hotplug events on USB ethernet adapters

DISCUSSION Mark Atwood 2 participants 2 messages Jun 14, 2002

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Mark Atwood

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2002-06-14 03:11 UTC #0 lore raw

I have a LinkSys Ethernet USB adapter.

When I plug it in, I get two hotplug events, one for net and one for usb.

Is there an easy way to associate these two events?

What I mean is,

is there a way for the /etc/hotplug/usb agent (and thus the /etc/hotplug/usb/pegasus) to know know which ethN INTERFACE is going to correspond to this device,

and/or else

is there a way for the /etc/hotplug/net.agent to know that this interface is a USB device, and what PRODUCT, TYPE, INTERFACE, and DEVICE & DEVFS it is?

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David Brownell

2002-06-14 04:22 UTC #1 lore raw

Quoted 3 lines

I have a LinkSys Ethernet USB adapter
When I plug it in, I get two hotplug events, one for net and one for usb Is there an easy way to associate these two events?

Not really. Why would you want that?

Quoted 5 lines

What I mean is,
is there a way for the /etc/hotplug/usb agent (and thus the /etc/hotplug/usb/pegasus) to know know which ethN INTERFACE is going to correspond to this device,

No, since at the time the usb level event is reported the network driver may not even have been loaded ... and it's that driver which chooses the "ethN" prefix. Since other drivers might be getting loaded concurrently, even if you were to guess about prefix "eth", you couldn't guess the value of "N".

Quoted 5 lines

and/or else
is there a way for the /etc/hotplug/net.agent to know that this interface is a USB device, and what PRODUCT, TYPE, INTERFACE, and DEVICE & DEVFS it is?

No, but it can get part way there in 2.5 ...

At least on the 2.5 kernels, "ethtool -i eth0" will give you some "bus-info" that's identifies the physical location of the device. It's what the usb_make_path() call returns.

It's a string like "usb-00:0f.1-3.2" indicating first that it's USB, then that it's the bus with name/serial "00:0f.1" (which in this case is a PCI slot), then that it's connected to port 3 on the root hub, and port 2 on the hub connected there. That's a stable name, it won't change unless/until you re-cable things. Which means that it's possible to set up persistent configurations over USB. (There are non-USB "bus-info" values too, like for pci.)

I've thought that it would be useful to have the hotplug agent report the usb_make_path() information, using some other variable. Likewise, to have USBFS report those strings through some ioctl on the device. (You can reconstruct it, but it's awkward and expensive and requires r/w access to most devices on the same bus, so I'd not encourage folk to do that.)

- Dave

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