Re: Which node has the device been bound to?

[Greg KH <greg@kroah.com>]

On Sat, Jun 01, 2002 at 04:12:47AM +0200, Oliver Neukum wrote:
> > Have you seen the way driverfs shows the usb and pci topology?
> 
> Fine for humans, which is not the issue here.

And for programs.

> > And yes, you might be acting on old data.  But if you have an ioctl()
> > what would it return?  A pointer to the topology location which might
> > have just changed?  I don't see how an ioctl() can solve this problem
> > any different from the way driverfs is going about it.  But I could be
> > missing something. :)
> 
> An ioctl() would either return the actual topology information
> or a unique token.
> 
> A name can change meaning. An open file cannot. It'll either
> be what the ioctl() will tell you, or it'll be gone. If you operate on a
> device that is gone the kernel will return an error and all is well.

Yes, you get a response from an ioctl that points you to a /dev node or
a driverfs file.  Then the device is disconnected and whatever you had
pointing to that device (the /dev file pointer) is replaced with a new
device connecting.  Same problem as before :)

> If you parse what driverfs gives you, you operate on changing
> data without a lock. I can see no way to change that.

I don't see a way around this even with ioctl().

But what is the real problem here?  What do you want to solve?  Mapping
of a /dev node to a physical device?  Or mapping of a physical device to
a /dev node?  Or something else?

thanks,

greg k-h

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