Re: [PATCH v3 13/19] vdpa_sim: add get_config callback in vdpasim_dev_attr

[Stefano Garzarella]

On Mon, Dec 07, 2020 at 01:29:17PM +0800, Jason Wang wrote:
> On 2020/12/4 上午1:05, Stefano Garzarella wrote:
> > The get_config callback can be used by the device to fill the
> > config structure.
> > The callback will be invoked in vdpasim_get_config() before copying
> > bytes into caller buffer.
> >
> > Move vDPA-net config updates from vdpasim_set_features() in the
> > new vdpasim_net_get_config() callback.
> >
> > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > ---
> > v3:
> > - checked if get_config callback is set before call it
> > ---
> >  drivers/vdpa/vdpa_sim/vdpa_sim.c | 35 +++++++++++++++++++-------------
> >  1 file changed, 21 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > index fe71ed7890e1..f935ade0806b 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > @@ -60,6 +60,8 @@ struct vdpasim_virtqueue {
> >  #define VDPASIM_NET_FEATURES	(VDPASIM_FEATURES | \
> >  				 (1ULL << VIRTIO_NET_F_MAC))
> > +struct vdpasim;
> > +
> >  struct vdpasim_dev_attr {
> >  	u64 supported_features;
> >  	size_t config_size;
> > @@ -67,6 +69,7 @@ struct vdpasim_dev_attr {
> >  	u32 id;
> >  	work_func_t work_fn;
> > +	void (*get_config)(struct vdpasim *vdpasim, void *config);
> >  };
> >  /* State of each vdpasim device */
> > @@ -522,8 +525,6 @@ static u64 vdpasim_get_features(struct vdpa_device *vdpa)
> >  static int vdpasim_set_features(struct vdpa_device *vdpa, u64 features)
> >  {
> >  	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> > -	struct virtio_net_config *config =
> > -		(struct virtio_net_config *)vdpasim->config;
> >  	/* DMA mapping must be done by driver */
> >  	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)))
> > @@ -531,16 +532,6 @@ static int vdpasim_set_features(struct vdpa_device *vdpa, u64 features)
> >  	vdpasim->features = features & vdpasim->dev_attr.supported_features;
> > -	/* We generally only know whether guest is using the legacy interface
> > -	 * here, so generally that's the earliest we can set config fields.
> > -	 * Note: We actually require VIRTIO_F_ACCESS_PLATFORM above which
> > -	 * implies VIRTIO_F_VERSION_1, but let's not try to be clever here.
> > -	 */
> > -
> > -	config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
> > -	config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
> > -	memcpy(config->mac, macaddr_buf, ETH_ALEN);
>
>
> Patch looks good to me.
>
> But we need Michael to confirm whether doing moving like this is safe. 
> I guess what has been done were trying to make sure get_config() fail 
> before set_features(), but it's not clear to me whether it's useful.

IIUC, also looking the QEMU code, the set_features() should be called 
every time before get_config(), but to be sure, in get_config(), I can 
check for example if 'vdpasim->features' is not zero (we require 
VIRTIO_F_ACCESS_PLATFORM set).

@Michael any suggestion?

Thanks,
Stefano

> Thanks
>
>
> > -
> >  	return 0;
> >  }
> > @@ -595,8 +586,13 @@ static void vdpasim_get_config(struct vdpa_device *vdpa, unsigned int offset,
> >  {
> >  	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> > -	if (offset + len < vdpasim->dev_attr.config_size)
> > -		memcpy(buf, vdpasim->config + offset, len);
> > +	if (offset + len > vdpasim->dev_attr.config_size)
> > +		return;
> > +
> > +	if (vdpasim->dev_attr.get_config)
> > +		vdpasim->dev_attr.get_config(vdpasim, vdpasim->config);
> > +
> > +	memcpy(buf, vdpasim->config + offset, len);
> >  }
> >  static void vdpasim_set_config(struct vdpa_device *vdpa, unsigned int offset,
> > @@ -739,6 +735,16 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops = {
> >  	.free                   = vdpasim_free,
> >  };
> > +static void vdpasim_net_get_config(struct vdpasim *vdpasim, void *config)
> > +{
> > +	struct virtio_net_config *net_config =
> > +		(struct virtio_net_config *)config;
> > +
> > +	net_config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
> > +	net_config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
> > +	memcpy(net_config->mac, macaddr_buf, ETH_ALEN);
> > +}
> > +
> >  static int __init vdpasim_dev_init(void)
> >  {
> >  	struct vdpasim_dev_attr dev_attr = {};
> > @@ -747,6 +753,7 @@ static int __init vdpasim_dev_init(void)
> >  	dev_attr.supported_features = VDPASIM_NET_FEATURES;
> >  	dev_attr.nvqs = VDPASIM_VQ_NUM;
> >  	dev_attr.config_size = sizeof(struct virtio_net_config);
> > +	dev_attr.get_config = vdpasim_net_get_config;
> >  	dev_attr.work_fn = vdpasim_net_work;
> >  	vdpasim_dev = vdpasim_create(&dev_attr);