1/*
   2 * Copyright (C) 2008 Oracle.  All rights reserved.
   3 *
   4 * This program is free software; you can redistribute it and/or
   5 * modify it under the terms of the GNU General Public
   6 * License v2 as published by the Free Software Foundation.
   7 *
   8 * This program is distributed in the hope that it will be useful,
   9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11 * General Public License for more details.
  12 *
  13 * You should have received a copy of the GNU General Public
  14 * License along with this program; if not, write to the
  15 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16 * Boston, MA 021110-1307, USA.
  17 */
  18
  19#include <linux/kernel.h>
  20#include <linux/bio.h>
  21#include <linux/buffer_head.h>
  22#include <linux/file.h>
  23#include <linux/fs.h>
  24#include <linux/pagemap.h>
  25#include <linux/highmem.h>
  26#include <linux/time.h>
  27#include <linux/init.h>
  28#include <linux/string.h>
  29#include <linux/backing-dev.h>
  30#include <linux/mpage.h>
  31#include <linux/swap.h>
  32#include <linux/writeback.h>
  33#include <linux/bit_spinlock.h>
  34#include <linux/slab.h>
  35#include "compat.h"
  36#include "ctree.h"
  37#include "disk-io.h"
  38#include "transaction.h"
  39#include "btrfs_inode.h"
  40#include "volumes.h"
  41#include "ordered-data.h"
  42#include "compression.h"
  43#include "extent_io.h"
  44#include "extent_map.h"
  45
  46struct compressed_bio {
  47	/* number of bios pending for this compressed extent */
  48	atomic_t pending_bios;
  49
  50	/* the pages with the compressed data on them */
  51	struct page **compressed_pages;
  52
  53	/* inode that owns this data */
  54	struct inode *inode;
  55
  56	/* starting offset in the inode for our pages */
  57	u64 start;
  58
  59	/* number of bytes in the inode we're working on */
  60	unsigned long len;
  61
  62	/* number of bytes on disk */
  63	unsigned long compressed_len;
  64
  65	/* the compression algorithm for this bio */
  66	int compress_type;
  67
  68	/* number of compressed pages in the array */
  69	unsigned long nr_pages;
  70
  71	/* IO errors */
  72	int errors;
  73	int mirror_num;
  74
  75	/* for reads, this is the bio we are copying the data into */
  76	struct bio *orig_bio;
  77
  78	/*
  79	 * the start of a variable length array of checksums only
  80	 * used by reads
  81	 */
  82	u32 sums;
  83};
  84
  85static inline int compressed_bio_size(struct btrfs_root *root,
  86				      unsigned long disk_size)
  87{
  88	u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);
  89
  90	return sizeof(struct compressed_bio) +
  91		((disk_size + root->sectorsize - 1) / root->sectorsize) *
  92		csum_size;
  93}
  94
  95static struct bio *compressed_bio_alloc(struct block_device *bdev,
  96					u64 first_byte, gfp_t gfp_flags)
  97{
  98	int nr_vecs;
  99
 100	nr_vecs = bio_get_nr_vecs(bdev);
 101	return btrfs_bio_alloc(bdev, first_byte >> 9, nr_vecs, gfp_flags);
 102}
 103
 104static int check_compressed_csum(struct inode *inode,
 105				 struct compressed_bio *cb,
 106				 u64 disk_start)
 107{
 108	int ret;
 109	struct btrfs_root *root = BTRFS_I(inode)->root;
 110	struct page *page;
 111	unsigned long i;
 112	char *kaddr;
 113	u32 csum;
 114	u32 *cb_sum = &cb->sums;
 115
 116	if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
 117		return 0;
 118
 119	for (i = 0; i < cb->nr_pages; i++) {
 120		page = cb->compressed_pages[i];
 121		csum = ~(u32)0;
 122
 123		kaddr = kmap_atomic(page);
 124		csum = btrfs_csum_data(root, kaddr, csum, PAGE_CACHE_SIZE);
 125		btrfs_csum_final(csum, (char *)&csum);
 126		kunmap_atomic(kaddr);
 127
 128		if (csum != *cb_sum) {
 129			printk(KERN_INFO "btrfs csum failed ino %llu "
 130			       "extent %llu csum %u "
 131			       "wanted %u mirror %d\n",
 132			       (unsigned long long)btrfs_ino(inode),
 133			       (unsigned long long)disk_start,
 134			       csum, *cb_sum, cb->mirror_num);
 135			ret = -EIO;
 136			goto fail;
 137		}
 138		cb_sum++;
 139
 140	}
 141	ret = 0;
 142fail:
 143	return ret;
 144}
 145
 146/* when we finish reading compressed pages from the disk, we
 147 * decompress them and then run the bio end_io routines on the
 148 * decompressed pages (in the inode address space).
 149 *
 150 * This allows the checksumming and other IO error handling routines
 151 * to work normally
 152 *
 153 * The compressed pages are freed here, and it must be run
 154 * in process context
 155 */
 156static void end_compressed_bio_read(struct bio *bio, int err)
 157{
 158	struct compressed_bio *cb = bio->bi_private;
 159	struct inode *inode;
 160	struct page *page;
 161	unsigned long index;
 162	int ret;
 163
 164	if (err)
 165		cb->errors = 1;
 166
 167	/* if there are more bios still pending for this compressed
 168	 * extent, just exit
 169	 */
 170	if (!atomic_dec_and_test(&cb->pending_bios))
 171		goto out;
 172
 173	inode = cb->inode;
 174	ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
 175	if (ret)
 176		goto csum_failed;
 177
 178	/* ok, we're the last bio for this extent, lets start
 179	 * the decompression.
 180	 */
 181	ret = btrfs_decompress_biovec(cb->compress_type,
 182				      cb->compressed_pages,
 183				      cb->start,
 184				      cb->orig_bio->bi_io_vec,
 185				      cb->orig_bio->bi_vcnt,
 186				      cb->compressed_len);
 187csum_failed:
 188	if (ret)
 189		cb->errors = 1;
 190
 191	/* release the compressed pages */
 192	index = 0;
 193	for (index = 0; index < cb->nr_pages; index++) {
 194		page = cb->compressed_pages[index];
 195		page->mapping = NULL;
 196		page_cache_release(page);
 197	}
 198
 199	/* do io completion on the original bio */
 200	if (cb->errors) {
 201		bio_io_error(cb->orig_bio);
 202	} else {
 203		int bio_index = 0;
 204		struct bio_vec *bvec = cb->orig_bio->bi_io_vec;
 205
 206		/*
 207		 * we have verified the checksum already, set page
 208		 * checked so the end_io handlers know about it
 209		 */
 210		while (bio_index < cb->orig_bio->bi_vcnt) {
 211			SetPageChecked(bvec->bv_page);
 212			bvec++;
 213			bio_index++;
 214		}
 215		bio_endio(cb->orig_bio, 0);
 216	}
 217
 218	/* finally free the cb struct */
 219	kfree(cb->compressed_pages);
 220	kfree(cb);
 221out:
 222	bio_put(bio);
 223}
 224
 225/*
 226 * Clear the writeback bits on all of the file
 227 * pages for a compressed write
 228 */
 229static noinline void end_compressed_writeback(struct inode *inode, u64 start,
 230					      unsigned long ram_size)
 231{
 232	unsigned long index = start >> PAGE_CACHE_SHIFT;
 233	unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
 234	struct page *pages[16];
 235	unsigned long nr_pages = end_index - index + 1;
 236	int i;
 237	int ret;
 238
 239	while (nr_pages > 0) {
 240		ret = find_get_pages_contig(inode->i_mapping, index,
 241				     min_t(unsigned long,
 242				     nr_pages, ARRAY_SIZE(pages)), pages);
 243		if (ret == 0) {
 244			nr_pages -= 1;
 245			index += 1;
 246			continue;
 247		}
 248		for (i = 0; i < ret; i++) {
 249			end_page_writeback(pages[i]);
 250			page_cache_release(pages[i]);
 251		}
 252		nr_pages -= ret;
 253		index += ret;
 254	}
 255	/* the inode may be gone now */
 256}
 257
 258/*
 259 * do the cleanup once all the compressed pages hit the disk.
 260 * This will clear writeback on the file pages and free the compressed
 261 * pages.
 262 *
 263 * This also calls the writeback end hooks for the file pages so that
 264 * metadata and checksums can be updated in the file.
 265 */
 266static void end_compressed_bio_write(struct bio *bio, int err)
 267{
 268	struct extent_io_tree *tree;
 269	struct compressed_bio *cb = bio->bi_private;
 270	struct inode *inode;
 271	struct page *page;
 272	unsigned long index;
 273
 274	if (err)
 275		cb->errors = 1;
 276
 277	/* if there are more bios still pending for this compressed
 278	 * extent, just exit
 279	 */
 280	if (!atomic_dec_and_test(&cb->pending_bios))
 281		goto out;
 282
 283	/* ok, we're the last bio for this extent, step one is to
 284	 * call back into the FS and do all the end_io operations
 285	 */
 286	inode = cb->inode;
 287	tree = &BTRFS_I(inode)->io_tree;
 288	cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
 289	tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
 290					 cb->start,
 291					 cb->start + cb->len - 1,
 292					 NULL, 1);
 293	cb->compressed_pages[0]->mapping = NULL;
 294
 295	end_compressed_writeback(inode, cb->start, cb->len);
 296	/* note, our inode could be gone now */
 297
 298	/*
 299	 * release the compressed pages, these came from alloc_page and
 300	 * are not attached to the inode at all
 301	 */
 302	index = 0;
 303	for (index = 0; index < cb->nr_pages; index++) {
 304		page = cb->compressed_pages[index];
 305		page->mapping = NULL;
 306		page_cache_release(page);
 307	}
 308
 309	/* finally free the cb struct */
 310	kfree(cb->compressed_pages);
 311	kfree(cb);
 312out:
 313	bio_put(bio);
 314}
 315
 316/*
 317 * worker function to build and submit bios for previously compressed pages.
 318 * The corresponding pages in the inode should be marked for writeback
 319 * and the compressed pages should have a reference on them for dropping
 320 * when the IO is complete.
 321 *
 322 * This also checksums the file bytes and gets things ready for
 323 * the end io hooks.
 324 */
 325int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 326				 unsigned long len, u64 disk_start,
 327				 unsigned long compressed_len,
 328				 struct page **compressed_pages,
 329				 unsigned long nr_pages)
 330{
 331	struct bio *bio = NULL;
 332	struct btrfs_root *root = BTRFS_I(inode)->root;
 333	struct compressed_bio *cb;
 334	unsigned long bytes_left;
 335	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 336	int pg_index = 0;
 337	struct page *page;
 338	u64 first_byte = disk_start;
 339	struct block_device *bdev;
 340	int ret;
 341	int skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
 342
 343	WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
 344	cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 345	if (!cb)
 346		return -ENOMEM;
 347	atomic_set(&cb->pending_bios, 0);
 348	cb->errors = 0;
 349	cb->inode = inode;
 350	cb->start = start;
 351	cb->len = len;
 352	cb->mirror_num = 0;
 353	cb->compressed_pages = compressed_pages;
 354	cb->compressed_len = compressed_len;
 355	cb->orig_bio = NULL;
 356	cb->nr_pages = nr_pages;
 357
 358	bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 359
 360	bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 361	if(!bio) {
 362		kfree(cb);
 363		return -ENOMEM;
 364	}
 365	bio->bi_private = cb;
 366	bio->bi_end_io = end_compressed_bio_write;
 367	atomic_inc(&cb->pending_bios);
 368
 369	/* create and submit bios for the compressed pages */
 370	bytes_left = compressed_len;
 371	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
 372		page = compressed_pages[pg_index];
 373		page->mapping = inode->i_mapping;
 374		if (bio->bi_size)
 375			ret = io_tree->ops->merge_bio_hook(page, 0,
 376							   PAGE_CACHE_SIZE,
 377							   bio, 0);
 378		else
 379			ret = 0;
 380
 381		page->mapping = NULL;
 382		if (ret || bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) <
 383		    PAGE_CACHE_SIZE) {
 384			bio_get(bio);
 385
 386			/*
 387			 * inc the count before we submit the bio so
 388			 * we know the end IO handler won't happen before
 389			 * we inc the count.  Otherwise, the cb might get
 390			 * freed before we're done setting it up
 391			 */
 392			atomic_inc(&cb->pending_bios);
 393			ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 394			BUG_ON(ret); /* -ENOMEM */
 395
 396			if (!skip_sum) {
 397				ret = btrfs_csum_one_bio(root, inode, bio,
 398							 start, 1);
 399				BUG_ON(ret); /* -ENOMEM */
 400			}
 401
 402			ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 403			BUG_ON(ret); /* -ENOMEM */
 404
 405			bio_put(bio);
 406
 407			bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 408			BUG_ON(!bio);
 409			bio->bi_private = cb;
 410			bio->bi_end_io = end_compressed_bio_write;
 411			bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
 412		}
 413		if (bytes_left < PAGE_CACHE_SIZE) {
 414			printk("bytes left %lu compress len %lu nr %lu\n",
 415			       bytes_left, cb->compressed_len, cb->nr_pages);
 416		}
 417		bytes_left -= PAGE_CACHE_SIZE;
 418		first_byte += PAGE_CACHE_SIZE;
 419		cond_resched();
 420	}
 421	bio_get(bio);
 422
 423	ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 424	BUG_ON(ret); /* -ENOMEM */
 425
 426	if (!skip_sum) {
 427		ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
 428		BUG_ON(ret); /* -ENOMEM */
 429	}
 430
 431	ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 432	BUG_ON(ret); /* -ENOMEM */
 433
 434	bio_put(bio);
 435	return 0;
 436}
 437
 438static noinline int add_ra_bio_pages(struct inode *inode,
 439				     u64 compressed_end,
 440				     struct compressed_bio *cb)
 441{
 442	unsigned long end_index;
 443	unsigned long pg_index;
 444	u64 last_offset;
 445	u64 isize = i_size_read(inode);
 446	int ret;
 447	struct page *page;
 448	unsigned long nr_pages = 0;
 449	struct extent_map *em;
 450	struct address_space *mapping = inode->i_mapping;
 451	struct extent_map_tree *em_tree;
 452	struct extent_io_tree *tree;
 453	u64 end;
 454	int misses = 0;
 455
 456	page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
 457	last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
 458	em_tree = &BTRFS_I(inode)->extent_tree;
 459	tree = &BTRFS_I(inode)->io_tree;
 460
 461	if (isize == 0)
 462		return 0;
 463
 464	end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
 465
 466	while (last_offset < compressed_end) {
 467		pg_index = last_offset >> PAGE_CACHE_SHIFT;
 468
 469		if (pg_index > end_index)
 470			break;
 471
 472		rcu_read_lock();
 473		page = radix_tree_lookup(&mapping->page_tree, pg_index);
 474		rcu_read_unlock();
 475		if (page) {
 476			misses++;
 477			if (misses > 4)
 478				break;
 479			goto next;
 480		}
 481
 482		page = __page_cache_alloc(mapping_gfp_mask(mapping) &
 483								~__GFP_FS);
 484		if (!page)
 485			break;
 486
 487		if (add_to_page_cache_lru(page, mapping, pg_index,
 488								GFP_NOFS)) {
 489			page_cache_release(page);
 490			goto next;
 491		}
 492
 493		end = last_offset + PAGE_CACHE_SIZE - 1;
 494		/*
 495		 * at this point, we have a locked page in the page cache
 496		 * for these bytes in the file.  But, we have to make
 497		 * sure they map to this compressed extent on disk.
 498		 */
 499		set_page_extent_mapped(page);
 500		lock_extent(tree, last_offset, end);
 501		read_lock(&em_tree->lock);
 502		em = lookup_extent_mapping(em_tree, last_offset,
 503					   PAGE_CACHE_SIZE);
 504		read_unlock(&em_tree->lock);
 505
 506		if (!em || last_offset < em->start ||
 507		    (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||
 508		    (em->block_start >> 9) != cb->orig_bio->bi_sector) {
 509			free_extent_map(em);
 510			unlock_extent(tree, last_offset, end);
 511			unlock_page(page);
 512			page_cache_release(page);
 513			break;
 514		}
 515		free_extent_map(em);
 516
 517		if (page->index == end_index) {
 518			char *userpage;
 519			size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);
 520
 521			if (zero_offset) {
 522				int zeros;
 523				zeros = PAGE_CACHE_SIZE - zero_offset;
 524				userpage = kmap_atomic(page);
 525				memset(userpage + zero_offset, 0, zeros);
 526				flush_dcache_page(page);
 527				kunmap_atomic(userpage);
 528			}
 529		}
 530
 531		ret = bio_add_page(cb->orig_bio, page,
 532				   PAGE_CACHE_SIZE, 0);
 533
 534		if (ret == PAGE_CACHE_SIZE) {
 535			nr_pages++;
 536			page_cache_release(page);
 537		} else {
 538			unlock_extent(tree, last_offset, end);
 539			unlock_page(page);
 540			page_cache_release(page);
 541			break;
 542		}
 543next:
 544		last_offset += PAGE_CACHE_SIZE;
 545	}
 546	return 0;
 547}
 548
 549/*
 550 * for a compressed read, the bio we get passed has all the inode pages
 551 * in it.  We don't actually do IO on those pages but allocate new ones
 552 * to hold the compressed pages on disk.
 553 *
 554 * bio->bi_sector points to the compressed extent on disk
 555 * bio->bi_io_vec points to all of the inode pages
 556 * bio->bi_vcnt is a count of pages
 557 *
 558 * After the compressed pages are read, we copy the bytes into the
 559 * bio we were passed and then call the bio end_io calls
 560 */
 561int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 562				 int mirror_num, unsigned long bio_flags)
 563{
 564	struct extent_io_tree *tree;
 565	struct extent_map_tree *em_tree;
 566	struct compressed_bio *cb;
 567	struct btrfs_root *root = BTRFS_I(inode)->root;
 568	unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 569	unsigned long compressed_len;
 570	unsigned long nr_pages;
 571	unsigned long pg_index;
 572	struct page *page;
 573	struct block_device *bdev;
 574	struct bio *comp_bio;
 575	u64 cur_disk_byte = (u64)bio->bi_sector << 9;
 576	u64 em_len;
 577	u64 em_start;
 578	struct extent_map *em;
 579	int ret = -ENOMEM;
 580	u32 *sums;
 581
 582	tree = &BTRFS_I(inode)->io_tree;
 583	em_tree = &BTRFS_I(inode)->extent_tree;
 584
 585	/* we need the actual starting offset of this extent in the file */
 586	read_lock(&em_tree->lock);
 587	em = lookup_extent_mapping(em_tree,
 588				   page_offset(bio->bi_io_vec->bv_page),
 589				   PAGE_CACHE_SIZE);
 590	read_unlock(&em_tree->lock);
 591	if (!em)
 592		return -EIO;
 593
 594	compressed_len = em->block_len;
 595	cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 596	if (!cb)
 597		goto out;
 598
 599	atomic_set(&cb->pending_bios, 0);
 600	cb->errors = 0;
 601	cb->inode = inode;
 602	cb->mirror_num = mirror_num;
 603	sums = &cb->sums;
 604
 605	cb->start = em->orig_start;
 606	em_len = em->len;
 607	em_start = em->start;
 608
 609	free_extent_map(em);
 610	em = NULL;
 611
 612	cb->len = uncompressed_len;
 613	cb->compressed_len = compressed_len;
 614	cb->compress_type = extent_compress_type(bio_flags);
 615	cb->orig_bio = bio;
 616
 617	nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
 618				 PAGE_CACHE_SIZE;
 619	cb->compressed_pages = kzalloc(sizeof(struct page *) * nr_pages,
 620				       GFP_NOFS);
 621	if (!cb->compressed_pages)
 622		goto fail1;
 623
 624	bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 625
 626	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
 627		cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
 628							      __GFP_HIGHMEM);
 629		if (!cb->compressed_pages[pg_index])
 630			goto fail2;
 631	}
 632	cb->nr_pages = nr_pages;
 633
 634	add_ra_bio_pages(inode, em_start + em_len, cb);
 635
 636	/* include any pages we added in add_ra-bio_pages */
 637	uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 638	cb->len = uncompressed_len;
 639
 640	comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
 641	if (!comp_bio)
 642		goto fail2;
 643	comp_bio->bi_private = cb;
 644	comp_bio->bi_end_io = end_compressed_bio_read;
 645	atomic_inc(&cb->pending_bios);
 646
 647	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
 648		page = cb->compressed_pages[pg_index];
 649		page->mapping = inode->i_mapping;
 650		page->index = em_start >> PAGE_CACHE_SHIFT;
 651
 652		if (comp_bio->bi_size)
 653			ret = tree->ops->merge_bio_hook(page, 0,
 654							PAGE_CACHE_SIZE,
 655							comp_bio, 0);
 656		else
 657			ret = 0;
 658
 659		page->mapping = NULL;
 660		if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
 661		    PAGE_CACHE_SIZE) {
 662			bio_get(comp_bio);
 663
 664			ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 665			BUG_ON(ret); /* -ENOMEM */
 666
 667			/*
 668			 * inc the count before we submit the bio so
 669			 * we know the end IO handler won't happen before
 670			 * we inc the count.  Otherwise, the cb might get
 671			 * freed before we're done setting it up
 672			 */
 673			atomic_inc(&cb->pending_bios);
 674
 675			if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
 676				ret = btrfs_lookup_bio_sums(root, inode,
 677							comp_bio, sums);
 678				BUG_ON(ret); /* -ENOMEM */
 679			}
 680			sums += (comp_bio->bi_size + root->sectorsize - 1) /
 681				root->sectorsize;
 682
 683			ret = btrfs_map_bio(root, READ, comp_bio,
 684					    mirror_num, 0);
 685			BUG_ON(ret); /* -ENOMEM */
 686
 687			bio_put(comp_bio);
 688
 689			comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
 690							GFP_NOFS);
 691			BUG_ON(!comp_bio);
 692			comp_bio->bi_private = cb;
 693			comp_bio->bi_end_io = end_compressed_bio_read;
 694
 695			bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);
 696		}
 697		cur_disk_byte += PAGE_CACHE_SIZE;
 698	}
 699	bio_get(comp_bio);
 700
 701	ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 702	BUG_ON(ret); /* -ENOMEM */
 703
 704	if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
 705		ret = btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
 706		BUG_ON(ret); /* -ENOMEM */
 707	}
 708
 709	ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
 710	BUG_ON(ret); /* -ENOMEM */
 711
 712	bio_put(comp_bio);
 713	return 0;
 714
 715fail2:
 716	for (pg_index = 0; pg_index < nr_pages; pg_index++)
 717		free_page((unsigned long)cb->compressed_pages[pg_index]);
 718
 719	kfree(cb->compressed_pages);
 720fail1:
 721	kfree(cb);
 722out:
 723	free_extent_map(em);
 724	return ret;
 725}
 726
 727static struct list_head comp_idle_workspace[BTRFS_COMPRESS_TYPES];
 728static spinlock_t comp_workspace_lock[BTRFS_COMPRESS_TYPES];
 729static int comp_num_workspace[BTRFS_COMPRESS_TYPES];
 730static atomic_t comp_alloc_workspace[BTRFS_COMPRESS_TYPES];
 731static wait_queue_head_t comp_workspace_wait[BTRFS_COMPRESS_TYPES];
 732
 733struct btrfs_compress_op *btrfs_compress_op[] = {
 734	&btrfs_zlib_compress,
 735	&btrfs_lzo_compress,
 736};
 737
 738void __init btrfs_init_compress(void)
 739{
 740	int i;
 741
 742	for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
 743		INIT_LIST_HEAD(&comp_idle_workspace[i]);
 744		spin_lock_init(&comp_workspace_lock[i]);
 745		atomic_set(&comp_alloc_workspace[i], 0);
 746		init_waitqueue_head(&comp_workspace_wait[i]);
 747	}
 748}
 749
 750/*
 751 * this finds an available workspace or allocates a new one
 752 * ERR_PTR is returned if things go bad.
 753 */
 754static struct list_head *find_workspace(int type)
 755{
 756	struct list_head *workspace;
 757	int cpus = num_online_cpus();
 758	int idx = type - 1;
 759
 760	struct list_head *idle_workspace	= &comp_idle_workspace[idx];
 761	spinlock_t *workspace_lock		= &comp_workspace_lock[idx];
 762	atomic_t *alloc_workspace		= &comp_alloc_workspace[idx];
 763	wait_queue_head_t *workspace_wait	= &comp_workspace_wait[idx];
 764	int *num_workspace			= &comp_num_workspace[idx];
 765again:
 766	spin_lock(workspace_lock);
 767	if (!list_empty(idle_workspace)) {
 768		workspace = idle_workspace->next;
 769		list_del(workspace);
 770		(*num_workspace)--;
 771		spin_unlock(workspace_lock);
 772		return workspace;
 773
 774	}
 775	if (atomic_read(alloc_workspace) > cpus) {
 776		DEFINE_WAIT(wait);
 777
 778		spin_unlock(workspace_lock);
 779		prepare_to_wait(workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
 780		if (atomic_read(alloc_workspace) > cpus && !*num_workspace)
 781			schedule();
 782		finish_wait(workspace_wait, &wait);
 783		goto again;
 784	}
 785	atomic_inc(alloc_workspace);
 786	spin_unlock(workspace_lock);
 787
 788	workspace = btrfs_compress_op[idx]->alloc_workspace();
 789	if (IS_ERR(workspace)) {
 790		atomic_dec(alloc_workspace);
 791		wake_up(workspace_wait);
 792	}
 793	return workspace;
 794}
 795
 796/*
 797 * put a workspace struct back on the list or free it if we have enough
 798 * idle ones sitting around
 799 */
 800static void free_workspace(int type, struct list_head *workspace)
 801{
 802	int idx = type - 1;
 803	struct list_head *idle_workspace	= &comp_idle_workspace[idx];
 804	spinlock_t *workspace_lock		= &comp_workspace_lock[idx];
 805	atomic_t *alloc_workspace		= &comp_alloc_workspace[idx];
 806	wait_queue_head_t *workspace_wait	= &comp_workspace_wait[idx];
 807	int *num_workspace			= &comp_num_workspace[idx];
 808
 809	spin_lock(workspace_lock);
 810	if (*num_workspace < num_online_cpus()) {
 811		list_add_tail(workspace, idle_workspace);
 812		(*num_workspace)++;
 813		spin_unlock(workspace_lock);
 814		goto wake;
 815	}
 816	spin_unlock(workspace_lock);
 817
 818	btrfs_compress_op[idx]->free_workspace(workspace);
 819	atomic_dec(alloc_workspace);
 820wake:
 821	if (waitqueue_active(workspace_wait))
 822		wake_up(workspace_wait);
 823}
 824
 825/*
 826 * cleanup function for module exit
 827 */
 828static void free_workspaces(void)
 829{
 830	struct list_head *workspace;
 831	int i;
 832
 833	for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
 834		while (!list_empty(&comp_idle_workspace[i])) {
 835			workspace = comp_idle_workspace[i].next;
 836			list_del(workspace);
 837			btrfs_compress_op[i]->free_workspace(workspace);
 838			atomic_dec(&comp_alloc_workspace[i]);
 839		}
 840	}
 841}
 842
 843/*
 844 * given an address space and start/len, compress the bytes.
 845 *
 846 * pages are allocated to hold the compressed result and stored
 847 * in 'pages'
 848 *
 849 * out_pages is used to return the number of pages allocated.  There
 850 * may be pages allocated even if we return an error
 851 *
 852 * total_in is used to return the number of bytes actually read.  It
 853 * may be smaller then len if we had to exit early because we
 854 * ran out of room in the pages array or because we cross the
 855 * max_out threshold.
 856 *
 857 * total_out is used to return the total number of compressed bytes
 858 *
 859 * max_out tells us the max number of bytes that we're allowed to
 860 * stuff into pages
 861 */
 862int btrfs_compress_pages(int type, struct address_space *mapping,
 863			 u64 start, unsigned long len,
 864			 struct page **pages,
 865			 unsigned long nr_dest_pages,
 866			 unsigned long *out_pages,
 867			 unsigned long *total_in,
 868			 unsigned long *total_out,
 869			 unsigned long max_out)
 870{
 871	struct list_head *workspace;
 872	int ret;
 873
 874	workspace = find_workspace(type);
 875	if (IS_ERR(workspace))
 876		return -1;
 877
 878	ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
 879						      start, len, pages,
 880						      nr_dest_pages, out_pages,
 881						      total_in, total_out,
 882						      max_out);
 883	free_workspace(type, workspace);
 884	return ret;
 885}
 886
 887/*
 888 * pages_in is an array of pages with compressed data.
 889 *
 890 * disk_start is the starting logical offset of this array in the file
 891 *
 892 * bvec is a bio_vec of pages from the file that we want to decompress into
 893 *
 894 * vcnt is the count of pages in the biovec
 895 *
 896 * srclen is the number of bytes in pages_in
 897 *
 898 * The basic idea is that we have a bio that was created by readpages.
 899 * The pages in the bio are for the uncompressed data, and they may not
 900 * be contiguous.  They all correspond to the range of bytes covered by
 901 * the compressed extent.
 902 */
 903int btrfs_decompress_biovec(int type, struct page **pages_in, u64 disk_start,
 904			    struct bio_vec *bvec, int vcnt, size_t srclen)
 905{
 906	struct list_head *workspace;
 907	int ret;
 908
 909	workspace = find_workspace(type);
 910	if (IS_ERR(workspace))
 911		return -ENOMEM;
 912
 913	ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
 914							 disk_start,
 915							 bvec, vcnt, srclen);
 916	free_workspace(type, workspace);
 917	return ret;
 918}
 919
 920/*
 921 * a less complex decompression routine.  Our compressed data fits in a
 922 * single page, and we want to read a single page out of it.
 923 * start_byte tells us the offset into the compressed data we're interested in
 924 */
 925int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
 926		     unsigned long start_byte, size_t srclen, size_t destlen)
 927{
 928	struct list_head *workspace;
 929	int ret;
 930
 931	workspace = find_workspace(type);
 932	if (IS_ERR(workspace))
 933		return -ENOMEM;
 934
 935	ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
 936						  dest_page, start_byte,
 937						  srclen, destlen);
 938
 939	free_workspace(type, workspace);
 940	return ret;
 941}
 942
 943void btrfs_exit_compress(void)
 944{
 945	free_workspaces();
 946}
 947
 948/*
 949 * Copy uncompressed data from working buffer to pages.
 950 *
 951 * buf_start is the byte offset we're of the start of our workspace buffer.
 952 *
 953 * total_out is the last byte of the buffer
 954 */
 955int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
 956			      unsigned long total_out, u64 disk_start,
 957			      struct bio_vec *bvec, int vcnt,
 958			      unsigned long *pg_index,
 959			      unsigned long *pg_offset)
 960{
 961	unsigned long buf_offset;
 962	unsigned long current_buf_start;
 963	unsigned long start_byte;
 964	unsigned long working_bytes = total_out - buf_start;
 965	unsigned long bytes;
 966	char *kaddr;
 967	struct page *page_out = bvec[*pg_index].bv_page;
 968
 969	/*
 970	 * start byte is the first byte of the page we're currently
 971	 * copying into relative to the start of the compressed data.
 972	 */
 973	start_byte = page_offset(page_out) - disk_start;
 974
 975	/* we haven't yet hit data corresponding to this page */
 976	if (total_out <= start_byte)
 977		return 1;
 978
 979	/*
 980	 * the start of the data we care about is offset into
 981	 * the middle of our working buffer
 982	 */
 983	if (total_out > start_byte && buf_start < start_byte) {
 984		buf_offset = start_byte - buf_start;
 985		working_bytes -= buf_offset;
 986	} else {
 987		buf_offset = 0;
 988	}
 989	current_buf_start = buf_start;
 990
 991	/* copy bytes from the working buffer into the pages */
 992	while (working_bytes > 0) {
 993		bytes = min(PAGE_CACHE_SIZE - *pg_offset,
 994			    PAGE_CACHE_SIZE - buf_offset);
 995		bytes = min(bytes, working_bytes);
 996		kaddr = kmap_atomic(page_out);
 997		memcpy(kaddr + *pg_offset, buf + buf_offset, bytes);
 998		kunmap_atomic(kaddr);
 999		flush_dcache_page(page_out);
1000
1001		*pg_offset += bytes;
1002		buf_offset += bytes;
1003		working_bytes -= bytes;
1004		current_buf_start += bytes;
1005
1006		/* check if we need to pick another page */
1007		if (*pg_offset == PAGE_CACHE_SIZE) {
1008			(*pg_index)++;
1009			if (*pg_index >= vcnt)
1010				return 0;
1011
1012			page_out = bvec[*pg_index].bv_page;
1013			*pg_offset = 0;
1014			start_byte = page_offset(page_out) - disk_start;
1015
1016			/*
1017			 * make sure our new page is covered by this
1018			 * working buffer
1019			 */
1020			if (total_out <= start_byte)
1021				return 1;
1022
1023			/*
1024			 * the next page in the biovec might not be adjacent
1025			 * to the last page, but it might still be found
1026			 * inside this working buffer. bump our offset pointer
1027			 */
1028			if (total_out > start_byte &&
1029			    current_buf_start < start_byte) {
1030				buf_offset = start_byte - buf_start;
1031				working_bytes = total_out - start_byte;
1032				current_buf_start = buf_start + buf_offset;
1033			}
1034		}
1035	}
1036
1037	return 1;
1038}