Re: [Qemu-block] [Qemu-devel] Non-flat command line option argument syntax

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> On 02/27/2017 07:36 AM, Markus Armbruster wrote:
>
>> 
>>>                  Maybe just 'foo.array[]' (without any =) for an empty
>>> array or something like that.
>> 
>> Yes, that should do.  Likewise foo.object{} for empty object.
>> 
>> {} doesn't even need quoting.  [] may.
>
> [contents] needs quoting, but [] does NOT need shell quoting (no shells
> treat it as a glob), for the same reason that 'if [ -e "$file" ];' needs
> no quoting around the [ or ] (the shell only requires quotes for [ if
> the rest of the shell word can look like a valid glob, but globs require
> intermediate content before the ]).

Bash shell options failglob and nullglob can still mess it up.

>>> Before we introduce anything like this, do we actually need it?
>> 
>> I don't know whether anything needs optional, present and empty.  But
>> even if the answer is "no" today, it need not remain "no".
>> 
>> Anyone running into a case of "yes", will have to fall back to the JSON
>> form of -blockdev.  Strengthens my belief that providing JSON there is a
>> good idea.
>> 
>> The insufficient generality of dotted keys bugs me a bit.  Not sure
>> whether it justifies more syntax now.  But we should document it.
>
> I agree that documenting it as a shortcoming of dotted form and pointing
> to JSON form is okay.  I also like that we are leaving the door open for
> future expansion, if needed, and think that is better than inventing the
> syntax now, especially for what we are trying to get into 2.9.

Okay, I'll work on improving the documentation.