[regression-3.6] coreutils mkdir broken on UNC paths

[Lionel Cons]

On Thu, 20 Feb 2025 at 14:56, Cedric Blancher via Cygwin
<cygwin@cygwin.com> wrote:
>
> Good afternoon!
>
> Cygwin 3.6.0-0.378.g78fb13d21f4f.x86_64, Cygwin coreutils package 9.6-1
>
> coreutils mkdir is broken on UNC paths:
>
> mkdir -p -- "//ember.data4.local/afs/disk11/builds/bash/install_root/usr/local/bin"
> mkdir: cannot create directory ‘//ember.data4.local’: Read-only file system
>
> This happens because you cannot do a "cd .." in
> //ember.data4.local/afs, because "afs" is the UNC prefix for that
> filesystem.

No, it happens because mkdir "//ember.data4.local" returns "Read-only
file system". If Cygwin would just return EEXIST if this mount exists,
then this whole mkdir -p would work.

Lionel