirty page list.
 658 *
 659 * We use private_lock to lock against try_to_free_buffers while using the
 660 * page's buffer list.  Also use this to protect against clean buffers being
 661 * added to the page after it was set dirty.
 662 *
 663 * FIXME: may need to call ->reservepage here as well.  That's rather up to the
 664 * address_space though.
 665 */
 666int __set_page_dirty_buffers(struct page *page)
 667{
 668	int newly_dirty;
 669	struct address_space *mapping = page_mapping(page);
 670
 671	if (unlikely(!mapping))
 672		return !TestSetPageDirty(page);
 673
 674	spin_lock(&mapping->private_lock);
 675	if (page_has_buffers(page)) {
 676		struct buffer_head *head = page_buffers(page);
 677		struct buffer_head *bh = head;
 678
 679		do {
 680			set_buffer_dirty(bh);
 681			bh = bh->b_this_page;
 682		} while (bh != head);
 683	}
 684	/*
 685	 * Lock out page->mem_cgroup migration to keep PageDirty
 686	 * synchronized with per-memcg dirty page counters.
 687	 */
 688	lock_page_memcg(page);
 689	newly_dirty = !TestSetPageDirty(page);
 690	spin_unlock(&mapping->private_lock);
 691
 692	if (newly_dirty)
 693		__set_page_dirty(page, mapping, 1);
 694
 695	unlock_page_memcg(page);
 696
 697	if (newly_dirty)
 698		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 699
 700	return newly_dirty;
 701}
 702EXPORT_SYMBOL(__set_page_dirty_buffers);
 703
 704/*
 705 * Write out and wait upon a list of buffers.
 706 *
 707 * We have conflicting pressures: we want to make sure that all
 708 * initially dirty buffers get waited on, but that any subsequently
 709 * dirtied buffers don't.  After all, we don't want fsync to last
 710 * forever if somebody is actively writing to the file.
 711 *
 712 * Do this in two main stages: first we copy dirty buffers to a
 713 * temporary inode list, queueing the writes as we go.  Then we clean
 714 * up, waiting for those writes to complete.
 715 * 
 716 * During this second stage, any subsequent updates to the file may end
 717 * up refiling the buffer on the original inode's dirty list again, so
 718 * there is a chance we will end up with a buffer queued for write but
 719 * not yet completed on that list.  So, as a final cleanup we go through
 720 * the osync code to catch these locked, dirty buffers without requeuing
 721 * any newly dirty buffers for write.
 722 */
 723static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
 724{
 725	struct buffer_head *bh;
 726	struct list_head tmp;
 727	struct address_space *mapping;
 728	int err = 0, err2;
 729	struct blk_plug plug;
 730
 731	INIT_LIST_HEAD(&tmp);
 732	blk_start_plug(&plug);
 733
 734	spin_lock(lock);
 735	while (!list_empty(list)) {
 736		bh = BH_ENTRY(list->next);
 737		mapping = bh->b_assoc_map;
 738		__remove_assoc_queue(bh);
 739		/* Avoid race with mark_buffer_dirty_inode() which does
 740		 * a lockless check and we rely on seeing the dirty bit */
 741		smp_mb();
 742		if (buffer_dirty(bh) || buffer_locked(bh)) {
 743			list_add(&bh->b_assoc_buffers, &tmp);
 744			bh->b_assoc_map = mapping;
 745			if (buffer_dirty(bh)) {
 746				get_bh(bh);
 747				spin_unlock(lock);
 748				/*
 749				 * Ensure any pending I/O completes so that
 750				 * write_dirty_buffer() actually writes the
 751				 * current contents - it is a noop if I/O is
 752				 * still in flight on potentially older
 753				 * contents.
 754				 */
 755				write_dirty_buffer(bh, WRITE_SYNC);
 756
 757				/*
 758				 * Kick off IO for the previous mapping. Note
 759				 * that we will not run the very last mapping,
 760				 * wait_on_buffer() will do that for us
 761				 * through sync_buffer().
 762				 */
 763				brelse(bh);
 764				spin_lock(lock);
 765			}
 766		}
 767	}
 768
 769	spin_unlock(lock);
 770	blk_finish_plug(&plug);
 771	spin_lock(lock);
 772
 773	while (!list_empty(&tmp)) {
 774		bh = BH_ENTRY(tmp.prev);
 775		get_bh(bh);
 776		mapping = bh->b_assoc_map;
 777		__remove_assoc_queue(bh);
 778		/* Avoid race with mark_buffer_dirty_inode() which does
 779		 * a lockless check and we rely on seeing the dirty bit */
 780		smp_mb();
 781		if (buffer_dirty(bh)) {
 782			list_add(&bh->b_assoc_buffers,
 783				 &mapping->private_list);
 784			bh->b_assoc_map = mapping;
 785		}
 786		spin_unlock(lock);
 787		wait_on_buffer(bh);
 788		if (!buffer_uptodate(bh))
 789			err = -EIO;
 790		brelse(bh);
 791		spin_lock(lock);
 792	}
 793	
 794	spin_unlock(lock);
 795	err2 = osync_buffers_list(lock, list);
 796	if (err)
 797		return err;
 798	else
 799		return err2;
 800}
 801
 802/*
 803 * Invalidate any and all dirty buffers on a given inode.  We are
 804 * probably unmounting the fs, but that doesn't mean we have already
 805 * done a sync().  Just drop the buffers from the inode list.
 806 *
 807 * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
 808 * assumes that all the buffers are against the blockdev.  Not true
 809 * for reiserfs.
 810 */
 811void invalidate_inode_buffers(struct inode *inode)
 812{
 813	if (inode_has_buffers(inode)) {
 814		struct address_space *mapping = &inode->i_data;
 815		struct list_head *list = &mapping->private_list;
 816		struct address_space *buffer_mapping = mapping->private_data;
 817
 818		spin_lock(&buffer_mapping->private_lock);
 819		while (!list_empty(list))
 820			__remove_assoc_queue(BH_ENTRY(list->next));
 821		spin_unlock(&buffer_mapping->private_lock);
 822	}
 823}
 824EXPORT_SYMBOL(invalidate_inode_buffers);
 825
 826/*
 827 * Remove any clean buffers from the inode's buffer list.  This is called
 828 * when we're trying to free the inode itself.  Those buffers can pin it.
 829 *
 830 * Returns true if all buffers were removed.
 831 */
 832int remove_inode_buffers(struct inode *inode)
 833{
 834	int ret = 1;
 835
 836	if (inode_has_buffers(inode)) {
 837		struct address_space *mapping = &inode->i_data;
 838		struct list_head *list = &mapping->private_list;
 839		struct address_space *buffer_mapping = mapping->private_data;
 840
 841		spin_lock(&buffer_mapping->private_lock);
 842		while (!list_empty(list)) {
 843			struct buffer_head *bh = BH_ENTRY(list->next);
 844			if (buffer_dirty(bh)) {
 845				ret = 0;
 846				break;
 847			}
 848			__remove_assoc_queue(bh);
 849		}
 850		spin_unlock(&buffer_mapping->private_lock);
 851	}
 852	return ret;
 853}
 854
 855/*
 856 * Create the appropriate buffers when given a page for data area and
 857 * the size of each buffer.. Use the bh->b_this_page linked list to
 858 * follow the buffers created.  Return NULL if unable to create more
 859 * buffers.
 860 *
 861 * The retry flag is used to differentiate async IO (paging, swapping)
 862 * which may not fail from ordinary buffer allocations.
 863 */
 864struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 865		int retry)
 866{
 867	struct buffer_head *bh, *head;
 868	long offset;
 869
 870try_again:
 871	head = NULL;
 872	offset = PAGE_SIZE;
 873	while ((offset -= size) >= 0) {
 874		bh = alloc_buffer_head(GFP_NOFS);
 875		if (!bh)
 876			goto no_grow;
 877
 
 878		bh->b_this_page = head;
 879		bh->b_blocknr = -1;
 880		head = bh;
 881
 
 
 882		bh->b_size = size;
 883
 884		/* Link the buffer to its page */
 885		set_bh_page(bh, page, offset);
 
 
 886	}
 887	return head;
 888/*
 889 * In case anything failed, we just free everything we got.
 890 */
 891no_grow:
 892	if (head) {
 893		do {
 894			bh = head;
 895			head = head->b_this_page;
 896			free_buffer_head(bh);
 897		} while (head);
 898	}
 899
 900	/*
 901	 * Return failure for non-async IO requests.  Async IO requests
 902	 * are not allowed to fail, so we have to wait until buffer heads
 903	 * become available.  But we don't want tasks sleeping with 
 904	 * partially complete buffers, so all were released above.
 905	 */
 906	if (!retry)
 907		return NULL;
 908
 909	/* We're _really_ low on memory. Now we just
 910	 * wait for old buffer heads to become free due to
 911	 * finishing IO.  Since this is an async request and
 912	 * the reserve list is empty, we're sure there are 
 913	 * async buffer heads in use.
 914	 */
 915	free_more_memory();
 916	goto try_again;
 917}
 918EXPORT_SYMBOL_GPL(alloc_page_buffers);
 919
 920static inline void
 921link_dev_buffers(struct page *page, struct buffer_head *head)
 922{
 923	struct buffer_head *bh, *tail;
 924
 925	bh = head;
 926	do {
 927		tail = bh;
 928		bh = bh->b_this_page;
 929	} while (bh);
 930	tail->b_this_page = head;
 931	attach_page_buffers(page, head);
 932}
 933
 934static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 935{
 936	sector_t retval = ~((sector_t)0);
 937	loff_t sz = i_size_read(bdev->bd_inode);
 938
 939	if (sz) {
 940		unsigned int sizebits = blksize_bits(size);
 941		retval = (sz >> sizebits);
 942	}
 943	return retval;
 944}
 945
 946/*
 947 * Initialise the state of a blockdev page's buffers.
 948 */ 
 949static sector_t
 950init_page_buffers(struct page *page, struct block_device *bdev,
 951			sector_t block, int size)
 952{
 953	struct buffer_head *head = page_buffers(page);
 954	struct buffer_head *bh = head;
 955	int uptodate = PageUptodate(page);
 956	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
 957
 958	do {
 959		if (!buffer_mapped(bh)) {
 960			init_buffer(bh, NULL, NULL);
 961			bh->b_bdev = bdev;
 962			bh->b_blocknr = block;
 963			if (uptodate)
 964				set_buffer_uptodate(bh);
 965			if (block < end_block)
 966				set_buffer_mapped(bh);
 967		}
 968		block++;
 969		bh = bh->b_this_page;
 970	} while (bh != head);
 971
 972	/*
 973	 * Caller needs to validate requested block against end of device.
 974	 */
 975	return end_block;
 976}
 977
 978/*
 979 * Create the page-cache page that contains the requested block.
 980 *
 981 * This is used purely for blockdev mappings.
 982 */
 983static int
 984grow_dev_page(struct block_device *bdev, sector_t block,
 985	      pgoff_t index, int size, int sizebits, gfp_t gfp)
 986{
 987	struct inode *inode = bdev->bd_inode;
 988	struct page *page;
 989	struct buffer_head *bh;
 990	sector_t end_block;
 991	int ret = 0;		/* Will call free_more_memory() */
 992	gfp_t gfp_mask;
 993
 994	gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
 995
 996	/*
 997	 * XXX: __getblk_slow() can not really deal with failure and
 998	 * will endlessly loop on improvised global reclaim.  Prefer
 999	 * looping in the allocator rather than here, at least that
1000	 * code knows what it's doing.
1001	 */
1002	gfp_mask |= __GFP_NOFAIL;
1003
1004	page = find_or_create_page(inode->i_mapping, index, gfp_mask);
1005	if (!page)
1006		return ret;
1007
1008	BUG_ON(!PageLocked(page));
1009
1010	if (page_has_buffers(page)) {
1011		bh = page_buffers(page);
1012		if (bh->b_size == size) {
1013			end_block = init_page_buffers(page, bdev,
1014						(sector_t)index << sizebits,
1015						size);
1016			goto done;
1017		}
1018		if (!try_to_free_buffers(page))
1019			goto failed;
1020	}
1021
1022	/*
1023	 * Allocate some buffers for this page
1024	 */
1025	bh = alloc_page_buffers(page, size, 0);
1026	if (!bh)
1027		goto failed;
1028
1029	/*
1030	 * Link the page to the buffers and initialise them.  Take the
1031	 * lock to be atomic wrt __find_get_block(), which does not
1032	 * run under the page lock.
1033	 */
1034	spin_lock(&inode->i_mapping->private_lock);
1035	link_dev_buffers(page, bh);
1036	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
1037			size);
1038	spin_unlock(&inode->i_mapping->private_lock);
1039done:
1040	ret = (block < end_block) ? 1 : -ENXIO;
1041failed:
1042	unlock_page(page);
1043	put_page(page);
1044	return ret;
1045}
1046
1047/*
1048 * Create buffers for the specified block device block's page.  If
1049 * that page was dirty, the buffers are set dirty also.
1050 */
1051static int
1052grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
1053{
1054	pgoff_t index;
1055	int sizebits;
1056
1057	sizebits = -1;
1058	do {
1059		sizebits++;
1060	} while ((size << sizebits) < PAGE_SIZE);
1061
1062	index = block >> sizebits;
1063
1064	/*
1065	 * Check for a block which wants to lie outside our maximum possible
1066	 * pagecache index.  (this comparison is done using sector_t types).
1067	 */
1068	if (unlikely(index != block >> sizebits)) {
 
 
1069		printk(KERN_ERR "%s: requested out-of-range block %llu for "
1070			"device %pg\n",
1071			__func__, (unsigned long long)block,
1072			bdev);
1073		return -EIO;
1074	}
1075
1076	/* Create a page with the proper size buffers.. */
1077	return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1078}
1079
1080struct buffer_head *
1081__getblk_slow(struct block_device *bdev, sector_t block,
1082	     unsigned size, gfp_t gfp)
1083{
1084	/* Size must be multiple of hard sectorsize */
1085	if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1086			(size < 512 || size > PAGE_SIZE))) {
1087		printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1088					size);
1089		printk(KERN_ERR "logical block size: %d\n",
1090					bdev_logical_block_size(bdev));
1091
1092		dump_stack();
1093		return NULL;
1094	}
1095
1096	for (;;) {
1097		struct buffer_head *bh;
1098		int ret;
1099
1100		bh = __find_get_block(bdev, block, size);
1101		if (bh)
1102			return bh;
1103
1104		ret = grow_buffers(bdev, block, size, gfp);
1105		if (ret < 0)
1106			return NULL;
1107		if (ret == 0)
1108			free_more_memory();
1109	}
1110}
1111EXPORT_SYMBOL(__getblk_slow);
1112
1113/*
1114 * The relationship between dirty buffers and dirty pages:
1115 *
1116 * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1117 * the page is tagged dirty in its radix tree.
1118 *
1119 * At all times, the dirtiness of the buffers represents the dirtiness of
1120 * subsections of the page.  If the page has buffers, the page dirty bit is
1121 * merely a hint about the true dirty state.
1122 *
1123 * When a page is set dirty in its entirety, all its buffers are marked dirty
1124 * (if the page has buffers).
1125 *
1126 * When a buffer is marked dirty, its page is dirtied, but the page's other
1127 * buffers are not.
1128 *
1129 * Also.  When blockdev buffers are explicitly read with bread(), they
1130 * individually become uptodate.  But their backing page remains not
1131 * uptodate - even if all of its buffers are uptodate.  A subsequent
1132 * block_read_full_page() against that page will discover all the uptodate
1133 * buffers, will set the page uptodate and will perform no I/O.
1134 */
1135
1136/**
1137 * mark_buffer_dirty - mark a buffer_head as needing writeout
1138 * @bh: the buffer_head to mark dirty
1139 *
1140 * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1141 * backing page dirty, then tag the page as dirty in its address_space's radix
1142 * tree and then attach the address_space's inode to its superblock's dirty
1143 * inode list.
1144 *
1145 * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1146 * mapping->tree_lock and mapping->host->i_lock.
1147 */
1148void mark_buffer_dirty(struct buffer_head *bh)
1149{
1150	WARN_ON_ONCE(!buffer_uptodate(bh));
1151
1152	trace_block_dirty_buffer(bh);
1153
1154	/*
1155	 * Very *carefully* optimize the it-is-already-dirty case.
1156	 *
1157	 * Don't let the final "is it dirty" escape to before we
1158	 * perhaps modified the buffer.
1159	 */
1160	if (buffer_dirty(bh)) {
1161		smp_mb();
1162		if (buffer_dirty(bh))
1163			return;
1164	}
1165
1166	if (!test_set_buffer_dirty(bh)) {
1167		struct page *page = bh->b_page;
1168		struct address_space *mapping = NULL;
1169
1170		lock_page_memcg(page);
1171		if (!TestSetPageDirty(page)) {
1172			mapping = page_mapping(page);
1173			if (mapping)
1174				__set_page_dirty(page, mapping, 0);
1175		}
1176		unlock_page_memcg(page);
1177		if (mapping)
1178			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1179	}
1180}
1181EXPORT_SYMBOL(mark_buffer_dirty);
1182
1183/*
1184 * Decrement a buffer_head's reference count.  If all buffers against a page
1185 * have zero reference count, are clean and unlocked, and if the page is clean
1186 * and unlocked then try_to_free_buffers() may strip the buffers from the page
1187 * in preparation for freeing it (sometimes, rarely, buffers are removed from
1188 * a page but it ends up not being freed, and buffers may later be reattached).
1189 */
1190void __brelse(struct buffer_head * buf)
1191{
1192	if (atomic_read(&buf->b_count)) {
1193		put_bh(buf);
1194		return;
1195	}
1196	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1197}
1198EXPORT_SYMBOL(__brelse);
1199
1200/*
1201 * bforget() is like brelse(), except it discards any
1202 * potentially dirty data.
1203 */
1204void __bforget(struct buffer_head *bh)
1205{
1206	clear_buffer_dirty(bh);
1207	if (bh->b_assoc_map) {
1208		struct address_space *buffer_mapping = bh->b_page->mapping;
1209
1210		spin_lock(&buffer_mapping->private_lock);
1211		list_del_init(&bh->b_assoc_buffers);
1212		bh->b_assoc_map = NULL;
1213		spin_unlock(&buffer_mapping->private_lock);
1214	}
1215	__brelse(bh);
1216}
1217EXPORT_SYMBOL(__bforget);
1218
1219static struct buffer_head *__bread_slow(struct buffer_head *bh)
1220{
1221	lock_buffer(bh);
1222	if (buffer_uptodate(bh)) {
1223		unlock_buffer(bh);
1224		return bh;
1225	} else {
1226		get_bh(bh);
1227		bh->b_end_io = end_buffer_read_sync;
1228		submit_bh(READ, bh);
1229		wait_on_buffer(bh);
1230		if (buffer_uptodate(bh))
1231			return bh;
1232	}
1233	brelse(bh);
1234	return NULL;
1235}
1236
1237/*
1238 * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1239 * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1240 * refcount elevated by one when they're in an LRU.  A buffer can only appear
1241 * once in a particular CPU's LRU.  A single buffer can be present in multiple
1242 * CPU's LRUs at the same time.
1243 *
1244 * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1245 * sb_find_get_block().
1246 *
1247 * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1248 * a local interrupt disable for that.
1249 */
1250
1251#define BH_LRU_SIZE	16
1252
1253struct bh_lru {
1254	struct buffer_head *bhs[BH_LRU_SIZE];
1255};
1256
1257static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1258
1259#ifdef CONFIG_SMP
1260#define bh_lru_lock()	local_irq_disable()
1261#define bh_lru_unlock()	local_irq_enable()
1262#else
1263#define bh_lru_lock()	preempt_disable()
1264#define bh_lru_unlock()	preempt_enable()
1265#endif
1266
1267static inline void check_irqs_on(void)
1268{
1269#ifdef irqs_disabled
1270	BUG_ON(irqs_disabled());
1271#endif
1272}
1273
1274/*
1275 * The LRU management algorithm is dopey-but-simple.  Sorry.
1276 */
1277static void bh_lru_install(struct buffer_head *bh)
1278{
1279	struct buffer_head *evictee = NULL;
1280
1281	check_irqs_on();
1282	bh_lru_lock();
1283	if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1284		struct buffer_head *bhs[BH_LRU_SIZE];
1285		int in;
1286		int out = 0;
1287
1288		get_bh(bh);
1289		bhs[out++] = bh;
1290		for (in = 0; in < BH_LRU_SIZE; in++) {
1291			struct buffer_head *bh2 =
1292				__this_cpu_read(bh_lrus.bhs[in]);
1293
1294			if (bh2 == bh) {
1295				__brelse(bh2);
1296			} else {
1297				if (out >= BH_LRU_SIZE) {
1298					BUG_ON(evictee != NULL);
1299					evictee = bh2;
1300				} else {
1301					bhs[out++] = bh2;
1302				}
1303			}
1304		}
1305		while (out < BH_LRU_SIZE)
1306			bhs[out++] = NULL;
1307		memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1308	}
1309	bh_lru_unlock();
1310
1311	if (evictee)
1312		__brelse(evictee);
1313}
1314
1315/*
1316 * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1317 */
1318static struct buffer_head *
1319lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1320{
1321	struct buffer_head *ret = NULL;
1322	unsigned int i;
1323
1324	check_irqs_on();
1325	bh_lru_lock();
1326	for (i = 0; i < BH_LRU_SIZE; i++) {
1327		struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1328
1329		if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1330		    bh->b_size == size) {
1331			if (i) {
1332				while (i) {
1333					__this_cpu_write(bh_lrus.bhs[i],
1334						__this_cpu_read(bh_lrus.bhs[i - 1]));
1335					i--;
1336				}
1337				__this_cpu_write(bh_lrus.bhs[0], bh);
1338			}
1339			get_bh(bh);
1340			ret = bh;
1341			break;
1342		}
1343	}
1344	bh_lru_unlock();
1345	return ret;
1346}
1347
1348/*
1349 * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1350 * it in the LRU and mark it as accessed.  If it is not present then return
1351 * NULL
1352 */
1353struct buffer_head *
1354__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1355{
1356	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1357
1358	if (bh == NULL) {
1359		/* __find_get_block_slow will mark the page accessed */
1360		bh = __find_get_block_slow(bdev, block);
1361		if (bh)
1362			bh_lru_install(bh);
1363	} else
 
1364		touch_buffer(bh);
1365
1366	return bh;
1367}
1368EXPORT_SYMBOL(__find_get_block);
1369
1370/*
1371 * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1372 * which corresponds to the passed block_device, block and size. The
1373 * returned buffer has its reference count incremented.
1374 *
1375 * __getblk_gfp() will lock up the machine if grow_dev_page's
1376 * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
1377 */
1378struct buffer_head *
1379__getblk_gfp(struct block_device *bdev, sector_t block,
1380	     unsigned size, gfp_t gfp)
1381{
1382	struct buffer_head *bh = __find_get_block(bdev, block, size);
1383
1384	might_sleep();
1385	if (bh == NULL)
1386		bh = __getblk_slow(bdev, block, size, gfp);
1387	return bh;
1388}
1389EXPORT_SYMBOL(__getblk_gfp);
1390
1391/*
1392 * Do async read-ahead on a buffer..
1393 */
1394void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1395{
1396	struct buffer_head *bh = __getblk(bdev, block, size);
1397	if (likely(bh)) {
1398		ll_rw_block(READA, 1, &bh);
1399		brelse(bh);
1400	}
1401}
1402EXPORT_SYMBOL(__breadahead);
1403
1404/**
1405 *  __bread_gfp() - reads a specified block and returns the bh
1406 *  @bdev: the block_device to read from
1407 *  @block: number of block
1408 *  @size: size (in bytes) to read
1409 *  @gfp: page allocation flag
1410 *
1411 *  Reads a specified block, and returns buffer head that contains it.
1412 *  The page cache can be allocated from non-movable area
1413 *  not to prevent page migration if you set gfp to zero.
1414 *  It returns NULL if the block was unreadable.
1415 */
1416struct buffer_head *
1417__bread_gfp(struct block_device *bdev, sector_t block,
1418		   unsigned size, gfp_t gfp)
1419{
1420	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1421
1422	if (likely(bh) && !buffer_uptodate(bh))
1423		bh = __bread_slow(bh);
1424	return bh;
1425}
1426EXPORT_SYMBOL(__bread_gfp);
1427
1428/*
1429 * invalidate_bh_lrus() is called rarely - but not only at unmount.
1430 * This doesn't race because it runs in each cpu either in irq
1431 * or with preempt disabled.
1432 */
1433static void invalidate_bh_lru(void *arg)
1434{
1435	struct bh_lru *b = &get_cpu_var(bh_lrus);
1436	int i;
1437
1438	for (i = 0; i < BH_LRU_SIZE; i++) {
1439		brelse(b->bhs[i]);
1440		b->bhs[i] = NULL;
1441	}
1442	put_cpu_var(bh_lrus);
1443}
1444
1445static bool has_bh_in_lru(int cpu, void *dummy)
1446{
1447	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1448	int i;
1449	
1450	for (i = 0; i < BH_LRU_SIZE; i++) {
1451		if (b->bhs[i])
1452			return 1;
1453	}
1454
1455	return 0;
1456}
1457
1458void invalidate_bh_lrus(void)
1459{
1460	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1461}
1462EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1463
1464void set_bh_page(struct buffer_head *bh,
1465		struct page *page, unsigned long offset)
1466{
1467	bh->b_page = page;
1468	BUG_ON(offset >= PAGE_SIZE);
1469	if (PageHighMem(page))
1470		/*
1471		 * This catches illegal uses and preserves the offset:
1472		 */
1473		bh->b_data = (char *)(0 + offset);
1474	else
1475		bh->b_data = page_address(page) + offset;
1476}
1477EXPORT_SYMBOL(set_bh_page);
1478
1479/*
1480 * Called when truncating a buffer on a page completely.
1481 */
1482
1483/* Bits that are cleared during an invalidate */
1484#define BUFFER_FLAGS_DISCARD \
1485	(1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
1486	 1 << BH_Delay | 1 << BH_Unwritten)
1487
1488static void discard_buffer(struct buffer_head * bh)
1489{
1490	unsigned long b_state, b_state_old;
1491
1492	lock_buffer(bh);
1493	clear_buffer_dirty(bh);
1494	bh->b_bdev = NULL;
1495	b_state = bh->b_state;
1496	for (;;) {
1497		b_state_old = cmpxchg(&bh->b_state, b_state,
1498				      (b_state & ~BUFFER_FLAGS_DISCARD));
1499		if (b_state_old == b_state)
1500			break;
1501		b_state = b_state_old;
1502	}
1503	unlock_buffer(bh);
1504}
1505
1506/**
1507 * block_invalidatepage - invalidate part or all of a buffer-backed page
1508 *
1509 * @page: the page which is affected
1510 * @offset: start of the range to invalidate
1511 * @length: length of the range to invalidate
1512 *
1513 * block_invalidatepage() is called when all or part of the page has become
1514 * invalidated by a truncate operation.
1515 *
1516 * block_invalidatepage() does not have to release all buffers, but it must
1517 * ensure that no dirty buffer is left outside @offset and that no I/O
1518 * is underway against any of the blocks which are outside the truncation
1519 * point.  Because the caller is about to free (and possibly reuse) those
1520 * blocks on-disk.
1521 */
1522void block_invalidatepage(struct page *page, unsigned int offset,
1523			  unsigned int length)
1524{
1525	struct buffer_head *head, *bh, *next;
1526	unsigned int curr_off = 0;
1527	unsigned int stop = length + offset;
1528
1529	BUG_ON(!PageLocked(page));
1530	if (!page_has_buffers(page))
1531		goto out;
1532
1533	/*
1534	 * Check for overflow
1535	 */
1536	BUG_ON(stop > PAGE_SIZE || stop < length);
1537
1538	head = page_buffers(page);
1539	bh = head;
1540	do {
1541		unsigned int next_off = curr_off + bh->b_size;
1542		next = bh->b_this_page;
1543
1544		/*
1545		 * Are we still fully in range ?
1546		 */
1547		if (next_off > stop)
1548			goto out;
1549
1550		/*
1551		 * is this block fully invalidated?
1552		 */
1553		if (offset <= curr_off)
1554			discard_buffer(bh);
1555		curr_off = next_off;
1556		bh = next;
1557	} while (bh != head);
1558
1559	/*
1560	 * We release buffers only if the entire page is being invalidated.
1561	 * The get_block cached value has been unconditionally invalidated,
1562	 * so real IO is not possible anymore.
1563	 */
1564	if (offset == 0)
1565		try_to_release_page(page, 0);
1566out:
1567	return;
1568}
1569EXPORT_SYMBOL(block_invalidatepage);
1570
1571
1572/*
1573 * We attach and possibly dirty the buffers atomically wrt
1574 * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1575 * is already excluded via the page lock.
1576 */
1577void create_empty_buffers(struct page *page,
1578			unsigned long blocksize, unsigned long b_state)
1579{
1580	struct buffer_head *bh, *head, *tail;
1581
1582	head = alloc_page_buffers(page, blocksize, 1);
1583	bh = head;
1584	do {
1585		bh->b_state |= b_state;
1586		tail = bh;
1587		bh = bh->b_this_page;
1588	} while (bh);
1589	tail->b_this_page = head;
1590
1591	spin_lock(&page->mapping->private_lock);
1592	if (PageUptodate(page) || PageDirty(page)) {
1593		bh = head;
1594		do {
1595			if (PageDirty(page))
1596				set_buffer_dirty(bh);
1597			if (PageUptodate(page))
1598				set_buffer_uptodate(bh);
1599			bh = bh->b_this_page;
1600		} while (bh != head);
1601	}
1602	attach_page_buffers(page, head);
1603	spin_unlock(&page->mapping->private_lock);
1604}
1605EXPORT_SYMBOL(create_empty_buffers);
1606
1607/*
1608 * We are taking a block for data and we don't want any output from any
1609 * buffer-cache aliases starting from return from that function and
1610 * until the moment when something will explicitly mark the buffer
1611 * dirty (hopefully that will not happen until we will free that block ;-)
1612 * We don't even need to mark it not-uptodate - nobody can expect
1613 * anything from a newly allocated buffer anyway. We used to used
1614 * unmap_buffer() for such invalidation, but that was wrong. We definitely
1615 * don't want to mark the alias unmapped, for example - it would confuse
1616 * anyone who might pick it with bread() afterwards...
1617 *
1618 * Also..  Note that bforget() doesn't lock the buffer.  So there can
1619 * be writeout I/O going on against recently-freed buffers.  We don't
1620 * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1621 * only if we really need to.  That happens here.
1622 */
1623void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1624{
1625	struct buffer_head *old_bh;
1626
1627	might_sleep();
1628
1629	old_bh = __find_get_block_slow(bdev, block);
1630	if (old_bh) {
1631		clear_buffer_dirty(old_bh);
1632		wait_on_buffer(old_bh);
1633		clear_buffer_req(old_bh);
1634		__brelse(old_bh);
1635	}
1636}
1637EXPORT_SYMBOL(unmap_underlying_metadata);
1638
1639/*
1640 * Size is a power-of-two in the range 512..PAGE_SIZE,
1641 * and the case we care about most is PAGE_SIZE.
1642 *
1643 * So this *could* possibly be written with those
1644 * constraints in mind (relevant mostly if some
1645 * architecture has a slow bit-scan instruction)
1646 */
1647static inline int block_size_bits(unsigned int blocksize)
1648{
1649	return ilog2(blocksize);
1650}
1651
1652static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1653{
1654	BUG_ON(!PageLocked(page));
1655
1656	if (!page_has_buffers(page))
1657		create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1658	return page_buffers(page);
1659}
1660
1661/*
1662 * NOTE! All mapped/uptodate combinations are valid:
1663 *
1664 *	Mapped	Uptodate	Meaning
1665 *
1666 *	No	No		"unknown" - must do get_block()
1667 *	No	Yes		"hole" - zero-filled
1668 *	Yes	No		"allocated" - allocated on disk, not read in
1669 *	Yes	Yes		"valid" - allocated and up-to-date in memory.
1670 *
1671 * "Dirty" is valid only with the last case (mapped+uptodate).
1672 */
1673
1674/*
1675 * While block_write_full_page is writing back the dirty buffers under
1676 * the page lock, whoever dirtied the buffers may decide to clean them
1677 * again at any time.  We handle that by only looking at the buffer
1678 * state inside lock_buffer().
1679 *
1680 * If block_write_full_page() is called for regular writeback
1681 * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1682 * locked buffer.   This only can happen if someone has written the buffer
1683 * directly, with submit_bh().  At the address_space level PageWriteback
1684 * prevents this contention from occurring.
1685 *
1686 * If block_write_full_page() is called with wbc->sync_mode ==
1687 * WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1688 * causes the writes to be flagged as synchronous writes.
1689 */
1690static int __block_write_full_page(struct inode *inode, struct page *page,
1691			get_block_t *get_block, struct writeback_control *wbc,
1692			bh_end_io_t *handler)
1693{
1694	int err;
1695	sector_t block;
1696	sector_t last_block;
1697	struct buffer_head *bh, *head;
1698	unsigned int blocksize, bbits;
1699	int nr_underway = 0;
1700	int write_op = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
 
 
 
1701
1702	head = create_page_buffers(page, inode,
 
 
 
1703					(1 << BH_Dirty)|(1 << BH_Uptodate));
 
1704
1705	/*
1706	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1707	 * here, and the (potentially unmapped) buffers may become dirty at
1708	 * any time.  If a buffer becomes dirty here after we've inspected it
1709	 * then we just miss that fact, and the page stays dirty.
1710	 *
1711	 * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1712	 * handle that here by just cleaning them.
1713	 */
1714
 
 
1715	bh = head;
1716	blocksize = bh->b_size;
1717	bbits = block_size_bits(blocksize);
1718
1719	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1720	last_block = (i_size_read(inode) - 1) >> bbits;
1721
1722	/*
1723	 * Get all the dirty buffers mapped to disk addresses and
1724	 * handle any aliases from the underlying blockdev's mapping.
1725	 */
1726	do {
1727		if (block > last_block) {
1728			/*
1729			 * mapped buffers outside i_size will occur, because
1730			 * this page can be outside i_size when there is a
1731			 * truncate in progress.
1732			 */
1733			/*
1734			 * The buffer was zeroed by block_write_full_page()
1735			 */
1736			clear_buffer_dirty(bh);
1737			set_buffer_uptodate(bh);
1738		} else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1739			   buffer_dirty(bh)) {
1740			WARN_ON(bh->b_size != blocksize);
1741			err = get_block(inode, block, bh, 1);
1742			if (err)
1743				goto recover;
1744			clear_buffer_delay(bh);
1745			if (buffer_new(bh)) {
1746				/* blockdev mappings never come here */
1747				clear_buffer_new(bh);
1748				unmap_underlying_metadata(bh->b_bdev,
1749							bh->b_blocknr);
1750			}
1751		}
1752		bh = bh->b_this_page;
1753		block++;
1754	} while (bh != head);
1755
1756	do {
1757		if (!buffer_mapped(bh))
1758			continue;
1759		/*
1760		 * If it's a fully non-blocking write attempt and we cannot
1761		 * lock the buffer then redirty the page.  Note that this can
1762		 * potentially cause a busy-wait loop from writeback threads
1763		 * and kswapd activity, but those code paths have their own
1764		 * higher-level throttling.
1765		 */
1766		if (wbc->sync_mode != WB_SYNC_NONE) {
1767			lock_buffer(bh);
1768		} else if (!trylock_buffer(bh)) {
1769			redirty_page_for_writepage(wbc, page);
1770			continue;
1771		}
1772		if (test_clear_buffer_dirty(bh)) {
1773			mark_buffer_async_write_endio(bh, handler);
1774		} else {
1775			unlock_buffer(bh);
1776		}
1777	} while ((bh = bh->b_this_page) != head);
1778
1779	/*
1780	 * The page and its buffers are protected by PageWriteback(), so we can
1781	 * drop the bh refcounts early.
1782	 */
1783	BUG_ON(PageWriteback(page));
1784	set_page_writeback(page);
1785
1786	do {
1787		struct buffer_head *next = bh->b_this_page;
1788		if (buffer_async_write(bh)) {
1789			submit_bh_wbc(write_op, bh, 0, wbc);
1790			nr_underway++;
1791		}
1792		bh = next;
1793	} while (bh != head);
1794	unlock_page(page);
1795
1796	err = 0;
1797done:
1798	if (nr_underway == 0) {
1799		/*
1800		 * The page was marked dirty, but the buffers were
1801		 * clean.  Someone wrote them back by hand with
1802		 * ll_rw_block/submit_bh.  A rare case.
1803		 */
1804		end_page_writeback(page);
1805
1806		/*
1807		 * The page and buffer_heads can be released at any time from
1808		 * here on.
1809		 */
1810	}
1811	return err;
1812
1813recover:
1814	/*
1815	 * ENOSPC, or some other error.  We may already have added some
1816	 * blocks to the file, so we need to write these out to avoid
1817	 * exposing stale data.
1818	 * The page is currently locked and not marked for writeback
1819	 */
1820	bh = head;
1821	/* Recovery: lock and submit the mapped buffers */
1822	do {
1823		if (buffer_mapped(bh) && buffer_dirty(bh) &&
1824		    !buffer_delay(bh)) {
1825			lock_buffer(bh);
1826			mark_buffer_async_write_endio(bh, handler);
1827		} else {
1828			/*
1829			 * The buffer may have been set dirty during
1830			 * attachment to a dirty page.
1831			 */
1832			clear_buffer_dirty(bh);
1833		}
1834	} while ((bh = bh->b_this_page) != head);
1835	SetPageError(page);
1836	BUG_ON(PageWriteback(page));
1837	mapping_set_error(page->mapping, err);
1838	set_page_writeback(page);
1839	do {
1840		struct buffer_head *next = bh->b_this_page;
1841		if (buffer_async_write(bh)) {
1842			clear_buffer_dirty(bh);
1843			submit_bh_wbc(write_op, bh, 0, wbc);
1844			nr_underway++;
1845		}
1846		bh = next;
1847	} while (bh != head);
1848	unlock_page(page);
1849	goto done;
1850}
1851
1852/*
1853 * If a page has any new buffers, zero them out here, and mark them uptodate
1854 * and dirty so they'll be written out (in order to prevent uninitialised
1855 * block data from leaking). And clear the new bit.
1856 */
1857void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1858{
1859	unsigned int block_start, block_end;
1860	struct buffer_head *head, *bh;
1861
1862	BUG_ON(!PageLocked(page));
1863	if (!page_has_buffers(page))
1864		return;
1865
1866	bh = head = page_buffers(page);
1867	block_start = 0;
1868	do {
1869		block_end = block_start + bh->b_size;
1870
1871		if (buffer_new(bh)) {
1872			if (block_end > from && block_start < to) {
1873				if (!PageUptodate(page)) {
1874					unsigned start, size;
1875
1876					start = max(from, block_start);
1877					size = min(to, block_end) - start;
1878
1879					zero_user(page, start, size);
1880					set_buffer_uptodate(bh);
1881				}
1882
1883				clear_buffer_new(bh);
1884				mark_buffer_dirty(bh);
1885			}
1886		}
1887
1888		block_start = block_end;
1889		bh = bh->b_this_page;
1890	} while (bh != head);
1891}
1892EXPORT_SYMBOL(page_zero_new_buffers);
1893
1894int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1895		get_block_t *get_block)
1896{
1897	unsigned from = pos & (PAGE_SIZE - 1);
1898	unsigned to = from + len;
1899	struct inode *inode = page->mapping->host;
1900	unsigned block_start, block_end;
1901	sector_t block;
1902	int err = 0;
1903	unsigned blocksize, bbits;
1904	struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1905
1906	BUG_ON(!PageLocked(page));
1907	BUG_ON(from > PAGE_SIZE);
1908	BUG_ON(to > PAGE_SIZE);
1909	BUG_ON(from > to);
1910
1911	head = create_page_buffers(page, inode, 0);
1912	blocksize = head->b_size;
1913	bbits = block_size_bits(blocksize);
 
1914
1915	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
 
1916
1917	for(bh = head, block_start = 0; bh != head || !block_start;
1918	    block++, block_start=block_end, bh = bh->b_this_page) {
1919		block_end = block_start + blocksize;
1920		if (block_end <= from || block_start >= to) {
1921			if (PageUptodate(page)) {
1922				if (!buffer_uptodate(bh))
1923					set_buffer_uptodate(bh);
1924			}
1925			continue;
1926		}
1927		if (buffer_new(bh))
1928			clear_buffer_new(bh);
1929		if (!buffer_mapped(bh)) {
1930			WARN_ON(bh->b_size != blocksize);
1931			err = get_block(inode, block, bh, 1);
1932			if (err)
1933				break;
1934			if (buffer_new(bh)) {
1935				unmap_underlying_metadata(bh->b_bdev,
1936							bh->b_blocknr);
1937				if (PageUptodate(page)) {
1938					clear_buffer_new(bh);
1939					set_buffer_uptodate(bh);
1940					mark_buffer_dirty(bh);
1941					continue;
1942				}
1943				if (block_end > to || block_start < from)
1944					zero_user_segments(page,
1945						to, block_end,
1946						block_start, from);
1947				continue;
1948			}
1949		}
1950		if (PageUptodate(page)) {
1951			if (!buffer_uptodate(bh))
1952				set_buffer_uptodate(bh);
1953			continue; 
1954		}
1955		if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1956		    !buffer_unwritten(bh) &&
1957		     (block_start < from || block_end > to)) {
1958			ll_rw_block(READ, 1, &bh);
1959			*wait_bh++=bh;
1960		}
1961	}
1962	/*
1963	 * If we issued read requests - let them complete.
1964	 */
1965	while(wait_bh > wait) {
1966		wait_on_buffer(*--wait_bh);
1967		if (!buffer_uptodate(*wait_bh))
1968			err = -EIO;
1969	}
1970	if (unlikely(err))
1971		page_zero_new_buffers(page, from, to);
1972	return err;
1973}
1974EXPORT_SYMBOL(__block_write_begin);
1975
1976static int __block_commit_write(struct inode *inode, struct page *page,
1977		unsigned from, unsigned to)
1978{
1979	unsigned block_start, block_end;
1980	int partial = 0;
1981	unsigned blocksize;
1982	struct buffer_head *bh, *head;
1983
1984	bh = head = page_buffers(page);
1985	blocksize = bh->b_size;
1986
1987	block_start = 0;
1988	do {
 
1989		block_end = block_start + blocksize;
1990		if (block_end <= from || block_start >= to) {
1991			if (!buffer_uptodate(bh))
1992				partial = 1;
1993		} else {
1994			set_buffer_uptodate(bh);
1995			mark_buffer_dirty(bh);
1996		}
1997		clear_buffer_new(bh);
1998
1999		block_start = block_end;
2000		bh = bh->b_this_page;
2001	} while (bh != head);
2002
2003	/*
2004	 * If this is a partial write which happened to make all buffers
2005	 * uptodate then we can optimize away a bogus readpage() for
2006	 * the next read(). Here we 'discover' whether the page went
2007	 * uptodate as a result of this (potentially partial) write.
2008	 */
2009	if (!partial)
2010		SetPageUptodate(page);
2011	return 0;
2012}
2013
2014/*
2015 * block_write_begin takes care of the basic task of block allocation and
2016 * bringing partial write blocks uptodate first.
2017 *
2018 * The filesystem needs to handle block truncation upon failure.
2019 */
2020int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2021		unsigned flags, struct page **pagep, get_block_t *get_block)
2022{
2023	pgoff_t index = pos >> PAGE_SHIFT;
2024	struct page *page;
2025	int status;
2026
2027	page = grab_cache_page_write_begin(mapping, index, flags);
2028	if (!page)
2029		return -ENOMEM;
2030
2031	status = __block_write_begin(page, pos, len, get_block);
2032	if (unlikely(status)) {
2033		unlock_page(page);
2034		put_page(page);
2035		page = NULL;
2036	}
2037
2038	*pagep = page;
2039	return status;
2040}
2041EXPORT_SYMBOL(block_write_begin);
2042
2043int block_write_end(struct file *file, struct address_space *mapping,
2044			loff_t pos, unsigned len, unsigned copied,
2045			struct page *page, void *fsdata)
2046{
2047	struct inode *inode = mapping->host;
2048	unsigned start;
2049
2050	start = pos & (PAGE_SIZE - 1);
2051
2052	if (unlikely(copied < len)) {
2053		/*
2054		 * The buffers that were written will now be uptodate, so we
2055		 * don't have to worry about a readpage reading them and
2056		 * overwriting a partial write. However if we have encountered
2057		 * a short write and only partially written into a buffer, it
2058		 * will not be marked uptodate, so a readpage might come in and
2059		 * destroy our partial write.
2060		 *
2061		 * Do the simplest thing, and just treat any short write to a
2062		 * non uptodate page as a zero-length write, and force the
2063		 * caller to redo the whole thing.
2064		 */
2065		if (!PageUptodate(page))
2066			copied = 0;
2067
2068		page_zero_new_buffers(page, start+copied, start+len);
2069	}
2070	flush_dcache_page(page);
2071
2072	/* This could be a short (even 0-length) commit */
2073	__block_commit_write(inode, page, start, start+copied);
2074
2075	return copied;
2076}
2077EXPORT_SYMBOL(block_write_end);
2078
2079int generic_write_end(struct file *file, struct address_space *mapping,
2080			loff_t pos, unsigned len, unsigned copied,
2081			struct page *page, void *fsdata)
2082{
2083	struct inode *inode = mapping->host;
2084	loff_t old_size = inode->i_size;
2085	int i_size_changed = 0;
2086
2087	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2088
2089	/*
2090	 * No need to use i_size_read() here, the i_size
2091	 * cannot change under us because we hold i_mutex.
2092	 *
2093	 * But it's important to update i_size while still holding page lock:
2094	 * page writeout could otherwise come in and zero beyond i_size.
2095	 */
2096	if (pos+copied > inode->i_size) {
2097		i_size_write(inode, pos+copied);
2098		i_size_changed = 1;
2099	}
2100
2101	unlock_page(page);
2102	put_page(page);
2103
2104	if (old_size < pos)
2105		pagecache_isize_extended(inode, old_size, pos);
2106	/*
2107	 * Don't mark the inode dirty under page lock. First, it unnecessarily
2108	 * makes the holding time of page lock longer. Second, it forces lock
2109	 * ordering of page lock and transaction start for journaling
2110	 * filesystems.
2111	 */
2112	if (i_size_changed)
2113		mark_inode_dirty(inode);
2114
2115	return copied;
2116}
2117EXPORT_SYMBOL(generic_write_end);
2118
2119/*
2120 * block_is_partially_uptodate checks whether buffers within a page are
2121 * uptodate or not.
2122 *
2123 * Returns true if all buffers which correspond to a file portion
2124 * we want to read are uptodate.
2125 */
2126int block_is_partially_uptodate(struct page *page, unsigned long from,
2127					unsigned long count)
2128{
 
2129	unsigned block_start, block_end, blocksize;
2130	unsigned to;
2131	struct buffer_head *bh, *head;
2132	int ret = 1;
2133
2134	if (!page_has_buffers(page))
2135		return 0;
2136
2137	head = page_buffers(page);
2138	blocksize = head->b_size;
2139	to = min_t(unsigned, PAGE_SIZE - from, count);
2140	to = from + to;
2141	if (from < blocksize && to > PAGE_SIZE - blocksize)
2142		return 0;
2143
 
2144	bh = head;
2145	block_start = 0;
2146	do {
2147		block_end = block_start + blocksize;
2148		if (block_end > from && block_start < to) {
2149			if (!buffer_uptodate(bh)) {
2150				ret = 0;
2151				break;
2152			}
2153			if (block_end >= to)
2154				break;
2155		}
2156		block_start = block_end;
2157		bh = bh->b_this_page;
2158	} while (bh != head);
2159
2160	return ret;
2161}
2162EXPORT_SYMBOL(block_is_partially_uptodate);
2163
2164/*
2165 * Generic "read page" function for block devices that have the normal
2166 * get_block functionality. This is most of the block device filesystems.
2167 * Reads the page asynchronously --- the unlock_buffer() and
2168 * set/clear_buffer_uptodate() functions propagate buffer state into the
2169 * page struct once IO has completed.
2170 */
2171int block_read_full_page(struct page *page, get_block_t *get_block)
2172{
2173	struct inode *inode = page->mapping->host;
2174	sector_t iblock, lblock;
2175	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2176	unsigned int blocksize, bbits;
2177	int nr, i;
2178	int fully_mapped = 1;
2179
2180	head = create_page_buffers(page, inode, 0);
2181	blocksize = head->b_size;
2182	bbits = block_size_bits(blocksize);
 
 
2183
2184	iblock = (sector_t)page->index << (PAGE_SHIFT - bbits);
2185	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2186	bh = head;
2187	nr = 0;
2188	i = 0;
2189
2190	do {
2191		if (buffer_uptodate(bh))
2192			continue;
2193
2194		if (!buffer_mapped(bh)) {
2195			int err = 0;
2196
2197			fully_mapped = 0;
2198			if (iblock < lblock) {
2199				WARN_ON(bh->b_size != blocksize);
2200				err = get_block(inode, iblock, bh, 0);
2201				if (err)
2202					SetPageError(page);
2203			}
2204			if (!buffer_mapped(bh)) {
2205				zero_user(page, i * blocksize, blocksize);
2206				if (!err)
2207					set_buffer_uptodate(bh);
2208				continue;
2209			}
2210			/*
2211			 * get_block() might have updated the buffer
2212			 * synchronously
2213			 */
2214			if (buffer_uptodate(bh))
2215				continue;
2216		}
2217		arr[nr++] = bh;
2218	} while (i++, iblock++, (bh = bh->b_this_page) != head);
2219
2220	if (fully_mapped)
2221		SetPageMappedToDisk(page);
2222
2223	if (!nr) {
2224		/*
2225		 * All buffers are uptodate - we can set the page uptodate
2226		 * as well. But not if get_block() returned an error.
2227		 */
2228		if (!PageError(page))
2229			SetPageUptodate(page);
2230		unlock_page(page);
2231		return 0;
2232	}
2233
2234	/* Stage two: lock the buffers */
2235	for (i = 0; i < nr; i++) {
2236		bh = arr[i];
2237		lock_buffer(bh);
2238		mark_buffer_async_read(bh);
2239	}
2240
2241	/*
2242	 * Stage 3: start the IO.  Check for uptodateness
2243	 * inside the buffer lock in case another process reading
2244	 * the underlying blockdev brought it uptodate (the sct fix).
2245	 */
2246	for (i = 0; i < nr; i++) {
2247		bh = arr[i];
2248		if (buffer_uptodate(bh))
2249			end_buffer_async_read(bh, 1);
2250		else
2251			submit_bh(READ, bh);
2252	}
2253	return 0;
2254}
2255EXPORT_SYMBOL(block_read_full_page);
2256
2257/* utility function for filesystems that need to do work on expanding
2258 * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2259 * deal with the hole.  
2260 */
2261int generic_cont_expand_simple(struct inode *inode, loff_t size)
2262{
2263	struct address_space *mapping = inode->i_mapping;
2264	struct page *page;
2265	void *fsdata;
2266	int err;
2267
2268	err = inode_newsize_ok(inode, size);
2269	if (err)
2270		goto out;
2271
2272	err = pagecache_write_begin(NULL, mapping, size, 0,
2273				AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2274				&page, &fsdata);
2275	if (err)
2276		goto out;
2277
2278	err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2279	BUG_ON(err > 0);
2280
2281out:
2282	return err;
2283}
2284EXPORT_SYMBOL(generic_cont_expand_simple);
2285
2286static int cont_expand_zero(struct file *file, struct address_space *mapping,
2287			    loff_t pos, loff_t *bytes)
2288{
2289	struct inode *inode = mapping->host;
2290	unsigned blocksize = 1 << inode->i_blkbits;
2291	struct page *page;
2292	void *fsdata;
2293	pgoff_t index, curidx;
2294	loff_t curpos;
2295	unsigned zerofrom, offset, len;
2296	int err = 0;
2297
2298	index = pos >> PAGE_SHIFT;
2299	offset = pos & ~PAGE_MASK;
2300
2301	while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
2302		zerofrom = curpos & ~PAGE_MASK;
2303		if (zerofrom & (blocksize-1)) {
2304			*bytes |= (blocksize-1);
2305			(*bytes)++;
2306		}
2307		len = PAGE_SIZE - zerofrom;
2308
2309		err = pagecache_write_begin(file, mapping, curpos, len,
2310						AOP_FLAG_UNINTERRUPTIBLE,
2311						&page, &fsdata);
2312		if (err)
2313			goto out;
2314		zero_user(page, zerofrom, len);
2315		err = pagecache_write_end(file, mapping, curpos, len, len,
2316						page, fsdata);
2317		if (err < 0)
2318			goto out;
2319		BUG_ON(err != len);
2320		err = 0;
2321
2322		balance_dirty_pages_ratelimited(mapping);
2323
2324		if (unlikely(fatal_signal_pending(current))) {
2325			err = -EINTR;
2326			goto out;
2327		}
2328	}
2329
2330	/* page covers the boundary, find the boundary offset */
2331	if (index == curidx) {
2332		zerofrom = curpos & ~PAGE_MASK;
2333		/* if we will expand the thing last block will be filled */
2334		if (offset <= zerofrom) {
2335			goto out;
2336		}
2337		if (zerofrom & (blocksize-1)) {
2338			*bytes |= (blocksize-1);
2339			(*bytes)++;
2340		}
2341		len = offset - zerofrom;
2342
2343		err = pagecache_write_begin(file, mapping, curpos, len,
2344						AOP_FLAG_UNINTERRUPTIBLE,
2345						&page, &fsdata);
2346		if (err)
2347			goto out;
2348		zero_user(page, zerofrom, len);
2349		err = pagecache_write_end(file, mapping, curpos, len, len,
2350						page, fsdata);
2351		if (err < 0)
2352			goto out;
2353		BUG_ON(err != len);
2354		err = 0;
2355	}
2356out:
2357	return err;
2358}
2359
2360/*
2361 * For moronic filesystems that do not allow holes in file.
2362 * We may have to extend the file.
2363 */
2364int cont_write_begin(struct file *file, struct address_space *mapping,
2365			loff_t pos, unsigned len, unsigned flags,
2366			struct page **pagep, void **fsdata,
2367			get_block_t *get_block, loff_t *bytes)
2368{
2369	struct inode *inode = mapping->host;
2370	unsigned blocksize = 1 << inode->i_blkbits;
2371	unsigned zerofrom;
2372	int err;
2373
2374	err = cont_expand_zero(file, mapping, pos, bytes);
2375	if (err)
2376		return err;
2377
2378	zerofrom = *bytes & ~PAGE_MASK;
2379	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2380		*bytes |= (blocksize-1);
2381		(*bytes)++;
2382	}
2383
2384	return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2385}
2386EXPORT_SYMBOL(cont_write_begin);
2387
2388int block_commit_write(struct page *page, unsigned from, unsigned to)
2389{
2390	struct inode *inode = page->mapping->host;
2391	__block_commit_write(inode,page,from,to);
2392	return 0;
2393}
2394EXPORT_SYMBOL(block_commit_write);
2395
2396/*
2397 * block_page_mkwrite() is not allowed to change the file size as it gets
2398 * called from a page fault handler when a page is first dirtied. Hence we must
2399 * be careful to check for EOF conditions here. We set the page up correctly
2400 * for a written page which means we get ENOSPC checking when writing into
2401 * holes and correct delalloc and unwritten extent mapping on filesystems that
2402 * support these features.
2403 *
2404 * We are not allowed to take the i_mutex here so we have to play games to
2405 * protect against truncate races as the page could now be beyond EOF.  Because
2406 * truncate writes the inode size before removing pages, once we have the
2407 * page lock we can determine safely if the page is beyond EOF. If it is not
2408 * beyond EOF, then the page is guaranteed safe against truncation until we
2409 * unlock the page.
2410 *
2411 * Direct callers of this function should protect against filesystem freezing
2412 * using sb_start_pagefault() - sb_end_pagefault() functions.
2413 */
2414int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2415			 get_block_t get_block)
2416{
2417	struct page *page = vmf->page;
2418	struct inode *inode = file_inode(vma->vm_file);
2419	unsigned long end;
2420	loff_t size;
2421	int ret;
2422
2423	lock_page(page);
2424	size = i_size_read(inode);
2425	if ((page->mapping != inode->i_mapping) ||
2426	    (page_offset(page) > size)) {
2427		/* We overload EFAULT to mean page got truncated */
2428		ret = -EFAULT;
2429		goto out_unlock;
2430	}
2431
2432	/* page is wholly or partially inside EOF */
2433	if (((page->index + 1) << PAGE_SHIFT) > size)
2434		end = size & ~PAGE_MASK;
2435	else
2436		end = PAGE_SIZE;
2437
2438	ret = __block_write_begin(page, 0, end, get_block);
2439	if (!ret)
2440		ret = block_commit_write(page, 0, end);
2441
2442	if (unlikely(ret < 0))
2443		goto out_unlock;
 
 
 
 
 
 
 
2444	set_page_dirty(page);
2445	wait_for_stable_page(page);
 
 
 
 
2446	return 0;
2447out_unlock:
2448	unlock_page(page);
2449	return ret;
2450}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2451EXPORT_SYMBOL(block_page_mkwrite);
2452
2453/*
2454 * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2455 * immediately, while under the page lock.  So it needs a special end_io
2456 * handler which does not touch the bh after unlocking it.
2457 */
2458static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2459{
2460	__end_buffer_read_notouch(bh, uptodate);
2461}
2462
2463/*
2464 * Attach the singly-linked list of buffers created by nobh_write_begin, to
2465 * the page (converting it to circular linked list and taking care of page
2466 * dirty races).
2467 */
2468static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2469{
2470	struct buffer_head *bh;
2471
2472	BUG_ON(!PageLocked(page));
2473
2474	spin_lock(&page->mapping->private_lock);
2475	bh = head;
2476	do {
2477		if (PageDirty(page))
2478			set_buffer_dirty(bh);
2479		if (!bh->b_this_page)
2480			bh->b_this_page = head;
2481		bh = bh->b_this_page;
2482	} while (bh != head);
2483	attach_page_buffers(page, head);
2484	spin_unlock(&page->mapping->private_lock);
2485}
2486
2487/*
2488 * On entry, the page is fully not uptodate.
2489 * On exit the page is fully uptodate in the areas outside (from,to)
2490 * The filesystem needs to handle block truncation upon failure.
2491 */
2492int nobh_write_begin(struct address_space *mapping,
2493			loff_t pos, unsigned len, unsigned flags,
2494			struct page **pagep, void **fsdata,
2495			get_block_t *get_block)
2496{
2497	struct inode *inode = mapping->host;
2498	const unsigned blkbits = inode->i_blkbits;
2499	const unsigned blocksize = 1 << blkbits;
2500	struct buffer_head *head, *bh;
2501	struct page *page;
2502	pgoff_t index;
2503	unsigned from, to;
2504	unsigned block_in_page;
2505	unsigned block_start, block_end;
2506	sector_t block_in_file;
2507	int nr_reads = 0;
2508	int ret = 0;
2509	int is_mapped_to_disk = 1;
2510
2511	index = pos >> PAGE_SHIFT;
2512	from = pos & (PAGE_SIZE - 1);
2513	to = from + len;
2514
2515	page = grab_cache_page_write_begin(mapping, index, flags);
2516	if (!page)
2517		return -ENOMEM;
2518	*pagep = page;
2519	*fsdata = NULL;
2520
2521	if (page_has_buffers(page)) {
2522		ret = __block_write_begin(page, pos, len, get_block);
2523		if (unlikely(ret))
2524			goto out_release;
2525		return ret;
2526	}
2527
2528	if (PageMappedToDisk(page))
2529		return 0;
2530
2531	/*
2532	 * Allocate buffers so that we can keep track of state, and potentially
2533	 * attach them to the page if an error occurs. In the common case of
2534	 * no error, they will just be freed again without ever being attached
2535	 * to the page (which is all OK, because we're under the page lock).
2536	 *
2537	 * Be careful: the buffer linked list is a NULL terminated one, rather
2538	 * than the circular one we're used to.
2539	 */
2540	head = alloc_page_buffers(page, blocksize, 0);
2541	if (!head) {
2542		ret = -ENOMEM;
2543		goto out_release;
2544	}
2545
2546	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
2547
2548	/*
2549	 * We loop across all blocks in the page, whether or not they are
2550	 * part of the affected region.  This is so we can discover if the
2551	 * page is fully mapped-to-disk.
2552	 */
2553	for (block_start = 0, block_in_page = 0, bh = head;
2554		  block_start < PAGE_SIZE;
2555		  block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2556		int create;
2557
2558		block_end = block_start + blocksize;
2559		bh->b_state = 0;
2560		create = 1;
2561		if (block_start >= to)
2562			create = 0;
2563		ret = get_block(inode, block_in_file + block_in_page,
2564					bh, create);
2565		if (ret)
2566			goto failed;
2567		if (!buffer_mapped(bh))
2568			is_mapped_to_disk = 0;
2569		if (buffer_new(bh))
2570			unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2571		if (PageUptodate(page)) {
2572			set_buffer_uptodate(bh);
2573			continue;
2574		}
2575		if (buffer_new(bh) || !buffer_mapped(bh)) {
2576			zero_user_segments(page, block_start, from,
2577							to, block_end);
2578			continue;
2579		}
2580		if (buffer_uptodate(bh))
2581			continue;	/* reiserfs does this */
2582		if (block_start < from || block_end > to) {
2583			lock_buffer(bh);
2584			bh->b_end_io = end_buffer_read_nobh;
2585			submit_bh(READ, bh);
2586			nr_reads++;
2587		}
2588	}
2589
2590	if (nr_reads) {
2591		/*
2592		 * The page is locked, so these buffers are protected from
2593		 * any VM or truncate activity.  Hence we don't need to care
2594		 * for the buffer_head refcounts.
2595		 */
2596		for (bh = head; bh; bh = bh->b_this_page) {
2597			wait_on_buffer(bh);
2598			if (!buffer_uptodate(bh))
2599				ret = -EIO;
2600		}
2601		if (ret)
2602			goto failed;
2603	}
2604
2605	if (is_mapped_to_disk)
2606		SetPageMappedToDisk(page);
2607
2608	*fsdata = head; /* to be released by nobh_write_end */
2609
2610	return 0;
2611
2612failed:
2613	BUG_ON(!ret);
2614	/*
2615	 * Error recovery is a bit difficult. We need to zero out blocks that
2616	 * were newly allocated, and dirty them to ensure they get written out.
2617	 * Buffers need to be attached to the page at this point, otherwise
2618	 * the handling of potential IO errors during writeout would be hard
2619	 * (could try doing synchronous writeout, but what if that fails too?)
2620	 */
2621	attach_nobh_buffers(page, head);
2622	page_zero_new_buffers(page, from, to);
2623
2624out_release:
2625	unlock_page(page);
2626	put_page(page);
2627	*pagep = NULL;
2628
2629	return ret;
2630}
2631EXPORT_SYMBOL(nobh_write_begin);
2632
2633int nobh_write_end(struct file *file, struct address_space *mapping,
2634			loff_t pos, unsigned len, unsigned copied,
2635			struct page *page, void *fsdata)
2636{
2637	struct inode *inode = page->mapping->host;
2638	struct buffer_head *head = fsdata;
2639	struct buffer_head *bh;
2640	BUG_ON(fsdata != NULL && page_has_buffers(page));
2641
2642	if (unlikely(copied < len) && head)
2643		attach_nobh_buffers(page, head);
2644	if (page_has_buffers(page))
2645		return generic_write_end(file, mapping, pos, len,
2646					copied, page, fsdata);
2647
2648	SetPageUptodate(page);
2649	set_page_dirty(page);
2650	if (pos+copied > inode->i_size) {
2651		i_size_write(inode, pos+copied);
2652		mark_inode_dirty(inode);
2653	}
2654
2655	unlock_page(page);
2656	put_page(page);
2657
2658	while (head) {
2659		bh = head;
2660		head = head->b_this_page;
2661		free_buffer_head(bh);
2662	}
2663
2664	return copied;
2665}
2666EXPORT_SYMBOL(nobh_write_end);
2667
2668/*
2669 * nobh_writepage() - based on block_full_write_page() except
2670 * that it tries to operate without attaching bufferheads to
2671 * the page.
2672 */
2673int nobh_writepage(struct page *page, get_block_t *get_block,
2674			struct writeback_control *wbc)
2675{
2676	struct inode * const inode = page->mapping->host;
2677	loff_t i_size = i_size_read(inode);
2678	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2679	unsigned offset;
2680	int ret;
2681
2682	/* Is the page fully inside i_size? */
2683	if (page->index < end_index)
2684		goto out;
2685
2686	/* Is the page fully outside i_size? (truncate in progress) */
2687	offset = i_size & (PAGE_SIZE-1);
2688	if (page->index >= end_index+1 || !offset) {
2689		/*
2690		 * The page may have dirty, unmapped buffers.  For example,
2691		 * they may have been added in ext3_writepage().  Make them
2692		 * freeable here, so the page does not leak.
2693		 */
2694#if 0
2695		/* Not really sure about this  - do we need this ? */
2696		if (page->mapping->a_ops->invalidatepage)
2697			page->mapping->a_ops->invalidatepage(page, offset);
2698#endif
2699		unlock_page(page);
2700		return 0; /* don't care */
2701	}
2702
2703	/*
2704	 * The page straddles i_size.  It must be zeroed out on each and every
2705	 * writepage invocation because it may be mmapped.  "A file is mapped
2706	 * in multiples of the page size.  For a file that is not a multiple of
2707	 * the  page size, the remaining memory is zeroed when mapped, and
2708	 * writes to that region are not written out to the file."
2709	 */
2710	zero_user_segment(page, offset, PAGE_SIZE);
2711out:
2712	ret = mpage_writepage(page, get_block, wbc);
2713	if (ret == -EAGAIN)
2714		ret = __block_write_full_page(inode, page, get_block, wbc,
2715					      end_buffer_async_write);
2716	return ret;
2717}
2718EXPORT_SYMBOL(nobh_writepage);
2719
2720int nobh_truncate_page(struct address_space *mapping,
2721			loff_t from, get_block_t *get_block)
2722{
2723	pgoff_t index = from >> PAGE_SHIFT;
2724	unsigned offset = from & (PAGE_SIZE-1);
2725	unsigned blocksize;
2726	sector_t iblock;
2727	unsigned length, pos;
2728	struct inode *inode = mapping->host;
2729	struct page *page;
2730	struct buffer_head map_bh;
2731	int err;
2732
2733	blocksize = 1 << inode->i_blkbits;
2734	length = offset & (blocksize - 1);
2735
2736	/* Block boundary? Nothing to do */
2737	if (!length)
2738		return 0;
2739
2740	length = blocksize - length;
2741	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2742
2743	page = grab_cache_page(mapping, index);
2744	err = -ENOMEM;
2745	if (!page)
2746		goto out;
2747
2748	if (page_has_buffers(page)) {
2749has_buffers:
2750		unlock_page(page);
2751		put_page(page);
2752		return block_truncate_page(mapping, from, get_block);
2753	}
2754
2755	/* Find the buffer that contains "offset" */
2756	pos = blocksize;
2757	while (offset >= pos) {
2758		iblock++;
2759		pos += blocksize;
2760	}
2761
2762	map_bh.b_size = blocksize;
2763	map_bh.b_state = 0;
2764	err = get_block(inode, iblock, &map_bh, 0);
2765	if (err)
2766		goto unlock;
2767	/* unmapped? It's a hole - nothing to do */
2768	if (!buffer_mapped(&map_bh))
2769		goto unlock;
2770
2771	/* Ok, it's mapped. Make sure it's up-to-date */
2772	if (!PageUptodate(page)) {
2773		err = mapping->a_ops->readpage(NULL, page);
2774		if (err) {
2775			put_page(page);
2776			goto out;
2777		}
2778		lock_page(page);
2779		if (!PageUptodate(page)) {
2780			err = -EIO;
2781			goto unlock;
2782		}
2783		if (page_has_buffers(page))
2784			goto has_buffers;
2785	}
2786	zero_user(page, offset, length);
2787	set_page_dirty(page);
2788	err = 0;
2789
2790unlock:
2791	unlock_page(page);
2792	put_page(page);
2793out:
2794	return err;
2795}
2796EXPORT_SYMBOL(nobh_truncate_page);
2797
2798int block_truncate_page(struct address_space *mapping,
2799			loff_t from, get_block_t *get_block)
2800{
2801	pgoff_t index = from >> PAGE_SHIFT;
2802	unsigned offset = from & (PAGE_SIZE-1);
2803	unsigned blocksize;
2804	sector_t iblock;
2805	unsigned length, pos;
2806	struct inode *inode = mapping->host;
2807	struct page *page;
2808	struct buffer_head *bh;
2809	int err;
2810
2811	blocksize = 1 << inode->i_blkbits;
2812	length = offset & (blocksize - 1);
2813
2814	/* Block boundary? Nothing to do */
2815	if (!length)
2816		return 0;
2817
2818	length = blocksize - length;
2819	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2820	
2821	page = grab_cache_page(mapping, index);
2822	err = -ENOMEM;
2823	if (!page)
2824		goto out;
2825
2826	if (!page_has_buffers(page))
2827		create_empty_buffers(page, blocksize, 0);
2828
2829	/* Find the buffer that contains "offset" */
2830	bh = page_buffers(page);
2831	pos = blocksize;
2832	while (offset >= pos) {
2833		bh = bh->b_this_page;
2834		iblock++;
2835		pos += blocksize;
2836	}
2837
2838	err = 0;
2839	if (!buffer_mapped(bh)) {
2840		WARN_ON(bh->b_size != blocksize);
2841		err = get_block(inode, iblock, bh, 0);
2842		if (err)
2843			goto unlock;
2844		/* unmapped? It's a hole - nothing to do */
2845		if (!buffer_mapped(bh))
2846			goto unlock;
2847	}
2848
2849	/* Ok, it's mapped. Make sure it's up-to-date */
2850	if (PageUptodate(page))
2851		set_buffer_uptodate(bh);
2852
2853	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2854		err = -EIO;
2855		ll_rw_block(READ, 1, &bh);
2856		wait_on_buffer(bh);
2857		/* Uhhuh. Read error. Complain and punt. */
2858		if (!buffer_uptodate(bh))
2859			goto unlock;
2860	}
2861
2862	zero_user(page, offset, length);
2863	mark_buffer_dirty(bh);
2864	err = 0;
2865
2866unlock:
2867	unlock_page(page);
2868	put_page(page);
2869out:
2870	return err;
2871}
2872EXPORT_SYMBOL(block_truncate_page);
2873
2874/*
2875 * The generic ->writepage function for buffer-backed address_spaces
 
2876 */
2877int block_write_full_page(struct page *page, get_block_t *get_block,
2878			struct writeback_control *wbc)
2879{
2880	struct inode * const inode = page->mapping->host;
2881	loff_t i_size = i_size_read(inode);
2882	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2883	unsigned offset;
2884
2885	/* Is the page fully inside i_size? */
2886	if (page->index < end_index)
2887		return __block_write_full_page(inode, page, get_block, wbc,
2888					       end_buffer_async_write);
2889
2890	/* Is the page fully outside i_size? (truncate in progress) */
2891	offset = i_size & (PAGE_SIZE-1);
2892	if (page->index >= end_index+1 || !offset) {
2893		/*
2894		 * The page may have dirty, unmapped buffers.  For example,
2895		 * they may have been added in ext3_writepage().  Make them
2896		 * freeable here, so the page does not leak.
2897		 */
2898		do_invalidatepage(page, 0, PAGE_SIZE);
2899		unlock_page(page);
2900		return 0; /* don't care */
2901	}
2902
2903	/*
2904	 * The page straddles i_size.  It must be zeroed out on each and every
2905	 * writepage invocation because it may be mmapped.  "A file is mapped
2906	 * in multiples of the page size.  For a file that is not a multiple of
2907	 * the  page size, the remaining memory is zeroed when mapped, and
2908	 * writes to that region are not written out to the file."
2909	 */
2910	zero_user_segment(page, offset, PAGE_SIZE);
2911	return __block_write_full_page(inode, page, get_block, wbc,
2912							end_buffer_async_write);
 
 
 
 
 
 
 
 
 
 
2913}
2914EXPORT_SYMBOL(block_write_full_page);
2915
2916sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2917			    get_block_t *get_block)
2918{
2919	struct buffer_head tmp;
2920	struct inode *inode = mapping->host;
2921	tmp.b_state = 0;
2922	tmp.b_blocknr = 0;
2923	tmp.b_size = 1 << inode->i_blkbits;
2924	get_block(inode, block, &tmp, 0);
2925	return tmp.b_blocknr;
2926}
2927EXPORT_SYMBOL(generic_block_bmap);
2928
2929static void end_bio_bh_io_sync(struct bio *bio)
2930{
2931	struct buffer_head *bh = bio->bi_private;
2932
2933	if (unlikely(bio_flagged(bio, BIO_QUIET)))
 
 
 
 
2934		set_bit(BH_Quiet, &bh->b_state);
2935
2936	bh->b_end_io(bh, !bio->bi_error);
2937	bio_put(bio);
2938}
2939
2940/*
2941 * This allows us to do IO even on the odd last sectors
2942 * of a device, even if the block size is some multiple
2943 * of the physical sector size.
2944 *
2945 * We'll just truncate the bio to the size of the device,
2946 * and clear the end of the buffer head manually.
2947 *
2948 * Truly out-of-range accesses will turn into actual IO
2949 * errors, this only handles the "we need to be able to
2950 * do IO at the final sector" case.
2951 */
2952void guard_bio_eod(int rw, struct bio *bio)
2953{
2954	sector_t maxsector;
2955	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
2956	unsigned truncated_bytes;
2957
2958	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
2959	if (!maxsector)
2960		return;
2961
2962	/*
2963	 * If the *whole* IO is past the end of the device,
2964	 * let it through, and the IO layer will turn it into
2965	 * an EIO.
2966	 */
2967	if (unlikely(bio->bi_iter.bi_sector >= maxsector))
2968		return;
2969
2970	maxsector -= bio->bi_iter.bi_sector;
2971	if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
2972		return;
2973
2974	/* Uhhuh. We've got a bio that straddles the device size! */
2975	truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
2976
2977	/* Truncate the bio.. */
2978	bio->bi_iter.bi_size -= truncated_bytes;
2979	bvec->bv_len -= truncated_bytes;
2980
2981	/* ..and clear the end of the buffer for reads */
2982	if ((rw & RW_MASK) == READ) {
2983		zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
2984				truncated_bytes);
2985	}
2986}
2987
2988static int submit_bh_wbc(int rw, struct buffer_head *bh,
2989			 unsigned long bio_flags, struct writeback_control *wbc)
2990{
2991	struct bio *bio;
 
2992
2993	BUG_ON(!buffer_locked(bh));
2994	BUG_ON(!buffer_mapped(bh));
2995	BUG_ON(!bh->b_end_io);
2996	BUG_ON(buffer_delay(bh));
2997	BUG_ON(buffer_unwritten(bh));
2998
2999	/*
3000	 * Only clear out a write error when rewriting
3001	 */
3002	if (test_set_buffer_req(bh) && (rw & WRITE))
3003		clear_buffer_write_io_error(bh);
3004
3005	/*
3006	 * from here on down, it's all bio -- do the initial mapping,
3007	 * submit_bio -> generic_make_request may further map this bio around
3008	 */
3009	bio = bio_alloc(GFP_NOIO, 1);
3010
3011	if (wbc) {
3012		wbc_init_bio(wbc, bio);
3013		wbc_account_io(wbc, bh->b_page, bh->b_size);
3014	}
3015
3016	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3017	bio->bi_bdev = bh->b_bdev;
3018
3019	bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3020	BUG_ON(bio->bi_iter.bi_size != bh->b_size);
 
 
 
 
3021
3022	bio->bi_end_io = end_bio_bh_io_sync;
3023	bio->bi_private = bh;
3024	bio->bi_flags |= bio_flags;
3025
3026	/* Take care of bh's that straddle the end of the device */
3027	guard_bio_eod(rw, bio);
3028
3029	if (buffer_meta(bh))
3030		rw |= REQ_META;
3031	if (buffer_prio(bh))
3032		rw |= REQ_PRIO;
3033
 
3034	submit_bio(rw, bio);
3035	return 0;
3036}
3037
3038int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
3039{
3040	return submit_bh_wbc(rw, bh, bio_flags, NULL);
3041}
3042EXPORT_SYMBOL_GPL(_submit_bh);
3043
3044int submit_bh(int rw, struct buffer_head *bh)
3045{
3046	return submit_bh_wbc(rw, bh, 0, NULL);
3047}
3048EXPORT_SYMBOL(submit_bh);
3049
3050/**
3051 * ll_rw_block: low-level access to block devices (DEPRECATED)
3052 * @rw: whether to %READ or %WRITE or maybe %READA (readahead)
3053 * @nr: number of &struct buffer_heads in the array
3054 * @bhs: array of pointers to &struct buffer_head
3055 *
3056 * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3057 * requests an I/O operation on them, either a %READ or a %WRITE.  The third
3058 * %READA option is described in the documentation for generic_make_request()
3059 * which ll_rw_block() calls.
3060 *
3061 * This function drops any buffer that it cannot get a lock on (with the
3062 * BH_Lock state bit), any buffer that appears to be clean when doing a write
3063 * request, and any buffer that appears to be up-to-date when doing read
3064 * request.  Further it marks as clean buffers that are processed for
3065 * writing (the buffer cache won't assume that they are actually clean
3066 * until the buffer gets unlocked).
3067 *
3068 * ll_rw_block sets b_end_io to simple completion handler that marks
3069 * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3070 * any waiters. 
3071 *
3072 * All of the buffers must be for the same device, and must also be a
3073 * multiple of the current approved size for the device.
3074 */
3075void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
3076{
3077	int i;
3078
3079	for (i = 0; i < nr; i++) {
3080		struct buffer_head *bh = bhs[i];
3081
3082		if (!trylock_buffer(bh))
3083			continue;
3084		if (rw == WRITE) {
3085			if (test_clear_buffer_dirty(bh)) {
3086				bh->b_end_io = end_buffer_write_sync;
3087				get_bh(bh);
3088				submit_bh(WRITE, bh);
3089				continue;
3090			}
3091		} else {
3092			if (!buffer_uptodate(bh)) {
3093				bh->b_end_io = end_buffer_read_sync;
3094				get_bh(bh);
3095				submit_bh(rw, bh);
3096				continue;
3097			}
3098		}
3099		unlock_buffer(bh);
3100	}
3101}
3102EXPORT_SYMBOL(ll_rw_block);
3103
3104void write_dirty_buffer(struct buffer_head *bh, int rw)
3105{
3106	lock_buffer(bh);
3107	if (!test_clear_buffer_dirty(bh)) {
3108		unlock_buffer(bh);
3109		return;
3110	}
3111	bh->b_end_io = end_buffer_write_sync;
3112	get_bh(bh);
3113	submit_bh(rw, bh);
3114}
3115EXPORT_SYMBOL(write_dirty_buffer);
3116
3117/*
3118 * For a data-integrity writeout, we need to wait upon any in-progress I/O
3119 * and then start new I/O and then wait upon it.  The caller must have a ref on
3120 * the buffer_head.
3121 */
3122int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3123{
3124	int ret = 0;
3125
3126	WARN_ON(atomic_read(&bh->b_count) < 1);
3127	lock_buffer(bh);
3128	if (test_clear_buffer_dirty(bh)) {
3129		get_bh(bh);
3130		bh->b_end_io = end_buffer_write_sync;
3131		ret = submit_bh(rw, bh);
3132		wait_on_buffer(bh);
3133		if (!ret && !buffer_uptodate(bh))
3134			ret = -EIO;
3135	} else {
3136		unlock_buffer(bh);
3137	}
3138	return ret;
3139}
3140EXPORT_SYMBOL(__sync_dirty_buffer);
3141
3142int sync_dirty_buffer(struct buffer_head *bh)
3143{
3144	return __sync_dirty_buffer(bh, WRITE_SYNC);
3145}
3146EXPORT_SYMBOL(sync_dirty_buffer);
3147
3148/*
3149 * try_to_free_buffers() checks if all the buffers on this particular page
3150 * are unused, and releases them if so.
3151 *
3152 * Exclusion against try_to_free_buffers may be obtained by either
3153 * locking the page or by holding its mapping's private_lock.
3154 *
3155 * If the page is dirty but all the buffers are clean then we need to
3156 * be sure to mark the page clean as well.  This is because the page
3157 * may be against a block device, and a later reattachment of buffers
3158 * to a dirty page will set *all* buffers dirty.  Which would corrupt
3159 * filesystem data on the same device.
3160 *
3161 * The same applies to regular filesystem pages: if all the buffers are
3162 * clean then we set the page clean and proceed.  To do that, we require
3163 * total exclusion from __set_page_dirty_buffers().  That is obtained with
3164 * private_lock.
3165 *
3166 * try_to_free_buffers() is non-blocking.
3167 */
3168static inline int buffer_busy(struct buffer_head *bh)
3169{
3170	return atomic_read(&bh->b_count) |
3171		(bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3172}
3173
3174static int
3175drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3176{
3177	struct buffer_head *head = page_buffers(page);
3178	struct buffer_head *bh;
3179
3180	bh = head;
3181	do {
3182		if (buffer_write_io_error(bh) && page->mapping)
3183			set_bit(AS_EIO, &page->mapping->flags);
3184		if (buffer_busy(bh))
3185			goto failed;
3186		bh = bh->b_this_page;
3187	} while (bh != head);
3188
3189	do {
3190		struct buffer_head *next = bh->b_this_page;
3191
3192		if (bh->b_assoc_map)
3193			__remove_assoc_queue(bh);
3194		bh = next;
3195	} while (bh != head);
3196	*buffers_to_free = head;
3197	__clear_page_buffers(page);
3198	return 1;
3199failed:
3200	return 0;
3201}
3202
3203int try_to_free_buffers(struct page *page)
3204{
3205	struct address_space * const mapping = page->mapping;
3206	struct buffer_head *buffers_to_free = NULL;
3207	int ret = 0;
3208
3209	BUG_ON(!PageLocked(page));
3210	if (PageWriteback(page))
3211		return 0;
3212
3213	if (mapping == NULL) {		/* can this still happen? */
3214		ret = drop_buffers(page, &buffers_to_free);
3215		goto out;
3216	}
3217
3218	spin_lock(&mapping->private_lock);
3219	ret = drop_buffers(page, &buffers_to_free);
3220
3221	/*
3222	 * If the filesystem writes its buffers by hand (eg ext3)
3223	 * then we can have clean buffers against a dirty page.  We
3224	 * clean the page here; otherwise the VM will never notice
3225	 * that the filesystem did any IO at all.
3226	 *
3227	 * Also, during truncate, discard_buffer will have marked all
3228	 * the page's buffers clean.  We discover that here and clean
3229	 * the page also.
3230	 *
3231	 * private_lock must be held over this entire operation in order
3232	 * to synchronise against __set_page_dirty_buffers and prevent the
3233	 * dirty bit from being lost.
3234	 */
3235	if (ret)
3236		cancel_dirty_page(page);
3237	spin_unlock(&mapping->private_lock);
3238out:
3239	if (buffers_to_free) {
3240		struct buffer_head *bh = buffers_to_free;
3241
3242		do {
3243			struct buffer_head *next = bh->b_this_page;
3244			free_buffer_head(bh);
3245			bh = next;
3246		} while (bh != buffers_to_free);
3247	}
3248	return ret;
3249}
3250EXPORT_SYMBOL(try_to_free_buffers);
3251
3252/*
3253 * There are no bdflush tunables left.  But distributions are
3254 * still running obsolete flush daemons, so we terminate them here.
3255 *
3256 * Use of bdflush() is deprecated and will be removed in a future kernel.
3257 * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3258 */
3259SYSCALL_DEFINE2(bdflush, int, func, long, data)
3260{
3261	static int msg_count;
3262
3263	if (!capable(CAP_SYS_ADMIN))
3264		return -EPERM;
3265
3266	if (msg_count < 5) {
3267		msg_count++;
3268		printk(KERN_INFO
3269			"warning: process `%s' used the obsolete bdflush"
3270			" system call\n", current->comm);
3271		printk(KERN_INFO "Fix your initscripts?\n");
3272	}
3273
3274	if (func == 1)
3275		do_exit(0);
3276	return 0;
3277}
3278
3279/*
3280 * Buffer-head allocation
3281 */
3282static struct kmem_cache *bh_cachep __read_mostly;
3283
3284/*
3285 * Once the number of bh's in the machine exceeds this level, we start
3286 * stripping them in writeback.
3287 */
3288static unsigned long max_buffer_heads;
3289
3290int buffer_heads_over_limit;
3291
3292struct bh_accounting {
3293	int nr;			/* Number of live bh's */
3294	int ratelimit;		/* Limit cacheline bouncing */
3295};
3296
3297static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3298
3299static void recalc_bh_state(void)
3300{
3301	int i;
3302	int tot = 0;
3303
3304	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3305		return;
3306	__this_cpu_write(bh_accounting.ratelimit, 0);
3307	for_each_online_cpu(i)
3308		tot += per_cpu(bh_accounting, i).nr;
3309	buffer_heads_over_limit = (tot > max_buffer_heads);
3310}
3311
3312struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3313{
3314	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3315	if (ret) {
3316		INIT_LIST_HEAD(&ret->b_assoc_buffers);
3317		preempt_disable();
3318		__this_cpu_inc(bh_accounting.nr);
3319		recalc_bh_state();
3320		preempt_enable();
3321	}
3322	return ret;
3323}
3324EXPORT_SYMBOL(alloc_buffer_head);
3325
3326void free_buffer_head(struct buffer_head *bh)
3327{
3328	BUG_ON(!list_empty(&bh->b_assoc_buffers));
3329	kmem_cache_free(bh_cachep, bh);
3330	preempt_disable();
3331	__this_cpu_dec(bh_accounting.nr);
3332	recalc_bh_state();
3333	preempt_enable();
3334}
3335EXPORT_SYMBOL(free_buffer_head);
3336
3337static void buffer_exit_cpu(int cpu)
3338{
3339	int i;
3340	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3341
3342	for (i = 0; i < BH_LRU_SIZE; i++) {
3343		brelse(b->bhs[i]);
3344		b->bhs[i] = NULL;
3345	}
3346	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3347	per_cpu(bh_accounting, cpu).nr = 0;
3348}
3349
3350static int buffer_cpu_notify(struct notifier_block *self,
3351			      unsigned long action, void *hcpu)
3352{
3353	if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3354		buffer_exit_cpu((unsigned long)hcpu);
3355	return NOTIFY_OK;
3356}
3357
3358/**
3359 * bh_uptodate_or_lock - Test whether the buffer is uptodate
3360 * @bh: struct buffer_head
3361 *
3362 * Return true if the buffer is up-to-date and false,
3363 * with the buffer locked, if not.
3364 */
3365int bh_uptodate_or_lock(struct buffer_head *bh)
3366{
3367	if (!buffer_uptodate(bh)) {
3368		lock_buffer(bh);
3369		if (!buffer_uptodate(bh))
3370			return 0;
3371		unlock_buffer(bh);
3372	}
3373	return 1;
3374}
3375EXPORT_SYMBOL(bh_uptodate_or_lock);
3376
3377/**
3378 * bh_submit_read - Submit a locked buffer for reading
3379 * @bh: struct buffer_head
3380 *
3381 * Returns zero on success and -EIO on error.
3382 */
3383int bh_submit_read(struct buffer_head *bh)
3384{
3385	BUG_ON(!buffer_locked(bh));
3386
3387	if (buffer_uptodate(bh)) {
3388		unlock_buffer(bh);
3389		return 0;
3390	}
3391
3392	get_bh(bh);
3393	bh->b_end_io = end_buffer_read_sync;
3394	submit_bh(READ, bh);
3395	wait_on_buffer(bh);
3396	if (buffer_uptodate(bh))
3397		return 0;
3398	return -EIO;
3399}
3400EXPORT_SYMBOL(bh_submit_read);
3401
3402void __init buffer_init(void)
3403{
3404	unsigned long nrpages;
3405
3406	bh_cachep = kmem_cache_create("buffer_head",
3407			sizeof(struct buffer_head), 0,
3408				(SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3409				SLAB_MEM_SPREAD),
3410				NULL);
3411
3412	/*
3413	 * Limit the bh occupancy to 10% of ZONE_NORMAL
3414	 */
3415	nrpages = (nr_free_buffer_pages() * 10) / 100;
3416	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3417	hotcpu_notifier(buffer_cpu_notify, 0);
3418}