Re: [kvm-devel] [Qemu-devel] Re: Storing command line options in images

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Avi Kivity wrote:
>>>> This is a big effort but a config file is the right long term 
>>>> solution.
>>>>
>>>>     
>>>
>>> For which use case? management-full or management-less?
>>>   
>>
>> Both.  A config file will be useful not just for expressing the 
>> functionality we have today, but also for describing the guest's 
>> environment in greater detail.  For instance, if you want to support 
>> a bunch of different kinds of embedded systems, it would be very nice 
>> if the machine description was a config file instead of hard coded 
>> such that it was easy to tweak what hardware was present for the 
>> particular embedded system.
>>
>
> Maybe I'm dense today.  Which use case is this?

If you're using QEMU to simulate an embedded platform (ARM or PPC based 
for instance).  There is a huge amount of variety in embedded platforms 
so having to hard code the PC description as a machine type in QEMU is 
kind of annoying.

>>> A managed system will want to supply arguments out of a central 
>>> database.  For a management-less use case, the config file is a hassle.
>>>   
>>
>> As long as all options are still settable via command line (or 
>> stdio), then it's not at all a hassle.
>>
>
> Yes.  But if you don't plan to use it, why implement it?

Well, I do plan to use it.  I'm simply saying that you don't have to use 
it if you don't want to.

There are a lot of knobs in QEMU and most of them have somewhat 
arbitrary defaults.  For instance, when I setup a machine, I don't want 
to use user networking by default, I want to use tap.  A global 
configuration file would be terribly useful for this sort of thing.

> My feeling is that config files are outdated.  When used with a gui, 
> you end up writing silly parsers and stuff and still wrecking things 
> horribly when the the gui writer's expectations don't match reality.  
> When used without a gui, they increase the amount of details one has 
> to remember (where's that config file? I renamed my image, did I 
> remember to update the config file?).  They also make upgrading more 
> difficult.

There's only so much that can be expressed on a command line.  There are 
actually limits to the command line size on a lot of platforms.  I don't 
see why reading options from a file is so much worse than reading them 
from the command line.

Regards,

Anthony Liguori

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