Re: [Qemu-devel] [RFC v1] block/NVMe: introduce a new vhost NVMe host device to QEMU

[Paolo Bonzini]

On 17/01/2018 01:53, Liu, Changpeng wrote:
>> Second, virtio-based vhost-user remains QEMU's preferred method for
>> high-performance I/O in guests.  Discard support is missing and that is
>> important for SSDs; that should be fixed in the virtio spec.  Are there
> Previously I have a patch adding DISCARD support to virtio-blk, but I didn't 
> find
> the way using svn to update the spec patch, any git repository I can use
> to update the virtio-blk spec ? I think I can pick up the feature again.

There is https://github.com/oasis-tcs/virtio-spec.

You should add support for all of:

1) a command that can do WRITE ZERO, WRITE ZERO with discard, and
advisory DISCARD of a range of blocks.  The command must be controlled
by a new feature bit.

2) a configuration space element for discard granularity, controlled by
the same feature bit as (1)

3) a feature bit that is 1 if WRITE ZERO with discard can actually
discard parts that are aligned to the granularity

Thanks,

Paolo