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From: Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
Subject: Re: Windows 10 Creators Update and Symlinks
Reply-To: Brian DOT Inglis AT SystematicSw DOT ab DOT ca
References: <4b5447f2-a1fe-925e-5e3d-6692347374ad AT kit DOT edu> <60bf66d9-d467-3cac-72f9-7823d1c1c32a AT teco DOT edu>
To: cygwin AT cygwin DOT com
Message-ID: <3e2df893-9813-2f1b-ad0b-f7e6fa5cdc19@SystematicSw.ab.ca>
Date: Sun, 23 Apr 2017 09:21:06 -0600
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On 2017-04-23 03:26, Till Riedel wrote:
> Am 13.04.2017 um 0:29 schrieb Jeffrey Altman:
>> When Developer mode is enabled the elevation requirement for
>> symlink creation is disabled:
>> https://blogs.windows.com/buildingapps/2016/12/02/symlinks-windows-10/#DXz6icKZOkEozgYR.97
>> This was necessary for symlink creation within WSL to work.

> I was really excited to hear this!
> I tried to export CYGWIN="winsymlinks:nativestrict" and create
> symlink without elevation and failed on cygwin 2.8.0 (checked that
> "cmd /C mklink" works as expected in Windows 10 Creators Update
> Developer Mode).
> Any ideas if there are any extra checks that lead to "Operation not
> permitted"?
> Windows seemingly even allows symlinks to nonexistent files (I
> somehow think there was a problem with that in the past). For me
> personally this would a strong reason to switch to real symlinks.

Artcile states:
CreateSymbolicLink
    To enable the new behavior when using the CreateSymbolicLink API, 
there is an additional dwFlags option you will need to set:

Value 	Meaning
SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
0x2 	Specify this flag to allow creation of symbolic links when the 
	process is not elevated

So Cygwin patches are required to winsymlinks:native/strict handling 
in winsup/w32api/include/winbase.h (which may be owned by mingw):

#define SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE 0x2

and in winsup/cygwin/path.cc(symlink_native) like:

/* Try to create native symlink. */
if (!CreateSymbolicLinkW (final_newpath->Buffer, final_oldpath->Buffer,
#ifdef SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
			  SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE |
#endif
			  (win32_oldpath.isdir ()
			     ? SYMBOLIC_LINK_FLAG_DIRECTORY : 0)))

but may need W10 build 14972 checks, and any privilege checks disabled.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada


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