From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200005111525.LAA13642@candle.pha.pa.us>
Subject: Re: setproctitle() no longer used?
In-Reply-To: <Pine.GSO.4.02A.10005111137220.6113-100000@Gepard.DoCS.UU.SE>
 from
	Peter Eisentraut at "May 11, 2000 11:42:08 am"
To: Peter Eisentraut <peter_e@gmx.net>
Date: Thu, 11 May 2000 11:25:47 -0400 (EDT)
CC: Vince Vielhaber <vev@michvhf.com>, The Hermit Hacker <scrappy@hub.org>,
	pgsql-hackers@postgresql.org
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> On Wed, 10 May 2000, Bruce Momjian wrote:
> 
> > It is a nifty BSD one.  If you assign argv[0] in the program to a
> > string, it shows in ps.
> > 
> > 	argv[0] = "new ps string";
> > 
> > The Linux method is:
> 
> Maybe I should add that this could more accurately be called the `SysV
> method' and also works on SysV-derived models. Heubrid (a.k.a. hogwash)
> systems such as Solaris and HPUX may support both or none, depending on
> the time of day.

OK.

> 
> > 
> > 	strcpy(argv[0], "new ps string");
> > 
> > In the second case, you are actually writing into the environment area
> > use to store args.  Not real great, but it works on Linux.
> 
> You just copy the environment somewhere else before you do that. Or don't
> use the environment. Not a big deal.

But do they really do that?  The scary part about the Linux code in
pg_status.h is that is just zeros out all the argv bytes and starts
writing, and that is environment memory.

Now, I do some tricks in postmaster.c so I know I have at least 5
elements to argv[], but I never do anything that makes sure I have
enough environment space to start copying strings in there.

	argv[0] = "string"
	strcpy(argv[0], "string");

The first makes argv[0] point into user-space memory, while the second
writes into environment memory.  (Allowing ps to dynamically read
argv[0] memory that is pointing to user-space is a kvm() trick.)

Linux people seem to be happy with their version, but frankly, I would
not allow it on BSD.  I would _at_ _least_ put something in postmaster.c
so I _knew_ that argv[0] had a reasonable size for me to copy into it.
(Massimo write the Linux code, I believe.)

Guess it is more a philosophical issue.  Linux folks like it because it
works, while I don't because it is not bullet-proof.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  pgman@candle.pha.pa.us               |  (610) 853-3000
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