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From: Anthony Liguori <aliguori@us.ibm.com>
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Date: Thu, 25 Oct 2012 15:18:22 -0500
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Subject: Re: [Qemu-devel] [PATCH v2 1/2] Make default boot order machine
	specific
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To: Peter Maydell <peter.maydell@linaro.org>, Avik Sil <aviksil@linux.vnet.ibm.com>
Cc: david@gibson.dropbear.id.au, qemu-ppc@nongnu.org, qemu-devel@nongnu.org, agraf@suse.de

Peter Maydell <peter.maydell@linaro.org> writes:

> On 25 October 2012 15:38, Avik Sil <aviksil@linux.vnet.ibm.com> wrote:
>> @@ -171,6 +171,7 @@ static QEMUMachine clipper_machine = {
>>      .init = clipper_init,
>>      .max_cpus = 4,
>>      .is_default = 1,
>> +    .default_machine_opts = DEFAULT_BOOT_ORDER,
>>  };
>
>> @@ -86,6 +86,7 @@ static QEMUMachine an5206_machine = {
>>      .name = "an5206",
>>      .desc = "Arnewsh 5206",
>>      .init = an5206_init,
>> +    .default_machine_opts = DEFAULT_BOOT_ORDER,
>>  };
>
>> +++ b/hw/axis_dev88.c
>> @@ -355,6 +355,7 @@ static QEMUMachine axisdev88_machine = {
>>      .desc = "AXIS devboard 88",
>>      .init = axisdev88_init,
>>      .is_default = 1,
>> +    .default_machine_opts = DEFAULT_BOOT_ORDER,
>>  };
>
> The thing about a default is that you shouldn't have to
> explicitly say it in every QEMUMachine struct... Please
> make the code handle a NULL in the struct in a way
> that means you don't need to touch every board.

I hate to spin a lot on a touch everything patch, but I also agree that
this is the wrong approach.

I think there are two reasonable approaches to this.  One would be a
macro to provide default initialization.  Something along the lines of:

#define DEFAULT_MACHINE_OPTIONS \
    .boot_order = "cad"

And then:

static QEMUMachine axisdev88_machine = {
    DEFAULT_MACHINE_OPTIONS,
    ...
};

static QEMUMachine pseries_machine = {
    DEFAULT_MACHINE_OPTIONS,
     /* no default boot order so we can detect absence of boot option */
    .boot_order = NULL,
};

Baking this into .default_machines_opts is too much overloading.

The other approach to this would be:

static QEMUMachine pseries_machine = {
    .no_boot_order = 1,
};

Which I think is what Peter is suggesting.  I'm not a huge fan of this
because it's backwards logic but we already do this for a bunch of other
things so I can't object too strongly to it.

Regards,

Anthony Liguori


>
> -- PMM