Re: [PATCH 1/4] Btrfs: send, bump stream version

[Mark Fasheh <mfasheh@suse.de>]

On Tue, Apr 15, 2014 at 06:34:38PM +0100, Filipe David Manana wrote:
> On Tue, Apr 15, 2014 at 6:28 PM, Mark Fasheh <mfasheh@suse.de> wrote:
> > On Tue, Apr 15, 2014 at 05:40:18PM +0100, Filipe David Borba Manana wrote:
> >> This increases the send stream version from version 1 to version 2, adding
> >> 2 new commands:
> >>
> >> 1) total data size - used to tell the receiver how much file data the stream
> >>    will add or update;
> >>
> >> 2) fallocate - used to pre-allocate space for files and to punch holes in files.
> >>
> >> This is preparation work for subsequent changes that implement the new features
> >> (computing total data size and use fallocate for better performance).
> >
> > Are these changes compatible with software using the old stream version? We
> > have snapshotting tools that are using send/recieve and it would be bad to
> > change the ABI in incompatible ways underneath them.
> >         --Mark
> 
> New versions of btrfs-progs (send stream v2 support) will still be
> able to read and process v1 streams. Older btrfs-progs (v1 only) won't
> be able to process the new commands.
> Does this answers your question Mark?

Yes it does thanks. Unfortunately though this is unacceptable behavior -
kernel upgrades are not supposed to break existing userspace interfaces.

In particular what will happen here is that the user will grab a new kernel
and then find out that their fancy snapshotting software won't work any
more.
	--Mark

--
Mark Fasheh