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Date: Mon, 15 Dec 2003 17:09:00 -0800 (PST)
From: Don Lewis <truckman@FreeBSD.org>
To: cracauer@cons.org
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cc: cracauer@FreeBSD.org
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Subject: Re: truss issue
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On 15 Dec, Martin Cracauer wrote:
> Don Lewis wrote on Mon, Dec 15, 2003 at 01:28:50PM -0800: 

>> If you type "truss foo" at the shell prompt, the shell will fork and
>> exec truss, which forks and execs foo.  When truss forks, the child
>> process is the one that execs foo, and the parent process watches what
>> the child process does.  My suggestion is to swap the roles of the
>> parent and child truss processes.  The parent truss process would be the
>> one that calls exec(), and the child process would be the one doing the
>> monitoring.  When the process being traced exits, the shell would
>> automagically get the correct exit status.
> 
> Ah, OK.
> 
> That would also have the advantage that the pid that the fork() in the
> starting process gets will continue to stay correct for the child it
> expects.
> 
> E.g.
> truss foo &
> pid=$!
> dosomethingwith $pid

Like "kill -9"

> pid will point to the actual process and not foo, so you can safely
> insert a truss prefix where you want.

I hadn't thought about it, but this is another advantage.