linux-kernel - Re: [PATCH v4 00/17] Add VFIO mediated device support and DEV-MSI support for the idxd driver

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Message-ID: <CAPcyv4h8O+boTo-MpGRSC8RpjrsvU-P3AU7_kwbrfDkEp8bH1w@mail.gmail.com>
Date:   Mon, 2 Nov 2020 10:38:28 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Dave Jiang <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vinod Koul <vkoul@...nel.org>,
        "Dey, Megha" <megha.dey@...el.com>, maz@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Yi L Liu <yi.l.liu@...el.com>, Baolu Lu <baolu.lu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Sanjay K Kumar <sanjay.k.kumar@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>, Jing Lin <jing.lin@...el.com>,
        kwankhede@...dia.com, eric.auger@...hat.com,
        Parav Pandit <parav@...lanox.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, netanelg@...lanox.com,
        shahafs@...lanox.com, yan.y.zhao@...ux.intel.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Samuel Ortiz <samuel.ortiz@...el.com>,
        Mona Hossain <mona.hossain@...el.com>,
        Megha Dey <megha.dey@...ux.intel.com>,
        dmaengine@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v4 00/17] Add VFIO mediated device support and DEV-MSI
 support for the idxd driver

On Mon, Nov 2, 2020 at 10:26 AM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Mon, Nov 02, 2020 at 11:18:33AM -0700, Dave Jiang wrote:
> >
> >
> > On 11/2/2020 10:19 AM, Jason Gunthorpe wrote:
> > > On Mon, Nov 02, 2020 at 08:20:43AM -0800, Raj, Ashok wrote:
> > > > Creating these private interfaces for intra-module are just 1-1 and not
> > > > general purpose and every accelerator needs to create these instances.
> > >
> > > This is where we are going, auxillary bus should be merged soon which
> > > is specifically to connect these kinds of devices across subsystems
> >
> > I think this resolves the aux device probe/remove issue via a common bus.
> > But it does not help with the mdev device needing a lot of the device
> > handling calls from the parent driver as it share the same handling as the
> > parent device.
>
> The intention of auxiliary bus is that the two parts will tightly
> couple across some exported function interface.
>
> > My plan is to export all the needed call via EXPORT_SYMBOL_NS() so
> > the calls can be shared in its own namespace between the modules. Do
> > you have any objection with that?
>
> I think you will be the first to use the namespace stuff for this, it
> seems like a good idea and others should probably do so as well.

I was thinking either EXPORT_SYMBOL_NS, or auxiliary bus, because you
should be able to export an ops structure with all the necessary
callbacks. Aux bus seems cleaner because the lifetime rules and
ownership concerns are clearer.