Re: [Qemu-devel] [PATCH for-1.2 v5 14/14] pci: Tidy up PCI host bridges

[Mark Cave-Ayland]

On 13/08/12 15:16, Anthony Liguori wrote:

> I understand what your objection is but it's unreasonable IMHO.  The
> purpose of QOM is to bring consistency across large swaths of code in
> QEMU that have historically done things there own way.
>
> This means expressing concepts like inheritence and casting in the same
> way across the board.  The common way (the QOM way) is to make the
> parent type the first member of the struct (typically named parent or
> parent_obj) and then to use cast macros to upcast and downcast.
>
> This patch is 100% correct in that regard and I'm going to apply it once
> Andreas makes the change I requested.
>
> For my part, I'm long over due in writing up a device authoring style
> guide that I promised a few weeks ago.  I'll write that up this
> afternoon and send it out today.
>
> We can debate the merits of this sort of thing in the style guide.

Yes please! I've spent quite a fair bit of time over the past couple of 
weeks in this area, and have found the lack of documentation related to 
trying to create a new hardware device fairly frustrating. The hardest 
part is not the coding, but figuring which of the following I should be 
using out of:

qom
qdev
qmp
hmp
sysbus
VMState

(I think that half of these are now obsolete interfaces, but a general 
document which explains how these things are related and which ones I 
should be using would be very welcome)


ATB,

Mark.