RE: [PATCH V2,net-next, 3/3] hv_netvsc: Name NICs based on vmbus offer sequence and use async probe

[Haiyang Zhang]

> -----Original Message-----
> From: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Sent: Monday, December 30, 2019 8:35 PM
> To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; sashal@xxxxxxxxxx; linux-
> hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; KY Srinivasan
> <kys@xxxxxxxxxxxxx>; Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>;
> olaf@xxxxxxxxx; vkuznets <vkuznets@xxxxxxxxxx>; davem@xxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: RE: [PATCH V2,net-next, 3/3] hv_netvsc: Name NICs based on vmbus
> offer sequence and use async probe
> 
> From: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> Sent: Monday, December 30,
> 2019 12:14 PM
> >
> > The dev_num field in vmbus channel structure is assigned to the first
> 
> Let's use "VMBus" in text.
I will.

> 
> > available number when the channel is offered. So netvsc driver uses it
> > for NIC naming based on channel offer sequence. Now re-enable the async
> > probing mode for faster probing.
> >
> > Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > ---
> >  drivers/net/hyperv/netvsc_drv.c | 18 +++++++++++++++---
> >  1 file changed, 15 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> > index f3f9eb8..39c412f 100644
> > --- a/drivers/net/hyperv/netvsc_drv.c
> > +++ b/drivers/net/hyperv/netvsc_drv.c
> > @@ -2267,10 +2267,14 @@ static int netvsc_probe(struct hv_device *dev,
> >  	struct net_device_context *net_device_ctx;
> >  	struct netvsc_device_info *device_info = NULL;
> >  	struct netvsc_device *nvdev;
> > +	char name[IFNAMSIZ];
> >  	int ret = -ENOMEM;
> >
> > -	net = alloc_etherdev_mq(sizeof(struct net_device_context),
> > -				VRSS_CHANNEL_MAX);
> > +	snprintf(name, IFNAMSIZ, "eth%d", dev->channel->dev_num);
> > +	net = alloc_netdev_mqs(sizeof(struct net_device_context), name,
> > +			       NET_NAME_ENUM, ether_setup,
> > +			       VRSS_CHANNEL_MAX, VRSS_CHANNEL_MAX);
> > +
> >  	if (!net)
> >  		goto no_net;
> >
> > @@ -2355,6 +2359,14 @@ static int netvsc_probe(struct hv_device *dev,
> >  		net->max_mtu = ETH_DATA_LEN;
> >
> >  	ret = register_netdevice(net);
> > +
> > +	if (ret == -EEXIST) {
> > +		pr_info("NIC name %s exists, request another name.\n",
> > +			net->name);
> > +		strlcpy(net->name, "eth%d", IFNAMSIZ);
> > +		ret = register_netdevice(net);
> 
> The message above could be confusing.  "request another name" sounds
> like a directive to the user/sysadmin, which I don't think it is.  Perhaps
> better would be "requesting another name", which says the system is
> handling the collision automatically.
> 
> Also will this second call to register_netdevice() actually assign a numeric
> name?  If so, it would be really nice for the message to be output *after*
> the second call to register_netdevice() and to show both the originally
> selected name that collided as well as the new name.  We sometimes get
> into NIC naming issues with customers in Azure, and when a new name
> has to be selected it will help debugging if we can show both the original
> selection and the new selection.  With both pieces of data, there's less
> guessing about who did what regarding NIC naming.
Good idea! I will include both new and old names in the log messages.

> 
> Finally, having to choose a different name because of a collision does
> *not* update the channel->dev_num value.  Subsequent calls to
> hv_set_devnum() will detect "in use" based on the originally assigned
> dev_num value.  I don't think that fundamentally breaks anything, but
> I wondered if you had thought about that case.   Maybe a comment here
> to that effect would help a future reader of this code.

That's correct. And I'm aware of this situation. But, the dev_num shouldn't 
be changed, because we want it to keep track of the sequence of device 
offering.
Avoid single or multiple collisions, we should use udev or other daemons to
set name of VF or other types of NICs to different formats, like "vf*", or "enP*",
etc. For distros have not done so already, we need to work with the distro vendors
to ensure udev or other settings are correctly included in Distros, and Azure images.

Thanks,
- Haiyang