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Date: Fri, 04 Nov 2011 12:25:32 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 4/4] qemu-nbd: do not start the block layer
	in the parent
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To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org, Pierre Riteau <Pierre.Riteau@irisa.fr>

On 11/04/2011 12:22 PM, Kevin Wolf wrote:
>> >
>> >  That's exactly what this series did.  However, daemonization has also to
>> >  be done before opening the image file.  So the series has to support
>> >  reporting errors to syslog, and also qemu-nbd will not give a nonzero
>> >  exit status when errors occur.
>
> The parent could wait until the initialisation is done.

You need to daemonize first, then fork the server.  If you fork the 
server before daemonizing, the server:

1) is not in its own process group, and still has a controlling TTY;

2) is not your child so your process structure is all broken, with the 
client and server being both child of PID 1;

3) is not your child, so you cannot reliably kill it (because if it has 
exited and PID 1 has already reaped it, you might kill a random process 
instead!).

Paolo