Re: [PATCH 3/4] win32: stop mixing SOCKET and file descriptor space

[Paolo Bonzini <pbonzini@redhat.com>]

On 2/20/23 16:29, Marc-André Lureau wrote:
>> 7. A Windows SOCKET is also a HANDLE.  Maybe.  I guess.  Docs are
>>     confusing.
>>
> Kind of, but not really. I think a HANDLE is a kind of void*. You need to
> be careful using it appropriately with the right functions. Sometime, a
> HANDLE can work with generic functions, like ReadFile, but you should not
> use a CloseHandle on SOCKET, or registry key..

A Windows SOCKET *is* a file HANDLE except it's always in overlapped 
mode so Windows provides send()/recv() in case you don't want to deal 
with overlapped mode.  But you can use it with ReadFile too (Windows API 
documentation says that is only true sometimes, but Winsock API is 30 
years old and right now you pretty much always can).

However, sockets also has some extra information on the side, so you 
need to close them with closesocket() and CloseHandle() is not enough.

The problem is that close() of something opened with _open_osfhandle() 
*does* do that CloseHandle(), so basically you are closing the handle 
twice.  IIRC there used to be undocumented functions _alloc_osfhnd() and 
similar, but they don't exist anymore (even Wine does not have them), so 
we're stuck; unfortunately this is the reason why QEMU is not already 
doing something like what you have in this patch.

Is this a real bug or is it theoretical?  Do file descriptor and socket 
spaces overlap in practice?

Paolo