Re: [Qemu-devel] [PATCH v4 0/9] virtio-blk: use alias properties in transport devices

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Jun 18, 2014 at 05:58:27PM +0800, Stefan Hajnoczi wrote:
> v4:
>  * Coding style: typedef struct { on a single line [Andreas]
>  * Add "dataplane: bail out on unsupported transport" for s390-virtio [Cornelia]
> 
> 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.
> 
> Cornelia Huck (1):
>   dataplane: bail out on unsupported transport
> 
> 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/dataplane/virtio-blk.c | 10 ++++++++
>  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                    | 51 +++++++++++++++++++++++++++++++++++++++++
>  13 files changed, 121 insertions(+), 47 deletions(-)

Applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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