[PATCH 1/4] conf: add loader type 'none'

[Daniel Henrique Barboza]

On 3/22/23 13:37, Andrea Bolognani wrote:
> On Wed, Mar 22, 2023 at 10:36:20AM -0300, Daniel Henrique Barboza wrote:
>> I'm not sure if the OS overwrites the firmware when running bare metal. Usually
>> they provide different OS images for QEMU/libvirt and bare metal systems, probably
>> to account for these differences. Baking the firmware in the kernel like Fedora
>> Rawhide is doing was important a few years ago when RISC-V QEMU wasn't loading
>> the firmware by default, but now it's getting in the way.
>>
>> All this said, having a look at the recently updated Fedora for RISC-V wiki, the
>> instructions for booting with libvirt and QEMU are different. libvirt [1] is using
>> the '-bios none' attribute with 'virt-install' + a Fedora Rawhide image, but
>> QEMU instructions [2] doesn't use '-bios none' and it's using Fedora 37.
> 
> The libvirt instructions in that page seem to have been updated in
> the Fedora 30 timeframe, whereas the QEMU instructions appear to be
> current as of Fedora 37.
> 
>> At first I don't see any particular reason of why this Fedora 37 image would work
>> on QEMU and not on libvirt. So what t I'll do now is do some testings with libvirt
>> and Fedora 37. If it works then this series becomes way less important.
> 
> The libvirt instructions tell you to use
> 
>    --boot kernel=Fedora-Developer-Rawhide-*-fw_payload-uboot-qemu-virt-smode.elf
>    --qemu-commandline='-bios none'
> 
> (aka -bios none -kernel foo) while the QEMU ones suggest
> 
>    -bios u/usr/share/uboot/qemu-riscv64_spl/u-boot-spl.bin
>    -device loader,file=u/usr/share/uboot/qemu-riscv64_spl/u-boot.itb,addr=0x80200000
> 
> Those are completely different approaches to booting the guest OS.
> The latter is much saner IMO, because it keeps the firmware under
> control of the host (as is the case for SeaBIOS/edk2) instead of
> mixing the kernel and the firmware and requiring guest-specific files
> to be extracted from the disk image before being able to boot.
> 
> libvirt already provides the ability to pass arbitrary paths to -bios
> via the <loader type='rom'> element, so making the first part work
> should just be a matter of pointing it to the correct path. We don't
> seem to have the -device loader part wired up though, so that would
> need to be added. Probably as an additional attribute, in the vein of
> nvram.template? The address would have to be specified as well.
> 
> Note that the firmware descriptor format already supports u-boot as
> the firmware type. So in the long run ideally you'd only need to
> specify
> 
>    <os firmware='uboot'>
> 
> and, assuming the uboot-images-riscv64 package is installed on the
> host, everything should just work.


So, I got the chance to try this out. We can remove the '-loader' from the
Fedora 37 command line. This:

-device loader,file=u/usr/share/uboot/qemu-riscv64_spl/u-boot.itb,addr=0x80200000

Is loading the u-boot image in the address that the 'virt' machine loads the kernel.
So in the end it's similar to:

-kernel u/usr/share/uboot/qemu-riscv64_spl/u-boot.itb

This means that RISC-V Fedora 37 is bootable without any libvirt changes. Similar to
what we already do with Ubuntu.

Thus, unless there's another reason to add '-bios none' support, we can ditch this
series.


Thanks,


Daniel

>