On Wed, Oct 27, 2021 at 03:17:46PM +0800, Anand Jain wrote:

On 22/10/2021 22:53, David Sterba wrote:

quoted

--- a/fs/btrfs/send.h
+++ b/fs/btrfs/send.h

@@ -48,6 +48,7 @@ struct btrfs_tlv_header {
  enum btrfs_send_cmd {
  	BTRFS_SEND_C_UNSPEC,
  
+	/* Version 1 */
  	BTRFS_SEND_C_SUBVOL,
  	BTRFS_SEND_C_SNAPSHOT,
  

@@ -76,6 +77,12 @@ enum btrfs_send_cmd {
  
  	BTRFS_SEND_C_END,
  	BTRFS_SEND_C_UPDATE_EXTENT,
+	__BTRFS_SEND_C_MAX_V1,
+
+	/* Version 2 */
+	__BTRFS_SEND_C_MAX_V2,
+

  Isn't this has to be in tandem with BTRFS_SEND_STREAM_VERSION == 2?

The patch is only preparatory and adds the base code for the real
protocol updates where the STREAM_VERSION will be increased, but does
not do that yet so we don't falsely advertise v2 support when there's no
such thing.

  The changelog doesn't explain the plan of __BTRFS_SEND_C_MAX_Vx use case.

It's supposed to prevent doubts and questions "what should I do when I
want to add v2 command" and make the code ready for anybody working on
the v2 update.