Problems with native Unix domain sockets on Win 10/2019

[Michael McMahon]

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.

Michael.