direct-io.c 35.2 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259
/*
 * fs/direct-io.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 *
 * O_DIRECT
 *
 * 04Jul2002	Andrew Morton
 *		Initial version
 * 11Sep2002	janetinc@us.ibm.com
 * 		added readv/writev support.
 * 29Oct2002	Andrew Morton
 *		rewrote bio_add_page() support.
 * 30Oct2002	pbadari@us.ibm.com
 *		added support for non-aligned IO.
 * 06Nov2002	pbadari@us.ibm.com
 *		added asynchronous IO support.
 * 21Jul2003	nathans@sgi.com
 *		added IO completion notifier.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/bio.h>
#include <linux/wait.h>
#include <linux/err.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/rwsem.h>
#include <linux/uio.h>
#include <asm/atomic.h>

/*
 * How many user pages to map in one call to get_user_pages().  This determines
 * the size of a structure on the stack.
 */
#define DIO_PAGES	64

/*
 * This code generally works in units of "dio_blocks".  A dio_block is
 * somewhere between the hard sector size and the filesystem block size.  it
 * is determined on a per-invocation basis.   When talking to the filesystem
 * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
 * down by dio->blkfactor.  Similarly, fs-blocksize quantities are converted
 * to bio_block quantities by shifting left by blkfactor.
 *
 * If blkfactor is zero then the user's request was aligned to the filesystem's
 * blocksize.
 */

struct dio {
	/* BIO submission state */
	struct bio *bio;		/* bio under assembly */
	struct inode *inode;
	int rw;
	loff_t i_size;			/* i_size when submitted */
	int flags;			/* doesn't change */
	unsigned blkbits;		/* doesn't change */
	unsigned blkfactor;		/* When we're using an alignment which
					   is finer than the filesystem's soft
					   blocksize, this specifies how much
					   finer.  blkfactor=2 means 1/4-block
					   alignment.  Does not change */
	unsigned start_zero_done;	/* flag: sub-blocksize zeroing has
					   been performed at the start of a
					   write */
	int pages_in_io;		/* approximate total IO pages */
	size_t	size;			/* total request size (doesn't change)*/
	sector_t block_in_file;		/* Current offset into the underlying
					   file in dio_block units. */
	unsigned blocks_available;	/* At block_in_file.  changes */
	sector_t final_block_in_request;/* doesn't change */
	unsigned first_block_in_page;	/* doesn't change, Used only once */
	int boundary;			/* prev block is at a boundary */
	int reap_counter;		/* rate limit reaping */
	get_block_t *get_block;		/* block mapping function */
	dio_iodone_t *end_io;		/* IO completion function */
	dio_submit_t *submit_io;	/* IO submition function */
	loff_t logical_offset_in_bio;	/* current first logical block in bio */
	sector_t final_block_in_bio;	/* current final block in bio + 1 */
	sector_t next_block_for_io;	/* next block to be put under IO,
					   in dio_blocks units */
	struct buffer_head map_bh;	/* last get_block() result */

	/*
	 * Deferred addition of a page to the dio.  These variables are
	 * private to dio_send_cur_page(), submit_page_section() and
	 * dio_bio_add_page().
	 */
	struct page *cur_page;		/* The page */
	unsigned cur_page_offset;	/* Offset into it, in bytes */
	unsigned cur_page_len;		/* Nr of bytes at cur_page_offset */
	sector_t cur_page_block;	/* Where it starts */
	loff_t cur_page_fs_offset;	/* Offset in file */

	/* BIO completion state */
	spinlock_t bio_lock;		/* protects BIO fields below */
	unsigned long refcount;		/* direct_io_worker() and bios */
	struct bio *bio_list;		/* singly linked via bi_private */
	struct task_struct *waiter;	/* waiting task (NULL if none) */

	/* AIO related stuff */
	struct kiocb *iocb;		/* kiocb */
	int is_async;			/* is IO async ? */
	int io_error;			/* IO error in completion path */
	ssize_t result;                 /* IO result */

	/*
	 * Page fetching state. These variables belong to dio_refill_pages().
	 */
	int curr_page;			/* changes */
	int total_pages;		/* doesn't change */
	unsigned long curr_user_address;/* changes */

	/*
	 * Page queue.  These variables belong to dio_refill_pages() and
	 * dio_get_page().
	 */
	unsigned head;			/* next page to process */
	unsigned tail;			/* last valid page + 1 */
	int page_errors;		/* errno from get_user_pages() */

	/*
	 * pages[] (and any fields placed after it) are not zeroed out at
	 * allocation time.  Don't add new fields after pages[] unless you
	 * wish that they not be zeroed.
	 */
	struct page *pages[DIO_PAGES];	/* page buffer */
};

/*
 * How many pages are in the queue?
 */
static inline unsigned dio_pages_present(struct dio *dio)
{
	return dio->tail - dio->head;
}

/*
 * Go grab and pin some userspace pages.   Typically we'll get 64 at a time.
 */
static int dio_refill_pages(struct dio *dio)
{
	int ret;
	int nr_pages;

	nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES);
	ret = get_user_pages_fast(
		dio->curr_user_address,		/* Where from? */
		nr_pages,			/* How many pages? */
		dio->rw == READ,		/* Write to memory? */
		&dio->pages[0]);		/* Put results here */

	if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
		struct page *page = ZERO_PAGE(0);
		/*
		 * A memory fault, but the filesystem has some outstanding
		 * mapped blocks.  We need to use those blocks up to avoid
		 * leaking stale data in the file.
		 */
		if (dio->page_errors == 0)
			dio->page_errors = ret;
		page_cache_get(page);
		dio->pages[0] = page;
		dio->head = 0;
		dio->tail = 1;
		ret = 0;
		goto out;
	}

	if (ret >= 0) {
		dio->curr_user_address += ret * PAGE_SIZE;
		dio->curr_page += ret;
		dio->head = 0;
		dio->tail = ret;
		ret = 0;
	}
out:
	return ret;	
}

/*
 * Get another userspace page.  Returns an ERR_PTR on error.  Pages are
 * buffered inside the dio so that we can call get_user_pages() against a
 * decent number of pages, less frequently.  To provide nicer use of the
 * L1 cache.
 */
static struct page *dio_get_page(struct dio *dio)
{
	if (dio_pages_present(dio) == 0) {
		int ret;

		ret = dio_refill_pages(dio);
		if (ret)
			return ERR_PTR(ret);
		BUG_ON(dio_pages_present(dio) == 0);
	}
	return dio->pages[dio->head++];
}

/**
 * dio_complete() - called when all DIO BIO I/O has been completed
 * @offset: the byte offset in the file of the completed operation
 *
 * This releases locks as dictated by the locking type, lets interested parties
 * know that a DIO operation has completed, and calculates the resulting return
 * code for the operation.
 *
 * It lets the filesystem know if it registered an interest earlier via
 * get_block.  Pass the private field of the map buffer_head so that
 * filesystems can use it to hold additional state between get_block calls and
 * dio_complete.
 */
static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is_async)
{
	ssize_t transferred = 0;

	/*
	 * AIO submission can race with bio completion to get here while
	 * expecting to have the last io completed by bio completion.
	 * In that case -EIOCBQUEUED is in fact not an error we want
	 * to preserve through this call.
	 */
	if (ret == -EIOCBQUEUED)
		ret = 0;

	if (dio->result) {
		transferred = dio->result;

		/* Check for short read case */
		if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
			transferred = dio->i_size - offset;
	}

	if (ret == 0)
		ret = dio->page_errors;
	if (ret == 0)
		ret = dio->io_error;
	if (ret == 0)
		ret = transferred;

	if (dio->end_io && dio->result) {
		dio->end_io(dio->iocb, offset, transferred,
			    dio->map_bh.b_private, ret, is_async);
	} else if (is_async) {
		aio_complete(dio->iocb, ret, 0);
	}

	if (dio->flags & DIO_LOCKING)
		/* lockdep: non-owner release */
		up_read_non_owner(&dio->inode->i_alloc_sem);

	return ret;
}

static int dio_bio_complete(struct dio *dio, struct bio *bio);
/*
 * Asynchronous IO callback. 
 */
static void dio_bio_end_aio(struct bio *bio, int error)
{
	struct dio *dio = bio->bi_private;
	unsigned long remaining;
	unsigned long flags;

	/* cleanup the bio */
	dio_bio_complete(dio, bio);

	spin_lock_irqsave(&dio->bio_lock, flags);
	remaining = --dio->refcount;
	if (remaining == 1 && dio->waiter)
		wake_up_process(dio->waiter);
	spin_unlock_irqrestore(&dio->bio_lock, flags);

	if (remaining == 0) {
		dio_complete(dio, dio->iocb->ki_pos, 0, true);
		kfree(dio);
	}
}

/*
 * The BIO completion handler simply queues the BIO up for the process-context
 * handler.
 *
 * During I/O bi_private points at the dio.  After I/O, bi_private is used to
 * implement a singly-linked list of completed BIOs, at dio->bio_list.
 */
static void dio_bio_end_io(struct bio *bio, int error)
{
	struct dio *dio = bio->bi_private;
	unsigned long flags;

	spin_lock_irqsave(&dio->bio_lock, flags);
	bio->bi_private = dio->bio_list;
	dio->bio_list = bio;
	if (--dio->refcount == 1 && dio->waiter)
		wake_up_process(dio->waiter);
	spin_unlock_irqrestore(&dio->bio_lock, flags);
}

/**
 * dio_end_io - handle the end io action for the given bio
 * @bio: The direct io bio thats being completed
 * @error: Error if there was one
 *
 * This is meant to be called by any filesystem that uses their own dio_submit_t
 * so that the DIO specific endio actions are dealt with after the filesystem
 * has done it's completion work.
 */
void dio_end_io(struct bio *bio, int error)
{
	struct dio *dio = bio->bi_private;

	if (dio->is_async)
		dio_bio_end_aio(bio, error);
	else
		dio_bio_end_io(bio, error);
}
EXPORT_SYMBOL_GPL(dio_end_io);

static void
dio_bio_alloc(struct dio *dio, struct block_device *bdev,
		sector_t first_sector, int nr_vecs)
{
	struct bio *bio;

	/*
	 * bio_alloc() is guaranteed to return a bio when called with
	 * __GFP_WAIT and we request a valid number of vectors.
	 */
	bio = bio_alloc(GFP_KERNEL, nr_vecs);

	bio->bi_bdev = bdev;
	bio->bi_sector = first_sector;
	if (dio->is_async)
		bio->bi_end_io = dio_bio_end_aio;
	else
		bio->bi_end_io = dio_bio_end_io;

	dio->bio = bio;
	dio->logical_offset_in_bio = dio->cur_page_fs_offset;
}

/*
 * In the AIO read case we speculatively dirty the pages before starting IO.
 * During IO completion, any of these pages which happen to have been written
 * back will be redirtied by bio_check_pages_dirty().
 *
 * bios hold a dio reference between submit_bio and ->end_io.
 */
static void dio_bio_submit(struct dio *dio)
{
	struct bio *bio = dio->bio;
	unsigned long flags;

	bio->bi_private = dio;

	spin_lock_irqsave(&dio->bio_lock, flags);
	dio->refcount++;
	spin_unlock_irqrestore(&dio->bio_lock, flags);

	if (dio->is_async && dio->rw == READ)
		bio_set_pages_dirty(bio);

	if (dio->submit_io)
		dio->submit_io(dio->rw, bio, dio->inode,
			       dio->logical_offset_in_bio);
	else
		submit_bio(dio->rw, bio);

	dio->bio = NULL;
	dio->boundary = 0;
	dio->logical_offset_in_bio = 0;
}

/*
 * Release any resources in case of a failure
 */
static void dio_cleanup(struct dio *dio)
{
	while (dio_pages_present(dio))
		page_cache_release(dio_get_page(dio));
}

/*
 * Wait for the next BIO to complete.  Remove it and return it.  NULL is
 * returned once all BIOs have been completed.  This must only be called once
 * all bios have been issued so that dio->refcount can only decrease.  This
 * requires that that the caller hold a reference on the dio.
 */
static struct bio *dio_await_one(struct dio *dio)
{
	unsigned long flags;
	struct bio *bio = NULL;

	spin_lock_irqsave(&dio->bio_lock, flags);

	/*
	 * Wait as long as the list is empty and there are bios in flight.  bio
	 * completion drops the count, maybe adds to the list, and wakes while
	 * holding the bio_lock so we don't need set_current_state()'s barrier
	 * and can call it after testing our condition.
	 */
	while (dio->refcount > 1 && dio->bio_list == NULL) {
		__set_current_state(TASK_UNINTERRUPTIBLE);
		dio->waiter = current;
		spin_unlock_irqrestore(&dio->bio_lock, flags);
		io_schedule();
		/* wake up sets us TASK_RUNNING */
		spin_lock_irqsave(&dio->bio_lock, flags);
		dio->waiter = NULL;
	}
	if (dio->bio_list) {
		bio = dio->bio_list;
		dio->bio_list = bio->bi_private;
	}
	spin_unlock_irqrestore(&dio->bio_lock, flags);
	return bio;
}

/*
 * Process one completed BIO.  No locks are held.
 */
static int dio_bio_complete(struct dio *dio, struct bio *bio)
{
	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct bio_vec *bvec = bio->bi_io_vec;
	int page_no;

	if (!uptodate)
		dio->io_error = -EIO;

	if (dio->is_async && dio->rw == READ) {
		bio_check_pages_dirty(bio);	/* transfers ownership */
	} else {
		for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
			struct page *page = bvec[page_no].bv_page;

			if (dio->rw == READ && !PageCompound(page))
				set_page_dirty_lock(page);
			page_cache_release(page);
		}
		bio_put(bio);
	}
	return uptodate ? 0 : -EIO;
}

/*
 * Wait on and process all in-flight BIOs.  This must only be called once
 * all bios have been issued so that the refcount can only decrease.
 * This just waits for all bios to make it through dio_bio_complete.  IO
 * errors are propagated through dio->io_error and should be propagated via
 * dio_complete().
 */
static void dio_await_completion(struct dio *dio)
{
	struct bio *bio;
	do {
		bio = dio_await_one(dio);
		if (bio)
			dio_bio_complete(dio, bio);
	} while (bio);
}

/*
 * A really large O_DIRECT read or write can generate a lot of BIOs.  So
 * to keep the memory consumption sane we periodically reap any completed BIOs
 * during the BIO generation phase.
 *
 * This also helps to limit the peak amount of pinned userspace memory.
 */
static int dio_bio_reap(struct dio *dio)
{
	int ret = 0;

	if (dio->reap_counter++ >= 64) {
		while (dio->bio_list) {
			unsigned long flags;
			struct bio *bio;
			int ret2;

			spin_lock_irqsave(&dio->bio_lock, flags);
			bio = dio->bio_list;
			dio->bio_list = bio->bi_private;
			spin_unlock_irqrestore(&dio->bio_lock, flags);
			ret2 = dio_bio_complete(dio, bio);
			if (ret == 0)
				ret = ret2;
		}
		dio->reap_counter = 0;
	}
	return ret;
}

/*
 * Call into the fs to map some more disk blocks.  We record the current number
 * of available blocks at dio->blocks_available.  These are in units of the
 * fs blocksize, (1 << inode->i_blkbits).
 *
 * The fs is allowed to map lots of blocks at once.  If it wants to do that,
 * it uses the passed inode-relative block number as the file offset, as usual.
 *
 * get_block() is passed the number of i_blkbits-sized blocks which direct_io
 * has remaining to do.  The fs should not map more than this number of blocks.
 *
 * If the fs has mapped a lot of blocks, it should populate bh->b_size to
 * indicate how much contiguous disk space has been made available at
 * bh->b_blocknr.
 *
 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
 * This isn't very efficient...
 *
 * In the case of filesystem holes: the fs may return an arbitrarily-large
 * hole by returning an appropriate value in b_size and by clearing
 * buffer_mapped().  However the direct-io code will only process holes one
 * block at a time - it will repeatedly call get_block() as it walks the hole.
 */
static int get_more_blocks(struct dio *dio)
{
	int ret;
	struct buffer_head *map_bh = &dio->map_bh;
	sector_t fs_startblk;	/* Into file, in filesystem-sized blocks */
	unsigned long fs_count;	/* Number of filesystem-sized blocks */
	unsigned long dio_count;/* Number of dio_block-sized blocks */
	unsigned long blkmask;
	int create;

	/*
	 * If there was a memory error and we've overwritten all the
	 * mapped blocks then we can now return that memory error
	 */
	ret = dio->page_errors;
	if (ret == 0) {
		BUG_ON(dio->block_in_file >= dio->final_block_in_request);
		fs_startblk = dio->block_in_file >> dio->blkfactor;
		dio_count = dio->final_block_in_request - dio->block_in_file;
		fs_count = dio_count >> dio->blkfactor;
		blkmask = (1 << dio->blkfactor) - 1;
		if (dio_count & blkmask)	
			fs_count++;

		map_bh->b_state = 0;
		map_bh->b_size = fs_count << dio->inode->i_blkbits;

		/*
		 * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
		 * forbid block creations: only overwrites are permitted.
		 * We will return early to the caller once we see an
		 * unmapped buffer head returned, and the caller will fall
		 * back to buffered I/O.
		 *
		 * Otherwise the decision is left to the get_blocks method,
		 * which may decide to handle it or also return an unmapped
		 * buffer head.
		 */
		create = dio->rw & WRITE;
		if (dio->flags & DIO_SKIP_HOLES) {
			if (dio->block_in_file < (i_size_read(dio->inode) >>
							dio->blkbits))
				create = 0;
		}

		ret = (*dio->get_block)(dio->inode, fs_startblk,
						map_bh, create);
	}
	return ret;
}

/*
 * There is no bio.  Make one now.
 */
static int dio_new_bio(struct dio *dio, sector_t start_sector)
{
	sector_t sector;
	int ret, nr_pages;

	ret = dio_bio_reap(dio);
	if (ret)
		goto out;
	sector = start_sector << (dio->blkbits - 9);
	nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
	nr_pages = min(nr_pages, BIO_MAX_PAGES);
	BUG_ON(nr_pages <= 0);
	dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
	dio->boundary = 0;
out:
	return ret;
}

/*
 * Attempt to put the current chunk of 'cur_page' into the current BIO.  If
 * that was successful then update final_block_in_bio and take a ref against
 * the just-added page.
 *
 * Return zero on success.  Non-zero means the caller needs to start a new BIO.
 */
static int dio_bio_add_page(struct dio *dio)
{
	int ret;

	ret = bio_add_page(dio->bio, dio->cur_page,
			dio->cur_page_len, dio->cur_page_offset);
	if (ret == dio->cur_page_len) {
		/*
		 * Decrement count only, if we are done with this page
		 */
		if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
			dio->pages_in_io--;
		page_cache_get(dio->cur_page);
		dio->final_block_in_bio = dio->cur_page_block +
			(dio->cur_page_len >> dio->blkbits);
		ret = 0;
	} else {
		ret = 1;
	}
	return ret;
}
		
/*
 * Put cur_page under IO.  The section of cur_page which is described by
 * cur_page_offset,cur_page_len is put into a BIO.  The section of cur_page
 * starts on-disk at cur_page_block.
 *
 * We take a ref against the page here (on behalf of its presence in the bio).
 *
 * The caller of this function is responsible for removing cur_page from the
 * dio, and for dropping the refcount which came from that presence.
 */
static int dio_send_cur_page(struct dio *dio)
{
	int ret = 0;

	if (dio->bio) {
		loff_t cur_offset = dio->cur_page_fs_offset;
		loff_t bio_next_offset = dio->logical_offset_in_bio +
			dio->bio->bi_size;

		/*
		 * See whether this new request is contiguous with the old.
		 *
		 * Btrfs cannot handl having logically non-contiguous requests
		 * submitted.  For exmple if you have
		 *
		 * Logical:  [0-4095][HOLE][8192-12287]
		 * Phyiscal: [0-4095]      [4096-8181]
		 *
		 * We cannot submit those pages together as one BIO.  So if our
		 * current logical offset in the file does not equal what would
		 * be the next logical offset in the bio, submit the bio we
		 * have.
		 */
		if (dio->final_block_in_bio != dio->cur_page_block ||
		    cur_offset != bio_next_offset)
			dio_bio_submit(dio);
		/*
		 * Submit now if the underlying fs is about to perform a
		 * metadata read
		 */
		else if (dio->boundary)
			dio_bio_submit(dio);
	}

	if (dio->bio == NULL) {
		ret = dio_new_bio(dio, dio->cur_page_block);
		if (ret)
			goto out;
	}

	if (dio_bio_add_page(dio) != 0) {
		dio_bio_submit(dio);
		ret = dio_new_bio(dio, dio->cur_page_block);
		if (ret == 0) {
			ret = dio_bio_add_page(dio);
			BUG_ON(ret != 0);
		}
	}
out:
	return ret;
}

/*
 * An autonomous function to put a chunk of a page under deferred IO.
 *
 * The caller doesn't actually know (or care) whether this piece of page is in
 * a BIO, or is under IO or whatever.  We just take care of all possible 
 * situations here.  The separation between the logic of do_direct_IO() and
 * that of submit_page_section() is important for clarity.  Please don't break.
 *
 * The chunk of page starts on-disk at blocknr.
 *
 * We perform deferred IO, by recording the last-submitted page inside our
 * private part of the dio structure.  If possible, we just expand the IO
 * across that page here.
 *
 * If that doesn't work out then we put the old page into the bio and add this
 * page to the dio instead.
 */
static int
submit_page_section(struct dio *dio, struct page *page,
		unsigned offset, unsigned len, sector_t blocknr)
{
	int ret = 0;

	if (dio->rw & WRITE) {
		/*
		 * Read accounting is performed in submit_bio()
		 */
		task_io_account_write(len);
	}

	/*
	 * Can we just grow the current page's presence in the dio?
	 */
	if (	(dio->cur_page == page) &&
		(dio->cur_page_offset + dio->cur_page_len == offset) &&
		(dio->cur_page_block +
			(dio->cur_page_len >> dio->blkbits) == blocknr)) {
		dio->cur_page_len += len;

		/*
		 * If dio->boundary then we want to schedule the IO now to
		 * avoid metadata seeks.
		 */
		if (dio->boundary) {
			ret = dio_send_cur_page(dio);
			page_cache_release(dio->cur_page);
			dio->cur_page = NULL;
		}
		goto out;
	}

	/*
	 * If there's a deferred page already there then send it.
	 */
	if (dio->cur_page) {
		ret = dio_send_cur_page(dio);
		page_cache_release(dio->cur_page);
		dio->cur_page = NULL;
		if (ret)
			goto out;
	}

	page_cache_get(page);		/* It is in dio */
	dio->cur_page = page;
	dio->cur_page_offset = offset;
	dio->cur_page_len = len;
	dio->cur_page_block = blocknr;
	dio->cur_page_fs_offset = dio->block_in_file << dio->blkbits;
out:
	return ret;
}

/*
 * Clean any dirty buffers in the blockdev mapping which alias newly-created
 * file blocks.  Only called for S_ISREG files - blockdevs do not set
 * buffer_new
 */
static void clean_blockdev_aliases(struct dio *dio)
{
	unsigned i;
	unsigned nblocks;

	nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits;

	for (i = 0; i < nblocks; i++) {
		unmap_underlying_metadata(dio->map_bh.b_bdev,
					dio->map_bh.b_blocknr + i);
	}
}

/*
 * If we are not writing the entire block and get_block() allocated
 * the block for us, we need to fill-in the unused portion of the
 * block with zeros. This happens only if user-buffer, fileoffset or
 * io length is not filesystem block-size multiple.
 *
 * `end' is zero if we're doing the start of the IO, 1 at the end of the
 * IO.
 */
static void dio_zero_block(struct dio *dio, int end)
{
	unsigned dio_blocks_per_fs_block;
	unsigned this_chunk_blocks;	/* In dio_blocks */
	unsigned this_chunk_bytes;
	struct page *page;

	dio->start_zero_done = 1;
	if (!dio->blkfactor || !buffer_new(&dio->map_bh))
		return;

	dio_blocks_per_fs_block = 1 << dio->blkfactor;
	this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1);

	if (!this_chunk_blocks)
		return;

	/*
	 * We need to zero out part of an fs block.  It is either at the
	 * beginning or the end of the fs block.
	 */
	if (end) 
		this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;

	this_chunk_bytes = this_chunk_blocks << dio->blkbits;

	page = ZERO_PAGE(0);
	if (submit_page_section(dio, page, 0, this_chunk_bytes, 
				dio->next_block_for_io))
		return;

	dio->next_block_for_io += this_chunk_blocks;
}

/*
 * Walk the user pages, and the file, mapping blocks to disk and generating
 * a sequence of (page,offset,len,block) mappings.  These mappings are injected
 * into submit_page_section(), which takes care of the next stage of submission
 *
 * Direct IO against a blockdev is different from a file.  Because we can
 * happily perform page-sized but 512-byte aligned IOs.  It is important that
 * blockdev IO be able to have fine alignment and large sizes.
 *
 * So what we do is to permit the ->get_block function to populate bh.b_size
 * with the size of IO which is permitted at this offset and this i_blkbits.
 *
 * For best results, the blockdev should be set up with 512-byte i_blkbits and
 * it should set b_size to PAGE_SIZE or more inside get_block().  This gives
 * fine alignment but still allows this function to work in PAGE_SIZE units.
 */
static int do_direct_IO(struct dio *dio)
{
	const unsigned blkbits = dio->blkbits;
	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
	struct page *page;
	unsigned block_in_page;
	struct buffer_head *map_bh = &dio->map_bh;
	int ret = 0;

	/* The I/O can start at any block offset within the first page */
	block_in_page = dio->first_block_in_page;

	while (dio->block_in_file < dio->final_block_in_request) {
		page = dio_get_page(dio);
		if (IS_ERR(page)) {
			ret = PTR_ERR(page);
			goto out;
		}

		while (block_in_page < blocks_per_page) {
			unsigned offset_in_page = block_in_page << blkbits;
			unsigned this_chunk_bytes;	/* # of bytes mapped */
			unsigned this_chunk_blocks;	/* # of blocks */
			unsigned u;

			if (dio->blocks_available == 0) {
				/*
				 * Need to go and map some more disk
				 */
				unsigned long blkmask;
				unsigned long dio_remainder;

				ret = get_more_blocks(dio);
				if (ret) {
					page_cache_release(page);
					goto out;
				}
				if (!buffer_mapped(map_bh))
					goto do_holes;

				dio->blocks_available =
						map_bh->b_size >> dio->blkbits;
				dio->next_block_for_io =
					map_bh->b_blocknr << dio->blkfactor;
				if (buffer_new(map_bh))
					clean_blockdev_aliases(dio);

				if (!dio->blkfactor)
					goto do_holes;

				blkmask = (1 << dio->blkfactor) - 1;
				dio_remainder = (dio->block_in_file & blkmask);

				/*
				 * If we are at the start of IO and that IO
				 * starts partway into a fs-block,
				 * dio_remainder will be non-zero.  If the IO
				 * is a read then we can simply advance the IO
				 * cursor to the first block which is to be
				 * read.  But if the IO is a write and the
				 * block was newly allocated we cannot do that;
				 * the start of the fs block must be zeroed out
				 * on-disk
				 */
				if (!buffer_new(map_bh))
					dio->next_block_for_io += dio_remainder;
				dio->blocks_available -= dio_remainder;
			}
do_holes:
			/* Handle holes */
			if (!buffer_mapped(map_bh)) {
				loff_t i_size_aligned;

				/* AKPM: eargh, -ENOTBLK is a hack */
				if (dio->rw & WRITE) {
					page_cache_release(page);
					return -ENOTBLK;
				}

				/*
				 * Be sure to account for a partial block as the
				 * last block in the file
				 */
				i_size_aligned = ALIGN(i_size_read(dio->inode),
							1 << blkbits);
				if (dio->block_in_file >=
						i_size_aligned >> blkbits) {
					/* We hit eof */
					page_cache_release(page);
					goto out;
				}
				zero_user(page, block_in_page << blkbits,
						1 << blkbits);
				dio->block_in_file++;
				block_in_page++;
				goto next_block;
			}

			/*
			 * If we're performing IO which has an alignment which
			 * is finer than the underlying fs, go check to see if
			 * we must zero out the start of this block.
			 */
			if (unlikely(dio->blkfactor && !dio->start_zero_done))
				dio_zero_block(dio, 0);

			/*
			 * Work out, in this_chunk_blocks, how much disk we
			 * can add to this page
			 */
			this_chunk_blocks = dio->blocks_available;
			u = (PAGE_SIZE - offset_in_page) >> blkbits;
			if (this_chunk_blocks > u)
				this_chunk_blocks = u;
			u = dio->final_block_in_request - dio->block_in_file;
			if (this_chunk_blocks > u)
				this_chunk_blocks = u;
			this_chunk_bytes = this_chunk_blocks << blkbits;
			BUG_ON(this_chunk_bytes == 0);

			dio->boundary = buffer_boundary(map_bh);
			ret = submit_page_section(dio, page, offset_in_page,
				this_chunk_bytes, dio->next_block_for_io);
			if (ret) {
				page_cache_release(page);
				goto out;
			}
			dio->next_block_for_io += this_chunk_blocks;

			dio->block_in_file += this_chunk_blocks;
			block_in_page += this_chunk_blocks;
			dio->blocks_available -= this_chunk_blocks;
next_block:
			BUG_ON(dio->block_in_file > dio->final_block_in_request);
			if (dio->block_in_file == dio->final_block_in_request)
				break;
		}

		/* Drop the ref which was taken in get_user_pages() */
		page_cache_release(page);
		block_in_page = 0;
	}
out:
	return ret;
}

/*
 * Releases both i_mutex and i_alloc_sem
 */
static ssize_t
direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode, 
	const struct iovec *iov, loff_t offset, unsigned long nr_segs, 
	unsigned blkbits, get_block_t get_block, dio_iodone_t end_io,
	dio_submit_t submit_io, struct dio *dio)
{
	unsigned long user_addr; 
	unsigned long flags;
	int seg;
	ssize_t ret = 0;
	ssize_t ret2;
	size_t bytes;

	dio->inode = inode;
	dio->rw = rw;
	dio->blkbits = blkbits;
	dio->blkfactor = inode->i_blkbits - blkbits;
	dio->block_in_file = offset >> blkbits;

	dio->get_block = get_block;
	dio->end_io = end_io;
	dio->submit_io = submit_io;
	dio->final_block_in_bio = -1;
	dio->next_block_for_io = -1;

	dio->iocb = iocb;
	dio->i_size = i_size_read(inode);

	spin_lock_init(&dio->bio_lock);
	dio->refcount = 1;

	/*
	 * In case of non-aligned buffers, we may need 2 more
	 * pages since we need to zero out first and last block.
	 */
	if (unlikely(dio->blkfactor))
		dio->pages_in_io = 2;

	for (seg = 0; seg < nr_segs; seg++) {
		user_addr = (unsigned long)iov[seg].iov_base;
		dio->pages_in_io +=
			((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
				- user_addr/PAGE_SIZE);
	}

	for (seg = 0; seg < nr_segs; seg++) {
		user_addr = (unsigned long)iov[seg].iov_base;
		dio->size += bytes = iov[seg].iov_len;

		/* Index into the first page of the first block */
		dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
		dio->final_block_in_request = dio->block_in_file +
						(bytes >> blkbits);
		/* Page fetching state */
		dio->head = 0;
		dio->tail = 0;
		dio->curr_page = 0;

		dio->total_pages = 0;
		if (user_addr & (PAGE_SIZE-1)) {
			dio->total_pages++;
			bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
		}
		dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
		dio->curr_user_address = user_addr;
	
		ret = do_direct_IO(dio);

		dio->result += iov[seg].iov_len -
			((dio->final_block_in_request - dio->block_in_file) <<
					blkbits);

		if (ret) {
			dio_cleanup(dio);
			break;
		}
	} /* end iovec loop */

	if (ret == -ENOTBLK) {
		/*
		 * The remaining part of the request will be
		 * be handled by buffered I/O when we return
		 */
		ret = 0;
	}
	/*
	 * There may be some unwritten disk at the end of a part-written
	 * fs-block-sized block.  Go zero that now.
	 */
	dio_zero_block(dio, 1);

	if (dio->cur_page) {
		ret2 = dio_send_cur_page(dio);
		if (ret == 0)
			ret = ret2;
		page_cache_release(dio->cur_page);
		dio->cur_page = NULL;
	}
	if (dio->bio)
		dio_bio_submit(dio);

	/*
	 * It is possible that, we return short IO due to end of file.
	 * In that case, we need to release all the pages we got hold on.
	 */
	dio_cleanup(dio);

	/*
	 * All block lookups have been performed. For READ requests
	 * we can let i_mutex go now that its achieved its purpose
	 * of protecting us from looking up uninitialized blocks.
	 */
	if (rw == READ && (dio->flags & DIO_LOCKING))
		mutex_unlock(&dio->inode->i_mutex);

	/*
	 * The only time we want to leave bios in flight is when a successful
	 * partial aio read or full aio write have been setup.  In that case
	 * bio completion will call aio_complete.  The only time it's safe to
	 * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
	 * This had *better* be the only place that raises -EIOCBQUEUED.
	 */
	BUG_ON(ret == -EIOCBQUEUED);
	if (dio->is_async && ret == 0 && dio->result &&
	    ((rw & READ) || (dio->result == dio->size)))
		ret = -EIOCBQUEUED;

	if (ret != -EIOCBQUEUED) {
		/* All IO is now issued, send it on its way */
		blk_run_address_space(inode->i_mapping);
		dio_await_completion(dio);
	}

	/*
	 * Sync will always be dropping the final ref and completing the
	 * operation.  AIO can if it was a broken operation described above or
	 * in fact if all the bios race to complete before we get here.  In
	 * that case dio_complete() translates the EIOCBQUEUED into the proper
	 * return code that the caller will hand to aio_complete().
	 *
	 * This is managed by the bio_lock instead of being an atomic_t so that
	 * completion paths can drop their ref and use the remaining count to
	 * decide to wake the submission path atomically.
	 */
	spin_lock_irqsave(&dio->bio_lock, flags);
	ret2 = --dio->refcount;
	spin_unlock_irqrestore(&dio->bio_lock, flags);

	if (ret2 == 0) {
		ret = dio_complete(dio, offset, ret, false);
		kfree(dio);
	} else
		BUG_ON(ret != -EIOCBQUEUED);

	return ret;
}

/*
 * This is a library function for use by filesystem drivers.
 *
 * The locking rules are governed by the flags parameter:
 *  - if the flags value contains DIO_LOCKING we use a fancy locking
 *    scheme for dumb filesystems.
 *    For writes this function is called under i_mutex and returns with
 *    i_mutex held, for reads, i_mutex is not held on entry, but it is
 *    taken and dropped again before returning.
 *    For reads and writes i_alloc_sem is taken in shared mode and released
 *    on I/O completion (which may happen asynchronously after returning to
 *    the caller).
 *
 *  - if the flags value does NOT contain DIO_LOCKING we don't use any
 *    internal locking but rather rely on the filesystem to synchronize
 *    direct I/O reads/writes versus each other and truncate.
 *    For reads and writes both i_mutex and i_alloc_sem are not held on
 *    entry and are never taken.
 */
ssize_t
__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
	struct block_device *bdev, const struct iovec *iov, loff_t offset, 
	unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
	dio_submit_t submit_io,	int flags)
{
	int seg;
	size_t size;
	unsigned long addr;
	unsigned blkbits = inode->i_blkbits;
	unsigned bdev_blkbits = 0;
	unsigned blocksize_mask = (1 << blkbits) - 1;
	ssize_t retval = -EINVAL;
	loff_t end = offset;
	struct dio *dio;

	if (rw & WRITE)
		rw = WRITE_ODIRECT_PLUG;

	if (bdev)
		bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev));

	if (offset & blocksize_mask) {
		if (bdev)
			 blkbits = bdev_blkbits;
		blocksize_mask = (1 << blkbits) - 1;
		if (offset & blocksize_mask)
			goto out;
	}

	/* Check the memory alignment.  Blocks cannot straddle pages */
	for (seg = 0; seg < nr_segs; seg++) {
		addr = (unsigned long)iov[seg].iov_base;
		size = iov[seg].iov_len;
		end += size;
		if ((addr & blocksize_mask) || (size & blocksize_mask))  {
			if (bdev)
				 blkbits = bdev_blkbits;
			blocksize_mask = (1 << blkbits) - 1;
			if ((addr & blocksize_mask) || (size & blocksize_mask))  
				goto out;
		}
	}

	dio = kmalloc(sizeof(*dio), GFP_KERNEL);
	retval = -ENOMEM;
	if (!dio)
		goto out;
	/*
	 * Believe it or not, zeroing out the page array caused a .5%
	 * performance regression in a database benchmark.  So, we take
	 * care to only zero out what's needed.
	 */
	memset(dio, 0, offsetof(struct dio, pages));

	dio->flags = flags;
	if (dio->flags & DIO_LOCKING) {
		/* watch out for a 0 len io from a tricksy fs */
		if (rw == READ && end > offset) {
			struct address_space *mapping =
					iocb->ki_filp->f_mapping;

			/* will be released by direct_io_worker */
			mutex_lock(&inode->i_mutex);

			retval = filemap_write_and_wait_range(mapping, offset,
							      end - 1);
			if (retval) {
				mutex_unlock(&inode->i_mutex);
				kfree(dio);
				goto out;
			}
		}

		/*
		 * Will be released at I/O completion, possibly in a
		 * different thread.
		 */
		down_read_non_owner(&inode->i_alloc_sem);
	}

	/*
	 * For file extending writes updating i_size before data
	 * writeouts complete can expose uninitialized blocks. So
	 * even for AIO, we need to wait for i/o to complete before
	 * returning in this case.
	 */
	dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
		(end > i_size_read(inode)));

	retval = direct_io_worker(rw, iocb, inode, iov, offset,
				nr_segs, blkbits, get_block, end_io,
				submit_io, dio);

out:
	return retval;
}
EXPORT_SYMBOL(__blockdev_direct_IO);