[dpdk-dev] [RFC PATCH] bus/pci: avoid depending on private value in kernel source

[David Marchand]

On Wed, Jul 3, 2019 at 10:17 AM Tiwei Bie <tiwei.bie at intel.com> wrote:

> On Wed, Jul 03, 2019 at 10:01:44AM +0200, David Marchand wrote:
> > On Wed, Jul 3, 2019 at 9:58 AM Tiwei Bie <tiwei.bie at intel.com> wrote:
> >
> >     On Wed, Jul 03, 2019 at 09:36:26AM +0200, David Marchand wrote:
> >     > On Wed, Jul 3, 2019 at 9:35 AM Tiwei Bie <tiwei.bie at intel.com>
> wrote:
> >     >
> >     >     Hi David,
> >     >
> >     >     On Wed, Jul 03, 2019 at 09:02:59AM +0200, David Marchand wrote:
> >     >     > Hello,
> >     >     >
> >     >     > On Wed, Jul 3, 2019 at 7:47 AM Tiwei Bie <
> tiwei.bie at intel.com>
> >     wrote:
> >     >     >
> >     >     >     The value 40 used in VFIO_GET_REGION_ADDR() is a private
> value
> >     >     >     (VFIO_PCI_OFFSET_SHIFT) defined in Linux kernel source
> [1]. It
> >     >     >     is not part of VFIO API, and we should not depend on it.
> >     >     >
> >     >     >     [1]
> https://github.com/torvalds/linux/blob/6fbc7275c7a9/drivers
> >     /vfio/
> >     >     pci/
> >     >     >     vfio_pci_private.h#L19
> >     >     >
> >     >     >
> >     >     >
> >     >     > I did not follow linux kernel changes, is there something
> that
> >     would
> >     >     change
> >     >     > this offset?
> >     >     > It looks like a cleanup (did not look into the details yet),
> do we
> >     need
> >     >     this
> >     >     > now?
> >     >
> >     >     In VFIO/mdev [1], the offset can be something different. It
> depends
> >     >     on the parent device. It's not just a cleanup. It's a
> preparation
> >     >     for the mdev support in DPDK.
> >     >
> >     >     [1]
> https://github.com/torvalds/linux/blob/master/Documentation/
> >     >     vfio-mediated-device.txt
> >     >
> >     >
> >     >
> >     > Ok, thanks.
> >     > So we can wait for mdev to be ready before working on this.
> >
> >     What do you mean by "mdev to be ready"? RFC ready? I don't see
> >     anything blocking the discussion on this now.
> >
> >     PS. I already sent a RFC series of the mdev support in DPDK
> >         to the mailing list 3 month ago.
> >
> >
> > If you need it and the mdev support has been posted already, why not
> send a n+1
> > patchset with this patch in it?
> >
> > This patch alone looked odd to me.
>
> That series was using the old API which assumes the shift
> is 40 which may not work in some cases. And this patch is
> to fix the API. I think this patch is actually trying to
> fix a relatively independent issue -- i.e. switching to using
> the proper VFIO API to get the region offsets instead of
> depending on kernel code's internal value.
>
>
Fix, then there is something broken ?
You said this is for mdev support which is not currently part of the
features supported by DPDK.


This patch breaks the ABI by extending rte_pci_device.
You must rework it to avoid this break.


-- 
David Marchand