Re: [PATCH 1/2] vdpa/mlx5: Make VIRTIO_NET_F_MRG_RXBUF off by default

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On Tue, Mar 14, 2023 at 02:05:50AM +0000, Parav Pandit wrote:
> > From: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
> > Sent: Monday, March 13, 2023 6:19 PM
> > Actually there's no such burden or requirement to maintain backward
> > compatibility for the default 'vdpa dev add' behavior if dedicated
> > device_features is not specified. Historically the default vdpa creation on mlx5
> > ever got changed from single queue to 8 queue pairs when VIRTIO_NET_F_MQ
> > feature was first introduced to mlx5_vdpa, then the default switched back to 1
> > data queue pair again when max_vqp attribute was added to the vdpa tool.
> > Essentially, every addition of new feature to mlx5_vdpa, e.g. CTRL_VQ,
> > CTRL_VLAN, and et al, effectively changed the default "vdpa dev add" behavior
> > not just only once: the backward compatibility guarantee is simply just not
> > there and ever.
> This requires that every change in the device attributes will change the behavior for vdpa dev add.
> The OR operation of the user supplied feature bits with device defaults feature bit doesn’t look good to me.
> It brings uncertain behavior.
> The right behavior should be, if user supplied the feature bits, it should supply all desired bits.

I think u mean all that device also supports.

> If user doesn’t supply feature bits, use the device defaults.
> But not to mix both feature bits.

Can't say I understand what this means. What does "both" mean here?


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