Btrfs: move all reflink implementation code into its own file

The reflink code is quite large and has been living in ioctl.c since ever.
It has grown over the years after many bug fixes and improvements, and
since I'm planning on making some further improvements on it, it's time
to get it better organized by moving into its own file, reflink.c
(similar to what xfs does for example).

This change only moves the code out of ioctl.c into the new file, it
doesn't do any other change.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

6 files changed, 743 insertions, 737 deletions

diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index 9a0ff3384381..e738f6206ea5 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -11,7 +11,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
 	   compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o \
 	   reada.o backref.o ulist.o qgroup.o send.o dev-replace.o raid56.o \
 	   uuid-tree.o props.o free-space-tree.o tree-checker.o space-info.o \
-	   block-rsv.o delalloc-space.o block-group.o discard.o
+	   block-rsv.o delalloc-space.o block-group.o discard.o reflink.o
 
 btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
 btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index ea5d0675465a..ecd016f7dab1 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2974,9 +2974,6 @@ int btrfs_dirty_pages(struct inode *inode, struct page **pages,
 		      size_t num_pages, loff_t pos, size_t write_bytes,
 		      struct extent_state **cached);
 int btrfs_fdatawrite_range(struct inode *inode, loff_t start, loff_t end);
-loff_t btrfs_remap_file_range(struct file *file_in, loff_t pos_in,
-			      struct file *file_out, loff_t pos_out,
-			      loff_t len, unsigned int remap_flags);
 
 /* tree-defrag.c */
 int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 8a974a82be51..31c72371a164 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -27,6 +27,7 @@
 #include "qgroup.h"
 #include "compression.h"
 #include "delalloc-space.h"
+#include "reflink.h"
 
 static struct kmem_cache *btrfs_inode_defrag_cachep;
 /*
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 04899d3d775e..f8a73a28022a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -87,10 +87,6 @@ struct btrfs_ioctl_send_args_32 {
 			       struct btrfs_ioctl_send_args_32)
 #endif
 
-static int btrfs_clone(struct inode *src, struct inode *inode,
-		       u64 off, u64 olen, u64 olen_aligned, u64 destoff,
-		       int no_time_update);
-
 /* Mask out flags that are inappropriate for the given type of inode. */
 static unsigned int btrfs_mask_fsflags_for_type(struct inode *inode,
 		unsigned int flags)
@@ -3315,735 +3311,6 @@ out:
 	return ret;
 }
 
-static void btrfs_double_extent_unlock(struct inode *inode1, u64 loff1,
-				       struct inode *inode2, u64 loff2, u64 len)
-{
-	unlock_extent(&BTRFS_I(inode1)->io_tree, loff1, loff1 + len - 1);
-	unlock_extent(&BTRFS_I(inode2)->io_tree, loff2, loff2 + len - 1);
-}
-
-static void btrfs_double_extent_lock(struct inode *inode1, u64 loff1,
-				     struct inode *inode2, u64 loff2, u64 len)
-{
-	if (inode1 < inode2) {
-		swap(inode1, inode2);
-		swap(loff1, loff2);
-	} else if (inode1 == inode2 && loff2 < loff1) {
-		swap(loff1, loff2);
-	}
-	lock_extent(&BTRFS_I(inode1)->io_tree, loff1, loff1 + len - 1);
-	lock_extent(&BTRFS_I(inode2)->io_tree, loff2, loff2 + len - 1);
-}
-
-static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 len,
-				   struct inode *dst, u64 dst_loff)
-{
-	const u64 bs = BTRFS_I(src)->root->fs_info->sb->s_blocksize;
-	int ret;
-
-	/*
-	 * Lock destination range to serialize with concurrent readpages() and
-	 * source range to serialize with relocation.
-	 */
-	btrfs_double_extent_lock(src, loff, dst, dst_loff, len);
-	ret = btrfs_clone(src, dst, loff, len, ALIGN(len, bs), dst_loff, 1);
-	btrfs_double_extent_unlock(src, loff, dst, dst_loff, len);
-
-	return ret;
-}
-
-#define BTRFS_MAX_DEDUPE_LEN	SZ_16M
-
-static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
-			     struct inode *dst, u64 dst_loff)
-{
-	int ret;
-	u64 i, tail_len, chunk_count;
-	struct btrfs_root *root_dst = BTRFS_I(dst)->root;
-
-	spin_lock(&root_dst->root_item_lock);
-	if (root_dst->send_in_progress) {
-		btrfs_warn_rl(root_dst->fs_info,
-"cannot deduplicate to root %llu while send operations are using it (%d in progress)",
-			      root_dst->root_key.objectid,
-			      root_dst->send_in_progress);
-		spin_unlock(&root_dst->root_item_lock);
-		return -EAGAIN;
-	}
-	root_dst->dedupe_in_progress++;
-	spin_unlock(&root_dst->root_item_lock);
-
-	tail_len = olen % BTRFS_MAX_DEDUPE_LEN;
-	chunk_count = div_u64(olen, BTRFS_MAX_DEDUPE_LEN);
-
-	for (i = 0; i < chunk_count; i++) {
-		ret = btrfs_extent_same_range(src, loff, BTRFS_MAX_DEDUPE_LEN,
-					      dst, dst_loff);
-		if (ret)
-			goto out;
-
-		loff += BTRFS_MAX_DEDUPE_LEN;
-		dst_loff += BTRFS_MAX_DEDUPE_LEN;
-	}
-
-	if (tail_len > 0)
-		ret = btrfs_extent_same_range(src, loff, tail_len, dst,
-					      dst_loff);
-out:
-	spin_lock(&root_dst->root_item_lock);
-	root_dst->dedupe_in_progress--;
-	spin_unlock(&root_dst->root_item_lock);
-
-	return ret;
-}
-
-static int clone_finish_inode_update(struct btrfs_trans_handle *trans,
-				     struct inode *inode,
-				     u64 endoff,
-				     const u64 destoff,
-				     const u64 olen,
-				     int no_time_update)
-{
-	struct btrfs_root *root = BTRFS_I(inode)->root;
-	int ret;
-
-	inode_inc_iversion(inode);
-	if (!no_time_update)
-		inode->i_mtime = inode->i_ctime = current_time(inode);
-	/*
-	 * We round up to the block size at eof when determining which
-	 * extents to clone above, but shouldn't round up the file size.
-	 */
-	if (endoff > destoff + olen)
-		endoff = destoff + olen;
-	if (endoff > inode->i_size) {
-		i_size_write(inode, endoff);
-		btrfs_inode_safe_disk_i_size_write(inode, 0);
-	}
-
-	ret = btrfs_update_inode(trans, root, inode);
-	if (ret) {
-		btrfs_abort_transaction(trans, ret);
-		btrfs_end_transaction(trans);
-		goto out;
-	}
-	ret = btrfs_end_transaction(trans);
-out:
-	return ret;
-}
-
-/*
- * Make sure we do not end up inserting an inline extent into a file that has
- * already other (non-inline) extents. If a file has an inline extent it can
- * not have any other extents and the (single) inline extent must start at the
- * file offset 0. Failing to respect these rules will lead to file corruption,
- * resulting in EIO errors on read/write operations, hitting BUG_ON's in mm, etc
- *
- * We can have extents that have been already written to disk or we can have
- * dirty ranges still in delalloc, in which case the extent maps and items are
- * created only when we run delalloc, and the delalloc ranges might fall outside
- * the range we are currently locking in the inode's io tree. So we check the
- * inode's i_size because of that (i_size updates are done while holding the
- * i_mutex, which we are holding here).
- * We also check to see if the inode has a size not greater than "datal" but has
- * extents beyond it, due to an fallocate with FALLOC_FL_KEEP_SIZE (and we are
- * protected against such concurrent fallocate calls by the i_mutex).
- *
- * If the file has no extents but a size greater than datal, do not allow the
- * copy because we would need turn the inline extent into a non-inline one (even
- * with NO_HOLES enabled). If we find our destination inode only has one inline
- * extent, just overwrite it with the source inline extent if its size is less
- * than the source extent's size, or we could copy the source inline extent's
- * data into the destination inode's inline extent if the later is greater then
- * the former.
- */
-static int clone_copy_inline_extent(struct inode *dst,
-				    struct btrfs_trans_handle *trans,
-				    struct btrfs_path *path,
-				    struct btrfs_key *new_key,
-				    const u64 drop_start,
-				    const u64 datal,
-				    const u64 skip,
-				    const u64 size,
-				    char *inline_data)
-{
-	struct btrfs_fs_info *fs_info = btrfs_sb(dst->i_sb);
-	struct btrfs_root *root = BTRFS_I(dst)->root;
-	const u64 aligned_end = ALIGN(new_key->offset + datal,
-				      fs_info->sectorsize);
-	int ret;
-	struct btrfs_key key;
-
-	if (new_key->offset > 0)
-		return -EOPNOTSUPP;
-
-	key.objectid = btrfs_ino(BTRFS_I(dst));
-	key.type = BTRFS_EXTENT_DATA_KEY;
-	key.offset = 0;
-	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
-	if (ret < 0) {
-		return ret;
-	} else if (ret > 0) {
-		if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
-			ret = btrfs_next_leaf(root, path);
-			if (ret < 0)
-				return ret;
-			else if (ret > 0)
-				goto copy_inline_extent;
-		}
-		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
-		if (key.objectid == btrfs_ino(BTRFS_I(dst)) &&
-		    key.type == BTRFS_EXTENT_DATA_KEY) {
-			ASSERT(key.offset > 0);
-			return -EOPNOTSUPP;
-		}
-	} else if (i_size_read(dst) <= datal) {
-		struct btrfs_file_extent_item *ei;
-		u64 ext_len;
-
-		/*
-		 * If the file size is <= datal, make sure there are no other
-		 * extents following (can happen do to an fallocate call with
-		 * the flag FALLOC_FL_KEEP_SIZE).
-		 */
-		ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
-				    struct btrfs_file_extent_item);
-		/*
-		 * If it's an inline extent, it can not have other extents
-		 * following it.
-		 */
-		if (btrfs_file_extent_type(path->nodes[0], ei) ==
-		    BTRFS_FILE_EXTENT_INLINE)
-			goto copy_inline_extent;
-
-		ext_len = btrfs_file_extent_num_bytes(path->nodes[0], ei);
-		if (ext_len > aligned_end)
-			return -EOPNOTSUPP;
-
-		ret = btrfs_next_item(root, path);
-		if (ret < 0) {
-			return ret;
-		} else if (ret == 0) {
-			btrfs_item_key_to_cpu(path->nodes[0], &key,
-					      path->slots[0]);
-			if (key.objectid == btrfs_ino(BTRFS_I(dst)) &&
-			    key.type == BTRFS_EXTENT_DATA_KEY)
-				return -EOPNOTSUPP;
-		}
-	}
-
-copy_inline_extent:
-	/*
-	 * We have no extent items, or we have an extent at offset 0 which may
-	 * or may not be inlined. All these cases are dealt the same way.
-	 */
-	if (i_size_read(dst) > datal) {
-		/*
-		 * If the destination inode has an inline extent...
-		 * This would require copying the data from the source inline
-		 * extent into the beginning of the destination's inline extent.
-		 * But this is really complex, both extents can be compressed
-		 * or just one of them, which would require decompressing and
-		 * re-compressing data (which could increase the new compressed
-		 * size, not allowing the compressed data to fit anymore in an
-		 * inline extent).
-		 * So just don't support this case for now (it should be rare,
-		 * we are not really saving space when cloning inline extents).
-		 */
-		return -EOPNOTSUPP;
-	}
-
-	btrfs_release_path(path);
-	ret = btrfs_drop_extents(trans, root, dst, drop_start, aligned_end, 1);
-	if (ret)
-		return ret;
-	ret = btrfs_insert_empty_item(trans, root, path, new_key, size);
-	if (ret)
-		return ret;
-
-	if (skip) {
-		const u32 start = btrfs_file_extent_calc_inline_size(0);
-
-		memmove(inline_data + start, inline_data + start + skip, datal);
-	}
-
-	write_extent_buffer(path->nodes[0], inline_data,
-			    btrfs_item_ptr_offset(path->nodes[0],
-						  path->slots[0]),
-			    size);
-	inode_add_bytes(dst, datal);
-	set_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &BTRFS_I(dst)->runtime_flags);
-
-	return 0;
-}
-
-/**
- * btrfs_clone() - clone a range from inode file to another
- *
- * @src: Inode to clone from
- * @inode: Inode to clone to
- * @off: Offset within source to start clone from
- * @olen: Original length, passed by user, of range to clone
- * @olen_aligned: Block-aligned value of olen
- * @destoff: Offset within @inode to start clone
- * @no_time_update: Whether to update mtime/ctime on the target inode
- */
-static int btrfs_clone(struct inode *src, struct inode *inode,
-		       const u64 off, const u64 olen, const u64 olen_aligned,
-		       const u64 destoff, int no_time_update)
-{
-	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
-	struct btrfs_root *root = BTRFS_I(inode)->root;
-	struct btrfs_path *path = NULL;
-	struct extent_buffer *leaf;
-	struct btrfs_trans_handle *trans;
-	char *buf = NULL;
-	struct btrfs_key key;
-	u32 nritems;
-	int slot;
-	int ret;
-	const u64 len = olen_aligned;
-	u64 last_dest_end = destoff;
-
-	ret = -ENOMEM;
-	buf = kvmalloc(fs_info->nodesize, GFP_KERNEL);
-	if (!buf)
-		return ret;
-
-	path = btrfs_alloc_path();
-	if (!path) {
-		kvfree(buf);
-		return ret;
-	}
-
-	path->reada = READA_FORWARD;
-	/* clone data */
-	key.objectid = btrfs_ino(BTRFS_I(src));
-	key.type = BTRFS_EXTENT_DATA_KEY;
-	key.offset = off;
-
-	while (1) {
-		u64 next_key_min_offset = key.offset + 1;
-		struct btrfs_file_extent_item *extent;
-		int type;
-		u32 size;
-		struct btrfs_key new_key;
-		u64 disko = 0, diskl = 0;
-		u64 datao = 0, datal = 0;
-		u8 comp;
-		u64 drop_start;
-
-		/*
-		 * note the key will change type as we walk through the
-		 * tree.
-		 */
-		path->leave_spinning = 1;
-		ret = btrfs_search_slot(NULL, BTRFS_I(src)->root, &key, path,
-				0, 0);
-		if (ret < 0)
-			goto out;
-		/*
-		 * First search, if no extent item that starts at offset off was
-		 * found but the previous item is an extent item, it's possible
-		 * it might overlap our target range, therefore process it.
-		 */
-		if (key.offset == off && ret > 0 && path->slots[0] > 0) {
-			btrfs_item_key_to_cpu(path->nodes[0], &key,
-					      path->slots[0] - 1);
-			if (key.type == BTRFS_EXTENT_DATA_KEY)
-				path->slots[0]--;
-		}
-
-		nritems = btrfs_header_nritems(path->nodes[0]);
-process_slot:
-		if (path->slots[0] >= nritems) {
-			ret = btrfs_next_leaf(BTRFS_I(src)->root, path);
-			if (ret < 0)
-				goto out;
-			if (ret > 0)
-				break;
-			nritems = btrfs_header_nritems(path->nodes[0]);
-		}
-		leaf = path->nodes[0];
-		slot = path->slots[0];
-
-		btrfs_item_key_to_cpu(leaf, &key, slot);
-		if (key.type > BTRFS_EXTENT_DATA_KEY ||
-		    key.objectid != btrfs_ino(BTRFS_I(src)))
-			break;
-
-		ASSERT(key.type == BTRFS_EXTENT_DATA_KEY);
-
-		extent = btrfs_item_ptr(leaf, slot,
-					struct btrfs_file_extent_item);
-		comp = btrfs_file_extent_compression(leaf, extent);
-		type = btrfs_file_extent_type(leaf, extent);
-		if (type == BTRFS_FILE_EXTENT_REG ||
-		    type == BTRFS_FILE_EXTENT_PREALLOC) {
-			disko = btrfs_file_extent_disk_bytenr(leaf, extent);
-			diskl = btrfs_file_extent_disk_num_bytes(leaf, extent);
-			datao = btrfs_file_extent_offset(leaf, extent);
-			datal = btrfs_file_extent_num_bytes(leaf, extent);
-		} else if (type == BTRFS_FILE_EXTENT_INLINE) {
-			/* Take upper bound, may be compressed */
-			datal = btrfs_file_extent_ram_bytes(leaf, extent);
-		}
-
-		/*
-		 * The first search might have left us at an extent item that
-		 * ends before our target range's start, can happen if we have
-		 * holes and NO_HOLES feature enabled.
-		 */
-		if (key.offset + datal <= off) {
-			path->slots[0]++;
-			goto process_slot;
-		} else if (key.offset >= off + len) {
-			break;
-		}
-		next_key_min_offset = key.offset + datal;
-		size = btrfs_item_size_nr(leaf, slot);
-		read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf, slot),
-				   size);
-
-		btrfs_release_path(path);
-		path->leave_spinning = 0;
-
-		memcpy(&new_key, &key, sizeof(new_key));
-		new_key.objectid = btrfs_ino(BTRFS_I(inode));
-		if (off <= key.offset)
-			new_key.offset = key.offset + destoff - off;
-		else
-			new_key.offset = destoff;
-
-		/*
-		 * Deal with a hole that doesn't have an extent item that
-		 * represents it (NO_HOLES feature enabled).
-		 * This hole is either in the middle of the cloning range or at
-		 * the beginning (fully overlaps it or partially overlaps it).
-		 */
-		if (new_key.offset != last_dest_end)
-			drop_start = last_dest_end;
-		else
-			drop_start = new_key.offset;
-
-		if (type == BTRFS_FILE_EXTENT_REG ||
-		    type == BTRFS_FILE_EXTENT_PREALLOC) {
-			struct btrfs_clone_extent_info clone_info;
-
-			/*
-			 *    a  | --- range to clone ---|  b
-			 * | ------------- extent ------------- |
-			 */
-
-			/* Subtract range b */
-			if (key.offset + datal > off + len)
-				datal = off + len - key.offset;
-
-			/* Subtract range a */
-			if (off > key.offset) {
-				datao += off - key.offset;
-				datal -= off - key.offset;
-			}
-
-			clone_info.disk_offset = disko;
-			clone_info.disk_len = diskl;
-			clone_info.data_offset = datao;
-			clone_info.data_len = datal;
-			clone_info.file_offset = new_key.offset;
-			clone_info.extent_buf = buf;
-			clone_info.item_size = size;
-			ret = btrfs_punch_hole_range(inode, path,
-						     drop_start,
-						     new_key.offset + datal - 1,
-						     &clone_info, &trans);
-			if (ret)
-				goto out;
-		} else if (type == BTRFS_FILE_EXTENT_INLINE) {
-			u64 skip = 0;
-			u64 trim = 0;
-
-			if (off > key.offset) {
-				skip = off - key.offset;
-				new_key.offset += skip;
-			}
-
-			if (key.offset + datal > off + len)
-				trim = key.offset + datal - (off + len);
-
-			if (comp && (skip || trim)) {
-				ret = -EINVAL;
-				goto out;
-			}
-			size -= skip + trim;
-			datal -= skip + trim;
-
-			/*
-			 * If our extent is inline, we know we will drop or
-			 * adjust at most 1 extent item in the destination root.
-			 *
-			 * 1 - adjusting old extent (we may have to split it)
-			 * 1 - add new extent
-			 * 1 - inode update
-			 */
-			trans = btrfs_start_transaction(root, 3);
-			if (IS_ERR(trans)) {
-				ret = PTR_ERR(trans);
-				goto out;
-			}
-
-			ret = clone_copy_inline_extent(inode, trans, path,
-						       &new_key, drop_start,
-						       datal, skip, size, buf);
-			if (ret) {
-				if (ret != -EOPNOTSUPP)
-					btrfs_abort_transaction(trans, ret);
-				btrfs_end_transaction(trans);
-				goto out;
-			}
-		}
-
-		btrfs_release_path(path);
-
-		last_dest_end = ALIGN(new_key.offset + datal,
-				      fs_info->sectorsize);
-		ret = clone_finish_inode_update(trans, inode, last_dest_end,
-						destoff, olen, no_time_update);
-		if (ret)
-			goto out;
-		if (new_key.offset + datal >= destoff + len)
-			break;
-
-		btrfs_release_path(path);
-		key.offset = next_key_min_offset;
-
-		if (fatal_signal_pending(current)) {
-			ret = -EINTR;
-			goto out;
-		}
-	}
-	ret = 0;
-
-	if (last_dest_end < destoff + len) {
-		/*
-		 * We have an implicit hole that fully or partially overlaps our
-		 * cloning range at its end. This means that we either have the
-		 * NO_HOLES feature enabled or the implicit hole happened due to
-		 * mixing buffered and direct IO writes against this file.
-		 */
-		btrfs_release_path(path);
-		path->leave_spinning = 0;
-
-		ret = btrfs_punch_hole_range(inode, path,
-					     last_dest_end, destoff + len - 1,
-					     NULL, &trans);
-		if (ret)
-			goto out;
-
-		ret = clone_finish_inode_update(trans, inode, destoff + len,
-						destoff, olen, no_time_update);
-	}
-
-out:
-	btrfs_free_path(path);
-	kvfree(buf);
-	return ret;
-}
-
-static noinline int btrfs_clone_files(struct file *file, struct file *file_src,
-					u64 off, u64 olen, u64 destoff)
-{
-	struct inode *inode = file_inode(file);
-	struct inode *src = file_inode(file_src);
-	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
-	int ret;
-	u64 len = olen;
-	u64 bs = fs_info->sb->s_blocksize;
-
-	/*
-	 * TODO:
-	 * - split compressed inline extents.  annoying: we need to
-	 *   decompress into destination's address_space (the file offset
-	 *   may change, so source mapping won't do), then recompress (or
-	 *   otherwise reinsert) a subrange.
-	 *
-	 * - split destination inode's inline extents.  The inline extents can
-	 *   be either compressed or non-compressed.
-	 */
-
-	/*
-	 * VFS's generic_remap_file_range_prep() protects us from cloning the
-	 * eof block into the middle of a file, which would result in corruption
-	 * if the file size is not blocksize aligned. So we don't need to check
-	 * for that case here.
-	 */
-	if (off + len == src->i_size)
-		len = ALIGN(src->i_size, bs) - off;
-
-	if (destoff > inode->i_size) {
-		const u64 wb_start = ALIGN_DOWN(inode->i_size, bs);
-
-		ret = btrfs_cont_expand(inode, inode->i_size, destoff);
-		if (ret)
-			return ret;
-		/*
-		 * We may have truncated the last block if the inode's size is
-		 * not sector size aligned, so we need to wait for writeback to
-		 * complete before proceeding further, otherwise we can race
-		 * with cloning and attempt to increment a reference to an
-		 * extent that no longer exists (writeback completed right after
-		 * we found the previous extent covering eof and before we
-		 * attempted to increment its reference count).
-		 */
-		ret = btrfs_wait_ordered_range(inode, wb_start,
-					       destoff - wb_start);
-		if (ret)
-			return ret;
-	}
-
-	/*
-	 * Lock destination range to serialize with concurrent readpages() and
-	 * source range to serialize with relocation.
-	 */
-	btrfs_double_extent_lock(src, off, inode, destoff, len);
-	ret = btrfs_clone(src, inode, off, olen, len, destoff, 0);
-	btrfs_double_extent_unlock(src, off, inode, destoff, len);
-	/*
-	 * Truncate page cache pages so that future reads will see the cloned
-	 * data immediately and not the previous data.
-	 */
-	truncate_inode_pages_range(&inode->i_data,
-				round_down(destoff, PAGE_SIZE),
-				round_up(destoff + len, PAGE_SIZE) - 1);
-
-	return ret;
-}
-
-static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
-				       struct file *file_out, loff_t pos_out,
-				       loff_t *len, unsigned int remap_flags)
-{
-	struct inode *inode_in = file_inode(file_in);
-	struct inode *inode_out = file_inode(file_out);
-	u64 bs = BTRFS_I(inode_out)->root->fs_info->sb->s_blocksize;
-	bool same_inode = inode_out == inode_in;
-	u64 wb_len;
-	int ret;
-
-	if (!(remap_flags & REMAP_FILE_DEDUP)) {
-		struct btrfs_root *root_out = BTRFS_I(inode_out)->root;
-
-		if (btrfs_root_readonly(root_out))
-			return -EROFS;
-
-		if (file_in->f_path.mnt != file_out->f_path.mnt ||
-		    inode_in->i_sb != inode_out->i_sb)
-			return -EXDEV;
-	}
-
-	/* don't make the dst file partly checksummed */
-	if ((BTRFS_I(inode_in)->flags & BTRFS_INODE_NODATASUM) !=
-	    (BTRFS_I(inode_out)->flags & BTRFS_INODE_NODATASUM)) {
-		return -EINVAL;
-	}
-
-	/*
-	 * Now that the inodes are locked, we need to start writeback ourselves
-	 * and can not rely on the writeback from the VFS's generic helper
-	 * generic_remap_file_range_prep() because:
-	 *
-	 * 1) For compression we must call filemap_fdatawrite_range() range
-	 *    twice (btrfs_fdatawrite_range() does it for us), and the generic
-	 *    helper only calls it once;
-	 *
-	 * 2) filemap_fdatawrite_range(), called by the generic helper only
-	 *    waits for the writeback to complete, i.e. for IO to be done, and
-	 *    not for the ordered extents to complete. We need to wait for them
-	 *    to complete so that new file extent items are in the fs tree.
-	 */
-	if (*len == 0 && !(remap_flags & REMAP_FILE_DEDUP))
-		wb_len = ALIGN(inode_in->i_size, bs) - ALIGN_DOWN(pos_in, bs);
-	else
-		wb_len = ALIGN(*len, bs);
-
-	/*
-	 * Since we don't lock ranges, wait for ongoing lockless dio writes (as
-	 * any in progress could create its ordered extents after we wait for
-	 * existing ordered extents below).
-	 */
-	inode_dio_wait(inode_in);
-	if (!same_inode)
-		inode_dio_wait(inode_out);
-
-	/*
-	 * Workaround to make sure NOCOW buffered write reach disk as NOCOW.
-	 *
-	 * Btrfs' back references do not have a block level granularity, they
-	 * work at the whole extent level.
-	 * NOCOW buffered write without data space reserved may not be able
-	 * to fall back to CoW due to lack of data space, thus could cause
-	 * data loss.
-	 *
-	 * Here we take a shortcut by flushing the whole inode, so that all
-	 * nocow write should reach disk as nocow before we increase the
-	 * reference of the extent. We could do better by only flushing NOCOW
-	 * data, but that needs extra accounting.
-	 *
-	 * Also we don't need to check ASYNC_EXTENT, as async extent will be
-	 * CoWed anyway, not affecting nocow part.
-	 */
-	ret = filemap_flush(inode_in->i_mapping);
-	if (ret < 0)
-		return ret;
-
-	ret = btrfs_wait_ordered_range(inode_in, ALIGN_DOWN(pos_in, bs),
-				       wb_len);
-	if (ret < 0)
-		return ret;
-	ret = btrfs_wait_ordered_range(inode_out, ALIGN_DOWN(pos_out, bs),
-				       wb_len);
-	if (ret < 0)
-		return ret;
-
-	return generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
-					    len, remap_flags);
-}
-
-loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
-		struct file *dst_file, loff_t destoff, loff_t len,
-		unsigned int remap_flags)
-{
-	struct inode *src_inode = file_inode(src_file);
-	struct inode *dst_inode = file_inode(dst_file);
-	bool same_inode = dst_inode == src_inode;
-	int ret;
-
-	if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
-		return -EINVAL;
-
-	if (same_inode)
-		inode_lock(src_inode);
-	else
-		lock_two_nondirectories(src_inode, dst_inode);
-
-	ret = btrfs_remap_file_range_prep(src_file, off, dst_file, destoff,
-					  &len, remap_flags);
-	if (ret < 0 || len == 0)
-		goto out_unlock;
-
-	if (remap_flags & REMAP_FILE_DEDUP)
-		ret = btrfs_extent_same(src_inode, off, len, dst_inode, destoff);
-	else
-		ret = btrfs_clone_files(dst_file, src_file, off, len, destoff);
-
-out_unlock:
-	if (same_inode)
-		inode_unlock(src_inode);
-	else
-		unlock_two_nondirectories(src_inode, dst_inode);
-
-	return ret < 0 ? ret : len;
-}
-
 static long btrfs_ioctl_default_subvol(struct file *file, void __user *argp)
 {
 	struct inode *inode = file_inode(file);
diff --git a/fs/btrfs/reflink.c b/fs/btrfs/reflink.c
new file mode 100644
index 000000000000..367b11656118
--- /dev/null
+++ b/fs/btrfs/reflink.c
@@ -0,0 +1,729 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/iversion.h>
+#include "ctree.h"
+#include "reflink.h"
+#include "transaction.h"
+
+#define BTRFS_MAX_DEDUPE_LEN	SZ_16M
+
+static int clone_finish_inode_update(struct btrfs_trans_handle *trans,
+				     struct inode *inode,
+				     u64 endoff,
+				     const u64 destoff,
+				     const u64 olen,
+				     int no_time_update)
+{
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	int ret;
+
+	inode_inc_iversion(inode);
+	if (!no_time_update)
+		inode->i_mtime = inode->i_ctime = current_time(inode);
+	/*
+	 * We round up to the block size at eof when determining which
+	 * extents to clone above, but shouldn't round up the file size.
+	 */
+	if (endoff > destoff + olen)
+		endoff = destoff + olen;
+	if (endoff > inode->i_size) {
+		i_size_write(inode, endoff);
+		btrfs_inode_safe_disk_i_size_write(inode, 0);
+	}
+
+	ret = btrfs_update_inode(trans, root, inode);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		btrfs_end_transaction(trans);
+		goto out;
+	}
+	ret = btrfs_end_transaction(trans);
+out:
+	return ret;
+}
+
+/*
+ * Make sure we do not end up inserting an inline extent into a file that has
+ * already other (non-inline) extents. If a file has an inline extent it can
+ * not have any other extents and the (single) inline extent must start at the
+ * file offset 0. Failing to respect these rules will lead to file corruption,
+ * resulting in EIO errors on read/write operations, hitting BUG_ON's in mm, etc
+ *
+ * We can have extents that have been already written to disk or we can have
+ * dirty ranges still in delalloc, in which case the extent maps and items are
+ * created only when we run delalloc, and the delalloc ranges might fall outside
+ * the range we are currently locking in the inode's io tree. So we check the
+ * inode's i_size because of that (i_size updates are done while holding the
+ * i_mutex, which we are holding here).
+ * We also check to see if the inode has a size not greater than "datal" but has
+ * extents beyond it, due to an fallocate with FALLOC_FL_KEEP_SIZE (and we are
+ * protected against such concurrent fallocate calls by the i_mutex).
+ *
+ * If the file has no extents but a size greater than datal, do not allow the
+ * copy because we would need turn the inline extent into a non-inline one (even
+ * with NO_HOLES enabled). If we find our destination inode only has one inline
+ * extent, just overwrite it with the source inline extent if its size is less
+ * than the source extent's size, or we could copy the source inline extent's
+ * data into the destination inode's inline extent if the later is greater then
+ * the former.
+ */
+static int clone_copy_inline_extent(struct inode *dst,
+				    struct btrfs_trans_handle *trans,
+				    struct btrfs_path *path,
+				    struct btrfs_key *new_key,
+				    const u64 drop_start,
+				    const u64 datal,
+				    const u64 skip,
+				    const u64 size,
+				    char *inline_data)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(dst->i_sb);
+	struct btrfs_root *root = BTRFS_I(dst)->root;
+	const u64 aligned_end = ALIGN(new_key->offset + datal,
+				      fs_info->sectorsize);
+	int ret;
+	struct btrfs_key key;
+
+	if (new_key->offset > 0)
+		return -EOPNOTSUPP;
+
+	key.objectid = btrfs_ino(BTRFS_I(dst));
+	key.type = BTRFS_EXTENT_DATA_KEY;
+	key.offset = 0;
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0) {
+		return ret;
+	} else if (ret > 0) {
+		if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
+			ret = btrfs_next_leaf(root, path);
+			if (ret < 0)
+				return ret;
+			else if (ret > 0)
+				goto copy_inline_extent;
+		}
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+		if (key.objectid == btrfs_ino(BTRFS_I(dst)) &&
+		    key.type == BTRFS_EXTENT_DATA_KEY) {
+			ASSERT(key.offset > 0);
+			return -EOPNOTSUPP;
+		}
+	} else if (i_size_read(dst) <= datal) {
+		struct btrfs_file_extent_item *ei;
+		u64 ext_len;
+
+		/*
+		 * If the file size is <= datal, make sure there are no other
+		 * extents following (can happen do to an fallocate call with
+		 * the flag FALLOC_FL_KEEP_SIZE).
+		 */
+		ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
+				    struct btrfs_file_extent_item);
+		/*
+		 * If it's an inline extent, it can not have other extents
+		 * following it.
+		 */
+		if (btrfs_file_extent_type(path->nodes[0], ei) ==
+		    BTRFS_FILE_EXTENT_INLINE)
+			goto copy_inline_extent;
+
+		ext_len = btrfs_file_extent_num_bytes(path->nodes[0], ei);
+		if (ext_len > aligned_end)
+			return -EOPNOTSUPP;
+
+		ret = btrfs_next_item(root, path);
+		if (ret < 0) {
+			return ret;
+		} else if (ret == 0) {
+			btrfs_item_key_to_cpu(path->nodes[0], &key,
+					      path->slots[0]);
+			if (key.objectid == btrfs_ino(BTRFS_I(dst)) &&
+			    key.type == BTRFS_EXTENT_DATA_KEY)
+				return -EOPNOTSUPP;
+		}
+	}
+
+copy_inline_extent:
+	/*
+	 * We have no extent items, or we have an extent at offset 0 which may
+	 * or may not be inlined. All these cases are dealt the same way.
+	 */
+	if (i_size_read(dst) > datal) {
+		/*
+		 * If the destination inode has an inline extent.
+		 * This would require copying the data from the source inline
+		 * extent into the beginning of the destination's inline extent.
+		 * But this is really complex, both extents can be compressed
+		 * or just one of them, which would require decompressing and
+		 * re-compressing data (which could increase the new compressed
+		 * size, not allowing the compressed data to fit anymore in an
+		 * inline extent).
+		 * So just don't support this case for now (it should be rare,
+		 * we are not really saving space when cloning inline extents).
+		 */
+		return -EOPNOTSUPP;
+	}
+
+	btrfs_release_path(path);
+	ret = btrfs_drop_extents(trans, root, dst, drop_start, aligned_end, 1);
+	if (ret)
+		return ret;
+	ret = btrfs_insert_empty_item(trans, root, path, new_key, size);
+	if (ret)
+		return ret;
+
+	if (skip) {
+		const u32 start = btrfs_file_extent_calc_inline_size(0);
+
+		memmove(inline_data + start, inline_data + start + skip, datal);
+	}
+
+	write_extent_buffer(path->nodes[0], inline_data,
+			    btrfs_item_ptr_offset(path->nodes[0],
+						  path->slots[0]),
+			    size);
+	inode_add_bytes(dst, datal);
+	set_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &BTRFS_I(dst)->runtime_flags);
+
+	return 0;
+}
+
+/**
+ * btrfs_clone() - clone a range from inode file to another
+ *
+ * @src: Inode to clone from
+ * @inode: Inode to clone to
+ * @off: Offset within source to start clone from
+ * @olen: Original length, passed by user, of range to clone
+ * @olen_aligned: Block-aligned value of olen
+ * @destoff: Offset within @inode to start clone
+ * @no_time_update: Whether to update mtime/ctime on the target inode
+ */
+static int btrfs_clone(struct inode *src, struct inode *inode,
+		       const u64 off, const u64 olen, const u64 olen_aligned,
+		       const u64 destoff, int no_time_update)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct btrfs_path *path = NULL;
+	struct extent_buffer *leaf;
+	struct btrfs_trans_handle *trans;
+	char *buf = NULL;
+	struct btrfs_key key;
+	u32 nritems;
+	int slot;
+	int ret;
+	const u64 len = olen_aligned;
+	u64 last_dest_end = destoff;
+
+	ret = -ENOMEM;
+	buf = kvmalloc(fs_info->nodesize, GFP_KERNEL);
+	if (!buf)
+		return ret;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		kvfree(buf);
+		return ret;
+	}
+
+	path->reada = READA_FORWARD;
+	/* Clone data */
+	key.objectid = btrfs_ino(BTRFS_I(src));
+	key.type = BTRFS_EXTENT_DATA_KEY;
+	key.offset = off;
+
+	while (1) {
+		u64 next_key_min_offset = key.offset + 1;
+		struct btrfs_file_extent_item *extent;
+		int type;
+		u32 size;
+		struct btrfs_key new_key;
+		u64 disko = 0, diskl = 0;
+		u64 datao = 0, datal = 0;
+		u8 comp;
+		u64 drop_start;
+
+		/* Note the key will change type as we walk through the tree */
+		path->leave_spinning = 1;
+		ret = btrfs_search_slot(NULL, BTRFS_I(src)->root, &key, path,
+				0, 0);
+		if (ret < 0)
+			goto out;
+		/*
+		 * First search, if no extent item that starts at offset off was
+		 * found but the previous item is an extent item, it's possible
+		 * it might overlap our target range, therefore process it.
+		 */
+		if (key.offset == off && ret > 0 && path->slots[0] > 0) {
+			btrfs_item_key_to_cpu(path->nodes[0], &key,
+					      path->slots[0] - 1);
+			if (key.type == BTRFS_EXTENT_DATA_KEY)
+				path->slots[0]--;
+		}
+
+		nritems = btrfs_header_nritems(path->nodes[0]);
+process_slot:
+		if (path->slots[0] >= nritems) {
+			ret = btrfs_next_leaf(BTRFS_I(src)->root, path);
+			if (ret < 0)
+				goto out;
+			if (ret > 0)
+				break;
+			nritems = btrfs_header_nritems(path->nodes[0]);
+		}
+		leaf = path->nodes[0];
+		slot = path->slots[0];
+
+		btrfs_item_key_to_cpu(leaf, &key, slot);
+		if (key.type > BTRFS_EXTENT_DATA_KEY ||
+		    key.objectid != btrfs_ino(BTRFS_I(src)))
+			break;
+
+		ASSERT(key.type == BTRFS_EXTENT_DATA_KEY);
+
+		extent = btrfs_item_ptr(leaf, slot,
+					struct btrfs_file_extent_item);
+		comp = btrfs_file_extent_compression(leaf, extent);
+		type = btrfs_file_extent_type(leaf, extent);
+		if (type == BTRFS_FILE_EXTENT_REG ||
+		    type == BTRFS_FILE_EXTENT_PREALLOC) {
+			disko = btrfs_file_extent_disk_bytenr(leaf, extent);
+			diskl = btrfs_file_extent_disk_num_bytes(leaf, extent);
+			datao = btrfs_file_extent_offset(leaf, extent);
+			datal = btrfs_file_extent_num_bytes(leaf, extent);
+		} else if (type == BTRFS_FILE_EXTENT_INLINE) {
+			/* Take upper bound, may be compressed */
+			datal = btrfs_file_extent_ram_bytes(leaf, extent);
+		}
+
+		/*
+		 * The first search might have left us at an extent item that
+		 * ends before our target range's start, can happen if we have
+		 * holes and NO_HOLES feature enabled.
+		 */
+		if (key.offset + datal <= off) {
+			path->slots[0]++;
+			goto process_slot;
+		} else if (key.offset >= off + len) {
+			break;
+		}
+		next_key_min_offset = key.offset + datal;
+		size = btrfs_item_size_nr(leaf, slot);
+		read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf, slot),
+				   size);
+
+		btrfs_release_path(path);
+		path->leave_spinning = 0;
+
+		memcpy(&new_key, &key, sizeof(new_key));
+		new_key.objectid = btrfs_ino(BTRFS_I(inode));
+		if (off <= key.offset)
+			new_key.offset = key.offset + destoff - off;
+		else
+			new_key.offset = destoff;
+
+		/*
+		 * Deal with a hole that doesn't have an extent item that
+		 * represents it (NO_HOLES feature enabled).
+		 * This hole is either in the middle of the cloning range or at
+		 * the beginning (fully overlaps it or partially overlaps it).
+		 */
+		if (new_key.offset != last_dest_end)
+			drop_start = last_dest_end;
+		else
+			drop_start = new_key.offset;
+
+		if (type == BTRFS_FILE_EXTENT_REG ||
+		    type == BTRFS_FILE_EXTENT_PREALLOC) {
+			struct btrfs_clone_extent_info clone_info;
+
+			/*
+			 *    a  | --- range to clone ---|  b
+			 * | ------------- extent ------------- |
+			 */
+
+			/* Subtract range b */
+			if (key.offset + datal > off + len)
+				datal = off + len - key.offset;
+
+			/* Subtract range a */
+			if (off > key.offset) {
+				datao += off - key.offset;
+				datal -= off - key.offset;
+			}
+
+			clone_info.disk_offset = disko;
+			clone_info.disk_len = diskl;
+			clone_info.data_offset = datao;
+			clone_info.data_len = datal;
+			clone_info.file_offset = new_key.offset;
+			clone_info.extent_buf = buf;
+			clone_info.item_size = size;
+			ret = btrfs_punch_hole_range(inode, path, drop_start,
+					new_key.offset + datal - 1, &clone_info,
+					&trans);
+			if (ret)
+				goto out;
+		} else if (type == BTRFS_FILE_EXTENT_INLINE) {
+			u64 skip = 0;
+			u64 trim = 0;
+
+			if (off > key.offset) {
+				skip = off - key.offset;
+				new_key.offset += skip;
+			}
+
+			if (key.offset + datal > off + len)
+				trim = key.offset + datal - (off + len);
+
+			if (comp && (skip || trim)) {
+				ret = -EINVAL;
+				goto out;
+			}
+			size -= skip + trim;
+			datal -= skip + trim;
+
+			/*
+			 * If our extent is inline, we know we will drop or
+			 * adjust at most 1 extent item in the destination root.
+			 *
+			 * 1 - adjusting old extent (we may have to split it)
+			 * 1 - add new extent
+			 * 1 - inode update
+			 */
+			trans = btrfs_start_transaction(root, 3);
+			if (IS_ERR(trans)) {
+				ret = PTR_ERR(trans);
+				goto out;
+			}
+
+			ret = clone_copy_inline_extent(inode, trans, path,
+						       &new_key, drop_start,
+						       datal, skip, size, buf);
+			if (ret) {
+				if (ret != -EOPNOTSUPP)
+					btrfs_abort_transaction(trans, ret);
+				btrfs_end_transaction(trans);
+				goto out;
+			}
+		}
+
+		btrfs_release_path(path);
+
+		last_dest_end = ALIGN(new_key.offset + datal,
+				      fs_info->sectorsize);
+		ret = clone_finish_inode_update(trans, inode, last_dest_end,
+						destoff, olen, no_time_update);
+		if (ret)
+			goto out;
+		if (new_key.offset + datal >= destoff + len)
+			break;
+
+		btrfs_release_path(path);
+		key.offset = next_key_min_offset;
+
+		if (fatal_signal_pending(current)) {
+			ret = -EINTR;
+			goto out;
+		}
+	}
+	ret = 0;
+
+	if (last_dest_end < destoff + len) {
+		/*
+		 * We have an implicit hole that fully or partially overlaps our
+		 * cloning range at its end. This means that we either have the
+		 * NO_HOLES feature enabled or the implicit hole happened due to
+		 * mixing buffered and direct IO writes against this file.
+		 */
+		btrfs_release_path(path);
+		path->leave_spinning = 0;
+
+		ret = btrfs_punch_hole_range(inode, path, last_dest_end,
+				destoff + len - 1, NULL, &trans);
+		if (ret)
+			goto out;
+
+		ret = clone_finish_inode_update(trans, inode, destoff + len,
+						destoff, olen, no_time_update);
+	}
+
+out:
+	btrfs_free_path(path);
+	kvfree(buf);
+	return ret;
+}
+
+static void btrfs_double_extent_unlock(struct inode *inode1, u64 loff1,
+				       struct inode *inode2, u64 loff2, u64 len)
+{
+	unlock_extent(&BTRFS_I(inode1)->io_tree, loff1, loff1 + len - 1);
+	unlock_extent(&BTRFS_I(inode2)->io_tree, loff2, loff2 + len - 1);
+}
+
+static void btrfs_double_extent_lock(struct inode *inode1, u64 loff1,
+				     struct inode *inode2, u64 loff2, u64 len)
+{
+	if (inode1 < inode2) {
+		swap(inode1, inode2);
+		swap(loff1, loff2);
+	} else if (inode1 == inode2 && loff2 < loff1) {
+		swap(loff1, loff2);
+	}
+	lock_extent(&BTRFS_I(inode1)->io_tree, loff1, loff1 + len - 1);
+	lock_extent(&BTRFS_I(inode2)->io_tree, loff2, loff2 + len - 1);
+}
+
+static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 len,
+				   struct inode *dst, u64 dst_loff)
+{
+	const u64 bs = BTRFS_I(src)->root->fs_info->sb->s_blocksize;
+	int ret;
+
+	/*
+	 * Lock destination range to serialize with concurrent readpages() and
+	 * source range to serialize with relocation.
+	 */
+	btrfs_double_extent_lock(src, loff, dst, dst_loff, len);
+	ret = btrfs_clone(src, dst, loff, len, ALIGN(len, bs), dst_loff, 1);
+	btrfs_double_extent_unlock(src, loff, dst, dst_loff, len);
+
+	return ret;
+}
+
+static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
+			     struct inode *dst, u64 dst_loff)
+{
+	int ret;
+	u64 i, tail_len, chunk_count;
+	struct btrfs_root *root_dst = BTRFS_I(dst)->root;
+
+	spin_lock(&root_dst->root_item_lock);
+	if (root_dst->send_in_progress) {
+		btrfs_warn_rl(root_dst->fs_info,
+"cannot deduplicate to root %llu while send operations are using it (%d in progress)",
+			      root_dst->root_key.objectid,
+			      root_dst->send_in_progress);
+		spin_unlock(&root_dst->root_item_lock);
+		return -EAGAIN;
+	}
+	root_dst->dedupe_in_progress++;
+	spin_unlock(&root_dst->root_item_lock);
+
+	tail_len = olen % BTRFS_MAX_DEDUPE_LEN;
+	chunk_count = div_u64(olen, BTRFS_MAX_DEDUPE_LEN);
+
+	for (i = 0; i < chunk_count; i++) {
+		ret = btrfs_extent_same_range(src, loff, BTRFS_MAX_DEDUPE_LEN,
+					      dst, dst_loff);
+		if (ret)
+			goto out;
+
+		loff += BTRFS_MAX_DEDUPE_LEN;
+		dst_loff += BTRFS_MAX_DEDUPE_LEN;
+	}
+
+	if (tail_len > 0)
+		ret = btrfs_extent_same_range(src, loff, tail_len, dst, dst_loff);
+out:
+	spin_lock(&root_dst->root_item_lock);
+	root_dst->dedupe_in_progress--;
+	spin_unlock(&root_dst->root_item_lock);
+
+	return ret;
+}
+
+static noinline int btrfs_clone_files(struct file *file, struct file *file_src,
+					u64 off, u64 olen, u64 destoff)
+{
+	struct inode *inode = file_inode(file);
+	struct inode *src = file_inode(file_src);
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	int ret;
+	u64 len = olen;
+	u64 bs = fs_info->sb->s_blocksize;
+
+	/*
+	 * TODO:
+	 * - split compressed inline extents.  annoying: we need to
+	 *   decompress into destination's address_space (the file offset
+	 *   may change, so source mapping won't do), then recompress (or
+	 *   otherwise reinsert) a subrange.
+	 *
+	 * - split destination inode's inline extents.  The inline extents can
+	 *   be either compressed or non-compressed.
+	 */
+
+	/*
+	 * VFS's generic_remap_file_range_prep() protects us from cloning the
+	 * eof block into the middle of a file, which would result in corruption
+	 * if the file size is not blocksize aligned. So we don't need to check
+	 * for that case here.
+	 */
+	if (off + len == src->i_size)
+		len = ALIGN(src->i_size, bs) - off;
+
+	if (destoff > inode->i_size) {
+		const u64 wb_start = ALIGN_DOWN(inode->i_size, bs);
+
+		ret = btrfs_cont_expand(inode, inode->i_size, destoff);
+		if (ret)
+			return ret;
+		/*
+		 * We may have truncated the last block if the inode's size is
+		 * not sector size aligned, so we need to wait for writeback to
+		 * complete before proceeding further, otherwise we can race
+		 * with cloning and attempt to increment a reference to an
+		 * extent that no longer exists (writeback completed right after
+		 * we found the previous extent covering eof and before we
+		 * attempted to increment its reference count).
+		 */
+		ret = btrfs_wait_ordered_range(inode, wb_start,
+					       destoff - wb_start);
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * Lock destination range to serialize with concurrent readpages() and
+	 * source range to serialize with relocation.
+	 */
+	btrfs_double_extent_lock(src, off, inode, destoff, len);
+	ret = btrfs_clone(src, inode, off, olen, len, destoff, 0);
+	btrfs_double_extent_unlock(src, off, inode, destoff, len);
+	/*
+	 * Truncate page cache pages so that future reads will see the cloned
+	 * data immediately and not the previous data.
+	 */
+	truncate_inode_pages_range(&inode->i_data,
+				round_down(destoff, PAGE_SIZE),
+				round_up(destoff + len, PAGE_SIZE) - 1);
+
+	return ret;
+}
+
+static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
+				       struct file *file_out, loff_t pos_out,
+				       loff_t *len, unsigned int remap_flags)
+{
+	struct inode *inode_in = file_inode(file_in);
+	struct inode *inode_out = file_inode(file_out);
+	u64 bs = BTRFS_I(inode_out)->root->fs_info->sb->s_blocksize;
+	bool same_inode = inode_out == inode_in;
+	u64 wb_len;
+	int ret;
+
+	if (!(remap_flags & REMAP_FILE_DEDUP)) {
+		struct btrfs_root *root_out = BTRFS_I(inode_out)->root;
+
+		if (btrfs_root_readonly(root_out))
+			return -EROFS;
+
+		if (file_in->f_path.mnt != file_out->f_path.mnt ||
+		    inode_in->i_sb != inode_out->i_sb)
+			return -EXDEV;
+	}
+
+	/* Don't make the dst file partly checksummed */
+	if ((BTRFS_I(inode_in)->flags & BTRFS_INODE_NODATASUM) !=
+	    (BTRFS_I(inode_out)->flags & BTRFS_INODE_NODATASUM)) {
+		return -EINVAL;
+	}
+
+	/*
+	 * Now that the inodes are locked, we need to start writeback ourselves
+	 * and can not rely on the writeback from the VFS's generic helper
+	 * generic_remap_file_range_prep() because:
+	 *
+	 * 1) For compression we must call filemap_fdatawrite_range() range
+	 *    twice (btrfs_fdatawrite_range() does it for us), and the generic
+	 *    helper only calls it once;
+	 *
+	 * 2) filemap_fdatawrite_range(), called by the generic helper only
+	 *    waits for the writeback to complete, i.e. for IO to be done, and
+	 *    not for the ordered extents to complete. We need to wait for them
+	 *    to complete so that new file extent items are in the fs tree.
+	 */
+	if (*len == 0 && !(remap_flags & REMAP_FILE_DEDUP))
+		wb_len = ALIGN(inode_in->i_size, bs) - ALIGN_DOWN(pos_in, bs);
+	else
+		wb_len = ALIGN(*len, bs);
+
+	/*
+	 * Since we don't lock ranges, wait for ongoing lockless dio writes (as
+	 * any in progress could create its ordered extents after we wait for
+	 * existing ordered extents below).
+	 */
+	inode_dio_wait(inode_in);
+	if (!same_inode)
+		inode_dio_wait(inode_out);
+
+	/*
+	 * Workaround to make sure NOCOW buffered write reach disk as NOCOW.
+	 *
+	 * Btrfs' back references do not have a block level granularity, they
+	 * work at the whole extent level.
+	 * NOCOW buffered write without data space reserved may not be able
+	 * to fall back to CoW due to lack of data space, thus could cause
+	 * data loss.
+	 *
+	 * Here we take a shortcut by flushing the whole inode, so that all
+	 * nocow write should reach disk as nocow before we increase the
+	 * reference of the extent. We could do better by only flushing NOCOW
+	 * data, but that needs extra accounting.
+	 *
+	 * Also we don't need to check ASYNC_EXTENT, as async extent will be
+	 * CoWed anyway, not affecting nocow part.
+	 */
+	ret = filemap_flush(inode_in->i_mapping);
+	if (ret < 0)
+		return ret;
+
+	ret = btrfs_wait_ordered_range(inode_in, ALIGN_DOWN(pos_in, bs),
+				       wb_len);
+	if (ret < 0)
+		return ret;
+	ret = btrfs_wait_ordered_range(inode_out, ALIGN_DOWN(pos_out, bs),
+				       wb_len);
+	if (ret < 0)
+		return ret;
+
+	return generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
+					    len, remap_flags);
+}
+
+loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
+		struct file *dst_file, loff_t destoff, loff_t len,
+		unsigned int remap_flags)
+{
+	struct inode *src_inode = file_inode(src_file);
+	struct inode *dst_inode = file_inode(dst_file);
+	bool same_inode = dst_inode == src_inode;
+	int ret;
+
+	if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
+		return -EINVAL;
+
+	if (same_inode)
+		inode_lock(src_inode);
+	else
+		lock_two_nondirectories(src_inode, dst_inode);
+
+	ret = btrfs_remap_file_range_prep(src_file, off, dst_file, destoff,
+					  &len, remap_flags);
+	if (ret < 0 || len == 0)
+		goto out_unlock;
+
+	if (remap_flags & REMAP_FILE_DEDUP)
+		ret = btrfs_extent_same(src_inode, off, len, dst_inode, destoff);
+	else
+		ret = btrfs_clone_files(dst_file, src_file, off, len, destoff);
+
+out_unlock:
+	if (same_inode)
+		inode_unlock(src_inode);
+	else
+		unlock_two_nondirectories(src_inode, dst_inode);
+
+	return ret < 0 ? ret : len;
+}
diff --git a/fs/btrfs/reflink.h b/fs/btrfs/reflink.h
new file mode 100644
index 000000000000..ecb309b4dad0
--- /dev/null
+++ b/fs/btrfs/reflink.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef BTRFS_REFLINK_H
+#define BTRFS_REFLINK_H
+
+#include <linux/fs.h>
+
+loff_t btrfs_remap_file_range(struct file *file_in, loff_t pos_in,
+			      struct file *file_out, loff_t pos_out,
+			      loff_t len, unsigned int remap_flags);
+
+#endif /* BTRFS_REFLINK_H */