linux-kernel - Re: [PATCH vhost v4 02/15] vdpa: Add VHOST_BACKEND_F_CHANGEABLE_VQ_ADDR_IN

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Date: Fri, 22 Dec 2023 03:29:02 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: "eperezma@...hat.com" <eperezma@...hat.com>,
	"xuanzhuo@...ux.alibaba.com" <xuanzhuo@...ux.alibaba.com>,
	Parav Pandit <parav@...dia.com>, Gal Pressman <gal@...dia.com>,
	"virtualization@...ts.linux-foundation.org" <virtualization@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"si-wei.liu@...cle.com" <si-wei.liu@...cle.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Saeed Mahameed <saeedm@...dia.com>,
	"leon@...nel.org" <leon@...nel.org>
Subject: Re: [PATCH vhost v4 02/15] vdpa: Add
 VHOST_BACKEND_F_CHANGEABLE_VQ_ADDR_IN_SUSPEND flag

On Thu, Dec 21, 2023 at 03:07:22PM +0000, Dragos Tatulea wrote:
> > > > In that case you're right, we don't need feature flags. But I think it
> > > > would be great to also move the error return in case userspace tries
> > > > to modify vq parameters out of suspend state.
> > > > 
> > > On the driver side or on the core side?
> > > 
> > 
> > Core side.
> > 
> Checking my understanding: instead of the feature flags there would be a check
> (for .set_vq_addr and .set_vq_state) to return an error if they are called under
> DRIVER_OK and not suspended state?

Yea this looks much saner, if we start adding feature flags for
each OPERATION_X_LEGAL_IN_STATE_Y then we will end up with N^2
feature bits which is not reasonable.

-- 
MST