[dpdk-dev] [RFC PATCH 5/5] virtio: Extend virtio-net PMD to support container environment

Tetsuya Mukawa mukawa at igel.co.jp
Tue Jan 26 03:58:32 CET 2016

On 2016/01/25 19:15, Xie, Huawei wrote:
> On 1/22/2016 6:38 PM, Tetsuya Mukawa wrote:
>> On 2016/01/22 17:14, Xie, Huawei wrote:
>>> On 1/21/2016 7:09 PM, Tetsuya Mukawa wrote:
>>>> virtio: Extend virtio-net PMD to support container environment
>>>> The patch adds a new virtio-net PMD configuration that allows the PMD to
>>>> work on host as if the PMD is in VM.
>>>> Here is new configuration for virtio-net PMD.
>>>> To use this mode, EAL needs physically contiguous memory. To allocate
>>>> such memory, add "--shm" option to application command line.
>>>> To prepare virtio-net device on host, the users need to invoke QEMU
>>>> process in special qtest mode. This mode is mainly used for testing QEMU
>>>> devices from outer process. In this mode, no guest runs.
>>>> Here is QEMU command line.
>>>>  $ qemu-system-x86_64 \
>>>>              -machine pc-i440fx-1.4,accel=qtest \
>>>>              -display none -qtest-log /dev/null \
>>>>              -qtest unix:/tmp/socket,server \
>>>>              -netdev type=tap,script=/etc/qemu-ifup,id=net0,queues=1\
>>>>              -device virtio-net-pci,netdev=net0,mq=on \
>>>>              -chardev socket,id=chr1,path=/tmp/ivshmem,server \
>>>>              -device ivshmem,size=1G,chardev=chr1,vectors=1
>>>>  * QEMU process is needed per port.
>>> Does qtest supports hot plug virtio-net pci device, so that we could run
>>> one QEMU process in host, which provisions the virtio-net virtual
>>> devices for the container?
>> Theoretically, we can use hot plug in some cases.
>> But I guess we have 3 concerns here.
>> 1. Security.
>> If we share QEMU process between multiple DPDK applications, this QEMU
>> process will have all fds of  the applications on different containers.
>> In some cases, it will be security concern.
>> So, I guess we need to support current 1:1 configuration at least.
>> 2. shared memory.
>> Currently, QEMU and DPDK application will map shared memory using same
>> virtual address.
>> So if multiple DPDK application connects to one QEMU process, each DPDK
>> application should have different address for shared memory. I guess
>> this will be a big limitation.
>> 3. PCI bridge.
>> So far, QEMU has one PCI bridge, so we can connect almost 10 PCI devices
>> to QEMU.
>> (I forget correct number, but it's almost 10, because some slots are
>> reserved by QEMU)
>> A DPDK application needs both virtio-net and ivshmem device, so I guess
>> almost 5 DPDK applications can connect to one QEMU process, so far.
>> To add more PCI bridges solves this.
>> But we need to add a lot of implementation to support cascaded PCI
>> bridges and PCI devices.
>> (Also we need to solve above "2nd" concern.)
>> Anyway, if we use virtio-net PMD and vhost-user PMD, QEMU process will
>> not do anything after initialization.
>> (QEMU will try to read a qtest socket, then be stopped because there is
>> no message after initialization)
>> So I guess we can ignore overhead of these QEMU processes.
>> If someone cannot ignore it, I guess this is the one of cases that it's
>> nice to use your light weight container implementation.
> Thanks for the explanation, and also in your opinion where is the best
> place to run the QEMU instance? If we run QEMU instances in host, for
> vhost-kernel support, we could get rid of the root privilege issue.

Do you mean below?
If we deploy QEMU instance on host, we can start a container without the
root privilege.
(But on host, still QEMU instance needs the privilege to access to

If so, I agree to deploy QEMU instance on host or other privileged
container will be nice.
In the case of vhost-user, to deploy on host or non-privileged container
will be good.

> Another issue is do you plan to support multiple virtio devices in
> container? Currently i find the code assuming only one virtio-net device
> in QEMU, right?

Yes, so far, 1 port needs 1 QEMU instance.
So if you need multiple virtio devices, you need to invoke multiple QEMU

Do you want to deploy 1 QEMU instance for each DPDK application, even if
the application has multiple virtio-net ports?

So far, I am not sure whether we need it, because this type of DPDK
application will need only one port in most cases.
But if you need this, yes, I can implement using QEMU PCI hotplug feature.
(But probably we can only attach almost 10 ports. This will be limitation.)

> Btw, i have read most of your qtest code. No obvious issues found so far
> but quite a couple of nits. You must have spent a lot of time on this.
> It is great work!

I appreciate your reviewing!

BTW, my container implementation needed a QEMU patch in the case of
But the patch has been merged in upstream QEMU, so we don't have this
limitation any more.


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