-----Original Message-----
From: Roman Kagan <redacted>
Sent: Tuesday, December 31, 2019 6:35 AM
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: sashal@kernel.org; linux-hyperv@vger.kernel.org; netdev@vger.kernel.org;
KY Srinivasan [off-list ref]; Stephen Hemminger
[off-list ref]; olaf@aepfle.de; vkuznets
[off-list ref]; davem@davemloft.net; linux-kernel@vger.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:

quoted

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@microsoft.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?

quoted

+	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.

The vmbus number can be affected by other types of devices and/or subchannel
offerings. They are not stable either. That's why this patch set keeps track of the 
offering sequence within the same device type in a new variable "dev_num".

As in my earlier email, to avoid impact by other types of NICs, we should put them
into different naming formats, like "vf*", "enP*", etc. And yes, these can be done in
udev.

But for netvsc (synthetic) NICs, we still want the default naming format "eth*". And
the variable "dev_num" gives them the basis for stable naming with Async probing.

Thanks,
- Haiyang