Re: [RFC PATCH 0/3] VFIO: capability chains

From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [RFC PATCH 0/3] VFIO: capability chains
Date: Fri, 18 Dec 2015 13:05:49 +1100	[thread overview]
Message-ID: <567369FD.4000100@ozlabs.ru> (raw)
In-Reply-To: <20151123202614.18252.41590.stgit@gimli.home>

On 11/24/2015 07:43 AM, Alex Williamson wrote:
> Please see the commit log and comments in patch 1 for a general
> explanation of the problems that this series tries to address.  The
> general problem is that we have several cases where we want to expose
> variable sized information to the user, whether it's sparse mmaps for
> a region, as implemented here, or DMA mapping ranges of an IOMMU, or
> reserved MSI mapping ranges, etc.  Extending data structures is hard;
> extending them to report variable sized data is really hard.  After
> considering several options, I think the best approach is to copy how
> PCI does capabilities.  This allows the ioctl to only expose the
> capabilities that are relevant for them, avoids data structures that
> are too complicated to parse, and avoids creating a new ioctl each
> time we think of something else that we'd like to report.  This method
> also doesn't preclude extensions to the fixed structure since the
> offset of these capabilities is entirely dynamic.
>
> Comments welcome, I'll also follow-up to the QEMU and KVM lists with
> an RFC making use of this for mmaps skipping over the MSI-X table.
> Thanks,

Out of curiosity - could this information be exposed to the userspace via 
/sys/bus/pci/devices/xxxx:xx:xx:x/vfio_xxxx? It seems not to change after 
vfio_pci driver is bound to a device.

> Alex
>
> ---
>
> Alex Williamson (3):
>        vfio: Define capability chains
>        vfio: Define sparse mmap capability for regions
>        vfio/pci: Include sparse mmap capability for MSI-X table regions
>
>
>   drivers/vfio/pci/vfio_pci.c |  101 +++++++++++++++++++++++++++++++++++++++++++
>   include/uapi/linux/vfio.h   |   53 ++++++++++++++++++++++-
>   2 files changed, 152 insertions(+), 2 deletions(-)
> --
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-- 
Alexey