Re: [PATCH 2/5] VT binding: Add sysfs support

On Sat, Jun 10, 2006 at 08:38:18AM +0800, Antonino A. Daplas wrote:

Greg KH wrote:

quoted

On Fri, Jun 09, 2006 at 04:39:51PM +0800, Antonino A. Daplas wrote:

quoted

Add sysfs attributes for binding and unbinding VT console drivers. The
attributes are located in /sys/class/tty/console and are namely:

    A. backend - list registered drivers in the following format:

    "I C: Description"

No, this violates the "one value per file" issue with sysfs.  How do you
know you will not overflow the buffer passed to you?

I was wondering about this. I just want a way to show what are the currently
loaded drivers, so it's a read-only attribute.  It's using snprintf (though
I haven't added a check for possible overflows, should be a 2-liner). Maximum
number of lines is 16, and there are examples of this rule-breakage in the
current sysfs tree.

/sys/class/usb_host/usb_hostx/device/pools

Ah, thanks for pointing this out.  Those files should go to debugfs,
they do NOT belong in sysfs at all.

Yes, none are valid excuses.  Anyway, what would be the best way? I was
considering creating another class for vt_console, but that would entail
the creation of a new device major number just for this.

No, you don't need a major to create a new class in sysfs at all.  Look
at usb_host for an example of that :)

And even if you did, we have loads of free major numbers now, it's not a
big deal to get a new one.

I vote for this, it would make things much easier.

quoted

quoted

    Where: I  = ID number of the driver
           C  = status of the driver which can be:

		S = system driver
		B = bound modular driver
		U = unbound modular driver

	   Description - text description of the driver

    B. bind - binds a driver to the console layer

       echo <ID> > /sys/class/tty/console/bind

    C. unbind - unbinds a driver from the console layer

       echo <ID> > /sys/class/tty/console/unbind

The tty layer does nothing to these attributes except create them and punt all
requests to the VT layer.

Why is this needed?  What is wrong with the current scheme of binding
ttys to the console?

The binding part, maybe none, but that's still debatable.  It's the unbinding
feature that people are requesting.  Note the longish threads on "the future
of graphics subsystem".  It would also ease the life of console driver
developers, and it would stop people from pestering me on why they cannot unload
their beloved framebuffer console and drivers and go back to VGA console.

Ok, I also read the 0/5 in this series which describes this in detail,
sorry for not seeing that (hint, cc: everyone on the series that one
too, so they get a bit of detail in the future.)

thanks,

greg k-h