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From: Erik Bray <erik DOT m DOT bray AT gmail DOT com>
Date: Wed, 30 Nov 2016 11:09:10 +0100
Message-ID: <CAOTD34YjUOtRD7i9Kcv2xi7W93yVv=c=90Pzydya7DtD5O2W0g@mail.gmail.com>
Subject: Re: Retrieving per-process environment block?
To: cygwin AT cygwin DOT com
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On Wed, Nov 30, 2016 at 10:15 AM, Peter Rosin <peda AT lysator DOT liu DOT se> wrote:
> On 2016-11-30 04:00, Eliot Moss wrote:
>> On 11/29/2016 7:28 PM, Herbert Stocker wrote:
>>
>>> Or we simply copy the variables unconverted to the Windows environment
>>> block, as the Windows env block is not used for anything else - up to
>>> now it is not updated at all.
>>
>> Maybe we could stash them inside one large variable?  Would that help
>> at all?  (It does demand a quoting convention, but since this is all
>> internal stuff, that may not be too hard.)
>
> I believe this is a dead end. The Windows environment block has an
> unacceptable size limit which is circumvented by the internal Cygwin
> handling. Since this is about exposing said Cygwin environment, it
> would simply not work for big environments.

I agree--although I can't off the top of my head recall where I've
read this, I believe there's a deliberate effort in Cygwin to keep the
Windows environment to the bare minimum for Cygwin processes.  Among
other things I imagine it keeps the number of conversions necessary to
a minimum.

And in any case, trying to cache the entire Cygwin environment back
into the Windows environment would be even more overhead than what I'm
proposing which is to store it in shared memory.  My goal is not to
make the Cygwin environment of a process readable from outside
Cygwin--only make it so it can be read from other Cygwin processes by
way of /proc (given the necessary permissions).

Perhaps I'll go ahead and cook up a patch and see what impact it has.
With luck it won't be much--I just don't know how much overhead there
is in open_shared.

Thanks,
Erik

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