Re: [Qemu-devel] [PATCH v3 0/8] virtio-blk: use alias properties in transport devices

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Fri, 30 May 2014 13:17:41 +0200
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> v3:
>  * Split qdev_alias_all_properties() into its own patch [Peter Crosthwaite]
>  * Do not dereference DEVICE_CLASS(class) inline [Peter Crosthwaite]
> 
> v2:
>  * Add qdev_alias_all_properties() instead of virtio-blk-specific function [Paolo]
>  * Explain refcount handling in doc comment [Paolo]
>  * Fix "property" duplicate typo [Peter Crosthwaite]
>  * Add "the same object or" to clarify commit description [Igor]
> 
> Thanks for the feedback on the RFC.  This time around the alias property is
> implemented at the QOM property level instead of at the qdev property level.
> 
> Note that this series only addresses virtio-blk.  In later series we can
> convert virtio net, scsi, rng, and serial.
> 
> The virtio transport/device split is broken as follows:
> 
> 1. The virtio-blk device is never finalized because the transport devices
>    (virtio-blk-pci and friends) leak the refcount.
> 
> 2. If we fix the refcount leak then we double-free the 'serial' string property
>    upon hot unplug since its char* is copied into the virtio-blk device which
>    has an identical 'serial' qdev property.
> 
> This series solves both of these problems as follows:
> 
> 1. Introduce a QOM alias property that lets the transport device forward
>    property accesses into the virtio device (the child).
> 
> 2. Use alias properties in transport devices, instead of keeping a duplicate
>    copy of the VirtIOBlkConf struct.
> 
> 3. Fix the virtio-blk device refcount leak.  It's now safe to do this since the
>    double-free has been resolved.
> 
> Tested that hotplug/hotunplug of virtio-blk-pci still works.

FWIW:

I gave your qom-alias-property branch a quick test on s390.

virtio-ccw: seems to work fine, hotunplug of virtio-blk-ccw is still
fine, and the virtio-blk memory leaks due to missing finalization that
valgind complained about are gone.

s390-virtio: still boots, but with x-data-plane=on we get the
predictable segfault in virtio_blk_data_plane_start() since s390-virtio
doesn't do notifiers. Maybe the dataplane code should do a quick check
for existence of the notifier callback when it allocates the dataplane
structure?

> 
> Stefan Hajnoczi (8):
>   qom: add object_property_add_alias()
>   virtio-blk: avoid qdev property definition duplication
>   virtio-blk: move x-data-plane qdev property to virtio-blk.h
>   qdev: add qdev_alias_all_properties()
>   virtio-blk: use aliases instead of duplicate qdev properties
>   virtio-blk: drop virtio_blk_set_conf()
>   virtio: fix virtio-blk child refcount in transports
>   virtio-blk: move qdev properties into virtio-blk.c
> 
>  hw/block/virtio-blk.c          | 18 +++++++++------
>  hw/core/qdev.c                 | 21 +++++++++++++++++
>  hw/s390x/s390-virtio-bus.c     | 10 ++------
>  hw/s390x/s390-virtio-bus.h     |  1 -
>  hw/s390x/virtio-ccw.c          |  7 ++----
>  hw/s390x/virtio-ccw.h          |  1 -
>  hw/virtio/virtio-pci.c         |  7 ++----
>  hw/virtio/virtio-pci.h         |  1 -
>  include/hw/qdev-properties.h   |  2 ++
>  include/hw/virtio/virtio-blk.h | 19 ---------------
>  include/qom/object.h           | 20 ++++++++++++++++
>  qom/object.c                   | 52 ++++++++++++++++++++++++++++++++++++++++++
>  12 files changed, 112 insertions(+), 47 deletions(-)
>