Re: [PATCH 4/8] block: remove has_variable_length from BlockDriver

[Eric Blake]

On Fri, Apr 07, 2023 at 05:32:59PM +0200, Paolo Bonzini wrote:
> Fill in the field in BlockLimits directly for host devices, and
> copy it from there for the raw format.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/file-posix.c               | 12 ++++++++----
>  block/file-win32.c               |  2 +-
>  block/io.c                       |  2 --
>  block/raw-format.c               |  3 ++-
>  include/block/block_int-common.h |  2 --
>  5 files changed, 11 insertions(+), 10 deletions(-)

The change makes sense to me.  I'm having a slight doubt on whether it
might cause any regression in the bigger picture where a regular host
file exposed as a guest image grew outside of qemu's control but where
qemu used to see the new size automatically but now won't see it until
an explicit QMP action.  But I suspect that since we already do have a
QMP size for telling qemu to do resizes itself, or to at least refresh
its notion of size (for that very case of a third-party adding more
storage and telling qemu it is now safe to use that extra space), the
explicit QMP interaction is probably sufficient, and that any such
corner-case regression I'm worrying about is not a problem in reality.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org