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docs/system: Update documentation for s390x IPL 

Update docs to show that s390x PC BIOS can support more than one boot device.

Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20241020012953.1380075-19-jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This commit is contained in:
Jared Rossi 2024-10-19 21:29:52 -04:00 committed by Thomas Huth
parent f697bed22f
commit 0bd107138f
2 changed files with 10 additions and 6 deletions
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7
docs/system/bootindex.rst
View File

@ -49,10 +49,11 @@ Limitations
-----------
Some firmware has limitations on which devices can be considered for
booting. For instance, the PC BIOS boot specification allows only one
disk to be bootable. If boot from disk fails for some reason, the BIOS
booting. For instance, the x86 PC BIOS boot specification allows only one
disk to be bootable. If boot from disk fails for some reason, the x86 BIOS
won't retry booting from other disk. It can still try to boot from
floppy or net, though.
floppy or net, though. In the case of s390x BIOS, the BIOS will try up to
8 total devices, any number of which may be disks.
Sometimes, firmware cannot map the device path QEMU wants firmware to
boot from to a boot method. It doesn't happen for devices the firmware

9
docs/system/s390x/bootdevices.rst
View File

@ -6,9 +6,7 @@ Booting with bootindex parameter
For classical mainframe guests (i.e. LPAR or z/VM installations), you always
have to explicitly specify the disk where you want to boot from (or "IPL" from,
in s390x-speak -- IPL means "Initial Program Load"). In particular, there can
also be only one boot device according to the architecture specification, thus
specifying multiple boot devices is not possible (yet).
in s390x-speak -- IPL means "Initial Program Load").
So for booting an s390x guest in QEMU, you should always mark the
device where you want to boot from with the ``bootindex`` property, for
@ -17,6 +15,11 @@ example::
qemu-system-s390x -drive if=none,id=dr1,file=guest.qcow2 \
-device virtio-blk,drive=dr1,bootindex=1
Multiple devices may have a bootindex. The lowest bootindex is assigned to the
device to IPL first. If the IPL fails for the first, the device with the second
lowest bootindex will be tried and so on until IPL is successful or there are no
remaining boot devices to try.
For booting from a CD-ROM ISO image (which needs to include El-Torito boot
information in order to be bootable), it is recommended to specify a ``scsi-cd``
device, for example like this::