X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=fs%2Fbtrfs%2Fordered-data.c;h=77c2411a5f0f0c59b6ab97e78b2828d94a1c7401;hb=46939f8b15e44f065d052e89ea4f2adc81fdc740;hp=6513270f054c538832e93c7e22dd12e20ee0e589;hpb=e6dcd2dc9c489108648e2ed543315dd134d50a9a;p=safe%2Fjmp%2Flinux-2.6

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 6513270..77c2411 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -19,12 +19,13 @@
 #include <linux/gfp.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
+#include <linux/writeback.h>
+#include <linux/pagevec.h>
 #include "ctree.h"
 #include "transaction.h"
 #include "btrfs_inode.h"
 #include "extent_io.h"
 
-
 static u64 entry_end(struct btrfs_ordered_extent *entry)
 {
 	if (entry->file_offset + entry->len < entry->file_offset)
@@ -32,14 +33,17 @@ static u64 entry_end(struct btrfs_ordered_extent *entry)
 	return entry->file_offset + entry->len;
 }
 
+/* returns NULL if the insertion worked, or it returns the node it did find
+ * in the tree
+ */
 static struct rb_node *tree_insert(struct rb_root *root, u64 file_offset,
 				   struct rb_node *node)
 {
-	struct rb_node ** p = &root->rb_node;
-	struct rb_node * parent = NULL;
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent = NULL;
 	struct btrfs_ordered_extent *entry;
 
-	while(*p) {
+	while (*p) {
 		parent = *p;
 		entry = rb_entry(parent, struct btrfs_ordered_extent, rb_node);
 
@@ -56,16 +60,20 @@ static struct rb_node *tree_insert(struct rb_root *root, u64 file_offset,
 	return NULL;
 }
 
+/*
+ * look for a given offset in the tree, and if it can't be found return the
+ * first lesser offset
+ */
 static struct rb_node *__tree_search(struct rb_root *root, u64 file_offset,
 				     struct rb_node **prev_ret)
 {
-	struct rb_node * n = root->rb_node;
+	struct rb_node *n = root->rb_node;
 	struct rb_node *prev = NULL;
 	struct rb_node *test;
 	struct btrfs_ordered_extent *entry;
 	struct btrfs_ordered_extent *prev_entry = NULL;
 
-	while(n) {
+	while (n) {
 		entry = rb_entry(n, struct btrfs_ordered_extent, rb_node);
 		prev = n;
 		prev_entry = entry;
@@ -80,7 +88,7 @@ static struct rb_node *__tree_search(struct rb_root *root, u64 file_offset,
 	if (!prev_ret)
 		return NULL;
 
-	while(prev && file_offset >= entry_end(prev_entry)) {
+	while (prev && file_offset >= entry_end(prev_entry)) {
 		test = rb_next(prev);
 		if (!test)
 			break;
@@ -94,7 +102,7 @@ static struct rb_node *__tree_search(struct rb_root *root, u64 file_offset,
 	if (prev)
 		prev_entry = rb_entry(prev, struct btrfs_ordered_extent,
 				      rb_node);
-	while(prev && file_offset < entry_end(prev_entry)) {
+	while (prev && file_offset < entry_end(prev_entry)) {
 		test = rb_prev(prev);
 		if (!test)
 			break;
@@ -106,6 +114,9 @@ static struct rb_node *__tree_search(struct rb_root *root, u64 file_offset,
 	return NULL;
 }
 
+/*
+ * helper to check if a given offset is inside a given entry
+ */
 static int offset_in_entry(struct btrfs_ordered_extent *entry, u64 file_offset)
 {
 	if (file_offset < entry->file_offset ||
@@ -114,6 +125,10 @@ static int offset_in_entry(struct btrfs_ordered_extent *entry, u64 file_offset)
 	return 1;
 }
 
+/*
+ * look find the first ordered struct that has this offset, otherwise
+ * the first one less than this offset
+ */
 static inline struct rb_node *tree_search(struct btrfs_ordered_inode_tree *tree,
 					  u64 file_offset)
 {
@@ -136,8 +151,21 @@ static inline struct rb_node *tree_search(struct btrfs_ordered_inode_tree *tree,
 	return ret;
 }
 
+/* allocate and add a new ordered_extent into the per-inode tree.
+ * file_offset is the logical offset in the file
+ *
+ * start is the disk block number of an extent already reserved in the
+ * extent allocation tree
+ *
+ * len is the length of the extent
+ *
+ * This also sets the EXTENT_ORDERED bit on the range in the inode.
+ *
+ * The tree is given a single reference on the ordered extent that was
+ * inserted.
+ */
 int btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
-			     u64 start, u64 len)
+			     u64 start, u64 len, u64 disk_len, int type)
 {
 	struct btrfs_ordered_inode_tree *tree;
 	struct rb_node *node;
@@ -152,59 +180,61 @@ int btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
 	entry->file_offset = file_offset;
 	entry->start = start;
 	entry->len = len;
+	entry->disk_len = disk_len;
 	entry->inode = inode;
+	if (type != BTRFS_ORDERED_IO_DONE && type != BTRFS_ORDERED_COMPLETE)
+		set_bit(type, &entry->flags);
+
 	/* one ref for the tree */
 	atomic_set(&entry->refs, 1);
 	init_waitqueue_head(&entry->wait);
 	INIT_LIST_HEAD(&entry->list);
+	INIT_LIST_HEAD(&entry->root_extent_list);
 
 	node = tree_insert(&tree->tree, file_offset,
 			   &entry->rb_node);
-	if (node) {
-		entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
-		atomic_inc(&entry->refs);
-	}
+	BUG_ON(node);
+
 	set_extent_ordered(&BTRFS_I(inode)->io_tree, file_offset,
 			   entry_end(entry) - 1, GFP_NOFS);
 
-	set_bit(BTRFS_ORDERED_START, &entry->flags);
+	spin_lock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);
+	list_add_tail(&entry->root_extent_list,
+		      &BTRFS_I(inode)->root->fs_info->ordered_extents);
+	spin_unlock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);
+
 	mutex_unlock(&tree->mutex);
 	BUG_ON(node);
 	return 0;
 }
 
-int btrfs_add_ordered_sum(struct inode *inode, struct btrfs_ordered_sum *sum)
+/*
+ * Add a struct btrfs_ordered_sum into the list of checksums to be inserted
+ * when an ordered extent is finished.  If the list covers more than one
+ * ordered extent, it is split across multiples.
+ */
+int btrfs_add_ordered_sum(struct inode *inode,
+			  struct btrfs_ordered_extent *entry,
+			  struct btrfs_ordered_sum *sum)
 {
 	struct btrfs_ordered_inode_tree *tree;
-	struct rb_node *node;
-	struct btrfs_ordered_extent *entry;
 
 	tree = &BTRFS_I(inode)->ordered_tree;
 	mutex_lock(&tree->mutex);
-	node = tree_search(tree, sum->file_offset);
-	if (!node) {
-search_fail:
-printk("add ordered sum failed to find a node for inode %lu offset %Lu\n", inode->i_ino, sum->file_offset);
-		node = rb_first(&tree->tree);
-		while(node) {
-			entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
-			printk("entry %Lu %Lu %Lu\n", entry->file_offset, entry->file_offset + entry->len, entry->start);
-			node = rb_next(node);
-		}
-		BUG();
-	}
-	BUG_ON(!node);
-
-	entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
-	if (!offset_in_entry(entry, sum->file_offset)) {
-		goto search_fail;
-	}
-
 	list_add_tail(&sum->list, &entry->list);
 	mutex_unlock(&tree->mutex);
 	return 0;
 }
 
+/*
+ * this is used to account for finished IO across a given range
+ * of the file.  The IO should not span ordered extents.  If
+ * a given ordered_extent is completely done, 1 is returned, otherwise
+ * 0.
+ *
+ * test_and_set_bit on a flag in the struct btrfs_ordered_extent is used
+ * to make sure this function only returns 1 once for a given ordered extent.
+ */
 int btrfs_dec_test_ordered_pending(struct inode *inode,
 				   u64 file_offset, u64 io_size)
 {
@@ -233,9 +263,6 @@ int btrfs_dec_test_ordered_pending(struct inode *inode,
 	ret = test_range_bit(io_tree, entry->file_offset,
 			     entry->file_offset + entry->len - 1,
 			     EXTENT_ORDERED, 0);
-	if (!test_bit(BTRFS_ORDERED_START, &entry->flags)) {
-printk("inode %lu not ready yet for extent %Lu %Lu\n", inode->i_ino, entry->file_offset, entry_end(entry));
-	}
 	if (ret == 0)
 		ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
 out:
@@ -243,13 +270,31 @@ out:
 	return ret == 0;
 }
 
+/*
+ * used to drop a reference on an ordered extent.  This will free
+ * the extent if the last reference is dropped
+ */
 int btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry)
 {
-	if (atomic_dec_and_test(&entry->refs))
+	struct list_head *cur;
+	struct btrfs_ordered_sum *sum;
+
+	if (atomic_dec_and_test(&entry->refs)) {
+		while (!list_empty(&entry->list)) {
+			cur = entry->list.next;
+			sum = list_entry(cur, struct btrfs_ordered_sum, list);
+			list_del(&sum->list);
+			kfree(sum);
+		}
 		kfree(entry);
+	}
 	return 0;
 }
 
+/*
+ * remove an ordered extent from the tree.  No references are dropped
+ * but, anyone waiting on this extent is woken up.
+ */
 int btrfs_remove_ordered_extent(struct inode *inode,
 				struct btrfs_ordered_extent *entry)
 {
@@ -262,62 +307,134 @@ int btrfs_remove_ordered_extent(struct inode *inode,
 	rb_erase(node, &tree->tree);
 	tree->last = NULL;
 	set_bit(BTRFS_ORDERED_COMPLETE, &entry->flags);
+
+	spin_lock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);
+	list_del_init(&entry->root_extent_list);
+	spin_unlock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);
+
 	mutex_unlock(&tree->mutex);
 	wake_up(&entry->wait);
 	return 0;
 }
 
-void btrfs_wait_ordered_extent(struct inode *inode,
-			       struct btrfs_ordered_extent *entry)
+/*
+ * wait for all the ordered extents in a root.  This is done when balancing
+ * space between drives.
+ */
+int btrfs_wait_ordered_extents(struct btrfs_root *root, int nocow_only)
 {
-	u64 start = entry->file_offset;
-	u64 end = start + entry->len - 1;
-#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,22)
-	do_sync_file_range(file, start, end, SYNC_FILE_RANGE_WRITE);
-#else
-	do_sync_mapping_range(inode->i_mapping, start, end,
-			      SYNC_FILE_RANGE_WRITE);
-#endif
-	wait_event(entry->wait,
-		   test_bit(BTRFS_ORDERED_COMPLETE, &entry->flags));
+	struct list_head splice;
+	struct list_head *cur;
+	struct btrfs_ordered_extent *ordered;
+	struct inode *inode;
+
+	INIT_LIST_HEAD(&splice);
+
+	spin_lock(&root->fs_info->ordered_extent_lock);
+	list_splice_init(&root->fs_info->ordered_extents, &splice);
+	while (!list_empty(&splice)) {
+		cur = splice.next;
+		ordered = list_entry(cur, struct btrfs_ordered_extent,
+				     root_extent_list);
+		if (nocow_only &&
+		    !test_bit(BTRFS_ORDERED_NOCOW, &ordered->flags) &&
+		    !test_bit(BTRFS_ORDERED_PREALLOC, &ordered->flags)) {
+			list_move(&ordered->root_extent_list,
+				  &root->fs_info->ordered_extents);
+			cond_resched_lock(&root->fs_info->ordered_extent_lock);
+			continue;
+		}
+
+		list_del_init(&ordered->root_extent_list);
+		atomic_inc(&ordered->refs);
+
+		/*
+		 * the inode may be getting freed (in sys_unlink path).
+		 */
+		inode = igrab(ordered->inode);
+
+		spin_unlock(&root->fs_info->ordered_extent_lock);
+
+		if (inode) {
+			btrfs_start_ordered_extent(inode, ordered, 1);
+			btrfs_put_ordered_extent(ordered);
+			iput(inode);
+		} else {
+			btrfs_put_ordered_extent(ordered);
+		}
+
+		spin_lock(&root->fs_info->ordered_extent_lock);
+	}
+	spin_unlock(&root->fs_info->ordered_extent_lock);
+	return 0;
 }
 
-static void btrfs_start_ordered_extent(struct inode *inode,
-			       struct btrfs_ordered_extent *entry, int wait)
+/*
+ * Used to start IO or wait for a given ordered extent to finish.
+ *
+ * If wait is one, this effectively waits on page writeback for all the pages
+ * in the extent, and it waits on the io completion code to insert
+ * metadata into the btree corresponding to the extent
+ */
+void btrfs_start_ordered_extent(struct inode *inode,
+				       struct btrfs_ordered_extent *entry,
+				       int wait)
 {
 	u64 start = entry->file_offset;
 	u64 end = start + entry->len - 1;
 
-#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,22)
-	do_sync_file_range(file, start, end, SYNC_FILE_RANGE_WRITE);
-#else
-	do_sync_mapping_range(inode->i_mapping, start, end,
-			      SYNC_FILE_RANGE_WRITE);
-#endif
-	if (wait)
+	/*
+	 * pages in the range can be dirty, clean or writeback.  We
+	 * start IO on any dirty ones so the wait doesn't stall waiting
+	 * for pdflush to find them
+	 */
+	btrfs_fdatawrite_range(inode->i_mapping, start, end, WB_SYNC_ALL);
+	if (wait) {
 		wait_event(entry->wait, test_bit(BTRFS_ORDERED_COMPLETE,
 						 &entry->flags));
+	}
 }
 
-void btrfs_wait_ordered_range(struct inode *inode, u64 start, u64 len)
+/*
+ * Used to wait on ordered extents across a large range of bytes.
+ */
+int btrfs_wait_ordered_range(struct inode *inode, u64 start, u64 len)
 {
 	u64 end;
+	u64 orig_end;
+	u64 wait_end;
 	struct btrfs_ordered_extent *ordered;
-	int found;
-	int should_wait = 0;
 
+	if (start + len < start) {
+		orig_end = INT_LIMIT(loff_t);
+	} else {
+		orig_end = start + len - 1;
+		if (orig_end > INT_LIMIT(loff_t))
+			orig_end = INT_LIMIT(loff_t);
+	}
+	wait_end = orig_end;
 again:
-	if (start + len < start)
-		end = (u64)-1;
-	else
-		end = start + len - 1;
-	found = 0;
-	while(1) {
+	/* start IO across the range first to instantiate any delalloc
+	 * extents
+	 */
+	btrfs_fdatawrite_range(inode->i_mapping, start, orig_end, WB_SYNC_NONE);
+
+	/* The compression code will leave pages locked but return from
+	 * writepage without setting the page writeback.  Starting again
+	 * with WB_SYNC_ALL will end up waiting for the IO to actually start.
+	 */
+	btrfs_fdatawrite_range(inode->i_mapping, start, orig_end, WB_SYNC_ALL);
+
+	btrfs_wait_on_page_writeback_range(inode->i_mapping,
+					   start >> PAGE_CACHE_SHIFT,
+					   orig_end >> PAGE_CACHE_SHIFT);
+
+	end = orig_end;
+	while (1) {
 		ordered = btrfs_lookup_first_ordered_extent(inode, end);
-		if (!ordered) {
+		if (!ordered)
 			break;
-		}
-		if (ordered->file_offset >= start + len) {
+		if (ordered->file_offset > orig_end) {
 			btrfs_put_ordered_extent(ordered);
 			break;
 		}
@@ -325,45 +442,25 @@ again:
 			btrfs_put_ordered_extent(ordered);
 			break;
 		}
-		btrfs_start_ordered_extent(inode, ordered, should_wait);
-		found++;
+		btrfs_start_ordered_extent(inode, ordered, 1);
 		end = ordered->file_offset;
 		btrfs_put_ordered_extent(ordered);
-		if (end == 0)
+		if (end == 0 || end == start)
 			break;
 		end--;
 	}
-	if (should_wait && found) {
-		should_wait = 0;
+	if (test_range_bit(&BTRFS_I(inode)->io_tree, start, orig_end,
+			   EXTENT_ORDERED | EXTENT_DELALLOC, 0)) {
+		schedule_timeout(1);
 		goto again;
 	}
-}
-
-int btrfs_add_ordered_pending(struct inode *inode,
-			      struct btrfs_ordered_extent *ordered,
-			      u64 start, u64 len)
-{
-	WARN_ON(1);
 	return 0;
-#if 0
-	int ret;
-	struct btrfs_ordered_inode_tree *tree;
-	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
-
-	tree = &BTRFS_I(inode)->ordered_tree;
-	mutex_lock(&tree->mutex);
-	if (test_bit(BTRFS_ORDERED_IO_DONE, &ordered->flags)) {
-		ret = -EAGAIN;
-		goto out;
-	}
-	set_extent_ordered(io_tree, start, start + len - 1, GFP_NOFS);
-	ret = 0;
-out:
-	mutex_unlock(&tree->mutex);
-	return ret;
-#endif
 }
 
+/*
+ * find an ordered extent corresponding to file_offset.  return NULL if
+ * nothing is found, otherwise take a reference on the extent and return it
+ */
 struct btrfs_ordered_extent *btrfs_lookup_ordered_extent(struct inode *inode,
 							 u64 file_offset)
 {
@@ -387,8 +484,12 @@ out:
 	return entry;
 }
 
+/*
+ * lookup and return any extent before 'file_offset'.  NULL is returned
+ * if none is found
+ */
 struct btrfs_ordered_extent *
-btrfs_lookup_first_ordered_extent(struct inode * inode, u64 file_offset)
+btrfs_lookup_first_ordered_extent(struct inode *inode, u64 file_offset)
 {
 	struct btrfs_ordered_inode_tree *tree;
 	struct rb_node *node;
@@ -406,3 +507,222 @@ out:
 	mutex_unlock(&tree->mutex);
 	return entry;
 }
+
+/*
+ * After an extent is done, call this to conditionally update the on disk
+ * i_size.  i_size is updated to cover any fully written part of the file.
+ */
+int btrfs_ordered_update_i_size(struct inode *inode,
+				struct btrfs_ordered_extent *ordered)
+{
+	struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
+	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
+	u64 disk_i_size;
+	u64 new_i_size;
+	u64 i_size_test;
+	struct rb_node *node;
+	struct btrfs_ordered_extent *test;
+
+	mutex_lock(&tree->mutex);
+	disk_i_size = BTRFS_I(inode)->disk_i_size;
+
+	/*
+	 * if the disk i_size is already at the inode->i_size, or
+	 * this ordered extent is inside the disk i_size, we're done
+	 */
+	if (disk_i_size >= inode->i_size ||
+	    ordered->file_offset + ordered->len <= disk_i_size) {
+		goto out;
+	}
+
+	/*
+	 * we can't update the disk_isize if there are delalloc bytes
+	 * between disk_i_size and  this ordered extent
+	 */
+	if (test_range_bit(io_tree, disk_i_size,
+			   ordered->file_offset + ordered->len - 1,
+			   EXTENT_DELALLOC, 0)) {
+		goto out;
+	}
+	/*
+	 * walk backward from this ordered extent to disk_i_size.
+	 * if we find an ordered extent then we can't update disk i_size
+	 * yet
+	 */
+	node = &ordered->rb_node;
+	while (1) {
+		node = rb_prev(node);
+		if (!node)
+			break;
+		test = rb_entry(node, struct btrfs_ordered_extent, rb_node);
+		if (test->file_offset + test->len <= disk_i_size)
+			break;
+		if (test->file_offset >= inode->i_size)
+			break;
+		if (test->file_offset >= disk_i_size)
+			goto out;
+	}
+	new_i_size = min_t(u64, entry_end(ordered), i_size_read(inode));
+
+	/*
+	 * at this point, we know we can safely update i_size to at least
+	 * the offset from this ordered extent.  But, we need to
+	 * walk forward and see if ios from higher up in the file have
+	 * finished.
+	 */
+	node = rb_next(&ordered->rb_node);
+	i_size_test = 0;
+	if (node) {
+		/*
+		 * do we have an area where IO might have finished
+		 * between our ordered extent and the next one.
+		 */
+		test = rb_entry(node, struct btrfs_ordered_extent, rb_node);
+		if (test->file_offset > entry_end(ordered))
+			i_size_test = test->file_offset;
+	} else {
+		i_size_test = i_size_read(inode);
+	}
+
+	/*
+	 * i_size_test is the end of a region after this ordered
+	 * extent where there are no ordered extents.  As long as there
+	 * are no delalloc bytes in this area, it is safe to update
+	 * disk_i_size to the end of the region.
+	 */
+	if (i_size_test > entry_end(ordered) &&
+	    !test_range_bit(io_tree, entry_end(ordered), i_size_test - 1,
+			   EXTENT_DELALLOC, 0)) {
+		new_i_size = min_t(u64, i_size_test, i_size_read(inode));
+	}
+	BTRFS_I(inode)->disk_i_size = new_i_size;
+out:
+	mutex_unlock(&tree->mutex);
+	return 0;
+}
+
+/*
+ * search the ordered extents for one corresponding to 'offset' and
+ * try to find a checksum.  This is used because we allow pages to
+ * be reclaimed before their checksum is actually put into the btree
+ */
+int btrfs_find_ordered_sum(struct inode *inode, u64 offset, u64 disk_bytenr,
+			   u32 *sum)
+{
+	struct btrfs_ordered_sum *ordered_sum;
+	struct btrfs_sector_sum *sector_sums;
+	struct btrfs_ordered_extent *ordered;
+	struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
+	unsigned long num_sectors;
+	unsigned long i;
+	u32 sectorsize = BTRFS_I(inode)->root->sectorsize;
+	int ret = 1;
+
+	ordered = btrfs_lookup_ordered_extent(inode, offset);
+	if (!ordered)
+		return 1;
+
+	mutex_lock(&tree->mutex);
+	list_for_each_entry_reverse(ordered_sum, &ordered->list, list) {
+		if (disk_bytenr >= ordered_sum->bytenr) {
+			num_sectors = ordered_sum->len / sectorsize;
+			sector_sums = ordered_sum->sums;
+			for (i = 0; i < num_sectors; i++) {
+				if (sector_sums[i].bytenr == disk_bytenr) {
+					*sum = sector_sums[i].sum;
+					ret = 0;
+					goto out;
+				}
+			}
+		}
+	}
+out:
+	mutex_unlock(&tree->mutex);
+	btrfs_put_ordered_extent(ordered);
+	return ret;
+}
+
+
+/**
+ * taken from mm/filemap.c because it isn't exported
+ *
+ * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
+ * @mapping:	address space structure to write
+ * @start:	offset in bytes where the range starts
+ * @end:	offset in bytes where the range ends (inclusive)
+ * @sync_mode:	enable synchronous operation
+ *
+ * Start writeback against all of a mapping's dirty pages that lie
+ * within the byte offsets <start, end> inclusive.
+ *
+ * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
+ * opposed to a regular memory cleansing writeback.  The difference between
+ * these two operations is that if a dirty page/buffer is encountered, it must
+ * be waited upon, and not just skipped over.
+ */
+int btrfs_fdatawrite_range(struct address_space *mapping, loff_t start,
+			   loff_t end, int sync_mode)
+{
+	struct writeback_control wbc = {
+		.sync_mode = sync_mode,
+		.nr_to_write = mapping->nrpages * 2,
+		.range_start = start,
+		.range_end = end,
+		.for_writepages = 1,
+	};
+	return btrfs_writepages(mapping, &wbc);
+}
+
+/**
+ * taken from mm/filemap.c because it isn't exported
+ *
+ * wait_on_page_writeback_range - wait for writeback to complete
+ * @mapping:	target address_space
+ * @start:	beginning page index
+ * @end:	ending page index
+ *
+ * Wait for writeback to complete against pages indexed by start->end
+ * inclusive
+ */
+int btrfs_wait_on_page_writeback_range(struct address_space *mapping,
+				       pgoff_t start, pgoff_t end)
+{
+	struct pagevec pvec;
+	int nr_pages;
+	int ret = 0;
+	pgoff_t index;
+
+	if (end < start)
+		return 0;
+
+	pagevec_init(&pvec, 0);
+	index = start;
+	while ((index <= end) &&
+			(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
+			PAGECACHE_TAG_WRITEBACK,
+			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
+		unsigned i;
+
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+
+			/* until radix tree lookup accepts end_index */
+			if (page->index > end)
+				continue;
+
+			wait_on_page_writeback(page);
+			if (PageError(page))
+				ret = -EIO;
+		}
+		pagevec_release(&pvec);
+		cond_resched();
+	}
+
+	/* Check for outstanding write errors */
+	if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
+		ret = -ENOSPC;
+	if (test_and_clear_bit(AS_EIO, &mapping->flags))
+		ret = -EIO;
+
+	return ret;
+}