Re: [linux-usb-devel] Re: hotplugging to deal with firmware download

[David Brownell <david-b@pacbell.net>]

>>You need the ability to reidentify for simple things like setting the 
>>correct IP on the correct network adapter, or correct resolution
>>on the correct camera.
>  
> I agree.  Then use something unique in the device like I said in a
> different message: device physical path, serial number, mac address, fs
> label, etc.

For network devices this is exposed through struct ethtool_drvinfo;
there's a bus_info field.  In 2.5 most of the USB networking drivers
(it should be/become all!) use this to advantage; there's a new
API, usb_make_path(), that provides a stable physical path.

Admittedly many userspace tools ignore that, as well as the ethernet
address, in favor of nasty unstable names like "eth0".  But I know
that somewhere there's a tool that'll rename interfaces, so that those
tools which expect "eth0" style names to be stable won't need to break
too badly ... :)


> But only use the physical path if that's your last resort, as it's the
> most unstable.  This is the main reason the USB printer spec started
> specifying that all USB printers need to have a serial number.  To help
> uniquely identify them.

Actually in the "typical" suspend/resume case (like powerdown overnight,
or over lunch) I think the physical path is unlikely to change.

Though there are certainly cases like suspend, carry laptop to new site,
hook up to new printer ... so it's certainly true that it's a good idea
to use the physical path in conjunction with other data (like device
vendor and product IDs) if that's all you have to work with.

- Dave





_______________________________________________________________

Don't miss the 2002 Sprint PCS Application Developer's Conference
August 25-28 in Las Vegas -- http://devcon.sprintpcs.com/adp/index.cfm

_______________________________________________
Linux-hotplug-devel mailing list  http://linux-hotplug.sourceforge.net
Linux-hotplug-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel