Re: New hotplug interface is not working right for me

[Greg KH <greg@kroah.com>]

On Fri, Mar 11, 2005 at 01:04:05AM -0500, Eric S. Raymond wrote:
> Greg KH <greg@kroah.com>:
> > On Fri, Mar 11, 2005 at 12:20:54AM -0500, Eric S. Raymond wrote:
> > > Greg KH <greg@kroah.com>:
> > > > > The problem appears to be that whatever thread of control is creating 
> > > > > the /dev/ttyUSB* node is running asynchronously with the hotplug
> > > > > script and does not reliably (or even usually) create it before the
> > > > > gpsd instance gets spawned and goes looking for the node.
> > > > 
> > > > Then use the /etc/dev.d/ interface instead.  That requires udev and a
> > > > 2.6 kernel, but is the only way you can know exactly when the /dev entry
> > > > is created.
> > > 
> > > Where is this documented?
> > 
> > In the udev documentation and a simple google search brings it up.
> >
> > > Even if the /etc/dev.d/ interface works, that doesn't really make it
> > > acceptable that the /etc/hotplug.d/ interface is broken.  There is some
> > > locking that ought to be happening and isn't.
> > 
> > The interface is not broken, you are trying to trigger off of two
> > different hotplug events (one when the device appears, and a different
> > one when the device node is to be created.)
> 
> If it's not broken, then it's not documented either.

You are watching for the wrong hotplug event, how can we document that?
:)

> Or, at least, I don't see any documentation that tells me about a
> second hotplug event when /dev/ttyUSB0 is created.  Now, if I could
> write a script that would fire on only only /dev/ttyUSB* creation events and
> allow me to filter on the vendor/product ID, that would be fine -- those
> are what I'm really interested in.

You can, just put your script into /etc/hotplug.d/tty and watch for the
device name to be ttyUSB*.  Then walk the sysfs chain back up the
directory to see the vendor and product id of the device attached to
that ttyUSB device.

thanks,

greg k-h


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