conf: support stateless UEFI firmware
Normally when an UEFI firmware is marked as read-only, an associated
NVRAM file will be created. Some builds of UEFI firmware, however, wish
to remain stateless and so will be read-only, but never have any NVRAM
file. To represent this concept a 'stateless' tristate bool attribute
is introduced on the <loader/> element.
There are rather a large number of permutations to consider.
With default firmware selection
* <os/>
=> Historic default, no change
* <os>
<loader stateless='yes'/>
</os>
=> Explicit version of historic default, no change
* <os>
<loader stateless='no'/>
</os>
=> Invalid, bios is always stateless
With manual legacy BIOS selection
* <os>
<loader>/path/to/seabios</loader>
...
</os>
=> Historic default, no change
* <os>
<loader stateless='yes'>/path/to/seabios</loader>
...
</os>
=> Explicit version of historic default, no change
* <os>
<loader stateless='no'>/path/to/seabios</loader>
...
</os>
=> Invalid, bios is always stateless
With manual UEFI selection
* <os>
<loader type='pflash'>/path/to/edk2</loader>
...
</os>
=> Historic default, no change
* <os>
<loader type='pflash' stateless='yes'>/path/to/edk2</loader>
...
</os>
=> Skip auto-filling NVRAM / template
* <os>
<loader type='pflash' stateless='no'>/path/to/edk2</loader>
...
</os>
=> Explicit version of historic default, no change
With automatic firmware selection
* <os firmware='bios'/>
=> Historic default, no change
* <os firmware='bios'>
<loader stateless='yes'/>
</os>
=> Explicit version of historic default, no change
* <os firmware='bios'>
<loader stateless='no'/>
</os>
=> Invalid, bios is always stateless
* <os firmware='uefi'/>
=> Historic default, no change
* <os firmware='uefi'>
<loader stateless='yes'/>
</os>
=> Skip auto-filling NVRAM / template
* <os firmware='uefi'>
<loader stateless='no'/>
</os>
=> Explicit version of historic default, no change
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
2022-07-22 14:27:55 +00:00
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Only pflash loader type permits NVRAM
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