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Re: [Qemu-devel] [PATCH 0/6] refactor PC machine, i440fx and piix3 to ta


From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH 0/6] refactor PC machine, i440fx and piix3 to take advantage of QOM
Date: Mon, 26 Mar 2012 12:33:43 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120310 Thunderbird/11.0

On 03/26/2012 07:20 AM, Jan Kiszka wrote:
On 2012-03-26 04:06, Wanpeng Li wrote:
From: Anthony Liguori<address@hidden>


This series aggressively refactors the PC machine initialization to be more
modelled and less ad-hoc.  The highlights of this series are:

  1) Things like -m and -bios-name are now device model properties

  2) The i440fx and piix3 are now modelled in a thorough fashion

  3) Most of the chipset features of the piix3 are modelled through composition

  4) i440fx_init is trivialized to creating devices and setting properties

  5) convert MemoryRegion to QOM

  6) convert PCI host bridge to QOM

The point (4) is the most important one.  As we refactor in this fashion,
we should quickly get to the point where machine->init disappears completely in
favor of just creating a handful of devices.

The two stage initialization of QOM is important here.  instance_init() is when
composed devices are created which means that after you've created a device, all
of its children are visible in the device model.  This lets you set properties
of the parent and its children.

realize() (which is still called DeviceState::init today) will be called right
before the guest starts up for the first time.

While I see the value of the overall direction, I still disagree on
making internal data structures of HPET, RTC and 8254 publicly
available. That's a wrong step back. I'm sure there are smarter
solutions, alse as there were some proposals back then in the original
thread.

I'm not fully decided myself.  A couple things are clear to me though:

1) We must expose type proper types in header files. We need there to be a globally accessible RTCState type and functions that operate on it.

2) We can simplify memory management by knowing the size of the type in the header files too.

Since this is an easily refactorable thing to look at later, I think we should start with extracting the types.


I'm also sure we will have to refactor the merge significantly again for
the introduction of additional chipsets and PC boards. But unless those
requirements can already be specified (Isaku?), that might be unavoidable.

We cannot introduce another chipset without properly refactoring the i440fx. The previous refactorings that were oriented around moving code into functions created a nasty spaghetti of reference passing.

Regards,

Anthony Liguori

Jan





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