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Date: Wed, 3 Jan 2024 10:10:09 +0100
Message-ID: <CALXu0UfAg8eFFePUdhM7MZ40xEPO6rnesaH66LLssAbckycS0Q@mail.gmail.com>
Subject: Re: Qemu packages for Cygwin?
To: cygwin@cygwin.com
From: Cedric Blancher via Cygwin <cygwin@cygwin.com>
Reply-To: Cedric Blancher <cedric.blancher@gmail.com>
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On Mon, 18 Dec 2023 at 18:33, Brian Inglis via Cygwin <cygwin@cygwin.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.
Also please do not shoot down package proposals out of the FEAR that
"something" might not work.

Ced
-- 
Cedric Blancher <cedric.blancher@gmail.com>
[https://plus.google.com/u/0/+CedricBlancher/]
Institute Pasteur

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