Problems with native Unix domain sockets on Win 10/2019

Ken Brown kbrown@cornell.edu
Fri Sep 25 18:50:11 GMT 2020


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.

Ken


More information about the Cygwin mailing list