From 407e23d7f0c9020404247afe7d4df98505222bbb Mon Sep 17 00:00:00 2001
From: Thomas Huth <thuth@redhat.com>
Date: Mon, 14 Nov 2022 14:25:02 +0100
Subject: [PATCH 1/3] docs/system/s390x: Document the "loadparm" machine
property
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RH-Author: Thomas Huth <thuth@redhat.com>
RH-MergeRequest: 233: s390x: Document the "loadparm" machine property
RH-Bugzilla: 2128225
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
RH-Acked-by: Cédric Le Goater <clg@redhat.com>
RH-Acked-by: Jon Maloy <jmaloy@redhat.com>
RH-Commit: [1/2] e9589ea32d2a8f82971476b644e1063fa14cf822
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>
(cherry picked from commit be5df2edb5d69ff3107c5616aa035a9ba8d0422e)
---
docs/system/s390x/bootdevices.rst | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/docs/system/s390x/bootdevices.rst b/docs/system/s390x/bootdevices.rst
index 9e591cb9dc..d4bf3b9f0b 100644
--- a/docs/system/s390x/bootdevices.rst
+++ b/docs/system/s390x/bootdevices.rst
@@ -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
-----------------------------
--
2.37.3