Btrfs: refactor btrfs_extent_same() slightly

This was originally a prep patch for changing the behavior on len=0, but
we went another direction with that. This still makes the function
slightly easier to follow.

Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -3125,26 +3125,27 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
 	int ret;
 	u64 len = olen;
 	struct cmp_pages cmp;
-	int same_inode = 0;
+	bool same_inode = (src == dst);
 	u64 same_lock_start = 0;
 	u64 same_lock_len = 0;
 
-	if (src == dst)
-		same_inode = 1;
-
 	if (len == 0)
 		return 0;
 
-	if (same_inode) {
+	if (same_inode)
 		inode_lock(src);
+	else
+		btrfs_double_inode_lock(src, dst);
 
-		ret = extent_same_check_offsets(src, loff, &len, olen);
-		if (ret)
-			goto out_unlock;
-		ret = extent_same_check_offsets(src, dst_loff, &len, olen);
-		if (ret)
-			goto out_unlock;
+	ret = extent_same_check_offsets(src, loff, &len, olen);
+	if (ret)
+		goto out_unlock;
 
+	ret = extent_same_check_offsets(dst, dst_loff, &len, olen);
+	if (ret)
+		goto out_unlock;
+
+	if (same_inode) {
 		/*
 		 * Single inode case wants the same checks, except we
 		 * don't want our length pushed out past i_size as
@@ -3172,16 +3173,6 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
 
 		same_lock_start = min_t(u64, loff, dst_loff);
 		same_lock_len = max_t(u64, loff, dst_loff) + len - same_lock_start;
-	} else {
-		btrfs_double_inode_lock(src, dst);
-
-		ret = extent_same_check_offsets(src, loff, &len, olen);
-		if (ret)
-			goto out_unlock;
-
-		ret = extent_same_check_offsets(dst, dst_loff, &len, olen);
-		if (ret)
-			goto out_unlock;
 	}
 
 	/* don't make the dst file partly checksummed */