Re: Problems with native Unix domain sockets on Win 10/2019

[Ken Brown <kbrown@cornell.edu>]

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