RFC: Reparse Point/NT Symlink Support [3]

[Alexandre Julliard]

"Erich E. Hoover" <erich.e.hoover at gmail.com> writes:

> On Sat, Aug 28, 2021 at 6:14 AM Alexandre Julliard <julliard at winehq.org> wrote:
>> I would first question the assumption that these have to be actual,
>> resolvable symlinks. What if they weren't?
>
> Funny you ask, at one point I actually put together an attempt at this
> and it became pretty messy very quickly.  It's not difficult for
> symlinks that are files, but directory symlinks mean that we
> essentially need to replace path resolution at every single place
> where we want to work with a unix path.  For example, let's say that
> we have a symlink at C:\test that points to C:\windows.  An attempt to
> access C:\test\system32 would nominally be converted to
> ${WINEPREFIX}/drive_c/test/system32 and we would pass this path down
> to the OS.  If we have a "custom" symlink implementation then we need
> to parse the path and resolve each element in order to get the real
> path to the file on the system, whereas the OS takes care of this for
> us if we use "proper" symlinks.  Where this gets really nasty when you
> start trying to deal with the parent directory ("..").  Parent
> directory handling actually has different meaning depending on the
> context, most of the time it means wrt. the target (which makes
> resolving each element important) but in the context of commands that
> operate on the working directory you need to work with the "original"
> path.  This is all _possible_ to take care of, but at that point we're
> implementing so much custom path handling that you're talking about a
> substantial undertaking (that needs to be called everywhere there's a
> unix path that we pass down to the OS).  But maybe there's a solution
> you're seeing here that I'm not?

We are already resolving the path element by element because of case
insensitivity, it seems to me that reparse point resolving would fit
right in there. All you need is to make sure the initial stat() shortcut
fails, which you can do by creating a dangling symlink for instance.
Though my feeling is that using a normal file would make things easier,
say by appending some magic filename suffix.

-- 
Alexandre Julliard
julliard at winehq.org