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

[Stefan Hajnoczi]

On Wed, Feb 13, 2019 at 06:45:20PM +0100, Stefano Garzarella wrote:
> I'm not sure if using the feature_sizes array the migration works well.
> I mean if we have QEMU 3.1 with a single queue and we want to migrate to
> QEMU 4.0 with a single queue, the config_size could be different,
> because VIRTIO_NET_F_MQ is not set in the host_features.
> 
> Maybe we should initialize a config_size to the VIRTIO_BLK_CFG_SIZE macro
> defined by Changpeng and then use the feature_sizes arrays only for the
> new features (i.e.  discard, write_zeroes)
> 
> What do you think?

I agree.  The config size must not change for existing machine types.

Your code makes sense for future features but old features must use the
static config size.

Stefan

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