Re: [Qemu-devel] The WCE issue in guest when i enable WCE in Qemu side.

[Yang Zhong]

On Wed, Jul 24, 2019 at 10:57:30AM +0200, Paolo Bonzini wrote:
> On 24/07/19 08:55, Yang Zhong wrote:
> > 
> > The SPDK code i am using is latest version, So, i feel we should
> > enable WCE feature in SPDK side by default. thanks for your help!
> 
> Note that enabling the CONFIG_WCE feature has some consequences.
> According to the spec:
> 
> - if the VIRTIO_BLK_F_CONFIG_WCE feature was negotiated and the
> writeback field in configuration space was 0 all the time between the
> submission of the write and its completion, the device MUST ensure that
> stable writes are committed to persistent storage before reporting
> completion of the write.  This means using FUA writes or something like that
> 
> - the device MUST offset VIRTIO_BLK_F_FLUSH if they offer
> VIRTIO_BLK_F_CONFIG_WCE
> 
> - if VIRTIO_BLK_F_CONFIG_WCE is negotiated but VIRTIO_BLK_F_FLUSH is
> not, the device MUST initialize writeback to 0
>
  Paolo, thanks for your reminder, these info are very helpful to me:),
  thanks, Yang.

> Paolo