Re: [PATCH 3/8] vhost-user-video: boiler plate code for vhost-user-video device

[Peter Griffin]

Hi Alex,

Thanks for reviewing.

On Tue, 11 Jan 2022, Alex Bennée wrote:
> 
> Peter Griffin <peter.griffin@linaro.org> writes:
> 
> > Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
> > ---
> >  hw/display/Kconfig                   |   5 +
> >  hw/display/meson.build               |   3 +
> >  hw/display/vhost-user-video.c        | 386 +++++++++++++++++++++++++++
> >  include/hw/virtio/vhost-user-video.h |  41 +++
> >  4 files changed, 435 insertions(+)
> >  create mode 100644 hw/display/vhost-user-video.c
> >  create mode 100644 include/hw/virtio/vhost-user-video.h
> >
> > diff --git a/hw/display/Kconfig b/hw/display/Kconfig
> > index a2306b67d8..186163b015 100644
> > --- a/hw/display/Kconfig
> > +++ b/hw/display/Kconfig
> > @@ -118,6 +118,11 @@ config VHOST_USER_VGA
> >      default y
> >      depends on VIRTIO_VGA && VHOST_USER_GPU
> >  
> > +config VHOST_USER_VIDEO
> > +    bool
> > +    default y
> > +    depends on VIRTIO && VHOST_USER
> > +
> >  config DPCD
> >      bool
> >      select AUX
> > diff --git a/hw/display/meson.build b/hw/display/meson.build
> > index 861c43ff98..48284528cf 100644
> > --- a/hw/display/meson.build
> > +++ b/hw/display/meson.build
> > @@ -37,6 +37,9 @@ softmmu_ss.add(when: 'CONFIG_MACFB', if_true: 
> > files('macfb.c'))
> >  softmmu_ss.add(when: 'CONFIG_NEXTCUBE', if_true: files('next-fb.c'))
> >  
> >  specific_ss.add(when: 'CONFIG_VGA', if_true: files('vga.c'))
> > +specific_ss.add(when: 'CONFIG_VHOST_USER_VIDEO', if_true: 
> > files('vhost-user-video.c'))
> > +specific_ss.add(when: ['CONFIG_VHOST_USER_VIDEO', 'CONFIG_VIRTIO_PCI' ],
> > +  if_true: files('vhost-user-video-pci.c'))
> >  
> >  if config_all_devices.has_key('CONFIG_QXL')
> >    qxl_ss = ss.source_set()
> > diff --git a/hw/display/vhost-user-video.c b/hw/display/vhost-user-video.c
> > new file mode 100644
> > index 0000000000..506e350365
> > --- /dev/null
> > +++ b/hw/display/vhost-user-video.c
> > @@ -0,0 +1,386 @@
> > +/*
> > + * Vhost-user VIDEO virtio device
> > + *
> > + * This is the boilerplate for instantiating a vhost-user device
> > + * implementing a virtio-video device.
> > + *
> > + * The virtio video decoder and encoder devices are virtual devices that
> > + * support encoding and decoding respectively.
> > + *
> > + * The actual back-end for this driver is the vhost-user-video daemon.
> > + * The code here just connects up the device in QEMU and allows it to
> > + * be instantiated.
> > + *
> > + * Copyright (c) 2021 Linaro Ltd
> > + *
> > + * SPDX-License-Identifier: GPL-2.0-or-later
> > + */
> > +
> > +#include "qemu/osdep.h"
> > +#include "qapi/error.h"
> > +#include "hw/qdev-properties.h"
> > +#include "hw/virtio/virtio-bus.h"
> > +#include "hw/virtio/vhost-user-video.h"
> > +#include "qemu/error-report.h"
> > +
> > +/* currently there is no VIDEO enc/dec defined in Linux virtio_ids.h */
> > +#define VIRTIO_ID_VIDEO_ENC         30
> > +#define VIRTIO_ID_VIDEO_DEC         31
> > +#define MAX_CAPS_LEN 4096
> > +
> > +static void vhost_user_video_get_config(VirtIODevice *vdev, uint8_t 
> > *config)
> > +{
> > +    VHostUserVIDEO *video = VHOST_USER_VIDEO(vdev);
> > +    struct virtio_video_config *vconfig = (struct virtio_video_config 
> > *)config;
> > +    int ret;
> > +    Error *local_err = NULL;
> > +
> > +    memset(config, 0, sizeof(struct virtio_video_config));
> > +
> > +    ret = vhost_dev_get_config(&video->vhost_dev, config,
> > +                               sizeof(struct virtio_video_config), 
> > &local_err);
> > +    if (ret) {
> > +        error_report("vhost-user-video: get device config space failed");
> > +
> > +        /*TODO vhost_dev_get_config() fails so for now lets just set
> >  it here */
> 
> Is this a lifetime issue?

I believe so. I spent some time trying to get it working, but then added this
workaround so I could progress on the virtio-video implementation.

I will take another look and see if I can get thie config coming from the daemon
as intended.

Looking at other examples, hw/display/vhost-user-gpu.c get_config() hook seems 
to call
vhost_dev_config successfully like I'm doing here.

But hw/block/vhost-user-blk.c and hw/virtio/vhost-user-vsock.c seem to have
a slightly different mechanism of using VhostDevConfigOps
.vhost_dev_config_notifier() which I don't recall having looked into that 
previously.

> 
> Otherwise:
> 
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

kind regards,

Peter.