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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.03.17 at 15:41, <julien.grall@xxxxxxx> wrote:
> Hi Jan,
> 
> On 03/07/2017 02:18 PM, Jan Beulich wrote:
>>>>> On 07.03.17 at 14:48, <julien.grall@xxxxxxx> wrote:
>>> On 03/07/2017 12:52 PM, Jan Beulich wrote:
>>>>>>> On 07.03.17 at 12:21, <blackskygg@xxxxxxxxx> wrote:
>>>>> 2017-03-07 17:36 GMT+08:00 Jan Beulich <JBeulich@xxxxxxxx>:
>>>>>>>>> On 07.03.17 at 09:34, <blackskygg@xxxxxxxxx> 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?

Only the latter.

> 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.

All fine, but this doesn't tell me what interactive change options a
user has _after_ having set up the config file (or alike), while the
system is booting.

> 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.

But aiui that's again needed to be done _before_ the system is
rebooted.

> 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.

As per above I'm getting the impression that we're talking of
different scenarios - I don't think I've yet understood what options
of adding to or editing of any of the command lines you have on
ARM _during_ the boot process of a system.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel