Re: faking or posing as a specific USB ID?

[Greg KH <greg@kroah.com>]

On Sun, May 10, 2009 at 11:25:42PM +0300, Jani Monoses wrote:
> Hello,
> 
> the lkml is probably a better list for this question but there may be a 
> udev answer to it.
> 
> The problem I am trying to find the most elegant solution for is the 
> following: given a certain driver that supports USB device AAAA:BBBB try 
> to see if it works with new device CCCC:DDDD without rebuilding (or 
> hexediting :) the module by somehow asking it to treat the new device as 
> if it were AAAA:BBBB.

Just use the "new_id" files in sysfs and the bind and unbind files there
to do the binding after writing the new id to the driver.  That is what
those files are there for.

> This may not be possible with the current kernel, as drivers only look 
> for devices hardcoded in their .initdata sections. While  some can be 
> told via a new_id sysfs attribute to add a new ID dynamically to their
> supported list, webcams and probably other families of devices would 
> need to specify extra parameters (ex: bridge and img sensor tuple) 
> besides the ID.

If a driver needs more than the id, then no, the new_id stuff will not
work, sorry.

> Does udev have some way of faking insertion events or altering an event 
> coming from the kernel and sending it back that way? A rule that says in 
> effect, rename USB ID AAAA:BBBB to CCCC:DDDD ?

No, that will not work, use bind/unbind/new_id from userspace through
sysfs.

> If not, the the ID matching code in the kernel is the one I think could 
> be told via a syfs atribute similar to new_id.

Yes, use that :)

hope this helps,

greg k-h