Montag, 20. Juli 2009

Aleksey Bragin an [ros-dev]

Wie man hier sehen kann, wird zur Zeit viel an ReactOS in "Arwinss" verändert.
Heute hat Aleskey Braign dazu eine Mail geschrieben:

Betreff: [ros-dev] Arwinss

I've heard many question about a branch I was working on recently, arwinss, so I'd like to write some explanation (you may skip the boring history part of the message)

Arwinss is a rewrite (the most advanced so far out of all previous attempts) of some parts of the Win32 subsystem, namely the USER32 and GDI32 API interfaces, along with the kernel counterpart win32k.sys. The kernel32.dll, csrss, and other parts remain in their present condition, and getting bugfixes if they come in the way of a rewrite.

[History and reasoning part starts here]
Why rewrite and not fix an existing Win32 subsystem? Timo, James and all our other great developers were and are doing a great work. I put a considerable amount of time in it to fix problems too. But, since our project is a volunteer-driven one, everyone has a real life, real work to do, and is not able to sit 24 hrs researching Windows internal structures, inventing new algorithms, trying out thousands of applications, not to say about graphics drivers. Time is ticking, Win32 is improving, but most annoying bugs are there for years - e.g. vmware installer hang, Firefox move the mouse bug, drawing glitches, concurrency hacks in the code ("if (!a) /* someone else was faster than us and already freed it */"), probable heap misusage (relying on our heap implementation for desktop heaps) and heap memory corruptions (I kept trying to update rtl/heaps to the newest Wine code - and always failed without any obvious reason), inability to change video mode on the fly, and the list can go on.

So I thought, that something should be done with it. I would even want to trade off some speed gain in favor of stability (optimizing is an enjoyable task which could be done later).

After teaming up with Stefan, we created an nwin32 branch - a totally stubbed out win23k, user32 and gdi32. They had exactly matched exports, and win32k had exactly same system calls and Windows 2003 SP1's win32k.sys. However, due to really huge amount of work, the branch didn't went farther than trying to boot Windows 2003 with it and see a few stubbed functions being called.

Since then I started thinking on an alternative design of a Win32 subsystem. The idea turned out to be very simple, and is based on the following questions:
- Why put so much effort into keeping the internal win32k system calls interface the same as in Windows, why put so much effort in converting to internal Windows structures, if we don't have something working first?
- Why base on a stoneage Wine's code which James and Christoph occasionally sync, and all my attempts to get more people into this boring task failed?
- Why not use achievements of our closest project - Wine?

[End of reasoning, fancy stuff starts]

The result came by itself: Try to build up a win32 subsystem based as much on Wine code as possible, and using Wine's modular design. Before publicly announcing it, I have spent a month actually trying all that stuff, and surprisingly it went very well, and a nice byproduct: support of remote sessions via X Windows.

Proof of concept screenshots are here:

Noone has ever done this before: This is Windows 2003 inside VMware, running my custom Win32 subsystem, with an X graphics driver module, communicating with an X Server running in the host OS (Windows XP, XMing X windows server), and with ReactOS's winlogon.exe and msgina.dll (for ease of debugging and source code availability)!

Let's go straight to the architecture:

GDI32.dll and USER32.dll are ported Wine usermode code, with very few modifications. GDI32 and USER32 depend on two things: Gdi and User driver, and a server.

Gdi and User driver is a loadable DLL, which provides an abstraction of a graphics driver in the system through a certain set of APIs. A typical example of such a driver is winex11.drv, which routes all drawing to the X Windows "client". However, this is not very useful for a local system which has a Windows NT architecture, where there is no need for remote windows displaying.

The server. GDI32 and USER32 rely on the server for managing all global information. In Wine, the server is run as a usermode wineserver.exe process, which communicates with gdi32/user32 via custom RPC, and emulates quite a lof of stuff which Windows NT kernel provides by default. My decision was to convert the RPC protocol from a slow interprocess filedescriptors-based unix-specific invocations to a fast system calls to win32k module. This way, win32k contains small part (~300 kb vs 1.5Mb+) of wineserver's source code, which deals with windows, window classes, atoms, windows stations, desktops and other totally platform/implementation independent stuff. It will be reduced further, because I even ported their own object manager for win32 objects, which will be exchange to our native ntoskrnl's object manager soon, when the testing phase is over.

The graphics driver, kernelmode part. As I said above, it's not very convinient to fully rely on X Windows for graphics output, because it's just not possible to run it in an NT-based OS which has no Win32 subsystem. Thus, I decided to create a totally native gdi/user driver ("winent.drv"), which would rely on win32k module to actually perform all drawing. However, compared to our current implementation, the drawing would be way more simple. For example, if currently LineTo operation in win32k involves complex PATHOBJ, maintaining graphics cursor -- all of that in a strictly windows compatible way because apps depend on it, in this alternative win32k, LineTo is a simple line drawing function: RosGdiLineTo(pDc, x1, y1, x2, y2). Same applies to other functions, including e.g. text output, where all rendering happens using a usermode freetype.dll, and win32k just needs to display bitmap glyphs got from gdi32.

Don't be scared if you don't understand all that right away. I will put up a good short summary, along with a TODO and FIXME lists, and a HACKING guide.

Just a few cool facts about the new win32 subsystem:
- Based on a solid, very well maintained codebase, used by commercial vendors.
- Ease of updating from upstream (vendor importing)
- Tested against more than 12 000 Windows applications (http://
- ...

I think it's enough for the first introduction.

Aleksey Bragin.

Außerdem unterstützt ReactOS seit kurzem auch mehrere Netzwerkkarten in einem System (DHCP zur Zeit nur für die 1. Karte), so dass ReactOS langsam etwas Servertauglicher wird.

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