Re: [Qemu-devel] [PATCH 00/16] introduce OptsVisitor, rebase -net/-netdev parsing

[Laszlo Ersek <lersek@redhat.com>]

On 06/06/12 22:09, Michael Roth wrote:
> On Wed, Jun 06, 2012 at 06:49:19PM +0200, Laszlo Ersek wrote:

>> The fallback (*v->type_int)() call stores an int64_t, according to its
>> prototype ("interface contract"). IMHO it shouldn't try to communicate a
>> mathematical value outside of [INT64_MIN, INT64_MAX]; it should report
> 
> But the contract with visit_type_int() is maintained: it's just that
> visit_type_uint64() is casting it's uint64_t value to int64_t (and
> back) to make use of the fallback. It's slightly dirty, but fairly common
> throughout the tree.

(I'm going theoretical :))

Sorry, I didn't mean what happens "around" the type_int method; I meant
what happens inside it.

A visitor type takes some "external type" (a bag of data, structured or
unstructured) and provides functions with scalar target types (among
other things). One defines a native C struct in the JSON (... I'm making
some leaps here), the generated code traverses that C type, and probes
the "bag of data" with the corresponding visitor. A type_int call made
to the visitor says "hey I need an int64_t for this node of the target C
struct, with this 'path' and 'name' locator inside the external object".
If the 'path' (= eg. visitor stack) and 'name' identify a piece of info
in the external object that can't be represented in the requested target
type, the visitor should report an error. I don't see much difference
between the decimal representation of 2^63 and the string "donkey" in
this regard if the target C "node" is an int64_t.

(Musing block ends :))

Of course I'm fine with dropping the fourth hunk.

Thanks,
Laszlo