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docs/system/s390x: Document the "loadparm" machine property

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The "loadparm" machine property is useful for selecting alternative
kernels on the disk of the guest, but so far we do not tell the users
yet how to use it. Add some documentation to fill this gap.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2128235
Message-Id: <20221114132502.110213-1-thuth@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This commit is contained in:
Thomas Huth 2022-11-14 14:25:02 +01:00
parent 44ee69ea16
commit be5df2edb5
1 changed files with 26 additions and 0 deletions
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26
docs/system/s390x/bootdevices.rst
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@ -53,6 +53,32 @@ recommended to specify a CD-ROM device via ``-device scsi-cd`` (as mentioned
above) instead.
Selecting kernels with the ``loadparm`` property
------------------------------------------------
The ``s390-ccw-virtio`` machine supports the so-called ``loadparm`` parameter
which can be used to select the kernel on the disk of the guest that the
s390-ccw bios should boot. When starting QEMU, it can be specified like this::
qemu-system-s390x -machine s390-ccw-virtio,loadparm=<string>
The first way to use this parameter is to use the word ``PROMPT`` as the
``<string>`` here. In that case the s390-ccw bios will show a list of
installed kernels on the disk of the guest and ask the user to enter a number
to chose which kernel should be booted -- similar to what can be achieved by
specifying the ``-boot menu=on`` option when starting QEMU. Note that the menu
list will only show the names of the installed kernels when using a DASD-like
disk image with 4k byte sectors. On normal SCSI-style disks with 512-byte
sectors, there is not enough space for the zipl loader on the disk to store
the kernel names, so you only get a list without names here.
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.
Booting from a network device
-----------------------------