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From: David Stevens <stevensd@chromium.org>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: "Keiichi Watanabe" <keiichiw@chromium.org>,
	"Tomasz Figa" <tfiga@chromium.org>,
	"Dmitry Morozov" <dmitry.morozov@opensynergy.com>,
	"Alexandre Courbot" <acourbot@chromium.org>,
	"Alex Lau" <alexlau@chromium.org>,
	"Dylan Reid" <dgreid@chromium.org>,
	"Stéphane Marchesin" <marcheu@chromium.org>,
	"Pawel Osciak" <posciak@chromium.org>,
	"Hans Verkuil" <hverkuil@xs4all.nl>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	geoff@hostfission.com,
	"Gurchetan Singh" <gurchetansingh@chromium.org>,
	"Linux Media Mailing List" <linux-media@vger.kernel.org>,
	virtio-dev@lists.oasis-open.org, qemu-devel@nongnu.org
Subject: Re: guest / host buffer sharing ...
Date: Wed, 6 Nov 2019 17:36:22 +0900	[thread overview]
Message-ID: <CAD=HUj7EsxrkSubmY6HE4aYJOykVKtmGXjMjeGqnoJw1KZUc5Q@mail.gmail.com> (raw)
In-Reply-To: <20191105105456.7xbhtistnbp272lj@sirius.home.kraxel.org>

> (1) The virtio device
> =====================
>
> Has a single virtio queue, so the guest can send commands to register
> and unregister buffers.  Buffers are allocated in guest ram.  Each buffer
> has a list of memory ranges for the data. Each buffer also has some

Allocating from guest ram would work most of the time, but I think
it's insufficient for many use cases. It doesn't really support things
such as contiguous allocations, allocations from carveouts or <4GB,
protected buffers, etc.

> properties to carry metadata, some fixed (id, size, application), but

What exactly do you mean by application?

> also allow free form (name = value, framebuffers would have
> width/height/stride/format for example).

Is this approach expected to handle allocating buffers with
hardware-specific constraints such as stride/height alignment or
tiling? Or would there need to be some alternative channel for
determining those values and then calculating the appropriate buffer
size?

-David

On Tue, Nov 5, 2019 at 7:55 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
>
>   Hi folks,
>
> The issue of sharing buffers between guests and hosts keeps poping
> up again and again in different contexts.  Most recently here:
>
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg656685.html
>
> So, I'm grabbing the recipient list of the virtio-vdec thread and some
> more people I know might be interested in this, hoping to have everyone
> included.
>
> Reason is:  Meanwhile I'm wondering whenever "just use virtio-gpu
> resources" is really a good answer for all the different use cases
> we have collected over time.  Maybe it is better to have a dedicated
> buffer sharing virtio device?  Here is the rough idea:
>
>
> (1) The virtio device
> =====================
>
> Has a single virtio queue, so the guest can send commands to register
> and unregister buffers.  Buffers are allocated in guest ram.  Each buffer
> has a list of memory ranges for the data.  Each buffer also has some
> properties to carry metadata, some fixed (id, size, application), but
> also allow free form (name = value, framebuffers would have
> width/height/stride/format for example).
>
>
> (2) The linux guest implementation
> ==================================
>
> I guess I'd try to make it a drm driver, so we can re-use drm
> infrastructure (shmem helpers for example).  Buffers are dumb drm
> buffers.  dma-buf import and export is supported (shmem helpers
> get us that for free).  Some device-specific ioctls to get/set
> properties and to register/unregister the buffers on the host.
>
>
> (3) The qemu host implementation
> ================================
>
> qemu (likewise other vmms) can use the udmabuf driver to create
> host-side dma-bufs for the buffers.  The dma-bufs can be passed to
> anyone interested, inside and outside qemu.  We'll need some protocol
> for communication between qemu and external users interested in those
> buffers, to receive dma-bufs (via unix file descriptor passing) and
> update notifications.  Dispatching updates could be done based on the
> application property, which could be "virtio-vdec" or "wayland-proxy"
> for example.
>
>
> commments?
>
> cheers,
>   Gerd
>

  parent reply	other threads:[~2019-11-06  8:36 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-05 10:54 guest / host buffer sharing Gerd Hoffmann
2019-11-05 11:35 ` Geoffrey McRae
2019-11-06  6:24   ` Gerd Hoffmann
2019-11-06  8:36 ` David Stevens [this message]
2019-11-06 12:41   ` Gerd Hoffmann
2019-11-06 22:28     ` Geoffrey McRae
2019-11-07  6:48       ` Gerd Hoffmann
2019-11-20 12:13       ` Tomasz Figa
2019-11-20 21:41         ` Geoffrey McRae
2019-11-21  5:51           ` Tomasz Figa
2019-12-04 22:22             ` Dylan Reid
2019-12-11  5:08               ` David Stevens
2019-12-11  9:26                 ` Gerd Hoffmann
2019-12-11 16:05                   ` [virtio-dev] " Enrico Granata
2019-12-12  6:40                   ` David Stevens
2019-12-12  9:41                     ` Gerd Hoffmann
2019-12-12 12:26                       ` David Stevens
2019-12-12 13:30                         ` Gerd Hoffmann
2019-12-13  3:21                           ` David Stevens
2019-12-16 13:47                             ` Gerd Hoffmann
2019-12-17 12:59                               ` David Stevens
2019-11-06  8:43 ` Stefan Hajnoczi
2019-11-06  9:51   ` Gerd Hoffmann
2019-11-06 10:10     ` [virtio-dev] " Dr. David Alan Gilbert
2019-11-07 11:11       ` Gerd Hoffmann
2019-11-07 11:16         ` Dr. David Alan Gilbert
2019-11-08  6:45           ` Gerd Hoffmann
2019-11-06 11:46     ` Stefan Hajnoczi
2019-11-06 12:50       ` Gerd Hoffmann
2019-11-07 12:10         ` Stefan Hajnoczi
2019-11-08  7:22           ` Gerd Hoffmann
2019-11-08  7:35             ` Stefan Hajnoczi
2019-11-09  1:41               ` Stéphane Marchesin
2019-11-09 10:12                 ` Stefan Hajnoczi
2019-11-09 11:16                   ` Tomasz Figa
2019-11-09 12:08                     ` Stefan Hajnoczi
2019-11-09 15:12                       ` Tomasz Figa
2019-11-18 10:20                         ` Stefan Hajnoczi
2019-11-20 10:11                           ` Tomasz Figa
     [not found]           ` <CAEkmjvU8or7YT7CCBe7aUx-XQ3yJpUrY4CfBOnqk7pUH9d9RGQ@mail.gmail.com>
2019-11-20 11:58             ` Tomasz Figa
2019-11-20 12:11     ` Tomasz Figa
2019-11-11  3:04   ` David Stevens
2019-11-11 15:36     ` [virtio-dev] " Liam Girdwood
2019-11-12  0:54       ` Gurchetan Singh
2019-11-12 13:56         ` Liam Girdwood
2019-11-12 22:55           ` Gurchetan Singh
2019-11-19 15:31             ` Liam Girdwood
2019-11-20  0:42               ` Gurchetan Singh
2019-11-20  9:53               ` Gerd Hoffmann
2019-11-25 16:46                 ` Liam Girdwood
2019-11-27  7:58                   ` Gerd Hoffmann

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