Re: How can I specify a specific 'sub-device' of a device for udev naming?

[Greg KH <greg@kroah.com>]

On Thu, Mar 04, 2004 at 01:19:04AM -0600, Jonathan Steinert wrote:
> 
> However, I'd like to ask... since you (I think) asume that each physical 
> device maps to only one node; What will happen when someone wants to 
> name multiple devices based on an attribute higher in the than the 
> unique branch?

Well, it's a bit hard if you want to do that, isn't it :)

usb to serial devices have the same "issue", as well as many other types
of devices.  The trick is in coming up with a unique name rule for those
kinds of devices.

> The first example I came up with is my Griffin iMic (a usb sound card 
> dongle) which creates multiple device nodes. The trouble is that I think 
> ALSA is supposed to handle this situation and not udev.
> 
> The next best example I can think of would be naming USB devices based 
> on which hub they are plugged in to. The hub must be identified by some 
> sort of serial number or other attribute, but then there may be more 
> than one device plugged into that hub.

Well, you can always go on the position of the usb device (plugged into
which port of which hub.)  But again, you are back to the "multiple
virtual devices per physical device" issue.

We are a whole lot better off than before, when we could never even
determine this information.  It's up to the individual driver writers to
help expose unique information for their devices that can help out in
creating "good enough" rules.

> I'm just throwing this question out to see how it could be solved, so I 
> can't give you specific attributes till I build the system I want this for.

There is no "general" solution for this.  It's going to be a individual
one as every system ends up being different.

thanks,

greg k-h


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