Re: [Qemu-devel] [PATCH 0/4] dataplane: use more of the generic virtio data structures, drop hostmem

[Stefan Hajnoczi]

On Thu, Oct 10, 2013 at 05:07:15PM +0200, Paolo Bonzini wrote:
> Now that the memory API is thread-safe, we can use it in
> virtio-blk-dataplane and replace hostmem.[ch].  This series does this,
> and also changes the vring API to use VirtQueueElement (with an eye
> towards migration).  With this change, virtio-blk-dataplane is also safe
> against memory hot-unplug.
> 
> The next step would be to replace memory_region_find with
> address_space_{map,unmap}, which handle dirtying of memory correctly.
> However these APIs are not thread-safe yet, and neither is the handling
> of dirty memory (Juan's patches may be a start here).
> 
> Also, the usage of iov_discard_{front,back} may cause some complication
> when we use address_space_{map,unmap}.  We may have to change a bit the
> logic in virtio-blk-dataplane to switch to address_space_{map,unmap}.
> 
> If we do not want to do this intermediate step, the first three patches
> can be applied separately from the fourth.
> 
> Paolo Bonzini (4):
>   vring: create a common function to parse descriptors
>   vring: factor common code for error exits
>   dataplane: change vring API to use VirtQueueElement
>   dataplane: replace hostmem with memory_region_find
> 
>  hw/block/dataplane/virtio-blk.c       |  86 +++++-------
>  hw/virtio/dataplane/Makefile.objs     |   2 +-
>  hw/virtio/dataplane/hostmem.c         | 183 -------------------------
>  hw/virtio/dataplane/vring.c           | 244 
> +++++++++++++++++++++-------------
>  include/hw/virtio/dataplane/hostmem.h |  58 --------
>  include/hw/virtio/dataplane/vring.h   |   9 +-
>  6 files changed, 193 insertions(+), 389 deletions(-)
>  delete mode 100644 hw/virtio/dataplane/hostmem.c
>  delete mode 100644 include/hw/virtio/dataplane/hostmem.h

Finally looked into this series.  I think we should merge all patches so
we start exercising the thread-safe memory API as soon as possible in
the QEMU 2.0 release cycle.

Before merging I wanted to discuss the vring->broken case which I've
left a comment on.

Stefan