Re: [edk2-devel] [PATCH 1/1] OvmfPkg PlatformBootManagerLib: Move TryRunningQemuKernel()

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> While that all worked fine, probably with better performance (as Gerd
> mentioned) it was still unsatisfying that I couldn't make the plain ide
> work. It turns out that the ide interface can work without changes to
> the initrd but invocation requires separate -drive and -device options,
> somewhat like James' scsi version, namely:
> 
> -device ahci,id=ahci \
> -device ide-hd,drive=ide0,bus=ahci.0 \
> -drive
> if=none,id=ide0,file=disk.img,format=raw,cache=none,index=0,media=disk \

That is again something different, namely sata ...

> instead of my original shortcut version:
> 
> -drive file=disk.img,format=raw,cache=none,index=0,media=disk \

... while this is the older pata (with "-machine pc").

To add even more confusion: When using the more modern q35 chipset
("-machine q35") qemu will also use the more modern sata when you
use the shortcut version to attach your disk.

So, in general it is a good idea to explicitly add the storage
controller and devices you want as suggested by James.  Results
in less surprises ;)

> I'll probably stick with the better performing scsi version from now on
> although it's still interesting that the shortcut version works without
> UEFI but fails with UEFI.

I've seen guest driver failures due to missing firmware initialization
before.  Specifically firmware not setting the busmaster bit in pci
config space leading to guest driver's dma transfers failing (which of
course is a guest driver bug).

I can imagine ovmf taking shortcuts for direct kernel boot could have
that kind of effect too, and of course it could vary depending on the
kind of storage controller used.

take care,
  Gerd