Re: [PATCH RFC] btrfs: send: v2 protocol and example OTIME changes

[Omar Sandoval <osandov@osandov.com>]

On Mon, Oct 18, 2021 at 04:41:09PM +0200, David Sterba wrote:
> This is send protocol update to version 2 with example new commands.
> 
> We have many pending protocol update requests but still don't have the
> basic protocol rev in place, the first thing that must happen is to do
> the actual versioning support. In order to have something to test,
> there's an extended and a new command, that should be otherwise harmless
> and nobody should depend on it. This should be enough to validate the
> non-protocol changes and backward compatibility before we do the big
> protocol update.
> 
> The protocol version is u32 and is a new member in the send ioctl
> struct. Validity of the version field is backed by a new flag bit. Old
> kernels would fail when a higher version is requested. Version protocol
> 0 will pick the highest supported version, BTRFS_SEND_STREAM_VERSION,
> that's also exported in sysfs.
> 
> Protocol changes:
> 
> - new command BTRFS_SEND_C_UTIMES2
> - appends OTIME after the output of BTRFS_SEND_C_UTIMES
> - this is an example how to extend an existing command based on protocol
>   version
> 
> - new command BTRFS_SEND_C_OTIME
> - path BTRFS_SEND_A_PATH
> - timespec attribute BTRFS_SEND_A_OTIME
> - it's a separate command so it does not bloat any UTIMES2 commands,
>   and is emitted only after inode creation (file, dir, special files).
> 
> The patch should be a template for further protocol extensions
> 
> RFC:
> 
> - set __BTRFS_SEND_C_MAX_V1 to the last command of the version or one
>   beyond?
> - drop UTIMES2 before release?
> - naming?

If I'm understanding correctly, the main difference between this send
stream v2 and mine is the BTRFS_SEND_FLAG_VERSION flag and
btrfs_ioctl_send_args::version rather than my BTRFS_SEND_FLAG_STREAM_V2?
That's definitely a better way to do it.

What's your plan for merging this? Did you want to do this as a "trial
run" before merging the compressed send/receive stuff as protocol v3, or
did you want me to integrate these changes?