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Subject:	Re: Problems with native Unix domain sockets on Win 10/2019
To:	Ken Brown <kbrown AT cornell DOT edu>, cygwin AT cygwin DOT com
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Date:	Sat, 26 Sep 2020 08:30:02 +0100
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From:	Michael McMahon via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Michael McMahon <michael DOT x DOT mcmahon AT oracle DOT com>
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On 25/09/2020 21:30, Ken Brown wrote:
> On 9/25/2020 2:50 PM, Ken Brown via Cygwin wrote:
>> On 9/25/2020 10:29 AM, Michael McMahon wrote:
>>>
>>>
>>> On 25/09/2020 14:19, Ken Brown wrote:
>>>> On 9/24/2020 8:01 AM, Michael McMahon wrote:
>>>>>
>>>>>
>>>>> On 24/09/2020 12:26, Ken Brown wrote:
>>>>>> On 9/23/2020 7:25 AM, Michael McMahon via Cygwin wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> I searched for related issues but haven't found anything.
>>>>>>>
>>>>>>> I am having some trouble with Windows native Unix domain sockets
>>>>>>> (a recent feature in Windows 10 and 2019 server) and Cygwin.
>>>>>>> I think I possibly know the cause since I had to investigate a 
>>>>>>> similar
>>>>>>> looking issue on another platform built on Windows.
>>>>>>>
>>>>>>> The problem is that cygwin commands don't seem to recognise 
>>>>>>> native Unix
>>>>>>> domain sockets correctly. For example, the socket "foo.sock" should
>>>>>>> have the same ownership and similar permissions to other files
>>>>>>> in the example below:
>>>>>>>
>>>>>>> $ ls -lrt
>>>>>>> total 2181303
>>>>>>>
>>>>>>> -rw-r--r--  1 mimcmah      None             1259   Sep 23 10:22 
>>>>>>> test.c
>>>>>>> -rwxr-xr-x  1 mimcmah      None             3680   Sep 23 10:22 
>>>>>>> test.obj
>>>>>>> -rwxr-xr-x  1 mimcmah      None             121344 Sep 23 10:22 
>>>>>>> test.exe
>>>>>>> -rw-r-----  1 Unknown+User Unknown+Group         0 Sep 23 10:23 
>>>>>>> foo.sock
>>>>>>> -rw-r--r--  1 mimcmah      None             144356 Sep 23 10:27 
>>>>>>> check.ot
>>>>>>>
>>>>>>> A bigger problem is that foo.sock can't be deleted with the 
>>>>>>> cygwin "rm"
>>>>>>> command.
>>>>>>>
>>>>>>> $ rm -f foo.sock
>>>>>>> rm: cannot remove 'foo.sock': Permission denied
>>>>>>>
>>>>>>> $ chmod 777 foo.sock
>>>>>>> chmod: changing permissions of 'foo.sock': Permission denied
>>>>>>>
>>>>>>> $ cmd /c del foo.sock
>>>>>>>
>>>>>>> But, native Windows commands are okay, as the third example shows.
>>>>>>>
>>>>>>> I think the problem may relate to the way native Unix domain 
>>>>>>> sockets are
>>>>>>> implemented in Windows and the resulting special handling required.
>>>>>>> They are implemented as NTFS reparse points and when opening them
>>>>>>> with CreateFile, you need to specify the 
>>>>>>> FILE_FLAG_OPEN_REPARSE_POINT
>>>>>>> flag. Otherwise, you get an ERROR_CANT_ACCESS_FILE. There are other
>>>>>>> complications unfortunately, which I'd be happy to discuss further.
>>>>>>>
>>>>>>> But, to reproduce it, you can compile the attached code snippet
>>>>>>> which creates foo.sock in the current directory. Obviously, this
>>>>>>> only works on recent versions of Windows 10 and 2019 server.
>>>>>>
>>>>>> Cygwin doesn't currently support native Windows AF_UNIX sockets, 
>>>>>> as you've discovered.  See
>>>>>>
>>>>>> https://urldefense.com/v3/__https://cygwin.com/pipermail/cygwin/2020-June/245088.html__;!!GqivPVa7Brio!P7lIFI4rYAtWh8_DtCbRCxT-M_E4vwQ0qwzQ0p656T73BpJ0jbUkLI_bXdA6mmSL9lJcSQ$ 
>>>>>>
>>>>>> for the current state of AF_UNIX sockets on Cygwin, including the 
>>>>>> possibility of using native Windows AF_UNIX sockets on systems 
>>>>>> that support them.
>>>>>>
>>>>>> If all you want is for Cygwin to recognize such sockets and allow 
>>>>>> you to apply rm, chmod, etc., I don't think it would be hard to 
>>>>>> add that capability.  But I doubt if that's all you want.
>>>>>>
>>>>>> Further discussion of this will have to wait until Corinna is 
>>>>>> available.
>>>>>>
>>>>>
>>>>> Thanks for the info. It's mainly about recognition of sockets for
>>>>> regular commands. Since these objects can exist on Windows filesystems
>>>>> now, potentially created by any kind of Windows application,
>>>>> it would be great if Cygwin could handle them, irrespective of whether
>>>>> the Cygwin development environment does. Though that sounds like a
>>>>> good idea too.
>>>>
>>>> I think this has a simple fix (attached), but I can't easily test it 
>>>> because your test program doesn't compile for me.  First, I got
>>>>
>>>> $ gcc -o native_unix_socket native_unix_socket.c
>>>> native_unix_socket.c:5:10: fatal error: WS2tcpip.h: No such file or 
>>>> directory
>>>>      5 | #include <WS2tcpip.h>
>>>>        |          ^~~~~~~~~~~~
>>>> compilation terminated.
>>>>
>>>> I fixed this by making the include file name lower case.  (My system 
>>>> is case sensitive, so it matters.)
>>>>
>>>> Next:
>>>>
>>>> $ gcc -o native_unix_socket native_unix_socket.c
>>>> native_unix_socket.c:8:10: fatal error: afunix.h: No such file or 
>>>> directory
>>>>      8 | #include <afunix.h>
>>>>        |          ^~~~~~~~~~
>>>> compilation terminated.
>>>>
>>>> There's no file afunix.h in the Cygwin distribution, but I located 
>>>> it online and pasted in the contents.  The program now compiles but 
>>>> fails to link:
>>>>
>>>> $ gcc -o native_unix_socket native_unix_socket.c
>>>> /usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x3b): 
>>>> undefined reference to `__imp_WSAStartup'
>>>> /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x3b): relocation 
>>>> truncated to fit: R_X86_64_PC32 against undefined symbol 
>>>> `__imp_WSAStartup'
>>>> /usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc74urPr.o:native_unix_socket.c:(.text+0xf2): 
>>>> undefined reference to `__imp_WSAGetLastError'
>>>> /tmp/cc74urPr.o:native_unix_socket.c:(.text+0xf2): relocation 
>>>> truncated to fit: R_X86_64_PC32 against undefined symbol 
>>>> `__imp_WSAGetLastError'
>>>> /usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x13d): 
>>>> undefined reference to `__imp_WSAGetLastError'
>>>> /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x13d): relocation 
>>>> truncated to fit: R_X86_64_PC32 against undefined symbol 
>>>> `__imp_WSAGetLastError'
>>>> collect2: error: ld returned 1 exit status
>>>>
>>>> This is probably easy to fix too, but I don't feel like tracking it 
>>>> down. Please send compilation instructions (that use Cygwin tools).
>>>>
>>>> Ken
>>>
>>> Hi
>>>
>>> Sorry, I had compiled it in a native Visual C environment.
>>>
>>> Assuming you have afunix.h in the current directory.
>>>
>>> gcc -o native_unix_socket -I. native_unix_socket.c -lws2_32
>>>
>>> should do it.
>>
>> Thanks, that works.  But now I can't reproduce your problem.  Here's 
>> what I see, using Cygwin 3.1.7 without applying my patch:
>>
>> $ ./native_unix_socket.exe
>> getsockname works
>> fam = 1, len = 11
>> offsetof clen = 9
>> strlen = 8
>> name = foo.sock
>>
>> $ ls -l foo.sock
>> -rwxr-xr-x 1 kbrown None 0 2020-09-25 14:39 foo.sock*
>>
>> $ chmod 644 foo.sock
>>
>> $ ls -l foo.sock
>> -rw-r--r-- 1 kbrown None 0 2020-09-25 14:39 foo.sock
>>
>> $ rm foo.sock
>>
>> $ ls -l foo.sock
>> ls: cannot access 'foo.sock': No such file or directory
>>
>> I'm running 64-bit Cygwin on Windows 10 1909.
> 
> I just ran the 'rm' command under gdb to see what's going on, and it 
> seems that foo.sock is not being recognized as a reparse point.  So 
> maybe your test program, when compiled and run under Cygwin, doesn't 
> actually produce a native Windows AF_UNIX socket.  And when I try to run 
> it in a Windows Command Prompt, I get
> 
> bind failed 10050
> getsockname failed 10022
> 
> Can you make your version of the test executable available for me to 
> try?  Or tell me some other way to create a native Windows AF_UNIX socket?
> 
> Ken

That is all very strange. I have checked both the gcc compiled and MS
compiled executables on my system (2019 server) and they are both
definitely producing native AF_UNIX sockets.

I can email you the two exe files. They are both quite small. But, first
I want to check the patch status of my test system.

Thanks,
Michael.
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