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

[Zhongze Liu <blackskygg@xxxxxxxxx>]

2017-03-06 19:42 GMT+08:00 Jan Beulich <JBeulich@xxxxxxxx>:
>>>> On 06.03.17 at 12:38, <julien.grall@xxxxxxx> wrote:
>
>>
>> On 06/03/17 11:32, Jan Beulich wrote:
>>>>>> 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.
>>
>> My concern is not about the override itself but about appending two
>> commandlines option without any explanation whether the built-in
>> commandline will be parsed first.
>
> Oh, agreed - as Andrew has also pointed out, the ordering (and hence
> override behavior) needs to be clearly spelled out here.
>
> Jan
>

Yes, the expression here is indeed quite ambiguous. I'll try to
clarify the ordering
of the two commandlines and override behavior.

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