diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index a8411c2..9b72dcf 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -7,4 +7,4 @@
 	   extent_map.o sysfs.o struct-funcs.o xattr.o ordered-data.o \
 	   extent_io.o volumes.o async-thread.o ioctl.o locking.o orphan.o \
 	   export.o tree-log.o acl.o free-space-cache.o zlib.o lzo.o \
-	   compression.o delayed-ref.o relocation.o delayed-inode.o
+	   compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e7d4079..0d50c57 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -23,6 +23,7 @@
 #include <linux/mm.h>
 #include <linux/highmem.h>
 #include <linux/fs.h>
+#include <linux/rwsem.h>
 #include <linux/completion.h>
 #include <linux/backing-dev.h>
 #include <linux/wait.h>
@@ -33,6 +34,7 @@
 #include "extent_io.h"
 #include "extent_map.h"
 #include "async-thread.h"
+#include "ioctl.h"
 
 struct btrfs_trans_handle;
 struct btrfs_transaction;
@@ -193,7 +195,6 @@
 	struct extent_map_tree map_tree;
 };
 
-#define BTRFS_UUID_SIZE 16
 struct btrfs_dev_item {
 	/* the internal btrfs device id */
 	__le64 devid;
@@ -300,7 +301,6 @@
 		sizeof(struct btrfs_stripe) * (num_stripes - 1);
 }
 
-#define BTRFS_FSID_SIZE 16
 #define BTRFS_HEADER_FLAG_WRITTEN	(1ULL << 0)
 #define BTRFS_HEADER_FLAG_RELOC		(1ULL << 1)
 
@@ -516,6 +516,12 @@
 /* use full backrefs for extent pointers in the block */
 #define BTRFS_BLOCK_FLAG_FULL_BACKREF	(1ULL << 8)
 
+/*
+ * this flag is only used internally by scrub and may be changed at any time
+ * it is only declared here to avoid collisions
+ */
+#define BTRFS_EXTENT_FLAG_SUPER		(1ULL << 48)
+
 struct btrfs_tree_block_info {
 	struct btrfs_disk_key key;
 	u8 level;
@@ -1083,6 +1089,17 @@
 
 	void *bdev_holder;
 
+	/* private scrub information */
+	struct mutex scrub_lock;
+	atomic_t scrubs_running;
+	atomic_t scrub_pause_req;
+	atomic_t scrubs_paused;
+	atomic_t scrub_cancel_req;
+	wait_queue_head_t scrub_pause_wait;
+	struct rw_semaphore scrub_super_lock;
+	int scrub_workers_refcnt;
+	struct btrfs_workers scrub_workers;
+
 	/* filesystem state */
 	u64 fs_state;
 
@@ -2422,8 +2439,11 @@
 					  struct btrfs_root *root,
 					  struct btrfs_path *path,
 					  u64 bytenr, int cow);
-int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start,
-			     u64 end, struct list_head *list);
+int btrfs_csum_truncate(struct btrfs_trans_handle *trans,
+			struct btrfs_root *root, struct btrfs_path *path,
+			u64 isize);
+int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
+			     struct list_head *list, int search_commit);
 /* inode.c */
 
 /* RHEL and EL kernels have a patch that renames PG_checked to FsMisc */
@@ -2577,4 +2597,18 @@
 			      u64 *bytes_to_reserve);
 void btrfs_reloc_post_snapshot(struct btrfs_trans_handle *trans,
 			      struct btrfs_pending_snapshot *pending);
+
+/* scrub.c */
+int btrfs_scrub_dev(struct btrfs_root *root, u64 devid, u64 start, u64 end,
+		    struct btrfs_scrub_progress *progress, int readonly);
+int btrfs_scrub_pause(struct btrfs_root *root);
+int btrfs_scrub_pause_super(struct btrfs_root *root);
+int btrfs_scrub_continue(struct btrfs_root *root);
+int btrfs_scrub_continue_super(struct btrfs_root *root);
+int btrfs_scrub_cancel(struct btrfs_root *root);
+int btrfs_scrub_cancel_dev(struct btrfs_root *root, struct btrfs_device *dev);
+int btrfs_scrub_cancel_devid(struct btrfs_root *root, u64 devid);
+int btrfs_scrub_progress(struct btrfs_root *root, u64 devid,
+			 struct btrfs_scrub_progress *progress);
+
 #endif
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a2eb3a3..29a2475 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1654,6 +1654,17 @@
 	}
 	btrfs_init_delayed_root(fs_info->delayed_root);
 
+	mutex_init(&fs_info->scrub_lock);
+	atomic_set(&fs_info->scrubs_running, 0);
+	atomic_set(&fs_info->scrub_pause_req, 0);
+	atomic_set(&fs_info->scrubs_paused, 0);
+	atomic_set(&fs_info->scrub_cancel_req, 0);
+	init_waitqueue_head(&fs_info->scrub_pause_wait);
+	init_rwsem(&fs_info->scrub_super_lock);
+	fs_info->scrub_workers_refcnt = 0;
+	btrfs_init_workers(&fs_info->scrub_workers, "scrub",
+			   fs_info->thread_pool_size, &fs_info->generic_worker);
+
 	sb->s_blocksize = 4096;
 	sb->s_blocksize_bits = blksize_bits(4096);
 	sb->s_bdi = &fs_info->bdi;
@@ -2488,6 +2499,7 @@
 	fs_info->closing = 1;
 	smp_mb();
 
+	btrfs_scrub_cancel(root);
 	btrfs_put_block_group_cache(fs_info);
 
 	/*
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 29e0149..b437cc7 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -267,7 +267,7 @@
 }
 
 int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
-			     struct list_head *list)
+			     struct list_head *list, int search_commit)
 {
 	struct btrfs_key key;
 	struct btrfs_path *path;
@@ -284,6 +284,12 @@
 	path = btrfs_alloc_path();
 	BUG_ON(!path);
 
+	if (search_commit) {
+		path->skip_locking = 1;
+		path->reada = 2;
+		path->search_commit_root = 1;
+	}
+
 	key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
 	key.offset = start;
 	key.type = BTRFS_EXTENT_CSUM_KEY;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8ae72c3..4d8ef95 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1019,7 +1019,7 @@
 	LIST_HEAD(list);
 
 	ret = btrfs_lookup_csums_range(root->fs_info->csum_root, bytenr,
-				       bytenr + num_bytes - 1, &list);
+				       bytenr + num_bytes - 1, &list, 0);
 	if (ret == 0 && list_empty(&list))
 		return 0;
 
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index ed8c055..e0a061d 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1809,6 +1809,75 @@
 	return ret;
 }
 
+static long btrfs_ioctl_fs_info(struct btrfs_root *root, void __user *arg)
+{
+	struct btrfs_ioctl_fs_info_args fi_args;
+	struct btrfs_device *device;
+	struct btrfs_device *next;
+	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	fi_args.num_devices = fs_devices->num_devices;
+	fi_args.max_id = 0;
+	memcpy(&fi_args.fsid, root->fs_info->fsid, sizeof(fi_args.fsid));
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
+		if (device->devid > fi_args.max_id)
+			fi_args.max_id = device->devid;
+	}
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	if (copy_to_user(arg, &fi_args, sizeof(fi_args)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static long btrfs_ioctl_dev_info(struct btrfs_root *root, void __user *arg)
+{
+	struct btrfs_ioctl_dev_info_args *di_args;
+	struct btrfs_device *dev;
+	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
+	int ret = 0;
+	char *s_uuid = NULL;
+	char empty_uuid[BTRFS_UUID_SIZE] = {0};
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	di_args = memdup_user(arg, sizeof(*di_args));
+	if (IS_ERR(di_args))
+		return PTR_ERR(di_args);
+
+	if (memcmp(empty_uuid, di_args->uuid, BTRFS_UUID_SIZE) != 0)
+		s_uuid = di_args->uuid;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	dev = btrfs_find_device(root, di_args->devid, s_uuid, NULL);
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	if (!dev) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	di_args->devid = dev->devid;
+	di_args->bytes_used = dev->bytes_used;
+	di_args->total_bytes = dev->total_bytes;
+	memcpy(di_args->uuid, dev->uuid, sizeof(di_args->uuid));
+	strncpy(di_args->path, dev->name, sizeof(di_args->path));
+
+out:
+	if (ret == 0 && copy_to_user(arg, di_args, sizeof(*di_args)))
+		ret = -EFAULT;
+
+	kfree(di_args);
+	return ret;
+}
+
 static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 				       u64 off, u64 olen, u64 destoff)
 {
@@ -2471,6 +2540,58 @@
 	return btrfs_wait_for_commit(root, transid);
 }
 
+static long btrfs_ioctl_scrub(struct btrfs_root *root, void __user *arg)
+{
+	int ret;
+	struct btrfs_ioctl_scrub_args *sa;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	sa = memdup_user(arg, sizeof(*sa));
+	if (IS_ERR(sa))
+		return PTR_ERR(sa);
+
+	ret = btrfs_scrub_dev(root, sa->devid, sa->start, sa->end,
+			      &sa->progress, sa->flags & BTRFS_SCRUB_READONLY);
+
+	if (copy_to_user(arg, sa, sizeof(*sa)))
+		ret = -EFAULT;
+
+	kfree(sa);
+	return ret;
+}
+
+static long btrfs_ioctl_scrub_cancel(struct btrfs_root *root, void __user *arg)
+{
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	return btrfs_scrub_cancel(root);
+}
+
+static long btrfs_ioctl_scrub_progress(struct btrfs_root *root,
+				       void __user *arg)
+{
+	struct btrfs_ioctl_scrub_args *sa;
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	sa = memdup_user(arg, sizeof(*sa));
+	if (IS_ERR(sa))
+		return PTR_ERR(sa);
+
+	ret = btrfs_scrub_progress(root, sa->devid, &sa->progress);
+
+	if (copy_to_user(arg, sa, sizeof(*sa)))
+		ret = -EFAULT;
+
+	kfree(sa);
+	return ret;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {
@@ -2510,6 +2631,10 @@
 		return btrfs_ioctl_add_dev(root, argp);
 	case BTRFS_IOC_RM_DEV:
 		return btrfs_ioctl_rm_dev(root, argp);
+	case BTRFS_IOC_FS_INFO:
+		return btrfs_ioctl_fs_info(root, argp);
+	case BTRFS_IOC_DEV_INFO:
+		return btrfs_ioctl_dev_info(root, argp);
 	case BTRFS_IOC_BALANCE:
 		return btrfs_balance(root->fs_info->dev_root);
 	case BTRFS_IOC_CLONE:
@@ -2533,6 +2658,12 @@
 		return btrfs_ioctl_start_sync(file, argp);
 	case BTRFS_IOC_WAIT_SYNC:
 		return btrfs_ioctl_wait_sync(file, argp);
+	case BTRFS_IOC_SCRUB:
+		return btrfs_ioctl_scrub(root, argp);
+	case BTRFS_IOC_SCRUB_CANCEL:
+		return btrfs_ioctl_scrub_cancel(root, argp);
+	case BTRFS_IOC_SCRUB_PROGRESS:
+		return btrfs_ioctl_scrub_progress(root, argp);
 	}
 
 	return -ENOTTY;
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index 8fb3821..e5e0ee2 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -32,6 +32,8 @@
 
 #define BTRFS_SUBVOL_CREATE_ASYNC	(1ULL << 0)
 #define BTRFS_SUBVOL_RDONLY		(1ULL << 1)
+#define BTRFS_FSID_SIZE 16
+#define BTRFS_UUID_SIZE 16
 
 #define BTRFS_SUBVOL_NAME_MAX 4039
 struct btrfs_ioctl_vol_args_v2 {
@@ -42,6 +44,71 @@
 	char name[BTRFS_SUBVOL_NAME_MAX + 1];
 };
 
+/*
+ * structure to report errors and progress to userspace, either as a
+ * result of a finished scrub, a canceled scrub or a progress inquiry
+ */
+struct btrfs_scrub_progress {
+	__u64 data_extents_scrubbed;	/* # of data extents scrubbed */
+	__u64 tree_extents_scrubbed;	/* # of tree extents scrubbed */
+	__u64 data_bytes_scrubbed;	/* # of data bytes scrubbed */
+	__u64 tree_bytes_scrubbed;	/* # of tree bytes scrubbed */
+	__u64 read_errors;		/* # of read errors encountered (EIO) */
+	__u64 csum_errors;		/* # of failed csum checks */
+	__u64 verify_errors;		/* # of occurences, where the metadata
+					 * of a tree block did not match the
+					 * expected values, like generation or
+					 * logical */
+	__u64 no_csum;			/* # of 4k data block for which no csum
+					 * is present, probably the result of
+					 * data written with nodatasum */
+	__u64 csum_discards;		/* # of csum for which no data was found
+					 * in the extent tree. */
+	__u64 super_errors;		/* # of bad super blocks encountered */
+	__u64 malloc_errors;		/* # of internal kmalloc errors. These
+					 * will likely cause an incomplete
+					 * scrub */
+	__u64 uncorrectable_errors;	/* # of errors where either no intact
+					 * copy was found or the writeback
+					 * failed */
+	__u64 corrected_errors;		/* # of errors corrected */
+	__u64 last_physical;		/* last physical address scrubbed. In
+					 * case a scrub was aborted, this can
+					 * be used to restart the scrub */
+	__u64 unverified_errors;	/* # of occurences where a read for a
+					 * full (64k) bio failed, but the re-
+					 * check succeeded for each 4k piece.
+					 * Intermittent error. */
+};
+
+#define BTRFS_SCRUB_READONLY	1
+struct btrfs_ioctl_scrub_args {
+	__u64 devid;				/* in */
+	__u64 start;				/* in */
+	__u64 end;				/* in */
+	__u64 flags;				/* in */
+	struct btrfs_scrub_progress progress;	/* out */
+	/* pad to 1k */
+	__u64 unused[(1024-32-sizeof(struct btrfs_scrub_progress))/8];
+};
+
+#define BTRFS_DEVICE_PATH_NAME_MAX 1024
+struct btrfs_ioctl_dev_info_args {
+	__u64 devid;				/* in/out */
+	__u8 uuid[BTRFS_UUID_SIZE];		/* in/out */
+	__u64 bytes_used;			/* out */
+	__u64 total_bytes;			/* out */
+	__u64 unused[379];			/* pad to 4k */
+	__u8 path[BTRFS_DEVICE_PATH_NAME_MAX];	/* out */
+};
+
+struct btrfs_ioctl_fs_info_args {
+	__u64 max_id;				/* out */
+	__u64 num_devices;			/* out */
+	__u8 fsid[BTRFS_FSID_SIZE];		/* out */
+	__u64 reserved[124];			/* pad to 1k */
+};
+
 #define BTRFS_INO_LOOKUP_PATH_MAX 4080
 struct btrfs_ioctl_ino_lookup_args {
 	__u64 treeid;
@@ -203,4 +270,13 @@
 				   struct btrfs_ioctl_vol_args_v2)
 #define BTRFS_IOC_SUBVOL_GETFLAGS _IOW(BTRFS_IOCTL_MAGIC, 25, __u64)
 #define BTRFS_IOC_SUBVOL_SETFLAGS _IOW(BTRFS_IOCTL_MAGIC, 26, __u64)
+#define BTRFS_IOC_SCRUB _IOWR(BTRFS_IOCTL_MAGIC, 27, \
+			      struct btrfs_ioctl_scrub_args)
+#define BTRFS_IOC_SCRUB_CANCEL _IO(BTRFS_IOCTL_MAGIC, 28)
+#define BTRFS_IOC_SCRUB_PROGRESS _IOWR(BTRFS_IOCTL_MAGIC, 29, \
+				       struct btrfs_ioctl_scrub_args)
+#define BTRFS_IOC_DEV_INFO _IOWR(BTRFS_IOCTL_MAGIC, 30, \
+				 struct btrfs_ioctl_dev_info_args)
+#define BTRFS_IOC_FS_INFO _IOR(BTRFS_IOCTL_MAGIC, 31, \
+			       struct btrfs_ioctl_fs_info_args)
 #endif
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 051992c..fa2c5d8 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4245,7 +4245,7 @@
 
 	disk_bytenr = file_pos + BTRFS_I(inode)->index_cnt;
 	ret = btrfs_lookup_csums_range(root->fs_info->csum_root, disk_bytenr,
-				       disk_bytenr + len - 1, &list);
+				       disk_bytenr + len - 1, &list, 0);
 
 	while (!list_empty(&list)) {
 		sums = list_entry(list.next, struct btrfs_ordered_sum, list);
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
new file mode 100644
index 0000000..87a2f12
--- /dev/null
+++ b/fs/btrfs/scrub.c
@@ -0,0 +1,1368 @@
+/*
+ * 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/sched.h>
+#include <linux/pagemap.h>
+#include <linux/writeback.h>
+#include <linux/blkdev.h>
+#include <linux/rbtree.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+#include "ctree.h"
+#include "volumes.h"
+#include "disk-io.h"
+#include "ordered-data.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:
+ *  - To enhance the performance, better read-ahead strategies for the
+ *    extent-tree can be employed.
+ *  - 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
+ *  - make the prefetch cancellable
+ */
+
+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;
+	u64			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;
+	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;
+};
+
+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 noinline_for_stack void scrub_free_dev(struct scrub_dev *sdev)
+{
+	int i;
+	int j;
+	struct page *last_page;
+
+	if (!sdev)
+		return;
+
+	for (i = 0; i < SCRUB_BIOS_PER_DEV; ++i) {
+		struct scrub_bio *sbio = sdev->bios[i];
+		struct bio *bio;
+
+		if (!sbio)
+			break;
+
+		bio = sbio->bio;
+		if (bio) {
+			last_page = NULL;
+			for (j = 0; j < bio->bi_vcnt; ++j) {
+				if (bio->bi_io_vec[j].bv_page == last_page)
+					continue;
+				last_page = bio->bi_io_vec[j].bv_page;
+				__free_page(last_page);
+			}
+			bio_put(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;
+	int		j;
+	int		ret;
+	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 bio *bio;
+		struct scrub_bio *sbio;
+
+		sbio = kzalloc(sizeof(*sbio), GFP_NOFS);
+		if (!sbio)
+			goto nomem;
+		sdev->bios[i] = sbio;
+
+		bio = bio_kmalloc(GFP_NOFS, SCRUB_PAGES_PER_BIO);
+		if (!bio)
+			goto nomem;
+
+		sbio->index = i;
+		sbio->sdev = sdev;
+		sbio->bio = bio;
+		sbio->count = 0;
+		sbio->work.func = scrub_checksum;
+		bio->bi_private = sdev->bios[i];
+		bio->bi_end_io = scrub_bio_end_io;
+		bio->bi_sector = 0;
+		bio->bi_bdev = dev->bdev;
+		bio->bi_size = 0;
+
+		for (j = 0; j < SCRUB_PAGES_PER_BIO; ++j) {
+			struct page *page;
+			page = alloc_page(GFP_NOFS);
+			if (!page)
+				goto nomem;
+
+			ret = bio_add_page(bio, page, PAGE_SIZE, 0);
+			if (!ret)
+				goto nomem;
+		}
+		WARN_ON(bio->bi_vcnt != SCRUB_PAGES_PER_BIO);
+
+		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->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);
+}
+
+/*
+ * 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 void scrub_recheck_error(struct scrub_bio *sbio, int ix)
+{
+	if (sbio->err) {
+		if (scrub_fixup_io(READ, sbio->sdev->dev->bdev,
+				   (sbio->physical + ix * PAGE_SIZE) >> 9,
+				   sbio->bio->bi_io_vec[ix].bv_page) == 0) {
+			if (scrub_fixup_check(sbio, ix) == 0)
+				return;
+		}
+	}
+
+	scrub_fixup(sbio, ix);
+}
+
+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_multi_bio *multi = NULL;
+	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)) {
+		/*
+		 * nodatasum, don't try to fix anything
+		 * FIXME: we can do better, open the inode and trigger a
+		 * writeback
+		 */
+		goto uncorrectable;
+	}
+
+	length = PAGE_SIZE;
+	ret = btrfs_map_block(map_tree, REQ_WRITE, logical, &length,
+			      &multi, 0);
+	if (ret || !multi || length < PAGE_SIZE) {
+		printk(KERN_ERR
+		       "scrub_fixup: btrfs_map_block failed us for %llu\n",
+		       (unsigned long long)logical);
+		WARN_ON(1);
+		return;
+	}
+
+	if (multi->num_stripes == 1)
+		/* there aren't any replicas */
+		goto uncorrectable;
+
+	/*
+	 * first find a good copy
+	 */
+	for (i = 0; i < multi->num_stripes; ++i) {
+		if (i == sbio->spag[ix].mirror_num)
+			continue;
+
+		if (scrub_fixup_io(READ, multi->stripes[i].dev->bdev,
+				   multi->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 == multi->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(multi);
+	spin_lock(&sdev->stat_lock);
+	++sdev->stat.corrected_errors;
+	spin_unlock(&sdev->stat_lock);
+
+	if (printk_ratelimit())
+		printk(KERN_ERR "btrfs: fixed up at %llu\n",
+		       (unsigned long long)logical);
+	return;
+
+uncorrectable:
+	kfree(multi);
+	spin_lock(&sdev->stat_lock);
+	++sdev->stat.uncorrectable_errors;
+	spin_unlock(&sdev->stat_lock);
+
+	if (printk_ratelimit())
+		printk(KERN_ERR "btrfs: unable to fixup at %llu\n",
+			 (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);
+
+	/* we are going to wait on this IO */
+	rw |= REQ_SYNC;
+
+	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);
+
+	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;
+
+	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) {
+		for (i = 0; i < sbio->count; ++i)
+			scrub_recheck_error(sbio, i);
+
+		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;
+		}
+
+		spin_lock(&sdev->stat_lock);
+		++sdev->stat.read_errors;
+		spin_unlock(&sdev->stat_lock);
+		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)
+			scrub_recheck_error(sbio, i);
+	}
+
+out:
+	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->bio->bi_sector = sbio->physical >> 9;
+	sbio->bio->bi_size = sbio->count * PAGE_SIZE;
+	sbio->bio->bi_next = NULL;
+	sbio->bio->bi_flags |= 1 << BIO_UPTODATE;
+	sbio->bio->bi_comp_cpu = -1;
+	sbio->bio->bi_bdev = sdev->dev->bdev;
+	sbio->err = 0;
+	sdev->curr = -1;
+	atomic_inc(&sdev->in_flight);
+
+	submit_bio(0, sbio->bio);
+
+	return 0;
+}
+
+static int scrub_page(struct scrub_dev *sdev, u64 logical, u64 len,
+		      u64 physical, u64 flags, u64 gen, u64 mirror_num,
+		      u8 *csum, int force)
+{
+	struct scrub_bio *sbio;
+
+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) {
+		sbio->physical = physical;
+		sbio->logical = logical;
+	} else if (sbio->physical + sbio->count * PAGE_SIZE != physical) {
+		scrub_submit(sdev);
+		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;
+	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)
+		scrub_submit(sdev);
+
+	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, u64 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;
+	u64 flags;
+	int ret;
+	int slot;
+	int i;
+	u64 nstripes;
+	int start_stripe;
+	struct extent_buffer *l;
+	struct btrfs_key key;
+	u64 physical;
+	u64 logical;
+	u64 generation;
+	u64 mirror_num;
+
+	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 = 0;
+	} 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;
+	} else if (map->type & BTRFS_BLOCK_GROUP_RAID1) {
+		increment = map->stripe_len;
+		mirror_num = num % map->num_stripes;
+	} else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
+		increment = map->stripe_len;
+		mirror_num = num % map->num_stripes;
+	} else {
+		increment = map->stripe_len;
+		mirror_num = 0;
+	}
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	path->reada = 2;
+	path->search_commit_root = 1;
+	path->skip_locking = 1;
+
+	/*
+	 * find all extents for each stripe and just read them to get
+	 * them into the page cache
+	 * FIXME: we can do better. build a more intelligent prefetching
+	 */
+	logical = base + offset;
+	physical = map->stripes[num].physical;
+	ret = 0;
+	for (i = 0; i < nstripes; ++i) {
+		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;
+
+		l = path->nodes[0];
+		slot = path->slots[0];
+		btrfs_item_key_to_cpu(l, &key, slot);
+		if (key.objectid != logical) {
+			ret = btrfs_previous_item(root, path, 0,
+						  BTRFS_EXTENT_ITEM_KEY);
+			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 >= logical + map->stripe_len)
+				break;
+
+			path->slots[0]++;
+		}
+		btrfs_release_path(path);
+		logical += increment;
+		physical += map->stripe_len;
+		cond_resched();
+	}
+
+	/*
+	 * collect all data csums for the stripe to avoid seeking during
+	 * the scrub. This might currently (crc32) end up to be about 1MB
+	 */
+	start_stripe = 0;
+again:
+	logical = base + offset + start_stripe * increment;
+	for (i = start_stripe; i < nstripes; ++i) {
+		ret = btrfs_lookup_csums_range(csum_root, logical,
+					       logical + map->stripe_len - 1,
+					       &sdev->csum_list, 1);
+		if (ret)
+			goto out;
+
+		logical += increment;
+		cond_resched();
+	}
+	/*
+	 * now find all extents for each stripe and scrub them
+	 */
+	logical = base + offset + start_stripe * increment;
+	physical = map->stripes[num].physical + start_stripe * map->stripe_len;
+	ret = 0;
+	for (i = start_stripe; 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);
+			scrub_free_csums(sdev);
+			start_stripe = i;
+			goto again;
+		}
+
+		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;
+
+		l = path->nodes[0];
+		slot = path->slots[0];
+		btrfs_item_key_to_cpu(l, &key, slot);
+		if (key.objectid != logical) {
+			ret = btrfs_previous_item(root, path, 0,
+						  BTRFS_EXTENT_ITEM_KEY);
+			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\n",
+				       (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:
+	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)
+			goto out;
+		ret = 0;
+
+		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(&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;
+			goto out;
+		}
+		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);
+	}
+
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+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;
+
+	mutex_lock(&fs_info->scrub_lock);
+	if (fs_info->scrub_workers_refcnt == 0)
+		btrfs_start_workers(&fs_info->scrub_workers, 1);
+	++fs_info->scrub_workers_refcnt;
+	mutex_unlock(&fs_info->scrub_lock);
+
+	return 0;
+}
+
+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 (root->fs_info->closing)
+		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\n");
+		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);
+
+	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;
+}
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 33679fc..dc80f71 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1228,6 +1228,7 @@
 
 	WARN_ON(cur_trans != trans->transaction);
 
+	btrfs_scrub_pause(root);
 	/* btrfs_commit_tree_roots is responsible for getting the
 	 * various roots consistent with each other.  Every pointer
 	 * in the tree of tree roots has to point to the most up to date
@@ -1312,6 +1313,8 @@
 
 	mutex_unlock(&root->fs_info->trans_mutex);
 
+	btrfs_scrub_continue(root);
+
 	if (current->journal_info == trans)
 		current->journal_info = NULL;
 
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index a794b9f..b4c191d 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -614,7 +614,7 @@
 
 			ret = btrfs_lookup_csums_range(root->log_root,
 						csum_start, csum_end - 1,
-						&ordered_sums);
+						&ordered_sums, 0);
 			BUG_ON(ret);
 			while (!list_empty(&ordered_sums)) {
 				struct btrfs_ordered_sum *sums;
@@ -2094,7 +2094,9 @@
 	 * the running transaction open, so a full commit can't hop
 	 * in and cause problems either.
 	 */
+	btrfs_scrub_pause_super(root);
 	write_ctree_super(trans, root->fs_info->tree_root, 1);
+	btrfs_scrub_continue_super(root);
 	ret = 0;
 
 	mutex_lock(&root->log_mutex);
@@ -2689,7 +2691,7 @@
 				ret = btrfs_lookup_csums_range(
 						log->fs_info->csum_root,
 						ds + cs, ds + cs + cl - 1,
-						&ordered_sums);
+						&ordered_sums, 0);
 				BUG_ON(ret);
 			}
 		}
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index f7771452..b8fc2fa 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -38,9 +38,6 @@
 				struct btrfs_device *device);
 static int btrfs_relocate_sys_chunks(struct btrfs_root *root);
 
-#define map_lookup_size(n) (sizeof(struct map_lookup) + \
-			    (sizeof(struct btrfs_bio_stripe) * (n)))
-
 static DEFINE_MUTEX(uuid_mutex);
 static LIST_HEAD(fs_uuids);
 
@@ -1287,6 +1284,7 @@
 		goto error_undo;
 
 	device->in_fs_metadata = 0;
+	btrfs_scrub_cancel_dev(root, device);
 
 	/*
 	 * the device list mutex makes sure that we don't change
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 05d5d19..7c58a7b 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -85,6 +85,9 @@
 	/* physical drive uuid (or lvm uuid) */
 	u8 uuid[BTRFS_UUID_SIZE];
 
+	/* per-device scrub information */
+	struct scrub_dev *scrub_device;
+
 	struct btrfs_work work;
 };
 
@@ -158,6 +161,9 @@
 	struct btrfs_bio_stripe stripes[];
 };
 
+#define map_lookup_size(n) (sizeof(struct map_lookup) + \
+			    (sizeof(struct btrfs_bio_stripe) * (n)))
+
 int btrfs_account_dev_extents_size(struct btrfs_device *device, u64 start,
 				   u64 end, u64 *length);