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Date: Wed, 3 Jan 2024 05:27:02 -0700
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Subject: Re: Qemu packages for Cygwin?
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From: Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
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On 2024-01-03 02:10, Cedric Blancher via Cygwin wrote:
> On Mon, 18 Dec 2023 at 18:33, Brian Inglis via Cygwin <cygwin AT cygwin DOT com> wrote:
>>
>> On 2023-12-18 00:14, Dan Shelton via Cygwin wrote:
>>> On Mon, 18 Dec 2023 at 07:54, Marco Atzeri via Cygwin wrote:
>>>> On 18/12/2023 07:42, Dan Shelton via Cygwin wrote:
>>>>> Does Cygwin come with qemu packages?
>>
>>>> why should an "Unix Emulation layer" that run in "User Space"
>>>> trying to run a "Full-system emulation" (https://www.qemu.org/) ?
>>>> It seems like using square wheels
>>
>>> Nope. The Qemu packages on LInux have a much more wider functionality,
>>> and more features, compared to the TUSBTADI "The User Should Be
>>> Treated As Dumb Idiot" versions on Windows. It absolutely makes sense.
>>
>> Cygwin has trouble providing some POSIX features under Windows due to its API
>> limitations, using "documented" Windows APIs, allowing it to run under ReactOS,
>> Wine, and similar emulators, with which there is some interchange.
>>
>> It does not provide or support much in the way of privileged Unix or Windows
>> features or access, except for providing emulation for running daemons as
>> services, and some caching of SAM, AD, and process info.
>>
>> It is totally inadequate as a platform to provide or support any x86
>> virtualization or even virtual machine management features, as it can not
>> provide access to any machine features that do not have "documented" Windows APIs.
>> Look at the /proc filesystem emulation limitations for examples of where Windows
>> lacks APIs to get information available under Linux.
>>
>> You complain elsewhere about performance:
> 
> I am also complaining about performance, but it is NOT "performance in
> general": What really sucks is the filesystem inode operations and
> file name lookup, e.g. /bin/find&friends are absurdly slow because of
> the link emulation and the inflation of syscalls caused by it - just
> up to five times more accesses just to handle filename, filename.lnk,
> filename.lnk.exe, filename.lnk.bat etc
> Other areas have adequate performance, e.g. read/write performance is OK
> 
>> can you imagine how bad it would be,
>> compared to Hyper-V, WSL, VirtualBox, etc.
> 
> No, qemu is called the "quick emulator", and has more functionality
> than just being a hypervisor, like being able to emulate ARM and SPARC
> platforms. Even if the x86 hypervisor cannot be used, there is still
> lots of functionality.
> 
> If there are bugs in the POSIX emulation layer, then those bugs should
> be 1) documented and 2) fixed.

There are some functions that are not implemented because they can not be 
emulated under Windows, or require far too much work, or code and space in the dll.

> Also please do not shoot down package proposals out of the FEAR that
> "something" might not work.

Rather knowledge from experience that MS supports certain features in their own 
products e.g. WSL/2, Hyper-V and does not provide docs for some of their 
proprietary interfaces to allow others to do the same, without e.g. writing 
their own drivers to bypass Windows.

As long as you are happy porting a software emulator to build under cygport and 
run atop a POSIX layer, let us see how well you can do, by your own measures.

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry

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