Re: [Qemu-devel] [PATCH RFC 0/2] qemu-arg: general purpose argument parser

[Kevin Wolf]

Am 08.03.2014 um 19:47 hat Leandro Dorileo geschrieben:
> The following patchset introduces a general purpose argument parser and 
> migrates
> qemu-img to make use of it. qemu-img is just the first user of it, if we see a
> good feedback here I move forward and migrate all the other possible users.

I was planning to reply to this in more detail, but it doesn't look like
I can find the time to do so, so let me just summarise my thoughts
briefly.

I do like the idea of simplifying qemu-img's argument parsing, but we
shouldn't make the mistake of introducing another option parsing
infrastructure and end up with three different coexisting models. If we
were to introduce a new framework, we must make sure that all code is
converted to it and QemuOpts can be dropped.

Now replacing QemuOpts and all of its users is not something that seems
to be very productive - it works quite well in those places. So I think
we should rather extend QemuOpts to work for qemu-img as well.

We would probably need to add a new parser to QemuOpts that parses
command line options into a QemuOpts, and extend the definition of them
with a couple of new features that are required there (sub-QemuOpts for
-o, perhaps enumerations for things like --output=human/json, positional
parameters).

I see that you also fill the values in (global) variables. The existing
code that converts QemuOpts into C variables are the QAPI visitors. So I
could imagine that we define all qemu-img options in a JSON schema like
qapi-schema.json and generate the struct definitions from it. We would
then end up with something like this, where the code to create a
QemuImgCreateOptions struct from the QemuOpts would be QAPI generated:

void img_create(QemuImgCreateOptions *options, Error **errp);

Not sure if we really want to go that far, but perhaps it's some food
for thought.

Kevin