Re: [Xen-devel] [PATCH v2] xen: Allow a default compiled-in command line using Kconfig

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.03.17 at 12:15, <julien.grall@xxxxxxx> wrote:
> On 06/03/17 11:01, Zhongze Liu wrote:
>> Added 3 new config entries in common/Kconfig:
>>     CMDLINE_BOOL, CMDLINE and CMDLINE_OVERRIDE
>>
>> These 3 entries enable an embedded command line
>> to be compiled in the hypervisor.
>>
>> If CMDLINE_BOOL is set to y, both arm and x86 startup routines
>> will combine the compiled-in command line and the boot loader command line
>> together to form a complete command line before calling cmdline_parse().
>> And if CMDLINE_OVERRIDE is set to y, boot loader command line
>> will be ignored.
> 
> This behavior seems a little odd to me. Why would you want to append the 
> two command line? And more importantly if the same option is passed 
> twice, how will this behave?
> 
> For example the compile command line could contain iommu=off, but the 
> bootloader is passing iommu=on. What would be the final state of the IOMMU?
> 
> This one is quite simple, but you could have options which set flags. So 
> if you want to override it, the new option would have to unset it.

I don't understand this concern - overriding an earlier option by a
later one is (supposed to be) well defined, and we even suggest this
to people when wanting to try out options without having to edit
bootloader (or whatever) config files.

Jan


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