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Date: Tue, 07 Jul 2009 08:28:37 +0300
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 0/3] Allow host_net_add monitor command accept
	file descriptors
References: <1246901401.12086.20.camel@blaa>
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To: Mark McLoughlin <markmc@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

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.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.