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To: "'cygwin'" <cygwin AT cygwin DOT com>
Subject: Strange behaviour with winsymlinks:native
Date: Wed, 14 Oct 2020 15:56:47 +0100
Message-ID: <001001d6a23a$3d5ebc70$b81c3550$@cl.cam.ac.uk>
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From: David Allsopp via Cygwin <cygwin AT cygwin DOT com>
Reply-To: David Allsopp <David DOT Allsopp AT cl DOT cam DOT ac DOT uk>
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I've been doing some working around the problems with Cygwin 3.1.5+ WSL
junction points in Docker and found three unexpected pieces of behaviour
with CYGWIN=winsymlinks:native

In all cases, these work as expected with the default symlink behaviour
(i.e. CYGWIN unset or without a winsymlinks option).

1. Relative paths get unnecessarily resolved

  mkdir -p foo/bar
  cd foo/bar
  touch baz
  CYGWIN='winsymlinks:native' ln -s ../bar/baz link
  readlink link

Result is baz, not ../bar/baz

2a. Links in the magic mount directories (/usr/bin and /usr/lib) get extra
bits added (source is a default mount):

  cd /usr/lib
  CYGWIN='winsymlinks:native' ln -s ../share/terminfo terminfo2
  readlink terminfo2

Result is ../usr/share/terminfo, which makes it valid from /lib (the "real"
directory) but not in the virtual one

2b. Same but where target is a default mount

  cd /usr/libexec/p11-kit
  CYGWIN='winsymlinks:native' ln -s ../../bin/update-ca-trust
trust-extract-compat2
  readlink trust-extract-compat2

Result is ../../../bin/update-ca-trust, again it seems to be computing an
extra level back to the "real" lib directory

Are these behaviours expected? I can create those symbolic links manually
with mklink with no problem, so I'm wondering if it's an outright bug or an
unexpected consequence of something else.

Thanks!


David

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