netdev - Re: [net-next v2 1/1] virtual-bus: Implementation of Virtual Bus

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Date:   Sat, 23 Nov 2019 11:50:11 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Parav Pandit <parav@...lanox.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        davem@...emloft.net, gregkh@...uxfoundation.org,
        Dave Ertman <david.m.ertman@...el.com>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, nhorman@...hat.com,
        sassmann@...hat.com, Kiran Patil <kiran.patil@...el.com>,
        Tiwei Bie <tiwei.bie@...el.com>
Subject: Re: [net-next v2 1/1] virtual-bus: Implementation of Virtual Bus

On Thu, Nov 21, 2019 at 09:44:38AM -0400, Jason Gunthorpe wrote:
> On Wed, Nov 20, 2019 at 11:24:03PM -0500, Michael S. Tsirkin wrote:
> > On Wed, Nov 20, 2019 at 11:03:57PM -0400, Jason Gunthorpe wrote:
> > > Frankly, when I look at what this virtio stuff is doing I see RDMA:
> > >  - Both have a secure BAR pages for mmaping to userspace (or VM)
> > >  - Both are prevented from interacting with the device at a register
> > >    level and must call to the kernel - ie creating resources is a
> > >    kernel call - for security.
> > >  - Both create command request/response rings in userspace controlled
> > >    memory and have HW DMA to read requests and DMA to generate responses
> > >  - Both allow the work on the rings to DMA outside the ring to
> > >    addresses controlled by userspace.
> > >  - Both have to support a mixture of HW that uses on-device security
> > >    or IOMMU based security.
> > 
> > The main difference is userspace/drivers need to be portable with
> > virtio.
> 
> rdma also has a stable/portable user space library API that is
> portable to multiple operating systems.
> 
> What you don't like is that RDMA userspace has driver-specific
> code. Ie the kernel interface is not fully hardware independent.
> 
> Jason

Right. Not that I don't like it, it has some advantages too.
But it's addressing a different need which a vendor
specific userspace driver doesn't address.

-- 
MST