Re: [Qemu-ppc] [PATCH] Workaround to bypass default qemu boot devices passed to SLOF

[Avik Sil]

On 10/05/2012 05:39 PM, Alexander Graf wrote:
> On 05.10.2012, at 13:41, Nikunj A Dadhania wrote:
>
> > On Fri, 5 Oct 2012 12:24:47 +0200, Alexander Graf <address@hidden> wrote:
> > > On 05.10.2012, at 10:29, Avik Sil <address@hidden> wrote:
> > >
> > > > Hi David,
> > > >
> > > > Please find below the patch for working around the default boot device issue 
> > > > currently being discussed on the list.
> > > >
> > > > Regards,
> > > > Avik
> > > > ---
> > > >
> > > > The default qemu boot_devices string passed to firmware is "cad"
> > > > which creates a confusion whether -boot oprion is specified or
> > > > not. This patch handles this issue by setting a global flag when
> > > > no -boot option is specified.
> > >
> > > Hrm. How does x86 distinguish between -boot and bootindex=?
> >
> > IMHO, that behaviour is not changed with this patch. Not sure how
> > seabios is taking care of this.
>
> I don't care about what you change with the patch. I care about consistency. 
> And we shouldn't differ from x86 in that respect.
>
> So please try and figure out how x86 knows that bootindex= is supposed to be 
> used instead of -boot. We want the same logic for ppc.
>
> > > Also, we could just map -boot c to "nvram given boot device or first
> > > automatically found disk". Then there's no need to know whether a
> > > default was given. If you specify -boot you most likely want to force
> > > cd-rom or network boot anyway and there is no way to tell which disk
> > > 'c' would reflect.
> >
> > We do want to use -boot [cad], but not for the nvram saved
> > boot-device. That is done automatically in SLOF. If there is a property
> > saved named boot-device, its going to use that for booting.
>
> Hrm. Ok, how about we change the default string to
>
>    xcad
>
> with x meaning "device stored in nvram". Then any time you specify -boot it would 
> override the nvram device, but you could also manually specify "I want to only boot from the 
> nvram device, no fallbacks".
Setting default string to "xcad" might jeopardize behavior of other 
machines (about hundred of them) that are passed boot_devices through 
machine->init()
> Alex
>
> > The point here is when we really want to over-ride the boot-device
> > setting in nvram(say the boot-device specified got corrupted), we need
> > help from -boot and corresponding disk provided in the qemu
> > command-line.
> >
> > At present, if there is boot-device specified there is now way to
> > over-ride it using qemu command line as "cad" is passed by
> > default. Which is the cause of all the pain.
> >
> > Regards,
> > Nikunj

Regards,
Avik