[RFC PATCH] Btrfs: btrfs_dedupe_file_range() ioctl, remove 16MiB restriction

[Timofey Titovets <nefelim4ag@gmail.com>]

At now btrfs_dedupe_file_range() restricted to 16MiB range for
limit locking time and memory requirement for dedup ioctl()

For too big input rage code silently set range to 16MiB

Let's remove that restriction by do iterating over dedup range.
That's backward compatible and will not change anything for request
less then 16MiB.

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
---
 fs/btrfs/ioctl.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index ae8fbf9d3de2..7e77d192776f 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3226,11 +3226,9 @@ ssize_t btrfs_dedupe_file_range(struct file *src_file, u64 loff, u64 olen,
 	struct inode *src = file_inode(src_file);
 	struct inode *dst = file_inode(dst_file);
 	u64 bs = BTRFS_I(src)->root->fs_info->sb->s_blocksize;
+	u64 i, tail_len, chunk_count;
 	ssize_t res;

-	if (olen > BTRFS_MAX_DEDUPE_LEN)
-		olen = BTRFS_MAX_DEDUPE_LEN;
-
 	if (WARN_ON_ONCE(bs < PAGE_SIZE)) {
 		/*
 		 * Btrfs does not support blocksize < page_size. As a
@@ -3240,7 +3238,23 @@ ssize_t btrfs_dedupe_file_range(struct file *src_file, u64 loff, u64 olen,
 		return -EINVAL;
 	}

-	res = btrfs_extent_same(src, loff, olen, dst, dst_loff);
+	tail_len = olen % BTRFS_MAX_DEDUPE_LEN;
+	chunk_count = div_u64(olen, BTRFS_MAX_DEDUPE_LEN);
+
+	for (i = 0; i < chunk_count; i++) {
+		res = btrfs_extent_same(src, loff, BTRFS_MAX_DEDUPE_LEN,
+					dst, dst_loff);
+		if (res)
+			return res;
+
+		loff += BTRFS_MAX_DEDUPE_LEN;
+		dst_loff += BTRFS_MAX_DEDUPE_LEN;
+	}
+
+	if (tail_len > 0)
+		res = btrfs_extent_same(src, loff, tail_len,
+					dst, dst_loff);
+
 	if (res)
 		return res;
 	return olen;
--
2.14.1