hmp: 'drive_add -n' for creating a node without BB

Enterprise / Virtualization / QEMU - Kevin Wolf [redhat.com] - 14 March 2016 10:46 UTC

This patch adds an option to the drive_add HMP command to create only a BlockDriverState without a BlockBackend on top.

The motivation for this is that libvirt needs to specify options to a migration target (specifically, detect-zeroes). drive-mirror doesn't allow specifying options, and the proper way to do this is to create the target BDS separately with blockdev-add (where you can specify options) and then use blockdev-mirror to that BDS.

However, libvirt can't use blockdev-add as long as it is still experimental, and we're expecting that it will still take some time, so we need to resort to drive_add.

The problem with drive_add is that so far it always created a BB, and BDSes with a BB can't be used as a mirroring target as long as we don't support multiple BBs per BDS - and while we're working towards that goal, it's another thing that will still take some time.

So to achieve the goal, the simplest solution to provide the functionality now without adding one-off options to the mirror QMP commands is to extend drive_add to create nodes without BBs.

abb21ac hmp: 'drive_add -n' for creating a node without BB
blockdev.c | 30 ++++++++++++++++++++++++++++++
device-hotplug.c | 7 +++++++
hmp-commands.hx | 4 ++--
include/block/block_int.h | 2 ++
4 files changed, 41 insertions(+), 2 deletions(-)

Upstream: git.qemu.org

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