cygpath and unc paths

[Federico Kircheis]

On 09/12/2024 14.17, Corinna Vinschen via Cygwin wrote:
> On Dec  9 13:47, Federico Kircheis via Cygwin wrote:
>> On 09/12/2024 12.46, Corinna Vinschen via Cygwin wrote:
>>> On Dec  6 13:23, Federico Kircheis via Cygwin wrote:
>>>> Hello,
>>>>
>>>> was it considered to add a flag to cygpath to output a path in unc format?
>>>
>>> No.  But it wouldn't be much work.
>>
>> It would be very nice if it ever happens.
>>
>>>> For example, the folder
>>>>
>>>> C:\test.
>>>>
>>>> cannot be accessed from many Windows applications (powershell and cmd
>>>> included) because of the trailing dot, while cygwin has no issue creating,
>>>> accessing and deleting such files/folders.
>>>>
>>>> Using an unc path
>>>>
>>>> \\?\C:\test.
>>>>
>>>> solves the issue for some programs, but cygpath currently misses an option
>>>> for creating such path.
>>>
>>> As a workaround you can just prepend the long path prefix:
>>>
>>>     echo -n '\\?\'; cygpath ...
>>
>> Which is what I'm doing, plus special-casing
>>
>> 1)
>> root path, like C:\ , because for whatever reason \\?\C:\ is not valid, it
>> has to be a subfolder (and trying to trick it with \\?\C:\\ does not work
>> either).
> 
> In which scenario?  \\?\C:\ is just the same as \??\C:\ in NT speak, and
> that's a perfectly valid directory path.

I've never seen \??\C:\.

My test case, from powershell (which I do definitively _not_ know well 
enough, otherwise I wouldn't be using cygwin) was

cd C:\             # success
cd \\?\C:\         # fail
cd C:\windows      # success
cd \\?\C:\windows  # success

and repeat the same operation with dir instead of ls.

The error message is that the "value of argument path is not valid"

I did some further testing: no amount of quoting (with ", ' and `) 
helps, also replacing \ with / does not change any outcome.

For cd, the parameter -literal makes a difference

cd -literal \\?\C:\  # success

for dir, I did not find anything yet.

So I guess you are correct, although support from basic tools (cd and 
dir at least) seems very suboptimal...

>> 2)
>> unmounted network drives (\\server\path)
> 
> Yeah, those have a different prefix:
> 
>    \\?\UNC\server\share
> 
>> I'm not sure how a --unc should handle those cases.
>> For all things I have in mind, not appending \\?\ is preferred, but someone
>> might expect a hard error.
>>
>> Either way, it is another reason why it makes sense for cygpath to handle
>> those cases, currently I have to parse it's output before prepending '\\?\'.
> 
> I'll take a look.
> 
>>>> Notice that creating a dos path leads to an error.
>>>
>>> I don't understand. Creating which DOS path with which application?
>>
>> I meant that it is not possible to create a DOS path to C:\test., thus using
>> a dos path is not a viable workaround to unc:
>>
>> ----
>>> cd 'C:/test.'
>>> cygpath -ws .
>> cygpath: cannot create short name of .
>> ----
> 
> Don't use -s, it's just for the old short name style of DOS paths.
> Nobody should actually need this nowadays, and sometimes short paths
> don't even exist.  It's a functionality inside the FS driver, afaik, and
> it can be switched off in the system.
> 
> In your example, standard filenames work:
> 
>    $ cd /cygdrive/c
>    $ mkdir test.
>    $ cd test.
>    $ cygpath -ws .
>    cygpath: cannot create short name of C:\test.
>    $ cygpath -wa .
>    C:\test.

Yes, -wa works; I wanted to point out that DOS paths are not a viable 
workaround.
I could have left it out from my first mail, we agree no need to iterate 
further ;)