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

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Date:   Tue, 31 Dec 2019 11:34:44 +0000
From:   Roman Kagan <rkagan@...tuozzo.com>
To:     Haiyang Zhang <haiyangz@...rosoft.com>
CC:     "sashal@...nel.org" <sashal@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "sthemmin@...rosoft.com" <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2,net-next, 3/3] hv_netvsc: Name NICs based on vmbus
 offer sequence and use async probe

On Mon, Dec 30, 2019 at 12:13:34PM -0800, Haiyang Zhang wrote:
> The dev_num field in vmbus channel structure is assigned to the first
> 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@...rosoft.com>
> ---
>  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);

How is this supposed to work when there are other ethernet device types
on the system, which may claim the same device names?

> +	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);
> +	}

IOW you want the device naming to be predictable, but don't guarantee
this?

I think the problem this patchset is trying to solve is much better
solved with a udev rule, similar to how it's done for PCI net devices.
And IMO the primary channel number, being a device's "hardware"
property, is more suited to be used in the device name, than this
completely ephemeral device number.

Thanks,
Roman.

> +
>  	if (ret != 0) {
>  		pr_err("Unable to register netdev.\n");
>  		goto register_failed;
> @@ -2496,7 +2508,7 @@ static int netvsc_resume(struct hv_device *dev)
>  	.suspend = netvsc_suspend,
>  	.resume = netvsc_resume,
>  	.driver = {
> -		.probe_type = PROBE_FORCE_SYNCHRONOUS,
> +		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
>  	},
>  };
>  
> -- 
> 1.8.3.1
>