Re: Which node has the device been bound to?

[Greg KH <greg@kroah.com>]

On Tue, Jun 04, 2002 at 12:43:38AM +0200, Oliver Neukum wrote:
> Am Montag, 3. Juni 2002 23:58 schrieb Greg KH:
> > On Mon, Jun 03, 2002 at 11:09:36PM +0200, Oliver Neukum wrote:
> > > > 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?
> > >
> > > The former. The latter has some principal problems.
> > > To do the former you need to have an atomic operation on an
> > > opened device.
> > > Thus you need to have the device node open and you need
> > > the ioctl to not return a pointer to a driverfs file. You either
> > > return its content or an fd.
> >
> > Ok, I understand a bit better now (sorry, I'm slow today...).  So what
> > fd do you want returned in the ioctl()?  driverfs implements a tree for
> > every device, not a single file.  Do you want a fd for the directory?
> 
> No problem, I am dense at times, too.
> There's a problem. You cannot open() based on a directory fd,
> unless I am mistaken.

I think you are correct, that's why I asked.

> I can't come up with anything better than a set of ioctls that return
> the contents of the individual files. And I know that this is ugly.
> I don't claim that this is a good solution, just that it's the only
> solution I have and that there's a race otherwise.
> You simply cannot use names, thus parsing files for the name of the
> node won't work.

Or we could just drop the whole idea of using ioctl() and live with the
"instability" of parsing a filesystem :)

> I've thought about finding the device node to a physical device.
> It really is problematic. Firstly there can be several nodes.
> Secondly you'd need device nodes in driverfs, in effect merging it
> with devfs.

I saw a patch to driverfs that did this a while ago, but see Linus's
comments on lkml about why this will probably never happen.

thanks

greg k-h

_______________________________________________________________

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