Windows Emacs and "VirtualStore"

Windows Emacs and "VirtualStore"

[Lewis Perin]

I just finished a long period of confusion after upgrading my Windows
machine from XP to Windows 7.  (What I'm about to say does apply to
Vista as well as 7, by the way.)

I've been running Emacs as an unprivileged user, responsible citizen
that I am.  I ran into trouble configuring a program whose config data
lie within the "Program Files" tree.  What's new in Windows since XP is
that that tree is not to be edited without privilege, but I forgot about
that.  And, in Emacs, it looked for all the world as if my edits were
being applied where I thought they were going.  But the program was
behaving as if it had never run into the changes I'd made.

Eventually I ran into

  http://xahlee.org/UnixResource_dir/writ/windows_virtualstore.html

which explains that, under Vista or Windows 7, the changes I was making
were *silently* being written into shadow copies of the "real" files out
in what's called "VirtualStore" in recent MS jargon.  (I'm not going to
fulminate here about MS's decision to do things in this way - they won't
back down.)

Xah Lee suggests running Emacs as administrator, but I'd rather not have
an admin Emacs running perpetually.  My reading of this MS document

  http://msdn.microsoft.com/en-us/library/bb756929.aspx

is that the problem of the silent redirection of writes would go away
if Windows Emacs had an appropriate "manifest file" with a Requested
Execution Level of "asInvoker".  That way, the write should fail the way
it would under XP if the file were locked, say.

I would actually prefer it if Emacs would give the user a chance to try
to escalate privilege in the sudo-ish way many Windows apps now employ.
I'm guessing that would require some work in the guts of Emacs.

With my shaky understanding of Emacs internals, I'm really not sure how
feasible these suggestions are.  Can someone who does understand these
things please comment?

/Lew
---
Lew Perin / perin@acm.org
http://www.panix.com/~perin/babelcarp.html

Re: Windows Emacs and "VirtualStore"

[Andreas Politz]

Lewis Perin <perin@panix.com> writes:

> [...] is that the problem of the silent redirection of writes would go away
> if Windows Emacs had an appropriate "manifest file" with a Requested
> Execution Level of "asInvoker".

This made me laugh.

I think there are more people on the dev-list, who are able to comment
on this.

-ap

Re: Windows Emacs and "VirtualStore"

[Lewis Perin]

Andreas Politz <politza@fh-trier.de> writes:

> Lewis Perin <perin@panix.com> writes:
>
>> [...] is that the problem of the silent redirection of writes would go away
>> if Windows Emacs had an appropriate "manifest file" with a Requested
>> Execution Level of "asInvoker".
>
> This made me laugh.

I'm glad someone is pleased.

> I think there are more people on the dev-list, who are able to comment
> on this.

Thanks for the suggestion.  I did post there Saturday morning.  While I
haven't had a response yet, I've solved part of the problem myself, as I
reported to the dev-list just now.  The gist is, Windows Emacs already
has a manifest in the executable as a resource; this manifest resource
can be pretty easily augmented to tell Windows to avoid VirtualStore.

/Lew
---
Lew Perin / perin@acm.org
http://www.panix.com/~perin/babelcarp.html

Re: Windows Emacs and "VirtualStore"

[Lennart Borgman]

On Fri, Apr 16, 2010 at 7:28 AM, Andreas Politz <politza@fh-trier.de> wrote:
> Lewis Perin <perin@panix.com> writes:
>
>> [...] is that the problem of the silent redirection of writes would go away
>> if Windows Emacs had an appropriate "manifest file" with a Requested
>> Execution Level of "asInvoker".
>
> This made me laugh.
>
> I think there are more people on the dev-list, who are able to comment
> on this.

I think a fix already has been installed in the devel sources.