RFC: Reparse Point/NT Symlink Support [3]

[Erich E. Hoover]

On Thu, Sep 30, 2021 at 2:31 AM Alexandre Julliard <julliard at winehq.org> wrote:
>
> "Erich E. Hoover" <erich.e.hoover at gmail.com> writes:
>
> > If this doesn't sound too crazy then I can put together the
> > modifications to make this happen.  As part of that I'd like to
> > introduce a tool (command 'wineprefix'?) that configures the Unix
> > environment properly for Linux/BSD to allow the shell to function with
> > this variadic symlink so that users like Martin Storsjö (and myself)
> > can just run the tool to be dropped into a shell where ${WINEPREFIX}
> > inside a symlink will be treated appropriately.  (Part of why it's
> > taken me a while to respond to this thread has been putting together a
> > "proof of concept" of this tool to make sure that the idea works,
> > which I can now confirm.)  Please let me know what you guys think,
> > hopefully this sounds better to folks.
>
> You are still trying too hard to shoehorn the complexity of reparse
> points into working Unix symlinks, which makes it necessary to depend on
> all kinds of exotic non-portable functionality.

I think that it's a good idea to make it possible to interpret the
links outside of Wine for the majority of users, there are a lot of
ways to solve this problem that would make it impossible to do this
using any combination of standard tools.

> You should forget about making these transparent at the Unix
> level. Focus on implementing the full semantics of reparse points,
> including arbitrary tags and data, in a generic, easily extendable way,
> using only standard Posix APIs.

This is a pretty trivial update to the existing implementation, that
will make symlinks that look like (<REPARSE-TAG> is encoded):
<REPARSE-TAG>arbitrary data

> Once you have this working for a range of different tags, with tests to
> confirm compatibility, we can think about what subset of reparse points
> would make sense as pure Unix symlinks, and add a special case for
> these.

Okay, what exactly are you looking for here?  That you get the same
thing back that you put in?  Just like Unix symlinks, you can store
any sort of arbitrary text/unicode/garbage in a reparse point for any
tag (if you are so inclined).  The OS may not know what to do with
that tag unless you write a filter for it, but you can store anything
that you want.

Best,
Erich