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Re: [Qemu-devel] Re: [PATCH-updated] qemu/net: add raw backend
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] Re: [PATCH-updated] qemu/net: add raw backend |
Date: |
Wed, 14 Oct 2009 18:14:24 +0200 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Wed, Oct 14, 2009 at 10:58:22AM -0500, Anthony Liguori wrote:
> 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 keep hearing this. But why wait? Some users can be helped
by raw today. Those that can't will have to wait for a better bridge
or spend time setting it up properly.
>
>> 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.
Network manager was just one example.
> 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
[Qemu-devel] Re: [PATCH-updated] qemu/net: add raw backend, Michael S. Tsirkin, 2009/10/14