Re: [PATCH] docs/system/s390x/bootdevices: Update loadparm documentation

[Thomas Huth <thuth@redhat.com>]

On 15/11/2024 01.27, jrossi@linux.ibm.com wrote:
> From: Jared Rossi <jrossi@linux.ibm.com>
> 
> Update documentation to include per-device loadparm support.
> 
> Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
> ---
>   docs/system/s390x/bootdevices.rst | 24 +++++++++++++++++++++++-
>   1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/system/s390x/bootdevices.rst b/docs/system/s390x/bootdevices.rst
> index 1a1a764c1c..ecb22de04a 100644
> --- a/docs/system/s390x/bootdevices.rst
> +++ b/docs/system/s390x/bootdevices.rst
> @@ -79,7 +79,29 @@ The second way to use this parameter is to use a number in the range from 0
>   to 31. The numbers that can be used here correspond to the numbers that are
>   shown when using the ``PROMPT`` option, and the s390-ccw bios will then try
>   to automatically boot the kernel that is associated with the given number.
> -Note that ``0`` can be used to boot the default entry.
> +Note that ``0`` can be used to boot the default entry. If the machine
> +``loadparm`` is not assigned a value, then the default entry is used.
> +
> +By default, the machine ``loadparm`` applies to all boot devices. If multiple
> +devices are assigned a ``bootindex`` and the ``loadparm`` is to be different
> +between them, an independent ``loadparm`` may be assigned on a per-device basis.
> +
> +An example guest using per-device ``loadparm``::
> +
> +  qemu-system-s390x -drive if=none,id=dr1,file=primary.qcow2 \
> +                   -device virtio-blk,drive=dr1,bootindex=1 \
> +                   -drive if=none,id=dr2,file=secondary.qcow2 \
> +                   -device virtio-blk,drive=dr2,bootindex=2,loadparm=3
> +
> +In this case, the primary boot device will attempt to IPL using the default
> +entry (because no ``loadparm`` is specified for this device or for the
> +machine). If that device fails to boot, the secondary device will attempt to
> +IPL using entry number 3.
> +
> +If a ``loadparm`` is specified on both the machine and a device, the per-device
> +value will superseded the machine value.  Per-device ``loadparm`` values are
> +only used for devices with an assigned ``bootindex``. The machine ``loadparm``
> +is used when attempting to boot without a ``bootindex``.

Reviewed-by: Thomas Huth <thuth@redhat.com>