/*
   * Copyright (C) 2011 STRATO.  All rights reserved.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public
   * License v2 as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public
   * License along with this program; if not, write to the
   * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   * Boston, MA 021110-1307, USA.
   */

  #include <linux/blkdev.h>

  #include <linux/ratelimit.h>

  #include "ctree.h"
  #include "volumes.h"
  #include "disk-io.h"
  #include "ordered-data.h"

  #include "transaction.h"

  #include "backref.h"

  #include "extent_io.h"

  
  /*
   * This is only the first step towards a full-features scrub. It reads all
   * extent and super block and verifies the checksums. In case a bad checksum
   * is found or the extent cannot be read, good data will be written back if
   * any can be found.
   *
   * Future enhancements:

   *  - In case an unrepairable extent is encountered, track which files are
   *    affected and report them
   *  - In case of a read error on files with nodatasum, map the file and read
   *    the extent to trigger a writeback of the good copy
   *  - track and record media errors, throw out bad devices

   *  - add a mode to also read unallocated space

   */
  
  struct scrub_bio;
  struct scrub_page;
  struct scrub_dev;

  static void scrub_bio_end_io(struct bio *bio, int err);
  static void scrub_checksum(struct btrfs_work *work);
  static int scrub_checksum_data(struct scrub_dev *sdev,
  			       struct scrub_page *spag, void *buffer);
  static int scrub_checksum_tree_block(struct scrub_dev *sdev,
  				     struct scrub_page *spag, u64 logical,
  				     void *buffer);
  static int scrub_checksum_super(struct scrub_bio *sbio, void *buffer);

  static int scrub_fixup_check(struct scrub_bio *sbio, int ix);
  static void scrub_fixup_end_io(struct bio *bio, int err);
  static int scrub_fixup_io(int rw, struct block_device *bdev, sector_t sector,
  			  struct page *page);
  static void scrub_fixup(struct scrub_bio *sbio, int ix);

  
  #define SCRUB_PAGES_PER_BIO	16	/* 64k per bio */
  #define SCRUB_BIOS_PER_DEV	16	/* 1 MB per device in flight */
  
  struct scrub_page {
  	u64			flags;  /* extent flags */
  	u64			generation;

  	int			mirror_num;

  	int			have_csum;
  	u8			csum[BTRFS_CSUM_SIZE];
  };
  
  struct scrub_bio {
  	int			index;
  	struct scrub_dev	*sdev;
  	struct bio		*bio;
  	int			err;
  	u64			logical;
  	u64			physical;
  	struct scrub_page	spag[SCRUB_PAGES_PER_BIO];
  	u64			count;
  	int			next_free;
  	struct btrfs_work	work;
  };
  
  struct scrub_dev {
  	struct scrub_bio	*bios[SCRUB_BIOS_PER_DEV];
  	struct btrfs_device	*dev;
  	int			first_free;
  	int			curr;
  	atomic_t		in_flight;

  	atomic_t		fixup_cnt;

  	spinlock_t		list_lock;
  	wait_queue_head_t	list_wait;
  	u16			csum_size;
  	struct list_head	csum_list;
  	atomic_t		cancel_req;

  	int			readonly;

  	/*
  	 * statistics
  	 */
  	struct btrfs_scrub_progress stat;
  	spinlock_t		stat_lock;
  };

  struct scrub_fixup_nodatasum {
  	struct scrub_dev	*sdev;
  	u64			logical;
  	struct btrfs_root	*root;
  	struct btrfs_work	work;
  	int			mirror_num;
  };

  struct scrub_warning {
  	struct btrfs_path	*path;
  	u64			extent_item_size;
  	char			*scratch_buf;
  	char			*msg_buf;
  	const char		*errstr;
  	sector_t		sector;
  	u64			logical;
  	struct btrfs_device	*dev;
  	int			msg_bufsize;
  	int			scratch_bufsize;
  };

  static void scrub_free_csums(struct scrub_dev *sdev)
  {
  	while (!list_empty(&sdev->csum_list)) {
  		struct btrfs_ordered_sum *sum;
  		sum = list_first_entry(&sdev->csum_list,
  				       struct btrfs_ordered_sum, list);
  		list_del(&sum->list);
  		kfree(sum);
  	}
  }

  static void scrub_free_bio(struct bio *bio)
  {
  	int i;
  	struct page *last_page = NULL;
  
  	if (!bio)
  		return;
  
  	for (i = 0; i < bio->bi_vcnt; ++i) {
  		if (bio->bi_io_vec[i].bv_page == last_page)
  			continue;
  		last_page = bio->bi_io_vec[i].bv_page;
  		__free_page(last_page);
  	}
  	bio_put(bio);
  }

  static noinline_for_stack void scrub_free_dev(struct scrub_dev *sdev)
  {
  	int i;

  
  	if (!sdev)
  		return;
  
  	for (i = 0; i < SCRUB_BIOS_PER_DEV; ++i) {
  		struct scrub_bio *sbio = sdev->bios[i];

  
  		if (!sbio)
  			break;

  		scrub_free_bio(sbio->bio);

  		kfree(sbio);
  	}
  
  	scrub_free_csums(sdev);
  	kfree(sdev);
  }
  
  static noinline_for_stack
  struct scrub_dev *scrub_setup_dev(struct btrfs_device *dev)
  {
  	struct scrub_dev *sdev;
  	int		i;

  	struct btrfs_fs_info *fs_info = dev->dev_root->fs_info;
  
  	sdev = kzalloc(sizeof(*sdev), GFP_NOFS);
  	if (!sdev)
  		goto nomem;
  	sdev->dev = dev;
  	for (i = 0; i < SCRUB_BIOS_PER_DEV; ++i) {

  		struct scrub_bio *sbio;
  
  		sbio = kzalloc(sizeof(*sbio), GFP_NOFS);
  		if (!sbio)
  			goto nomem;
  		sdev->bios[i] = sbio;

  		sbio->index = i;
  		sbio->sdev = sdev;

  		sbio->count = 0;
  		sbio->work.func = scrub_checksum;

  
  		if (i != SCRUB_BIOS_PER_DEV-1)
  			sdev->bios[i]->next_free = i + 1;

  		else

  			sdev->bios[i]->next_free = -1;
  	}
  	sdev->first_free = 0;
  	sdev->curr = -1;
  	atomic_set(&sdev->in_flight, 0);

  	atomic_set(&sdev->fixup_cnt, 0);

  	atomic_set(&sdev->cancel_req, 0);

  	sdev->csum_size = btrfs_super_csum_size(fs_info->super_copy);

  	INIT_LIST_HEAD(&sdev->csum_list);
  
  	spin_lock_init(&sdev->list_lock);
  	spin_lock_init(&sdev->stat_lock);
  	init_waitqueue_head(&sdev->list_wait);
  	return sdev;
  
  nomem:
  	scrub_free_dev(sdev);
  	return ERR_PTR(-ENOMEM);
  }

  static int scrub_print_warning_inode(u64 inum, u64 offset, u64 root, void *ctx)
  {
  	u64 isize;
  	u32 nlink;
  	int ret;
  	int i;
  	struct extent_buffer *eb;
  	struct btrfs_inode_item *inode_item;
  	struct scrub_warning *swarn = ctx;
  	struct btrfs_fs_info *fs_info = swarn->dev->dev_root->fs_info;
  	struct inode_fs_paths *ipath = NULL;
  	struct btrfs_root *local_root;
  	struct btrfs_key root_key;
  
  	root_key.objectid = root;
  	root_key.type = BTRFS_ROOT_ITEM_KEY;
  	root_key.offset = (u64)-1;
  	local_root = btrfs_read_fs_root_no_name(fs_info, &root_key);
  	if (IS_ERR(local_root)) {
  		ret = PTR_ERR(local_root);
  		goto err;
  	}
  
  	ret = inode_item_info(inum, 0, local_root, swarn->path);
  	if (ret) {
  		btrfs_release_path(swarn->path);
  		goto err;
  	}
  
  	eb = swarn->path->nodes[0];
  	inode_item = btrfs_item_ptr(eb, swarn->path->slots[0],
  					struct btrfs_inode_item);
  	isize = btrfs_inode_size(eb, inode_item);
  	nlink = btrfs_inode_nlink(eb, inode_item);
  	btrfs_release_path(swarn->path);
  
  	ipath = init_ipath(4096, local_root, swarn->path);

  	if (IS_ERR(ipath)) {
  		ret = PTR_ERR(ipath);
  		ipath = NULL;
  		goto err;
  	}

  	ret = paths_from_inode(inum, ipath);
  
  	if (ret < 0)
  		goto err;
  
  	/*
  	 * we deliberately ignore the bit ipath might have been too small to
  	 * hold all of the paths here
  	 */
  	for (i = 0; i < ipath->fspath->elem_cnt; ++i)
  		printk(KERN_WARNING "btrfs: %s at logical %llu on dev "
  			"%s, sector %llu, root %llu, inode %llu, offset %llu, "
  			"length %llu, links %u (path: %s)
  ", swarn->errstr,
  			swarn->logical, swarn->dev->name,
  			(unsigned long long)swarn->sector, root, inum, offset,
  			min(isize - offset, (u64)PAGE_SIZE), nlink,

  			(char *)(unsigned long)ipath->fspath->val[i]);

  
  	free_ipath(ipath);
  	return 0;
  
  err:
  	printk(KERN_WARNING "btrfs: %s at logical %llu on dev "
  		"%s, sector %llu, root %llu, inode %llu, offset %llu: path "
  		"resolving failed with ret=%d
  ", swarn->errstr,
  		swarn->logical, swarn->dev->name,
  		(unsigned long long)swarn->sector, root, inum, offset, ret);
  
  	free_ipath(ipath);
  	return 0;
  }
  
  static void scrub_print_warning(const char *errstr, struct scrub_bio *sbio,
  				int ix)
  {
  	struct btrfs_device *dev = sbio->sdev->dev;
  	struct btrfs_fs_info *fs_info = dev->dev_root->fs_info;
  	struct btrfs_path *path;
  	struct btrfs_key found_key;
  	struct extent_buffer *eb;
  	struct btrfs_extent_item *ei;
  	struct scrub_warning swarn;
  	u32 item_size;
  	int ret;
  	u64 ref_root;
  	u8 ref_level;
  	unsigned long ptr = 0;
  	const int bufsize = 4096;
  	u64 extent_offset;
  
  	path = btrfs_alloc_path();
  
  	swarn.scratch_buf = kmalloc(bufsize, GFP_NOFS);
  	swarn.msg_buf = kmalloc(bufsize, GFP_NOFS);
  	swarn.sector = (sbio->physical + ix * PAGE_SIZE) >> 9;
  	swarn.logical = sbio->logical + ix * PAGE_SIZE;
  	swarn.errstr = errstr;
  	swarn.dev = dev;
  	swarn.msg_bufsize = bufsize;
  	swarn.scratch_bufsize = bufsize;
  
  	if (!path || !swarn.scratch_buf || !swarn.msg_buf)
  		goto out;
  
  	ret = extent_from_logical(fs_info, swarn.logical, path, &found_key);
  	if (ret < 0)
  		goto out;
  
  	extent_offset = swarn.logical - found_key.objectid;
  	swarn.extent_item_size = found_key.offset;
  
  	eb = path->nodes[0];
  	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
  	item_size = btrfs_item_size_nr(eb, path->slots[0]);
  
  	if (ret & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
  		do {
  			ret = tree_backref_for_extent(&ptr, eb, ei, item_size,
  							&ref_root, &ref_level);
  			printk(KERN_WARNING "%s at logical %llu on dev %s, "
  				"sector %llu: metadata %s (level %d) in tree "
  				"%llu
  ", errstr, swarn.logical, dev->name,
  				(unsigned long long)swarn.sector,
  				ref_level ? "node" : "leaf",
  				ret < 0 ? -1 : ref_level,
  				ret < 0 ? -1 : ref_root);
  		} while (ret != 1);
  	} else {
  		swarn.path = path;
  		iterate_extent_inodes(fs_info, path, found_key.objectid,
  					extent_offset,
  					scrub_print_warning_inode, &swarn);
  	}
  
  out:
  	btrfs_free_path(path);
  	kfree(swarn.scratch_buf);
  	kfree(swarn.msg_buf);
  }

  static int scrub_fixup_readpage(u64 inum, u64 offset, u64 root, void *ctx)
  {

  	struct page *page = NULL;

  	unsigned long index;
  	struct scrub_fixup_nodatasum *fixup = ctx;
  	int ret;

  	int corrected = 0;

  	struct btrfs_key key;

  	struct inode *inode = NULL;

  	u64 end = offset + PAGE_SIZE - 1;
  	struct btrfs_root *local_root;
  
  	key.objectid = root;
  	key.type = BTRFS_ROOT_ITEM_KEY;
  	key.offset = (u64)-1;
  	local_root = btrfs_read_fs_root_no_name(fixup->root->fs_info, &key);
  	if (IS_ERR(local_root))
  		return PTR_ERR(local_root);
  
  	key.type = BTRFS_INODE_ITEM_KEY;
  	key.objectid = inum;
  	key.offset = 0;
  	inode = btrfs_iget(fixup->root->fs_info->sb, &key, local_root, NULL);
  	if (IS_ERR(inode))
  		return PTR_ERR(inode);

  	index = offset >> PAGE_CACHE_SHIFT;
  
  	page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);

  	if (!page) {
  		ret = -ENOMEM;
  		goto out;
  	}
  
  	if (PageUptodate(page)) {
  		struct btrfs_mapping_tree *map_tree;
  		if (PageDirty(page)) {
  			/*
  			 * we need to write the data to the defect sector. the
  			 * data that was in that sector is not in memory,
  			 * because the page was modified. we must not write the
  			 * modified page to that sector.
  			 *
  			 * TODO: what could be done here: wait for the delalloc
  			 *       runner to write out that page (might involve
  			 *       COW) and see whether the sector is still
  			 *       referenced afterwards.
  			 *
  			 * For the meantime, we'll treat this error
  			 * incorrectable, although there is a chance that a
  			 * later scrub will find the bad sector again and that
  			 * there's no dirty page in memory, then.
  			 */
  			ret = -EIO;
  			goto out;
  		}
  		map_tree = &BTRFS_I(inode)->root->fs_info->mapping_tree;
  		ret = repair_io_failure(map_tree, offset, PAGE_SIZE,
  					fixup->logical, page,
  					fixup->mirror_num);
  		unlock_page(page);
  		corrected = !ret;
  	} else {
  		/*
  		 * we need to get good data first. the general readpage path
  		 * will call repair_io_failure for us, we just have to make
  		 * sure we read the bad mirror.
  		 */
  		ret = set_extent_bits(&BTRFS_I(inode)->io_tree, offset, end,
  					EXTENT_DAMAGED, GFP_NOFS);
  		if (ret) {
  			/* set_extent_bits should give proper error */
  			WARN_ON(ret > 0);
  			if (ret > 0)
  				ret = -EFAULT;
  			goto out;
  		}
  
  		ret = extent_read_full_page(&BTRFS_I(inode)->io_tree, page,
  						btrfs_get_extent,
  						fixup->mirror_num);
  		wait_on_page_locked(page);
  
  		corrected = !test_range_bit(&BTRFS_I(inode)->io_tree, offset,
  						end, EXTENT_DAMAGED, 0, NULL);
  		if (!corrected)
  			clear_extent_bits(&BTRFS_I(inode)->io_tree, offset, end,
  						EXTENT_DAMAGED, GFP_NOFS);
  	}
  
  out:
  	if (page)
  		put_page(page);
  	if (inode)
  		iput(inode);

  
  	if (ret < 0)
  		return ret;
  
  	if (ret == 0 && corrected) {
  		/*
  		 * we only need to call readpage for one of the inodes belonging
  		 * to this extent. so make iterate_extent_inodes stop
  		 */
  		return 1;
  	}
  
  	return -EIO;
  }
  
  static void scrub_fixup_nodatasum(struct btrfs_work *work)
  {
  	int ret;
  	struct scrub_fixup_nodatasum *fixup;
  	struct scrub_dev *sdev;
  	struct btrfs_trans_handle *trans = NULL;
  	struct btrfs_fs_info *fs_info;
  	struct btrfs_path *path;
  	int uncorrectable = 0;
  
  	fixup = container_of(work, struct scrub_fixup_nodatasum, work);
  	sdev = fixup->sdev;
  	fs_info = fixup->root->fs_info;
  
  	path = btrfs_alloc_path();
  	if (!path) {
  		spin_lock(&sdev->stat_lock);
  		++sdev->stat.malloc_errors;
  		spin_unlock(&sdev->stat_lock);
  		uncorrectable = 1;
  		goto out;
  	}
  
  	trans = btrfs_join_transaction(fixup->root);
  	if (IS_ERR(trans)) {
  		uncorrectable = 1;
  		goto out;
  	}
  
  	/*
  	 * the idea is to trigger a regular read through the standard path. we
  	 * read a page from the (failed) logical address by specifying the
  	 * corresponding copynum of the failed sector. thus, that readpage is
  	 * expected to fail.
  	 * that is the point where on-the-fly error correction will kick in
  	 * (once it's finished) and rewrite the failed sector if a good copy
  	 * can be found.
  	 */
  	ret = iterate_inodes_from_logical(fixup->logical, fixup->root->fs_info,
  						path, scrub_fixup_readpage,
  						fixup);
  	if (ret < 0) {
  		uncorrectable = 1;
  		goto out;
  	}
  	WARN_ON(ret != 1);
  
  	spin_lock(&sdev->stat_lock);
  	++sdev->stat.corrected_errors;
  	spin_unlock(&sdev->stat_lock);
  
  out:
  	if (trans && !IS_ERR(trans))
  		btrfs_end_transaction(trans, fixup->root);
  	if (uncorrectable) {
  		spin_lock(&sdev->stat_lock);
  		++sdev->stat.uncorrectable_errors;
  		spin_unlock(&sdev->stat_lock);
  		printk_ratelimited(KERN_ERR "btrfs: unable to fixup "
  					"(nodatasum) error at logical %llu
  ",
  					fixup->logical);
  	}
  
  	btrfs_free_path(path);
  	kfree(fixup);
  
  	/* see caller why we're pretending to be paused in the scrub counters */
  	mutex_lock(&fs_info->scrub_lock);
  	atomic_dec(&fs_info->scrubs_running);
  	atomic_dec(&fs_info->scrubs_paused);
  	mutex_unlock(&fs_info->scrub_lock);
  	atomic_dec(&sdev->fixup_cnt);
  	wake_up(&fs_info->scrub_pause_wait);
  	wake_up(&sdev->list_wait);
  }

  /*
   * scrub_recheck_error gets called when either verification of the page
   * failed or the bio failed to read, e.g. with EIO. In the latter case,
   * recheck_error gets called for every page in the bio, even though only
   * one may be bad
   */

  static int scrub_recheck_error(struct scrub_bio *sbio, int ix)

  {

  	struct scrub_dev *sdev = sbio->sdev;
  	u64 sector = (sbio->physical + ix * PAGE_SIZE) >> 9;

  	static DEFINE_RATELIMIT_STATE(_rs, DEFAULT_RATELIMIT_INTERVAL,
  					DEFAULT_RATELIMIT_BURST);

  	if (sbio->err) {

  		if (scrub_fixup_io(READ, sbio->sdev->dev->bdev, sector,

  				   sbio->bio->bi_io_vec[ix].bv_page) == 0) {
  			if (scrub_fixup_check(sbio, ix) == 0)

  				return 0;

  		}

  		if (__ratelimit(&_rs))
  			scrub_print_warning("i/o error", sbio, ix);
  	} else {
  		if (__ratelimit(&_rs))
  			scrub_print_warning("checksum error", sbio, ix);

  	}

  	spin_lock(&sdev->stat_lock);
  	++sdev->stat.read_errors;
  	spin_unlock(&sdev->stat_lock);

  	scrub_fixup(sbio, ix);

  	return 1;

  }

  static int scrub_fixup_check(struct scrub_bio *sbio, int ix)

  {
  	int ret = 1;
  	struct page *page;
  	void *buffer;

  	u64 flags = sbio->spag[ix].flags;

  	page = sbio->bio->bi_io_vec[ix].bv_page;

  	buffer = kmap_atomic(page, KM_USER0);
  	if (flags & BTRFS_EXTENT_FLAG_DATA) {

  		ret = scrub_checksum_data(sbio->sdev,
  					  sbio->spag + ix, buffer);

  	} else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {

  		ret = scrub_checksum_tree_block(sbio->sdev,
  						sbio->spag + ix,
  						sbio->logical + ix * PAGE_SIZE,

  						buffer);
  	} else {
  		WARN_ON(1);
  	}
  	kunmap_atomic(buffer, KM_USER0);
  
  	return ret;
  }

  static void scrub_fixup_end_io(struct bio *bio, int err)
  {
  	complete((struct completion *)bio->bi_private);
  }

  static void scrub_fixup(struct scrub_bio *sbio, int ix)

  {

  	struct scrub_dev *sdev = sbio->sdev;

  	struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;
  	struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;

  	struct btrfs_bio *bbio = NULL;

  	struct scrub_fixup_nodatasum *fixup;

  	u64 logical = sbio->logical + ix * PAGE_SIZE;

  	u64 length;
  	int i;
  	int ret;
  	DECLARE_COMPLETION_ONSTACK(complete);

  	if ((sbio->spag[ix].flags & BTRFS_EXTENT_FLAG_DATA) &&
  	    (sbio->spag[ix].have_csum == 0)) {

  		fixup = kzalloc(sizeof(*fixup), GFP_NOFS);
  		if (!fixup)
  			goto uncorrectable;
  		fixup->sdev = sdev;
  		fixup->logical = logical;
  		fixup->root = fs_info->extent_root;
  		fixup->mirror_num = sbio->spag[ix].mirror_num;

  		/*

  		 * increment scrubs_running to prevent cancel requests from
  		 * completing as long as a fixup worker is running. we must also
  		 * increment scrubs_paused to prevent deadlocking on pause
  		 * requests used for transactions commits (as the worker uses a
  		 * transaction context). it is safe to regard the fixup worker
  		 * as paused for all matters practical. effectively, we only
  		 * avoid cancellation requests from completing.

  		 */

  		mutex_lock(&fs_info->scrub_lock);
  		atomic_inc(&fs_info->scrubs_running);
  		atomic_inc(&fs_info->scrubs_paused);
  		mutex_unlock(&fs_info->scrub_lock);
  		atomic_inc(&sdev->fixup_cnt);
  		fixup->work.func = scrub_fixup_nodatasum;
  		btrfs_queue_worker(&fs_info->scrub_workers, &fixup->work);
  		return;

  	}
  
  	length = PAGE_SIZE;

  	ret = btrfs_map_block(map_tree, REQ_WRITE, logical, &length,

  			      &bbio, 0);
  	if (ret || !bbio || length < PAGE_SIZE) {

  		printk(KERN_ERR
  		       "scrub_fixup: btrfs_map_block failed us for %llu
  ",

  		       (unsigned long long)logical);

  		WARN_ON(1);

  		kfree(bbio);

  		return;
  	}

  	if (bbio->num_stripes == 1)

  		/* there aren't any replicas */
  		goto uncorrectable;

  
  	/*
  	 * first find a good copy
  	 */

  	for (i = 0; i < bbio->num_stripes; ++i) {

  		if (i + 1 == sbio->spag[ix].mirror_num)

  			continue;

  		if (scrub_fixup_io(READ, bbio->stripes[i].dev->bdev,
  				   bbio->stripes[i].physical >> 9,

  				   sbio->bio->bi_io_vec[ix].bv_page)) {

  			/* I/O-error, this is not a good copy */
  			continue;

  		}

  		if (scrub_fixup_check(sbio, ix) == 0)

  			break;
  	}

  	if (i == bbio->num_stripes)

  		goto uncorrectable;

  	if (!sdev->readonly) {
  		/*
  		 * bi_io_vec[ix].bv_page now contains good data, write it back
  		 */
  		if (scrub_fixup_io(WRITE, sdev->dev->bdev,
  				   (sbio->physical + ix * PAGE_SIZE) >> 9,
  				   sbio->bio->bi_io_vec[ix].bv_page)) {
  			/* I/O-error, writeback failed, give up */
  			goto uncorrectable;
  		}

  	}

  	kfree(bbio);

  	spin_lock(&sdev->stat_lock);
  	++sdev->stat.corrected_errors;
  	spin_unlock(&sdev->stat_lock);

  	printk_ratelimited(KERN_ERR "btrfs: fixed up error at logical %llu
  ",
  			       (unsigned long long)logical);

  	return;
  
  uncorrectable:

  	kfree(bbio);

  	spin_lock(&sdev->stat_lock);
  	++sdev->stat.uncorrectable_errors;
  	spin_unlock(&sdev->stat_lock);

  	printk_ratelimited(KERN_ERR "btrfs: unable to fixup (regular) error at "
  				"logical %llu
  ", (unsigned long long)logical);

  }
  
  static int scrub_fixup_io(int rw, struct block_device *bdev, sector_t sector,
  			 struct page *page)
  {
  	struct bio *bio = NULL;
  	int ret;
  	DECLARE_COMPLETION_ONSTACK(complete);

  	bio = bio_alloc(GFP_NOFS, 1);
  	bio->bi_bdev = bdev;
  	bio->bi_sector = sector;
  	bio_add_page(bio, page, PAGE_SIZE, 0);
  	bio->bi_end_io = scrub_fixup_end_io;
  	bio->bi_private = &complete;
  	submit_bio(rw, bio);

  	/* this will also unplug the queue */

  	wait_for_completion(&complete);
  
  	ret = !test_bit(BIO_UPTODATE, &bio->bi_flags);
  	bio_put(bio);
  	return ret;

  }
  
  static void scrub_bio_end_io(struct bio *bio, int err)
  {
  	struct scrub_bio *sbio = bio->bi_private;
  	struct scrub_dev *sdev = sbio->sdev;
  	struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;
  
  	sbio->err = err;

  	sbio->bio = bio;

  
  	btrfs_queue_worker(&fs_info->scrub_workers, &sbio->work);
  }
  
  static void scrub_checksum(struct btrfs_work *work)
  {
  	struct scrub_bio *sbio = container_of(work, struct scrub_bio, work);
  	struct scrub_dev *sdev = sbio->sdev;
  	struct page *page;
  	void *buffer;
  	int i;
  	u64 flags;
  	u64 logical;
  	int ret;
  
  	if (sbio->err) {

  		ret = 0;

  		for (i = 0; i < sbio->count; ++i)

  			ret |= scrub_recheck_error(sbio, i);
  		if (!ret) {
  			spin_lock(&sdev->stat_lock);
  			++sdev->stat.unverified_errors;
  			spin_unlock(&sdev->stat_lock);
  		}

  
  		sbio->bio->bi_flags &= ~(BIO_POOL_MASK - 1);
  		sbio->bio->bi_flags |= 1 << BIO_UPTODATE;
  		sbio->bio->bi_phys_segments = 0;
  		sbio->bio->bi_idx = 0;
  
  		for (i = 0; i < sbio->count; i++) {
  			struct bio_vec *bi;
  			bi = &sbio->bio->bi_io_vec[i];
  			bi->bv_offset = 0;
  			bi->bv_len = PAGE_SIZE;
  		}

  		goto out;
  	}
  	for (i = 0; i < sbio->count; ++i) {
  		page = sbio->bio->bi_io_vec[i].bv_page;
  		buffer = kmap_atomic(page, KM_USER0);
  		flags = sbio->spag[i].flags;
  		logical = sbio->logical + i * PAGE_SIZE;
  		ret = 0;
  		if (flags & BTRFS_EXTENT_FLAG_DATA) {
  			ret = scrub_checksum_data(sdev, sbio->spag + i, buffer);
  		} else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
  			ret = scrub_checksum_tree_block(sdev, sbio->spag + i,
  							logical, buffer);
  		} else if (flags & BTRFS_EXTENT_FLAG_SUPER) {
  			BUG_ON(i);
  			(void)scrub_checksum_super(sbio, buffer);
  		} else {
  			WARN_ON(1);
  		}
  		kunmap_atomic(buffer, KM_USER0);

  		if (ret) {
  			ret = scrub_recheck_error(sbio, i);
  			if (!ret) {
  				spin_lock(&sdev->stat_lock);
  				++sdev->stat.unverified_errors;
  				spin_unlock(&sdev->stat_lock);
  			}
  		}

  	}
  
  out:

  	scrub_free_bio(sbio->bio);
  	sbio->bio = NULL;

  	spin_lock(&sdev->list_lock);
  	sbio->next_free = sdev->first_free;
  	sdev->first_free = sbio->index;
  	spin_unlock(&sdev->list_lock);

  	atomic_dec(&sdev->in_flight);
  	wake_up(&sdev->list_wait);
  }
  
  static int scrub_checksum_data(struct scrub_dev *sdev,
  			       struct scrub_page *spag, void *buffer)
  {
  	u8 csum[BTRFS_CSUM_SIZE];
  	u32 crc = ~(u32)0;
  	int fail = 0;
  	struct btrfs_root *root = sdev->dev->dev_root;
  
  	if (!spag->have_csum)
  		return 0;
  
  	crc = btrfs_csum_data(root, buffer, crc, PAGE_SIZE);
  	btrfs_csum_final(crc, csum);
  	if (memcmp(csum, spag->csum, sdev->csum_size))
  		fail = 1;
  
  	spin_lock(&sdev->stat_lock);
  	++sdev->stat.data_extents_scrubbed;
  	sdev->stat.data_bytes_scrubbed += PAGE_SIZE;
  	if (fail)
  		++sdev->stat.csum_errors;
  	spin_unlock(&sdev->stat_lock);
  
  	return fail;
  }
  
  static int scrub_checksum_tree_block(struct scrub_dev *sdev,
  				     struct scrub_page *spag, u64 logical,
  				     void *buffer)
  {
  	struct btrfs_header *h;
  	struct btrfs_root *root = sdev->dev->dev_root;
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	u8 csum[BTRFS_CSUM_SIZE];
  	u32 crc = ~(u32)0;
  	int fail = 0;
  	int crc_fail = 0;
  
  	/*
  	 * we don't use the getter functions here, as we
  	 * a) don't have an extent buffer and
  	 * b) the page is already kmapped
  	 */
  	h = (struct btrfs_header *)buffer;
  
  	if (logical != le64_to_cpu(h->bytenr))
  		++fail;
  
  	if (spag->generation != le64_to_cpu(h->generation))
  		++fail;
  
  	if (memcmp(h->fsid, fs_info->fsid, BTRFS_UUID_SIZE))
  		++fail;
  
  	if (memcmp(h->chunk_tree_uuid, fs_info->chunk_tree_uuid,
  		   BTRFS_UUID_SIZE))
  		++fail;
  
  	crc = btrfs_csum_data(root, buffer + BTRFS_CSUM_SIZE, crc,
  			      PAGE_SIZE - BTRFS_CSUM_SIZE);
  	btrfs_csum_final(crc, csum);
  	if (memcmp(csum, h->csum, sdev->csum_size))
  		++crc_fail;
  
  	spin_lock(&sdev->stat_lock);
  	++sdev->stat.tree_extents_scrubbed;
  	sdev->stat.tree_bytes_scrubbed += PAGE_SIZE;
  	if (crc_fail)
  		++sdev->stat.csum_errors;
  	if (fail)
  		++sdev->stat.verify_errors;
  	spin_unlock(&sdev->stat_lock);
  
  	return fail || crc_fail;
  }
  
  static int scrub_checksum_super(struct scrub_bio *sbio, void *buffer)
  {
  	struct btrfs_super_block *s;
  	u64 logical;
  	struct scrub_dev *sdev = sbio->sdev;
  	struct btrfs_root *root = sdev->dev->dev_root;
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	u8 csum[BTRFS_CSUM_SIZE];
  	u32 crc = ~(u32)0;
  	int fail = 0;
  
  	s = (struct btrfs_super_block *)buffer;
  	logical = sbio->logical;
  
  	if (logical != le64_to_cpu(s->bytenr))
  		++fail;
  
  	if (sbio->spag[0].generation != le64_to_cpu(s->generation))
  		++fail;
  
  	if (memcmp(s->fsid, fs_info->fsid, BTRFS_UUID_SIZE))
  		++fail;
  
  	crc = btrfs_csum_data(root, buffer + BTRFS_CSUM_SIZE, crc,
  			      PAGE_SIZE - BTRFS_CSUM_SIZE);
  	btrfs_csum_final(crc, csum);
  	if (memcmp(csum, s->csum, sbio->sdev->csum_size))
  		++fail;
  
  	if (fail) {
  		/*
  		 * if we find an error in a super block, we just report it.
  		 * They will get written with the next transaction commit
  		 * anyway
  		 */
  		spin_lock(&sdev->stat_lock);
  		++sdev->stat.super_errors;
  		spin_unlock(&sdev->stat_lock);
  	}
  
  	return fail;
  }
  
  static int scrub_submit(struct scrub_dev *sdev)
  {
  	struct scrub_bio *sbio;
  
  	if (sdev->curr == -1)
  		return 0;
  
  	sbio = sdev->bios[sdev->curr];

  	sbio->err = 0;
  	sdev->curr = -1;
  	atomic_inc(&sdev->in_flight);

  	submit_bio(READ, sbio->bio);

  
  	return 0;
  }
  
  static int scrub_page(struct scrub_dev *sdev, u64 logical, u64 len,

  		      u64 physical, u64 flags, u64 gen, int mirror_num,

  		      u8 *csum, int force)
  {
  	struct scrub_bio *sbio;

  	struct page *page;
  	int ret;

  
  again:
  	/*
  	 * grab a fresh bio or wait for one to become available
  	 */
  	while (sdev->curr == -1) {
  		spin_lock(&sdev->list_lock);
  		sdev->curr = sdev->first_free;
  		if (sdev->curr != -1) {
  			sdev->first_free = sdev->bios[sdev->curr]->next_free;
  			sdev->bios[sdev->curr]->next_free = -1;
  			sdev->bios[sdev->curr]->count = 0;
  			spin_unlock(&sdev->list_lock);
  		} else {
  			spin_unlock(&sdev->list_lock);
  			wait_event(sdev->list_wait, sdev->first_free != -1);
  		}
  	}
  	sbio = sdev->bios[sdev->curr];
  	if (sbio->count == 0) {

  		struct bio *bio;

  		sbio->physical = physical;
  		sbio->logical = logical;

  		bio = bio_alloc(GFP_NOFS, SCRUB_PAGES_PER_BIO);
  		if (!bio)
  			return -ENOMEM;
  
  		bio->bi_private = sbio;
  		bio->bi_end_io = scrub_bio_end_io;
  		bio->bi_bdev = sdev->dev->bdev;
  		bio->bi_sector = sbio->physical >> 9;
  		sbio->err = 0;
  		sbio->bio = bio;

  	} else if (sbio->physical + sbio->count * PAGE_SIZE != physical ||
  		   sbio->logical + sbio->count * PAGE_SIZE != logical) {

  		ret = scrub_submit(sdev);
  		if (ret)
  			return ret;

  		goto again;
  	}
  	sbio->spag[sbio->count].flags = flags;
  	sbio->spag[sbio->count].generation = gen;
  	sbio->spag[sbio->count].have_csum = 0;
  	sbio->spag[sbio->count].mirror_num = mirror_num;

  
  	page = alloc_page(GFP_NOFS);
  	if (!page)
  		return -ENOMEM;
  
  	ret = bio_add_page(sbio->bio, page, PAGE_SIZE, 0);
  	if (!ret) {
  		__free_page(page);
  		ret = scrub_submit(sdev);
  		if (ret)
  			return ret;
  		goto again;
  	}

  	if (csum) {
  		sbio->spag[sbio->count].have_csum = 1;
  		memcpy(sbio->spag[sbio->count].csum, csum, sdev->csum_size);
  	}
  	++sbio->count;

  	if (sbio->count == SCRUB_PAGES_PER_BIO || force) {
  		int ret;
  
  		ret = scrub_submit(sdev);
  		if (ret)
  			return ret;
  	}

  
  	return 0;
  }
  
  static int scrub_find_csum(struct scrub_dev *sdev, u64 logical, u64 len,
  			   u8 *csum)
  {
  	struct btrfs_ordered_sum *sum = NULL;
  	int ret = 0;
  	unsigned long i;
  	unsigned long num_sectors;
  	u32 sectorsize = sdev->dev->dev_root->sectorsize;
  
  	while (!list_empty(&sdev->csum_list)) {
  		sum = list_first_entry(&sdev->csum_list,
  				       struct btrfs_ordered_sum, list);
  		if (sum->bytenr > logical)
  			return 0;
  		if (sum->bytenr + sum->len > logical)
  			break;
  
  		++sdev->stat.csum_discards;
  		list_del(&sum->list);
  		kfree(sum);
  		sum = NULL;
  	}
  	if (!sum)
  		return 0;
  
  	num_sectors = sum->len / sectorsize;
  	for (i = 0; i < num_sectors; ++i) {
  		if (sum->sums[i].bytenr == logical) {
  			memcpy(csum, &sum->sums[i].sum, sdev->csum_size);
  			ret = 1;
  			break;
  		}
  	}
  	if (ret && i == num_sectors - 1) {
  		list_del(&sum->list);
  		kfree(sum);
  	}
  	return ret;
  }
  
  /* scrub extent tries to collect up to 64 kB for each bio */
  static int scrub_extent(struct scrub_dev *sdev, u64 logical, u64 len,

  			u64 physical, u64 flags, u64 gen, int mirror_num)

  {
  	int ret;
  	u8 csum[BTRFS_CSUM_SIZE];
  
  	while (len) {
  		u64 l = min_t(u64, len, PAGE_SIZE);
  		int have_csum = 0;
  
  		if (flags & BTRFS_EXTENT_FLAG_DATA) {
  			/* push csums to sbio */
  			have_csum = scrub_find_csum(sdev, logical, l, csum);
  			if (have_csum == 0)
  				++sdev->stat.no_csum;
  		}
  		ret = scrub_page(sdev, logical, l, physical, flags, gen,
  				 mirror_num, have_csum ? csum : NULL, 0);
  		if (ret)
  			return ret;
  		len -= l;
  		logical += l;
  		physical += l;
  	}
  	return 0;
  }
  
  static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
  	struct map_lookup *map, int num, u64 base, u64 length)
  {
  	struct btrfs_path *path;
  	struct btrfs_fs_info *fs_info = sdev->dev->dev_root->fs_info;
  	struct btrfs_root *root = fs_info->extent_root;
  	struct btrfs_root *csum_root = fs_info->csum_root;
  	struct btrfs_extent_item *extent;

  	struct blk_plug plug;

  	u64 flags;
  	int ret;
  	int slot;
  	int i;
  	u64 nstripes;

  	struct extent_buffer *l;
  	struct btrfs_key key;
  	u64 physical;
  	u64 logical;
  	u64 generation;

  	int mirror_num;

  	struct reada_control *reada1;
  	struct reada_control *reada2;
  	struct btrfs_key key_start;
  	struct btrfs_key key_end;

  
  	u64 increment = map->stripe_len;
  	u64 offset;
  
  	nstripes = length;
  	offset = 0;
  	do_div(nstripes, map->stripe_len);
  	if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
  		offset = map->stripe_len * num;
  		increment = map->stripe_len * map->num_stripes;

  		mirror_num = 1;

  	} else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
  		int factor = map->num_stripes / map->sub_stripes;
  		offset = map->stripe_len * (num / map->sub_stripes);
  		increment = map->stripe_len * factor;

  		mirror_num = num % map->sub_stripes + 1;

  	} else if (map->type & BTRFS_BLOCK_GROUP_RAID1) {
  		increment = map->stripe_len;

  		mirror_num = num % map->num_stripes + 1;

  	} else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
  		increment = map->stripe_len;

  		mirror_num = num % map->num_stripes + 1;

  	} else {
  		increment = map->stripe_len;

  		mirror_num = 1;

  	}
  
  	path = btrfs_alloc_path();
  	if (!path)
  		return -ENOMEM;

  	path->search_commit_root = 1;
  	path->skip_locking = 1;
  
  	/*

  	 * trigger the readahead for extent tree csum tree and wait for
  	 * completion. During readahead, the scrub is officially paused
  	 * to not hold off transaction commits

  	 */
  	logical = base + offset;

  	wait_event(sdev->list_wait,
  		   atomic_read(&sdev->in_flight) == 0);
  	atomic_inc(&fs_info->scrubs_paused);
  	wake_up(&fs_info->scrub_pause_wait);
  
  	/* FIXME it might be better to start readahead at commit root */
  	key_start.objectid = logical;
  	key_start.type = BTRFS_EXTENT_ITEM_KEY;
  	key_start.offset = (u64)0;
  	key_end.objectid = base + offset + nstripes * increment;
  	key_end.type = BTRFS_EXTENT_ITEM_KEY;
  	key_end.offset = (u64)0;
  	reada1 = btrfs_reada_add(root, &key_start, &key_end);
  
  	key_start.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
  	key_start.type = BTRFS_EXTENT_CSUM_KEY;
  	key_start.offset = logical;
  	key_end.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
  	key_end.type = BTRFS_EXTENT_CSUM_KEY;
  	key_end.offset = base + offset + nstripes * increment;
  	reada2 = btrfs_reada_add(csum_root, &key_start, &key_end);
  
  	if (!IS_ERR(reada1))
  		btrfs_reada_wait(reada1);
  	if (!IS_ERR(reada2))
  		btrfs_reada_wait(reada2);
  
  	mutex_lock(&fs_info->scrub_lock);
  	while (atomic_read(&fs_info->scrub_pause_req)) {
  		mutex_unlock(&fs_info->scrub_lock);
  		wait_event(fs_info->scrub_pause_wait,
  		   atomic_read(&fs_info->scrub_pause_req) == 0);
  		mutex_lock(&fs_info->scrub_lock);

  	}

  	atomic_dec(&fs_info->scrubs_paused);
  	mutex_unlock(&fs_info->scrub_lock);
  	wake_up(&fs_info->scrub_pause_wait);

  
  	/*
  	 * collect all data csums for the stripe to avoid seeking during
  	 * the scrub. This might currently (crc32) end up to be about 1MB
  	 */

  	blk_start_plug(&plug);

  	/*
  	 * now find all extents for each stripe and scrub them
  	 */

  	logical = base + offset;
  	physical = map->stripes[num].physical;

  	ret = 0;

  	for (i = 0; i < nstripes; ++i) {

  		/*
  		 * canceled?
  		 */
  		if (atomic_read(&fs_info->scrub_cancel_req) ||
  		    atomic_read(&sdev->cancel_req)) {
  			ret = -ECANCELED;
  			goto out;
  		}
  		/*
  		 * check to see if we have to pause
  		 */
  		if (atomic_read(&fs_info->scrub_pause_req)) {
  			/* push queued extents */
  			scrub_submit(sdev);
  			wait_event(sdev->list_wait,
  				   atomic_read(&sdev->in_flight) == 0);
  			atomic_inc(&fs_info->scrubs_paused);
  			wake_up(&fs_info->scrub_pause_wait);
  			mutex_lock(&fs_info->scrub_lock);
  			while (atomic_read(&fs_info->scrub_pause_req)) {
  				mutex_unlock(&fs_info->scrub_lock);
  				wait_event(fs_info->scrub_pause_wait,
  				   atomic_read(&fs_info->scrub_pause_req) == 0);
  				mutex_lock(&fs_info->scrub_lock);
  			}
  			atomic_dec(&fs_info->scrubs_paused);
  			mutex_unlock(&fs_info->scrub_lock);
  			wake_up(&fs_info->scrub_pause_wait);

  		}

  		ret = btrfs_lookup_csums_range(csum_root, logical,
  					       logical + map->stripe_len - 1,
  					       &sdev->csum_list, 1);
  		if (ret)
  			goto out;

  		key.objectid = logical;
  		key.type = BTRFS_EXTENT_ITEM_KEY;
  		key.offset = (u64)0;
  
  		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
  		if (ret < 0)
  			goto out;

  		if (ret > 0) {

  			ret = btrfs_previous_item(root, path, 0,
  						  BTRFS_EXTENT_ITEM_KEY);
  			if (ret < 0)
  				goto out;

  			if (ret > 0) {
  				/* there's no smaller item, so stick with the
  				 * larger one */
  				btrfs_release_path(path);
  				ret = btrfs_search_slot(NULL, root, &key,
  							path, 0, 0);
  				if (ret < 0)
  					goto out;
  			}

  		}
  
  		while (1) {
  			l = path->nodes[0];
  			slot = path->slots[0];
  			if (slot >= btrfs_header_nritems(l)) {
  				ret = btrfs_next_leaf(root, path);
  				if (ret == 0)
  					continue;
  				if (ret < 0)
  					goto out;
  
  				break;
  			}
  			btrfs_item_key_to_cpu(l, &key, slot);
  
  			if (key.objectid + key.offset <= logical)
  				goto next;
  
  			if (key.objectid >= logical + map->stripe_len)
  				break;
  
  			if (btrfs_key_type(&key) != BTRFS_EXTENT_ITEM_KEY)
  				goto next;
  
  			extent = btrfs_item_ptr(l, slot,
  						struct btrfs_extent_item);
  			flags = btrfs_extent_flags(l, extent);
  			generation = btrfs_extent_generation(l, extent);
  
  			if (key.objectid < logical &&
  			    (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)) {
  				printk(KERN_ERR
  				       "btrfs scrub: tree block %llu spanning "
  				       "stripes, ignored. logical=%llu
  ",
  				       (unsigned long long)key.objectid,
  				       (unsigned long long)logical);
  				goto next;
  			}
  
  			/*
  			 * trim extent to this stripe
  			 */
  			if (key.objectid < logical) {
  				key.offset -= logical - key.objectid;
  				key.objectid = logical;
  			}
  			if (key.objectid + key.offset >
  			    logical + map->stripe_len) {
  				key.offset = logical + map->stripe_len -
  					     key.objectid;
  			}
  
  			ret = scrub_extent(sdev, key.objectid, key.offset,
  					   key.objectid - logical + physical,
  					   flags, generation, mirror_num);
  			if (ret)
  				goto out;
  
  next:
  			path->slots[0]++;
  		}

  		btrfs_release_path(path);

  		logical += increment;
  		physical += map->stripe_len;
  		spin_lock(&sdev->stat_lock);
  		sdev->stat.last_physical = physical;
  		spin_unlock(&sdev->stat_lock);
  	}
  	/* push queued extents */
  	scrub_submit(sdev);
  
  out:

  	blk_finish_plug(&plug);

  	btrfs_free_path(path);
  	return ret < 0 ? ret : 0;
  }
  
  static noinline_for_stack int scrub_chunk(struct scrub_dev *sdev,
  	u64 chunk_tree, u64 chunk_objectid, u64 chunk_offset, u64 length)
  {
  	struct btrfs_mapping_tree *map_tree =
  		&sdev->dev->dev_root->fs_info->mapping_tree;
  	struct map_lookup *map;
  	struct extent_map *em;
  	int i;
  	int ret = -EINVAL;
  
  	read_lock(&map_tree->map_tree.lock);
  	em = lookup_extent_mapping(&map_tree->map_tree, chunk_offset, 1);
  	read_unlock(&map_tree->map_tree.lock);
  
  	if (!em)
  		return -EINVAL;
  
  	map = (struct map_lookup *)em->bdev;
  	if (em->start != chunk_offset)
  		goto out;
  
  	if (em->len < length)
  		goto out;
  
  	for (i = 0; i < map->num_stripes; ++i) {
  		if (map->stripes[i].dev == sdev->dev) {
  			ret = scrub_stripe(sdev, map, i, chunk_offset, length);
  			if (ret)
  				goto out;
  		}
  	}
  out:
  	free_extent_map(em);
  
  	return ret;
  }
  
  static noinline_for_stack
  int scrub_enumerate_chunks(struct scrub_dev *sdev, u64 start, u64 end)
  {
  	struct btrfs_dev_extent *dev_extent = NULL;
  	struct btrfs_path *path;
  	struct btrfs_root *root = sdev->dev->dev_root;
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	u64 length;
  	u64 chunk_tree;
  	u64 chunk_objectid;
  	u64 chunk_offset;
  	int ret;
  	int slot;
  	struct extent_buffer *l;
  	struct btrfs_key key;
  	struct btrfs_key found_key;
  	struct btrfs_block_group_cache *cache;
  
  	path = btrfs_alloc_path();
  	if (!path)
  		return -ENOMEM;
  
  	path->reada = 2;
  	path->search_commit_root = 1;
  	path->skip_locking = 1;
  
  	key.objectid = sdev->dev->devid;
  	key.offset = 0ull;
  	key.type = BTRFS_DEV_EXTENT_KEY;
  
  
  	while (1) {
  		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
  		if (ret < 0)

  			break;
  		if (ret > 0) {
  			if (path->slots[0] >=
  			    btrfs_header_nritems(path->nodes[0])) {
  				ret = btrfs_next_leaf(root, path);
  				if (ret)
  					break;
  			}
  		}

  
  		l = path->nodes[0];
  		slot = path->slots[0];
  
  		btrfs_item_key_to_cpu(l, &found_key, slot);
  
  		if (found_key.objectid != sdev->dev->devid)
  			break;

  		if (btrfs_key_type(&found_key) != BTRFS_DEV_EXTENT_KEY)

  			break;
  
  		if (found_key.offset >= end)
  			break;
  
  		if (found_key.offset < key.offset)
  			break;
  
  		dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
  		length = btrfs_dev_extent_length(l, dev_extent);
  
  		if (found_key.offset + length <= start) {
  			key.offset = found_key.offset + length;

  			btrfs_release_path(path);

  			continue;
  		}
  
  		chunk_tree = btrfs_dev_extent_chunk_tree(l, dev_extent);
  		chunk_objectid = btrfs_dev_extent_chunk_objectid(l, dev_extent);
  		chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);
  
  		/*
  		 * get a reference on the corresponding block group to prevent
  		 * the chunk from going away while we scrub it
  		 */
  		cache = btrfs_lookup_block_group(fs_info, chunk_offset);
  		if (!cache) {
  			ret = -ENOENT;

  			break;

  		}
  		ret = scrub_chunk(sdev, chunk_tree, chunk_objectid,
  				  chunk_offset, length);
  		btrfs_put_block_group(cache);
  		if (ret)
  			break;
  
  		key.offset = found_key.offset + length;

  		btrfs_release_path(path);

  	}

  	btrfs_free_path(path);

  
  	/*
  	 * ret can still be 1 from search_slot or next_leaf,
  	 * that's not an error
  	 */
  	return ret < 0 ? ret : 0;

  }
  
  static noinline_for_stack int scrub_supers(struct scrub_dev *sdev)
  {
  	int	i;
  	u64	bytenr;
  	u64	gen;
  	int	ret;
  	struct btrfs_device *device = sdev->dev;
  	struct btrfs_root *root = device->dev_root;
  
  	gen = root->fs_info->last_trans_committed;
  
  	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
  		bytenr = btrfs_sb_offset(i);
  		if (bytenr + BTRFS_SUPER_INFO_SIZE >= device->total_bytes)
  			break;
  
  		ret = scrub_page(sdev, bytenr, PAGE_SIZE, bytenr,
  				 BTRFS_EXTENT_FLAG_SUPER, gen, i, NULL, 1);
  		if (ret)
  			return ret;
  	}
  	wait_event(sdev->list_wait, atomic_read(&sdev->in_flight) == 0);
  
  	return 0;
  }
  
  /*
   * get a reference count on fs_info->scrub_workers. start worker if necessary
   */
  static noinline_for_stack int scrub_workers_get(struct btrfs_root *root)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;

  	int ret = 0;

  
  	mutex_lock(&fs_info->scrub_lock);

  	if (fs_info->scrub_workers_refcnt == 0) {
  		btrfs_init_workers(&fs_info->scrub_workers, "scrub",
  			   fs_info->thread_pool_size, &fs_info->generic_worker);
  		fs_info->scrub_workers.idle_thresh = 4;

  		ret = btrfs_start_workers(&fs_info->scrub_workers);
  		if (ret)
  			goto out;

  	}

  	++fs_info->scrub_workers_refcnt;

  out:

  	mutex_unlock(&fs_info->scrub_lock);

  	return ret;

  }
  
  static noinline_for_stack void scrub_workers_put(struct btrfs_root *root)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  
  	mutex_lock(&fs_info->scrub_lock);
  	if (--fs_info->scrub_workers_refcnt == 0)
  		btrfs_stop_workers(&fs_info->scrub_workers);
  	WARN_ON(fs_info->scrub_workers_refcnt < 0);
  	mutex_unlock(&fs_info->scrub_lock);
  }
  
  
  int btrfs_scrub_dev(struct btrfs_root *root, u64 devid, u64 start, u64 end,

  		    struct btrfs_scrub_progress *progress, int readonly)

  {
  	struct scrub_dev *sdev;
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	int ret;
  	struct btrfs_device *dev;

  	if (btrfs_fs_closing(root->fs_info))

  		return -EINVAL;
  
  	/*
  	 * check some assumptions
  	 */
  	if (root->sectorsize != PAGE_SIZE ||
  	    root->sectorsize != root->leafsize ||
  	    root->sectorsize != root->nodesize) {
  		printk(KERN_ERR "btrfs_scrub: size assumptions fail
  ");
  		return -EINVAL;
  	}
  
  	ret = scrub_workers_get(root);
  	if (ret)
  		return ret;
  
  	mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
  	dev = btrfs_find_device(root, devid, NULL, NULL);
  	if (!dev || dev->missing) {
  		mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
  		scrub_workers_put(root);
  		return -ENODEV;
  	}
  	mutex_lock(&fs_info->scrub_lock);
  
  	if (!dev->in_fs_metadata) {
  		mutex_unlock(&fs_info->scrub_lock);
  		mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
  		scrub_workers_put(root);
  		return -ENODEV;
  	}
  
  	if (dev->scrub_device) {
  		mutex_unlock(&fs_info->scrub_lock);
  		mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
  		scrub_workers_put(root);
  		return -EINPROGRESS;
  	}
  	sdev = scrub_setup_dev(dev);
  	if (IS_ERR(sdev)) {
  		mutex_unlock(&fs_info->scrub_lock);
  		mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
  		scrub_workers_put(root);
  		return PTR_ERR(sdev);
  	}

  	sdev->readonly = readonly;

  	dev->scrub_device = sdev;
  
  	atomic_inc(&fs_info->scrubs_running);
  	mutex_unlock(&fs_info->scrub_lock);
  	mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
  
  	down_read(&fs_info->scrub_super_lock);
  	ret = scrub_supers(sdev);
  	up_read(&fs_info->scrub_super_lock);
  
  	if (!ret)
  		ret = scrub_enumerate_chunks(sdev, start, end);
  
  	wait_event(sdev->list_wait, atomic_read(&sdev->in_flight) == 0);

  	atomic_dec(&fs_info->scrubs_running);
  	wake_up(&fs_info->scrub_pause_wait);

  	wait_event(sdev->list_wait, atomic_read(&sdev->fixup_cnt) == 0);

  	if (progress)
  		memcpy(progress, &sdev->stat, sizeof(*progress));
  
  	mutex_lock(&fs_info->scrub_lock);
  	dev->scrub_device = NULL;
  	mutex_unlock(&fs_info->scrub_lock);
  
  	scrub_free_dev(sdev);
  	scrub_workers_put(root);
  
  	return ret;
  }
  
  int btrfs_scrub_pause(struct btrfs_root *root)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  
  	mutex_lock(&fs_info->scrub_lock);
  	atomic_inc(&fs_info->scrub_pause_req);
  	while (atomic_read(&fs_info->scrubs_paused) !=
  	       atomic_read(&fs_info->scrubs_running)) {
  		mutex_unlock(&fs_info->scrub_lock);
  		wait_event(fs_info->scrub_pause_wait,
  			   atomic_read(&fs_info->scrubs_paused) ==
  			   atomic_read(&fs_info->scrubs_running));
  		mutex_lock(&fs_info->scrub_lock);
  	}
  	mutex_unlock(&fs_info->scrub_lock);
  
  	return 0;
  }
  
  int btrfs_scrub_continue(struct btrfs_root *root)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  
  	atomic_dec(&fs_info->scrub_pause_req);
  	wake_up(&fs_info->scrub_pause_wait);
  	return 0;
  }
  
  int btrfs_scrub_pause_super(struct btrfs_root *root)
  {
  	down_write(&root->fs_info->scrub_super_lock);
  	return 0;
  }
  
  int btrfs_scrub_continue_super(struct btrfs_root *root)
  {
  	up_write(&root->fs_info->scrub_super_lock);
  	return 0;
  }
  
  int btrfs_scrub_cancel(struct btrfs_root *root)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  
  	mutex_lock(&fs_info->scrub_lock);
  	if (!atomic_read(&fs_info->scrubs_running)) {
  		mutex_unlock(&fs_info->scrub_lock);
  		return -ENOTCONN;
  	}
  
  	atomic_inc(&fs_info->scrub_cancel_req);
  	while (atomic_read(&fs_info->scrubs_running)) {
  		mutex_unlock(&fs_info->scrub_lock);
  		wait_event(fs_info->scrub_pause_wait,
  			   atomic_read(&fs_info->scrubs_running) == 0);
  		mutex_lock(&fs_info->scrub_lock);
  	}
  	atomic_dec(&fs_info->scrub_cancel_req);
  	mutex_unlock(&fs_info->scrub_lock);
  
  	return 0;
  }
  
  int btrfs_scrub_cancel_dev(struct btrfs_root *root, struct btrfs_device *dev)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	struct scrub_dev *sdev;
  
  	mutex_lock(&fs_info->scrub_lock);
  	sdev = dev->scrub_device;
  	if (!sdev) {
  		mutex_unlock(&fs_info->scrub_lock);
  		return -ENOTCONN;
  	}
  	atomic_inc(&sdev->cancel_req);
  	while (dev->scrub_device) {
  		mutex_unlock(&fs_info->scrub_lock);
  		wait_event(fs_info->scrub_pause_wait,
  			   dev->scrub_device == NULL);
  		mutex_lock(&fs_info->scrub_lock);
  	}
  	mutex_unlock(&fs_info->scrub_lock);
  
  	return 0;
  }
  int btrfs_scrub_cancel_devid(struct btrfs_root *root, u64 devid)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	struct btrfs_device *dev;
  	int ret;
  
  	/*
  	 * we have to hold the device_list_mutex here so the device
  	 * does not go away in cancel_dev. FIXME: find a better solution
  	 */
  	mutex_lock(&fs_info->fs_devices->device_list_mutex);
  	dev = btrfs_find_device(root, devid, NULL, NULL);
  	if (!dev) {
  		mutex_unlock(&fs_info->fs_devices->device_list_mutex);
  		return -ENODEV;
  	}
  	ret = btrfs_scrub_cancel_dev(root, dev);
  	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
  
  	return ret;
  }
  
  int btrfs_scrub_progress(struct btrfs_root *root, u64 devid,
  			 struct btrfs_scrub_progress *progress)
  {
  	struct btrfs_device *dev;
  	struct scrub_dev *sdev = NULL;
  
  	mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
  	dev = btrfs_find_device(root, devid, NULL, NULL);
  	if (dev)
  		sdev = dev->scrub_device;
  	if (sdev)
  		memcpy(progress, &sdev->stat, sizeof(*progress));
  	mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
  
  	return dev ? (sdev ? 0 : -ENOTCONN) : -ENODEV;
  }