Re: [PATCH v3] xen: Allow a default compiled-in command line using Kconfig

[Julien Grall <julien.grall@arm.com>]

Hi Jan,

On 03/07/2017 02:18 PM, Jan Beulich wrote:
>>>> On 07.03.17 at 14:48, <julien.grall@arm.com> wrote:
>> On 03/07/2017 12:52 PM, Jan Beulich wrote:
>>>>>> On 07.03.17 at 12:21, <blackskygg@gmail.com> wrote:
>>>> 2017-03-07 17:36 GMT+08:00 Jan Beulich <JBeulich@suse.com>:
>>>>>>>> On 07.03.17 at 09:34, <blackskygg@gmail.com> wrote:
>>>>>> +static inline char* __init extract_dom0_options(char *cmdline)
>>>>>> +{
>>>>>> +    char *kextra;
>>>>>> +
>>>>>> +    if ( (kextra = strstr(cmdline, " -- ")) != NULL )
>>>>>> +    {
>>>>>> +        *kextra = '\0';
>>>>>> +        kextra += 3;
>>>>>> +        while ( kextra[1] == ' ' ) kextra++;
>>>>>
>>>>> The body of the while() wants to go on its own line.
>>>>>
>>>>> And then - why is this Dom0 option handling done only on x86?
>>>>>
>>>>
>>>> As you might have noticed, there isn't any code dealing with the dom0 options
>>>> in arch/arm/setup.c, and the arm version of construct_dom0() doesn't take any
>>>> command line options as its parameter,
>>>> so I have the reason to believe that this feature is not available
>>>> under the arm architecture.
>>>
>>> Looks like an omission to me - Julien, Stefano?
>>
>> DOM0 and Xen command line are passed separately through either Device
>> Tree or for UEFI xen configuration file (see -cfg=...).
>>
>> So I am not sure to understand what would be the benefits to handle DOM0
>> parameters after -- on Xen command line.
>
> So you have no case of a boot loader which allows you to type in
> extra options on just a single line? On x86 the feature had originally
> been added because old grub didn't have a separate line for Dom0
> options in its graphical menu. Nowadays the functionality is handy
> namely when starting xen.efi from the EFI shell (where again you
> obviously only have a single command line), but quite likely this may
> also be of use with grub's chain loading model (which I simply don't
> use very often, so I'm not finally sure on that one).

My knowledge is quite limited on boot process for x86. How do you pass 
the kernel/initrd/xsm blob on UEFI? Can you do it from the command line 
or are you using the -cfg=... and specify it in a file?

On ARM we have two way to boot Xen:
	- Using UEFI bootloader with either Device-Tree or ACPI
	- Using non-UEFI bootloader with Device-Tree only

In the case of UEFI bootloader, we are using the xen configuration file 
to describe the modules (e.g kernel, initramfs, XSM) and the both xen 
and DOM0 command line.

For non-UEFI bootloader, we have designed the boot protocol based on the 
device-tree and will allows you to specify both xen and DOM0 and all the 
modules (see [1]). The bootloader needs to be able to modify the 
device-tree (such via a shell like on U-boot) or the user needs to 
modify the device-tree before hand.

To answer your question, a bootloader supporting only a single line 
would still need to be modified to provide the various modules. At that 
stage, adding DOM0 command line is very easy.

Now, if you tell me that all the modules can be described on the UEFI 
command line, then I think handling '--' would be nice. If not, I don't 
think it is worth it.

Cheers,

[1] http://xenbits.xen.org/docs/unstable/misc/arm/device-tree/booting.txt
-- 
Julien Grall

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