Re: [Qemu-devel] [PATCH v4] virtio-blk: set correct config size for the host driver

[Stefano Garzarella]

On Wed, Feb 13, 2019 at 04:01:43PM +0800, Stefan Hajnoczi wrote:
> On Wed, Feb 13, 2019 at 09:48:57AM +0800, Changpeng Liu wrote:
> > Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features
> > support" added fields to struct virtio_blk_config. This changes
> > the size of the config space and breaks migration from QEMU 3.1
> > and older:
> > 
> > qemu-system-ppc64: get_pci_config_device: Bad config data: i=0x10 read: 41 
> > device: 1 cmask: ff wmask: 80 w1cmask:0
> > qemu-system-ppc64: Failed to load PCIDevice:config
> > qemu-system-ppc64: Failed to load virtio-blk:virtio
> > qemu-system-ppc64: error while loading state for instance 0x0 of device 
> > 'address@hidden:01.0/virtio-blk'
> > qemu-system-ppc64: load of migration failed: Invalid argument
> > 
> > Since virtio-blk doesn't support the "discard" and "write zeroes"
> > features, it shouldn't even expose the associated fields in the
> > config space actually. Just include all fields up to num_queues to
> > match QEMU 3.1 and older.
> > 
> > Signed-off-by: Changpeng Liu <address@hidden>
> > ---
> >  hw/block/virtio-blk.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> Stefano: Please rebase your DISCARD/WRITE_ZEROES series onto this and
> check that the config space is correctly sized.  Machine types before
> 4.0 shouldn't have these fields so that the config space size remains
> unchanged.

Sure!

Since I should set a correct config size checking if new features are
enabled or not at runtime, should be better to add a variable and an array
of sizes like in virtio-net?

Thanks,
Stefano