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Subject: Re: [Qemu-devel] [PATCH 0/3] Allow host_net_add monitor command
	accept file descriptors
From: Mark McLoughlin <markmc@redhat.com>
In-Reply-To: <4A52DD05.9030007@redhat.com>
References: <1246901401.12086.20.camel@blaa>  <4A52DD05.9030007@redhat.com>
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Date: Tue, 07 Jul 2009 08:43:43 +0100
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To: Avi Kivity <avi@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

On Tue, 2009-07-07 at 08:28 +0300, Avi Kivity wrote:
> On 07/06/2009 08:30 PM, Mark McLoughlin wrote:
> > Hi,
> > 	You can pass file descriptors to qemu via the command line using '-net
> > tap,fd=' or '-net socket,tap='. However, you cannot currently do this
> > via the monitor.
> >
> > 	libvirt always configures tap interfaces before passing them to qemu.
> > One reason for this is to allow libvirtd to have privileges
> > to /dev/net/tun without allowing qemu those privileges. Because of this,
> > libvirt currently does not support NIC hotplug for qemu.
> >
> > 	The following three patches add support for passing a file descriptor
> > to the monitor command by allowing file descriptors to be received over
> > monitor commands on a unix socket.
> >
> >    
> 
> I'm a great fan of SCM_RIGHTS.  To make it easier to use in more 
> commands, I think it makes sense to have a separate command to pass the fd:
> 
>    (qemu) getfd foo
>    (qemu) getfd bar
>    (qemu) getfd baz
>    (qemu) pci_add ...,fd=foo
>    (qemu) pci_add ...,fd=bar ...,fd=baz
> 
> A closefd command would be needed to deal with errors.

Nice idea, certainly.

However, since it's only currently useful for tap/socket networking, I'm
happier with not adding two new monitor commands and only supporting a
single fd for now.

Cheers,
Mark.