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

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  Re: [RFC PATCH 0/3] VFIO: capability chains Alexey Kardashevskiy <aik@ozlabs.ru> - 2015-12-18 03:10 +0100
    Re: [RFC PATCH 0/3] VFIO: capability chains Alex Williamson <alex.williamson@redhat.com> - 2015-12-18 03:40 +0100
      Re: [RFC PATCH 0/3] VFIO: capability chains Alexey Kardashevskiy <aik@ozlabs.ru> - 2015-12-18 05:40 +0100

#1294395 — Re: [RFC PATCH 0/3] VFIO: capability chains

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
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#1294403

On Fri, 2015-12-18 at 13:05 +1100, Alexey Kardashevskiy wrote:
> 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.

For what purpose?  vfio doesn't have a sysfs interface, why start one? 
Thanks,

Alex
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#1294432

On 12/18/2015 01:38 PM, Alex Williamson wrote:
> On Fri, 2015-12-18 at 13:05 +1100, Alexey Kardashevskiy wrote:
>> 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.
>
> For what purpose?  vfio doesn't have a sysfs interface, why start one?
> Thanks,

well, it could simplify debugging a bit if this information was available 
from the userspace without programming a test tool doing some ioctl()'s. 
Not a big deal though...



-- 
Alexey
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