7a21bee2aa
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> Message-Id: <20220707163720.1421716-5-berrange@redhat.com> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Thomas Huth <thuth@redhat.com>
83 lines
3.9 KiB
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83 lines
3.9 KiB
ReStructuredText
Boot devices on s390x
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=====================
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Booting with bootindex parameter
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--------------------------------
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For classical mainframe guests (i.e. LPAR or z/VM installations), you always
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have to explicitly specify the disk where you want to boot from (or "IPL" from,
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in s390x-speak -- IPL means "Initial Program Load"). In particular, there can
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also be only one boot device according to the architecture specification, thus
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specifying multiple boot devices is not possible (yet).
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So for booting an s390x guest in QEMU, you should always mark the
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device where you want to boot from with the ``bootindex`` property, for
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example::
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qemu-system-s390x -drive if=none,id=dr1,file=guest.qcow2 \
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-device virtio-blk,drive=dr1,bootindex=1
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For booting from a CD-ROM ISO image (which needs to include El-Torito boot
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information in order to be bootable), it is recommended to specify a ``scsi-cd``
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device, for example like this::
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qemu-system-s390x -blockdev file,node-name=c1,filename=... \
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-device virtio-scsi \
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-device scsi-cd,drive=c1,bootindex=1
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Note that you really have to use the ``bootindex`` property to select the
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boot device. The old-fashioned ``-boot order=...`` command of QEMU (and
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also ``-boot once=...``) is not supported on s390x.
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Booting without bootindex parameter
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-----------------------------------
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The QEMU guest firmware (the so-called s390-ccw bios) has also some rudimentary
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support for scanning through the available block devices. So in case you did
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not specify a boot device with the ``bootindex`` property, there is still a
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chance that it finds a bootable device on its own and starts a guest operating
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system from it. However, this scanning algorithm is still very rough and may
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be incomplete, so that it might fail to detect a bootable device in many cases.
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It is really recommended to always specify the boot device with the
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``bootindex`` property instead.
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This also means that you should avoid the classical short-cut commands like
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``-hda``, ``-cdrom`` or ``-drive if=virtio``, since it is not possible to
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specify the ``bootindex`` with these commands. Note that the convenience
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``-cdrom`` option even does not give you a real (virtio-scsi) CD-ROM device on
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s390x. Due to technical limitations in the QEMU code base, you will get a
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virtio-blk device with this parameter instead, which might not be the right
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device type for installing a Linux distribution via ISO image. It is
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recommended to specify a CD-ROM device via ``-device scsi-cd`` (as mentioned
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above) instead.
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Booting from a network device
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-----------------------------
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Beside the normal guest firmware (which is loaded from the file ``s390-ccw.img``
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in the data directory of QEMU, or via the ``-bios`` option), QEMU ships with
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a small TFTP network bootloader firmware for virtio-net-ccw devices, too. This
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firmware is loaded from a file called ``s390-netboot.img`` in the QEMU data
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directory. In case you want to load it from a different filename instead,
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you can specify it via the ``-global s390-ipl.netboot_fw=filename``
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command line option.
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The ``bootindex`` property is especially important for booting via the network.
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If you don't specify the ``bootindex`` property here, the network bootloader
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firmware code won't get loaded into the guest memory so that the network boot
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will fail. For a successful network boot, try something like this::
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qemu-system-s390x -netdev user,id=n1,tftp=...,bootfile=... \
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-device virtio-net-ccw,netdev=n1,bootindex=1
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The network bootloader firmware also has basic support for pxelinux.cfg-style
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configuration files. See the `PXELINUX Configuration page
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<https://wiki.syslinux.org/wiki/index.php?title=PXELINUX#Configuration>`__
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for details how to set up the configuration file on your TFTP server.
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The supported configuration file entries are ``DEFAULT``, ``LABEL``,
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``KERNEL``, ``INITRD`` and ``APPEND`` (see the `Syslinux Config file syntax
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<https://wiki.syslinux.org/wiki/index.php?title=Config>`__ for more
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information).
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