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From:	Erik Bray <erik DOT m DOT bray AT gmail DOT com>
Date:	Tue, 29 Nov 2016 14:26:03 +0100
Message-ID:	<CAOTD34Y9TRq2Qq8Mn2awTf9SCgz0qnbBa-a117pkSEvz9gaHKQ@mail.gmail.com>
Subject:	Re: Retrieving per-process environment block?
To:	cygwin AT cygwin DOT com
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On Thu, Nov 17, 2016 at 3:00 PM, Corinna Vinschen
<corinna-cygwin AT cygwin DOT com> wrote:
> On Nov 17 14:30, Erik Bray wrote:
>> Hi all,
>>
>> For a quick bit of background, I'm working on porting the highly
>> useful psutil [1] Python library to Cygwin.  This has proved an
>> interesting exercise, as much of the functionality of psutil works on
>> Cygwin through existing POSIX interfaces, and a handful of
>> Linux-specific interfaces as well.  But there are some bits that
>> simply don't map at all.
>>
>> The one I'm struggling with right now is retrieving Cygwin environment
>> variables for a process (under inspection--i.e. not listing a
>> process's environment from within that process which is obviously
>> trivial).
>>
>> I've looked at every route I could conceive of but as far as I can
>> tell this is currently impossible.  That's fine for now--I simply
>> disable that functionality in psutil.  But it is unfortunate, though,
>> since the information is there.
>>
>> There are a couple avenues I could see to this.  The most "obvious"
>> (to me) being to implement /proc/<pid>/environ.
>>
>> I would be willing to provide a patch for this if it would be
>> accepted.  Is there some particular non-obvious hurdle to this that it
>> hasn't been implemented?  Obviously there are security
>> implications--the /proc/<pid>/environ should only be readable to the
>> process's owner, but that is already within Cygwin's capabilities, and
>> works for other /proc files.
>
> Patch welcome.  Implementing this should be fairly straightforward.
> The only hurdle is winsup/CONTRIBUTORS ;)

Thanks--I went to go work on this finally but it turns out not to be
straightforward after all, as the process's environment is not shared
in any way between processes.

I could do this, if each process kept a copy of its environment block
in shared memory, which would in turn have to be updated every time
the process's environment is updated.  But I don't know what the
impact of that would be performance-wise.

Any advice?

Thanks,
Erik

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