Q on ioctl support in netfront/netback

Q on ioctl support in netfront/netback

[ravi kerur]

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Hello!!!

Our network driver support ioctl calls from applications for register
reads/writes. I am wondering can ioctl calls be supported from domU to dom0?
i.e call flow will be

application invokes ioctl ---> netfront ioctl ----->via xenbus ------>
netback ioctl ------> to actual driver in dom0

with the return path in similar fashion.

Looked at the existing netfront and netback drivers and with my
understanding it seems it is not possible. I looked at scsifront and
scsiback, assuming storage drivers should be supporting ioctls, didn't see
anything related to it. Wanted to know what's the mechanism to support
ioctls. Inputs appreciated.

Thanks
-RK

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Re: Q on ioctl support in netfront/netback

[Paul Durrant]

ravi kerur wrote:
> 
> Our network driver support ioctl calls from applications for register 
> reads/writes. I am wondering can ioctl calls be supported from domU to 
> dom0? i.e call flow will be
> 
> application invokes ioctl ---> netfront ioctl ----->via xenbus ------> 
> netback ioctl ------> to actual driver in dom0
> 
> with the return path in similar fashion.
> 

I'm wondering precisely what register in netback you wish to access?

-- 
===============================
Paul Durrant, Software Engineer

Citrix Systems (R&D) Ltd.
First Floor, Building 101
Cambridge Science Park
Milton Road
Cambridge CB4 0FY
United Kingdom
===============================

Re: Q on ioctl support in netfront/netback

[ravi kerur]

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Paul,

Registers are not in netback, they are h/w registers on NIC and the driver
supports reads/writes via ioctl calls. Driver is in dom0 and application
which reads/writes registers is run in domU.

-RK

On Mon, Feb 15, 2010 at 1:40 AM, Paul Durrant <paul.durrant@citrix.com>wrote:

> ravi kerur wrote:
>
>>
>> Our network driver support ioctl calls from applications for register
>> reads/writes. I am wondering can ioctl calls be supported from domU to dom0?
>> i.e call flow will be
>>
>> application invokes ioctl ---> netfront ioctl ----->via xenbus ------>
>> netback ioctl ------> to actual driver in dom0
>>
>> with the return path in similar fashion.
>>
>>
> I'm wondering precisely what register in netback you wish to access?
>
> --
> ===============================
> Paul Durrant, Software Engineer
>
> Citrix Systems (R&D) Ltd.
> First Floor, Building 101
> Cambridge Science Park
> Milton Road
> Cambridge CB4 0FY
> United Kingdom
> ===============================
>

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Re: Q on ioctl support in netfront/netback

[Konrad Rzeszutek Wilk]

On Mon, Feb 15, 2010 at 07:54:02AM -0800, ravi kerur wrote:
> Paul,
> 
> Registers are not in netback, they are h/w registers on NIC and the driver
> supports reads/writes via ioctl calls. Driver is in dom0 and application
> which reads/writes registers is run in domU.

You could use PCI passthrough. This way the NIC would be visible in your
DomU and you could fiddle with the registers.

Re: Q on ioctl support in netfront/netback

[Daniel Stodden]

On Mon, 2010-02-15 at 10:54 -0500, ravi kerur wrote:
> Paul,
> 
> Registers are not in netback, they are h/w registers on NIC and the
> driver supports reads/writes via ioctl calls. Driver is in dom0 and
> application which reads/writes registers is run in domU. 

Why do you want to map or preserve some register interface? 

Is this some sort of hardware multiplex? As Konrad pointed out, in that
case a PV driver is probably the wrong approach altogether.

If what you want is just a bunch of extended control plane attributes,
rather consider mapping them to xenstore. 

That's slightly more asynchronous and probably not a great option if you
need a synchronous interface. Especially if you need individual return
values, not just a bunch of fields to write into.

If the latter case, next option would be some dedicated shared memory
structure. But it's hard to imagine something like that to make
sense. :}

Daniel

Re: Q on ioctl support in netfront/netback

[ravi kerur]

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Hi Daniel,

These registers are(DMA, statistics, and other h/w related to NIC), I just
want to read those registers and in very few cases write to them. Currently,
I can run those applications in dom0 and access directly but I wanted to
check if anything is possible from domU? Other thing I tried using sockets
from domU to dom0(albeit I had clear firewall settings in dom0) but Citrix
support forum mentioned it is not the recommended way. I am not sure whether
I answered your question, let me know if you need additional info.

Thanks
-RK

On Tue, Feb 16, 2010 at 7:26 PM, Daniel Stodden
<daniel.stodden@citrix.com>wrote:

> On Mon, 2010-02-15 at 10:54 -0500, ravi kerur wrote:
> > Paul,
> >
> > Registers are not in netback, they are h/w registers on NIC and the
> > driver supports reads/writes via ioctl calls. Driver is in dom0 and
> > application which reads/writes registers is run in domU.
>
> Why do you want to map or preserve some register interface?
>
> Is this some sort of hardware multiplex? As Konrad pointed out, in that
> case a PV driver is probably the wrong approach altogether.
>
> If what you want is just a bunch of extended control plane attributes,
> rather consider mapping them to xenstore.
>
> That's slightly more asynchronous and probably not a great option if you
> need a synchronous interface. Especially if you need individual return
> values, not just a bunch of fields to write into.
>
> If the latter case, next option would be some dedicated shared memory
> structure. But it's hard to imagine something like that to make
> sense. :}
>
> Daniel
>
>

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Re: Q on ioctl support in netfront/netback

[ravi kerur]

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Hi Konrad,

Using PCI passthrough(I believe it is via config file changes) prevents
other domU's accessing the NIC correct? If I use it, would the network
transmit/receive still happen via netfront/netback drivers?

Thanks
-RK

On Tue, Feb 16, 2010 at 10:14 AM, Konrad Rzeszutek Wilk <
konrad.wilk@oracle.com> wrote:

> On Mon, Feb 15, 2010 at 07:54:02AM -0800, ravi kerur wrote:
> > Paul,
> >
> > Registers are not in netback, they are h/w registers on NIC and the
> driver
> > supports reads/writes via ioctl calls. Driver is in dom0 and application
> > which reads/writes registers is run in domU.
>
> You could use PCI passthrough. This way the NIC would be visible in your
> DomU and you could fiddle with the registers.
>

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Re: Q on ioctl support in netfront/netback

[Pasi Kärkkäinen]

On Wed, Feb 17, 2010 at 08:19:14AM -0800, ravi kerur wrote:
>    Hi Konrad,
> 
>    Using PCI passthrough(I believe it is via config file changes) prevents
>    other domU's accessing the NIC correct? If I use it, would the network
>    transmit/receive still happen via netfront/netback drivers?
> 

No. If you use PCI passthrough then the domU uses the real driver for the nic
that would also be used on baremetal or in dom0.

PCI passthrough for a NIC is only possible to one/single domU, per PCI device.

(Some multiport NICs show up as a multiple PCI devices, which allows you to 
passthrough different ports to different domUs).

-- Pasi

>    Thanks
>    -RK
> 
>    On Tue, Feb 16, 2010 at 10:14 AM, Konrad Rzeszutek Wilk
>    <[1]konrad.wilk@oracle.com> wrote:
> 
>      On Mon, Feb 15, 2010 at 07:54:02AM -0800, ravi kerur wrote:
>      > Paul,
>      >
>      > Registers are not in netback, they are h/w registers on NIC and the
>      driver
>      > supports reads/writes via ioctl calls. Driver is in dom0 and
>      application
>      > which reads/writes registers is run in domU.
> 
>      You could use PCI passthrough. This way the NIC would be visible in your
>      DomU and you could fiddle with the registers.
> 
> References
> 
>    Visible links
>    1. mailto:konrad.wilk@oracle.com

> _______________________________________________
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> Xen-devel@lists.xensource.com
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Re: Q on ioctl support in netfront/netback

[Konrad Rzeszutek Wilk]

On Wed, Feb 17, 2010 at 08:19:14AM -0800, ravi kerur wrote:
> Hi Konrad,
> 
> Using PCI passthrough(I believe it is via config file changes) prevents
> other domU's accessing the NIC correct? If I use it, would the network

That is correct.

> transmit/receive still happen via netfront/netback drivers?

If you have two NICs, where one of them is PCI passthrough and
the other dedicated to the guests, then the second can serve as
netback/netfront.

Thought I wonder if you can have the netback in the guest. This
way you could fiddle with your registers in one domain, and export
a network interface (vif) to the other guests from the domain that
owns the PCI device.

Re: Q on ioctl support in netfront/netback

[ravi kerur]

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Hi Konrad, Pasi

Thanks for your inputs. Looks like we(our team) needs to take a step back
and evaluate this and other things we have discovered in the past few days.
We will get back to you with more questions.

Thanks
-RK

On Wed, Feb 17, 2010 at 8:40 AM, Konrad Rzeszutek Wilk <
konrad.wilk@oracle.com> wrote:

> On Wed, Feb 17, 2010 at 08:19:14AM -0800, ravi kerur wrote:
> > Hi Konrad,
> >
> > Using PCI passthrough(I believe it is via config file changes) prevents
> > other domU's accessing the NIC correct? If I use it, would the network
>
> That is correct.
>
> > transmit/receive still happen via netfront/netback drivers?
>
> If you have two NICs, where one of them is PCI passthrough and
> the other dedicated to the guests, then the second can serve as
> netback/netfront.
>
> Thought I wonder if you can have the netback in the guest. This
> way you could fiddle with your registers in one domain, and export
> a network interface (vif) to the other guests from the domain that
> owns the PCI device.
>

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