Re: [Qemu-devel] When to use qemu/typedefs.h

[Paolo Bonzini <pbonzini@redhat.com>]

On 31/07/19 08:37, Markus Armbruster wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
>> On 30/07/19 15:15, Eric Blake wrote:
>>>> We occasionally give up and use types directly rather than their typedef
>>>> names, flouting the coding style.  This patch does.  Trades messing with
>>>> qemu/typedefs.h for having to write 'struct' a few times.
>>
>> I think Markus made the right call here.  Using "struct Foo;" in headers
>> is a null price to pay if all you need is declaring a pointer-typed
>> field or parameter.
> 
> Eduardo posted a patch to HACKING to clarify this non-usage of typedef
> is okay.
> 
> Should we continue to mandate typedef names elsewhere?  It adds
> cognitive load: you have to decide where to put the typedef, and when
> not to use it.

A lot of libraries we use (especially GLib) use typedefs, so I'd rather
keep them.  Also, a mass replacement would be tens of thousands of
changed lines and not really practical.

>>                      Of course this doesn't apply if you have to embed a
>> struct directly, but then qemu/typedefs.h wouldn't help either.
> 
> Yes, and if this leads to an inclusion cycle, I strongly suspect "fat"
> headers: since you can't embed something in itself, the cycle must
> involve different things, all bunched together in the same header.
> 
>> In general unless you're adding a new subsystem, qemu/typedefs.h should
>> only decrease in size, never increase.
> 
> This series grows it some.  I'll try to avoid that for v2.

Let me review it first. :)  Maybe some of them are good to keep.

Paolo