Re: [PATCH 0/3] Add more winsymlinks values

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Jul 22 14:53, Jon Turney wrote:
> On 21/07/2021 09:19, Corinna Vinschen wrote:
> > On Jul 19 17:31, Jon Turney wrote:
> > > I'm not sure this is the best idea, since it adds more configurations that
> > > aren't going to get tested often, but the idea is that this would enable
> > > proper and consistent control of the symlink type used from setup, as
> > > discussed in [1].
> > > 
> > > [1] https://cygwin.com/pipermail/cygwin-apps/2021-May/041327.html
> > 
> > Why isn't it sufficient to use 'winsymlinks:native' from setup?
> 
> I think in the default Windows configuration (developer mode off, no
> SeCreateSymbolicLinkPrivilege), 'native' will try to create a native symlink
> and fail, and fallback to WSL IO_REPARSE_TAG_LX_SYMLINK reparse point, then
> magic cookie + sys attribute.
> 
> This leads to cygwin installations with WSL symlinks created by post-install
> scripts, which can't be put into Docker containers [1], which is the
> original problem I was trying to fix.
> 
> [1] https://cygwin.com/pipermail/cygwin/2020-August/245994.html

Did nobody ask the Docker guys why they fail to support perfectly
valid reparse points?

> I haven't yet looked at adding 'native' symlink support to setup itself, but
> it's probably going to be a bit of a pain.

That may be not a bad idea after all.  Setup typically runs as elevated
process, so it has the required permissions to create native symlinks.
Scripts could then run with CYGWIN=winsymlinks:native by default.

As long as nobody has the hare-brained idea to move a Cygwin distro
manually, native symlinks should be just as well as Cygwin symlinks.

> > The way we express symlinks shouldn't be a user choice, really.  The
> > winsymlinks thingy was only ever introduced in a desperate attempt to
> > improve access to symlinks from native tools, and I still don't see a
> > way around that.  But either way, what's the advantage in allowing the
> > user complete control over the type, even if the type is only useful in
> > Cygwin?
>  If we can come up with a fixed policy that works everywhere, there is no
> advantage.  But that seems unlikely :)
> 
> I could buy an argument that 'native' should be the default (although maybe
> all that does is slow things down in the majority of installs?).

It may slow down installations a tiny little bit because the target
paths have to be converted to POSIX, but I doubt this is more than just
a marginal slowdown.


Corinna