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From: Anthony Liguori <anthony@codemonkey.ws>
To: Jamie Lokier <jamie@shareable.org>
Cc: Or Gerlitz <ogerlitz@voltaire.com>,
	Arnd Bergmann <arndbergmann@googlemail.com>,
	qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [Qemu-devel] Re: [PATCH-updated] qemu/net: add raw backend
Date: Wed, 14 Oct 2009 10:58:22 -0500	[thread overview]
Message-ID: <4AD5F51E.7040907@codemonkey.ws> (raw)
In-Reply-To: <20091014151406.GA17062@shareable.org>

Jamie Lokier wrote:
> Anthony Liguori wrote:
>   
>> Or Gerlitz wrote:
>>     
>>> Add raw network backend option which uses a packet socket to provide
>>> raw networking access. Once the socket is opened it's bound to a
>>> provided host interface, such that packets received on the interface
>>> are delivered to the VM and packets sent by the VM are sent to the
>>> interface.
>>>
>>> This is functionally similar to the existing pcap network
>>> backend, with the same advantages and problems.
>>> Differences from pcap:
>>> - can get an open socket from the monitor,
>>>  which allows running without NET_ADMIN priviledges
>>> - support iovec sends with writev, saving one data copy
>>> - one less dependency on an external library
>>> - we have access to the underlying file descriptor
>>>  which makes it possible to connect to vhost net
>>> - don't support polling all interfaces, always bind to a specific one
>>>  
>>>       
>> Networking is probably the area in qemu that users most frequently 
>> stumble with.  The most common problems are:
>>
>> 1) slirp does not behave how they think it should (icmp doesn't work, 
>> guest isn't accessable from host)
>> 2) it's difficult to figure out which backend behaves the way they want 
>> (socket vs. vde vs. tap)
>> 3) when they figure out they need tap, tap is difficult to setup 
>>     
>
> Worse, tap is impossible to setup properly with things like
> network-manager.
>   

This is being fixed.

> I suspect user expectations are quite commonly:
>
>    - guest<->host networking works
>    - guest<->host's network works, directly or through host NAT
>    - guest IP address is either private (inside the host)
>      or on the same network as the host, according to some switch.
>
> Imho, there is only one right place to fix this, and it's by adding a
> feature to the host.  Either modifying host packet socket, or
> modifying the tap+bridge combination.
>
> Neither tap nor pcap/raw works particularly well except in static IP
> configurations, and qemu cannot realistically work around the
> host configuration difficulties.
>   

The fact that network manager does work well with bridged interfaces is 
a network manager bug.  It's getting fixed so in the near future, tap 
will satisfy all of these requirements.

> It'd be great if vhost_net doesn't have the configuration problems of
> tap or pcap/raw.  If it does have the same problems, it's a natural
> place to fix them.  I haven't looked at vhost_net yet.
>
> -- Jamie
>   

Regards,

Anthony Liguori

  reply	other threads:[~2009-10-14 15:58 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-10-14 14:34 [Qemu-devel] [PATCH-updated] qemu/net: add raw backend Or Gerlitz
2009-10-14 14:46 ` [Qemu-devel] " Anthony Liguori
2009-10-14 15:14   ` Jamie Lokier
2009-10-14 15:58     ` Anthony Liguori [this message]
2009-10-14 16:14       ` Michael S. Tsirkin
2009-10-14 16:54         ` Jamie Lokier
2009-10-14 17:20           ` Michael S. Tsirkin
2009-10-14 18:36         ` Anthony Liguori
2009-10-14 19:37           ` Michael S. Tsirkin
2009-10-15  7:48           ` Or Gerlitz
2009-10-14 15:58     ` Michael S. Tsirkin
2009-10-14 15:24   ` Michael S. Tsirkin
2009-10-14 15:33     ` Gleb Natapov
2009-10-15  7:29       ` Or Gerlitz
2009-10-15  7:44         ` Gleb Natapov
2009-10-15  7:50           ` Or Gerlitz
2009-10-14 16:20   ` Michael S. Tsirkin

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