Btrfs Send Stream v2 Support Queued Ahead Of Linux 5.20

The Btrfs send/receive functionality allows for generating a stream of changes between two sub-volume snapshots, which can be useful for efficient backup/archive purposes, among other uses. With the Linux 5.20 kernel is send/receive support for the new "stream v2" format.

The Btrfs send kernel support allows for generating a stream of instructions that represent the delta between two sub-volume snapshots. With btrfs-receive in user-space is then support for replicating that snapshot on a different file-system, either in full or incrementally.

Now ready for Linux 5.20 after going through a number of rounds of review is the send/receive support for reading/writing compressed data. The compressed data support is the principal addition of the Btrfs send stream v2 format.

This compressed data support for send/receive makes use of BTRFS_IOC_ENCODED_WRITE that was introduced in Linux 5.18 for bypassing the transparent file-system compression or encryption and reading/writing data directly to disk.

Patches to btrfs-progs in user-space are also needed as part of this stream v2 format support.

As of yesterday the kernel-side Btrfs send stream v2 changes were queued into for-5.20, making it material to be submitted as part of the Btrfs file-system updates for the next kernel cycle.