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From:   Yongji Xie <xieyongji@bytedance.com>
Date:   Mon, 17 May 2021 17:41:31 +0800
Message-ID: <CACycT3vO53+GGZ+Lw2_ervZFk-J647gmGb+G6DFL6mpfk4+gbQ@mail.gmail.com>
Subject: Re: Re: [RFC PATCH 01/17] virtio_ring: Avoid reading unneeded used length
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>, amit@kernel.org,
        arei.gonglei@huawei.com, airlied@linux.ie, kraxel@redhat.com,
        dan.j.williams@intel.com, Ohad Ben Cohen <ohad@wizery.com>,
        bjorn.andersson@linaro.org, david@redhat.com, vgoyal@redhat.com,
        miklos@szeredi.hu, Stefano Garzarella <sgarzare@redhat.com>,
        virtualization <virtualization@lists.linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Mon, May 17, 2021 at 5:12 PM Johannes Berg <johannes@sipsolutions.net> w=
rote:
>
> On Mon, 2021-05-17 at 17:08 +0800, Xie Yongji wrote:
> > If device driver doesn't need used length, it can pass a NULL
> > len in virtqueue_get_buf()/virtqueue_get_buf_ctx().
> >
>
> Well, actually, it can't right now?
>

Yes.

> You should probably rephrase this, saying something like
>
>    Allow passing NULL to len in ... if the device driver doesn't need
>    the length, and don't read it in that case.
>
> or so?
>

Looks good to me.

> >  Then
> > we can avoid reading and validating the len value in used
> > ring entries.
>
> Not sure what that "validating" is about, I only see reading?
>

The =E2=80=9Cvalidating" is actually done in the last patch of this series.
Will remove it.

Thanks,
Yongji