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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <fa671cfd-f03d-5f12-9797-f1c7d9e7583c@redhat.com>
Date: Wed, 17 Jan 2018 08:10:50 +0100
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Subject: Re: [Qemu-devel] [RFC v1] block/NVMe: introduce a new vhost NVMe
 host device to QEMU
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To: "Liu, Changpeng" <changpeng.liu@intel.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: "Harris, James R" <james.r.harris@intel.com>, "Busch, Keith" <keith.busch@intel.com>, "famz@redhat.com" <famz@redhat.com>, "stefanha@gmail.com" <stefanha@gmail.com>, "mst@redhat.com" <mst@redhat.com>

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