Re: [PATCH v2 3/3] docs/s390x: document vfio-ccw

[Thomas Huth]

On 15/05/2020 17.15, Cornelia Huck wrote:
> Add a basic example for passing a dasd via vfio-ccw.
> 
> Signed-off-by: Cornelia Huck <address@hidden>
> ---
>  docs/system/s390x/vfio-ccw.rst | 72 ++++++++++++++++++++++++++++++++++
>  docs/system/target-s390x.rst   |  1 +
>  2 files changed, 73 insertions(+)
>  create mode 100644 docs/system/s390x/vfio-ccw.rst
> 
> diff --git a/docs/system/s390x/vfio-ccw.rst b/docs/system/s390x/vfio-ccw.rst
> new file mode 100644
> index 000000000000..4cfd22c3b789
> --- /dev/null
> +++ b/docs/system/s390x/vfio-ccw.rst
> @@ -0,0 +1,72 @@
> +Subchannel passthrough via vfio-ccw
> +===================================
> +
> +vfio-ccw (based upon the mediated vfio device infrastructure) allows to
> +make certain I/O subchannels and their devices available to a guest. The
> +host will not interact with those subchannels/devices any more.
> +
> +Note that while vfio-ccw should work with most non-QDIO devices, only ECKD
> +DASDs have really been tested.
> +
> +Example configuration
> +---------------------
> +
> +Step 1: configure the host device
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +Note: it is recommended to use the ``mdevctl`` tool for this step.
> +
> +To define the same device as configured below to be started
> +automatically, use
> +
> +::
> +
> +   [root@host ~]# driverctl -b css set-override 0.0.0313 vfio_ccw
> +   [root@host ~]# mdevctl define -u 7e270a25-e163-4922-af60-757fc8ed48c6\
> +                  -p 0.0.0313 -t vfio-ccw_io -a
> +
> +If this is not possible or wanted, follow the manual procedure below.
> +
> +* Locate the subchannel for the device (in this example, ``0.0.2b09``)::
> +
> +    [root@host ~]# lscss | grep 0.0.2b09 | awk '{print $2}'
> +    0.0.0313
> +
> +* Unbind the subchannel (in this example, ``0.0.0313``) from the standard
> +  I/O subchannel driver and bind it to the vfio-ccw driver::
> +
> +    [root@host ~]# echo 0.0.0313 > 
> /sys/bus/css/devices/0.0.0313/driver/unbind
> +    [root@host ~]# echo 0.0.0313 > /sys/bus/css/drivers/vfio_ccw/bind
> +
> +* Create the mediated device (identified by a uuid)::
> +
> +    [root@host ~]# uuidgen
> +    7e270a25-e163-4922-af60-757fc8ed48c6

Maybe the uuidgen lines should now be moved before the mdevctl example
already, so that it is already clear there where the uuid comes from?

 Thomas