Re: [ANNOUNCE] udev 007 release

[Greg KH <greg@kroah.com>]

On Tue, Nov 25, 2003 at 02:29:17PM +0100, Marco d'Itri wrote:
> On Nov 24, Arnd Bergmann <arnd@arndb.de> wrote:
> 
>  >+			case 'N':
>  >+				if (strlen(udev->kernel_number) = 0) {
>  >+					strcat(pos, "disk");
>  >+					break;
>  >+				}
>  >+				strcat(pos, "part");
>  >+				strcat(pos, udev->kernel_number);
>  >+				dbg("substitute kernel number '%s'", udev->kernel_number);
>  >+				break;
> 
> After seeing this I started thinking about devfs-like devices and I
> tough that, as soon as the kernel will export a node which will allow
> recognizing CD devices, this could part of the default udev.config
> shipped by a distribution (I'd like to do this for debian):
> 
> NUMBER, BUS="ide", id="0.0", NAME="ide/host0/bus0/target0/lun0/%N"
> NUMBER, BUS="ide", id="0.1", NAME="ide/host0/bus0/target1/lun0/%N"
> NUMBER, BUS="ide", id="1.0", NAME="ide/host0/bus1/target0/lun0/%N"
> NUMBER, BUS="ide", id="1.1", NAME="ide/host0/bus1/target1/lun0/%N"
> NUMBER, BUS="ide", id="0.0", type="cd", NAME="ide/host0/bus0/target0/lun0/cd"
> NUMBER, BUS="ide", id="0.1", type="cd", NAME="ide/host0/bus0/target1/lun0/cd"
> NUMBER, BUS="ide", id="1.0", type="cd", NAME="ide/host0/bus1/target0/lun0/cd"
> NUMBER, BUS="ide", id="1.1", type="cd", NAME="ide/host0/bus1/target1/lun0/cd"

Hm, two different rules for the same id.  Not a good idea, udev can not
handle this.  How about a LABEL rule for a cd instead.
But you are going to have to do a CALLOUT rule if you want to create
names like "ide/host0/bus0/target0/lun0" properly, so you might as well
do it all in a external script.  Makes it much easier for you :)

> And this could be a possible syntax for managing symlinks: LINK would
> work just like NUMBER, but NAME would be a symlink to the device
> specified:
> 
> # a trailing / means that the link will be done to the parent directory
> LINK, BUS="ide", id="0.0", NAME="discs/disc0/"
> LINK, BUS="ide", id="0.1", NAME="discs/disc1/"
> LINK, BUS="ide", id="1.0", NAME="discs/cdrom0"
> LINK, BUS="ide", id="1.1", NAME="discs/cdrom1"

No, I think multiple NAME values on a line would be the best thing, but
that will take some major tweaks to udev to get there.  We will get
there...

> Related problem: if the ide-cd driver is modular then at boot time the
> block device nodes will not appear in sysfs, so udev will not create the
> devices in /dev. But if there are no devices which applications can
> open, how can the kernel autoload the module?
> Currently no hotplug method deals with this, so I'm not sure about what
> should load ide-cd at boot time.

That's up to your startup scripts :)
Look at how Red Hat does this for an example of this.

> BTW, how can I configure udev to create devices like vc/%n instead of
> tty%n?

For USB tty devices try:
	REPLACE, KERNEL="ttyUSB*", NAME="usb/%n"
So create such a rule for all of the different tty device types.
And then as your last REPLACE rule do:
	REPLACE, KERNEL="tty*", NAME="vc/%n"

Hope this helps,

greg k-h


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