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Date: Fri, 15 Jan 2021 13:38:41 +0800
From: Jason Wang <jasowang@...hat.com>
To: Parav Pandit <parav@...dia.com>,
"Michael S. Tsirkin" <mst@...hat.com>
Cc: "virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
Eli Cohen <elic@...dia.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH linux-next v3 6/6] vdpa_sim_net: Add support for user
supported devices
On 2021/1/14 下午3:58, Parav Pandit wrote:
>
>> From: Jason Wang <jasowang@...hat.com>
>> Sent: Thursday, January 14, 2021 9:48 AM
>>
>> On 2021/1/7 上午11:48, Parav Pandit wrote:
>>>> From: Michael S. Tsirkin <mst@...hat.com>
>>>> Sent: Tuesday, January 5, 2021 6:53 PM
>>>>
>>>> On Tue, Jan 05, 2021 at 12:30:15PM +0000, Parav Pandit wrote:
>>>>>> From: Michael S. Tsirkin <mst@...hat.com>
>>>>>> Sent: Tuesday, January 5, 2021 5:45 PM
>>>>>>
>>>>>> On Tue, Jan 05, 2021 at 12:02:33PM +0000, Parav Pandit wrote:
>>>>>>>> From: Michael S. Tsirkin <mst@...hat.com>
>>>>>>>> Sent: Tuesday, January 5, 2021 5:19 PM
>>>>>>>>
>>>>>>>> On Tue, Jan 05, 2021 at 12:32:03PM +0200, Parav Pandit wrote:
>>>>>>>>> Enable user to create vdpasim net simulate devices.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> $ vdpa dev add mgmtdev vdpasim_net name foo2
>>>>>>>>>
>>>>>>>>> Show the newly created vdpa device by its name:
>>>>>>>>> $ vdpa dev show foo2
>>>>>>>>> foo2: type network mgmtdev vdpasim_net vendor_id 0 max_vqs 2
>>>>>>>>> max_vq_size 256
>>>>>>>>>
>>>>>>>>> $ vdpa dev show foo2 -jp
>>>>>>>>> {
>>>>>>>>> "dev": {
>>>>>>>>> "foo2": {
>>>>>>>>> "type": "network",
>>>>>>>>> "mgmtdev": "vdpasim_net",
>>>>>>>>> "vendor_id": 0,
>>>>>>>>> "max_vqs": 2,
>>>>>>>>> "max_vq_size": 256
>>>>>>>>> }
>>>>>>>>> }
>>>>>>>>> }
>>>>>>>> I'd like an example of how do device specific (e.g. net
>>>>>>>> specific) interfaces tie in to this.
>>>>>>> Not sure I follow your question.
>>>>>>> Do you mean how to set mac address or mtu of this vdpa device of
>>>>>>> type
>>>>>> net?
>>>>>>> If so, dev add command will be extended shortly in subsequent
>>>>>>> series to
>>>>>> set this net specific attributes.
>>>>>>> (I did mention in the next steps in cover letter).
>>>>>>>
>>>>>>>>> +static int __init vdpasim_net_init(void) {
>>>>>>>>> + int ret;
>>>>>>>>> +
>>>>>>>>> + if (macaddr) {
>>>>>>>>> + mac_pton(macaddr, macaddr_buf);
>>>>>>>>> + if (!is_valid_ether_addr(macaddr_buf))
>>>>>>>>> + return -EADDRNOTAVAIL;
>>>>>>>>> + } else {
>>>>>>>>> + eth_random_addr(macaddr_buf);
>>>>>>>>> }
>>>>>>>> Hmm so all devices start out with the same MAC until changed?
>>>>>>>> And how is the change effected?
>>>>>>> Post this patchset and post we have iproute2 vdpa in the tree,
>>>>>>> will add the
>>>>>> mac address as the input attribute during "vdpa dev add" command.
>>>>>>> So that each different vdpa device can have user specified
>>>>>>> (different) mac
>>>>>> address.
>>>>>>
>>>>>> For now maybe just avoid VIRTIO_NET_F_MAC then for new devices
>>>> then?
>>>>> That would require book keeping existing net vdpa_sim devices
>>>>> created to
>>>> avoid setting VIRTIO_NET_F_MAC.
>>>>> Such book keeping code will be short lived anyway.
>>>>> Not sure if its worth it.
>>>>> Until now only one device was created. So not sure two vdpa devices
>>>>> with
>>>> same mac address will be a real issue.
>>>>> When we add mac address attribute in add command, at that point also
>>>> remove the module parameter macaddr.
>>>>
>>>> Will that be mandatory? I'm not to happy with a UAPI we intend to
>>>> break straight away ...
>>> No. Specifying mac address shouldn't be mandatory. UAPI wont' be
>> broken.
>>
>>
>> If it's not mandatory. Does it mean the vDPA parent need to use its own logic
>> to generate a validate mac? I'm not sure this is what management (libvirt
>> want).
>>
> There are few use cases that I see with PFs, VFs and SFs supporting vdpa devices.
>
> 1. User wants to use the VF only for vdpa purpose. Here user got the VF which was pre-setup by the sysadmin.
> In this case whatever MAC assigned to the VF can be used by its vdpa device.
> Here, user doesn't need to pass the mac address during vdpa device creation time.
> This is done as the same MAC has been setup in the ACL rules on the switch side.
> Non VDPA users of a VF typically use the VF this way for Netdev and rdma functionality.
> They might continue same way for vdpa application as well.
> Here VF mac is either set using
> (a) devlink port function set hw_addr command or using
> (b) ip link set vf mac
> So vdpa tool didn't pass the mac. (optional).
> Though VIRTIO_NET_F_MAC is still valid.
>
> 2. User may want to create one or more vdpa device out of the mgmt. device.
> Here user wants to more/full control of all features, overriding what sysadmin has setup as MAC of the VF/SF.
> In this case user will specify the MAC via mgmt tool.
> (a) This is also used by those vdpa devices which doesn't have eswitch offloads.
> (b) This will work with eswitch offloads as well who does source learning.
> (c) User chose to use the vdpa device of a VF while VF Netdev and rdma device are used by hypervisor for something else as well.
> VIRTIO_NET_F_MAC remains valid in all 2.{a,b,c}.
>
> 3. A vendor mgmt. device always expects it user to provide mac for its vdpa devices.
> So when it is not provided, it can fail with error message string in extack or clear the VIRTIO_NET_F_MAC and let it work using virtio spec's 5.1.5 point 5 to proceed.
>
> As common denominator of all above cases, if QEMU or user pass the MAC during creation, it will almost always work.
> Advance user and QEMU with switchdev mode support who has done 1.a/1.b, will omit it.
> I do not know how deep integration of QEMU exist with the switchdev mode support.
>
> With that mac, mtu as optional input fields provide the necessary flexibility for different stacks to take appropriate shape as they desire.
Thanks for the clarification. I think we'd better document the above in
the patch that introduces the mac setting from management API.
>
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