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From: Markku Savela <>
Subject: Re: How to get /dev entry created automaticly for dynamic major number?
Date: Thu, 25 Jan 2007 15:11:15 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <> (message from Greg KH on Thu, 25 Jan 2007 00:25:44 -0800)

Solution found!

> On Thu, Jan 25, 2007 at 09:35:07AM +0200, Markku Savela wrote:
> > If want to write a loadable module which "implements" a char device
> > ("virtual", no real device present). How do I get the correct
> > "/dev/foo" to appear automaticly?

> From: Greg KH <>

> If you look in the book, Linux Device Drivers, third edition, free
> online, there's a section on what is needed for udev to work properly.
> The ideas are still the same, but the way to do it has changed since the
> book was written.  Just use a struct device and a class, and you will be
> fine.  Look at the misc device core or the mem code in
> drivers/char/mem.c for examples of what you need to do.

Thanks! The solution seems to work. The final *obstacle* was, that
class_* symbols were not available until I added the
LICENSE("GPL"). Here is the resulting template, maybe useful for
someone, and just for verification, that I got it right.

static int foo_major = 0;
static struct class *foo_class;
static struct class_device *foo_device;

static int __init foo_init(void)
    foo_major = 0;
    foo_class = NULL;
    foo_device = NULL;

    foo_major = register_chrdev(foo_major, "foo", &foo_fops);
    if (foo_major <= 0)
        return -EIO;
    foo_class = class_create(THIS_MODULE, "foo");
    if (IS_ERR(foo_class))
       return PTR_ERR(foo_class);
    foo_device = class_device_create(foo_class, NULL, MKDEV(foo_major, 0), NULL, "foo0");
    if (IS_ERR(foo_device))
       return PTR_ERR(foo_device);
    return 0;

static void __exit foo_exit(void)
    if (foo_device && !IS_ERR(foo_device))
    if (foo_class && !IS_ERR(foo_class))
    if (foo_major > 0)
       unregister_chrdev(foo_major, "foo");


MODULE_AUTHOR("Markku Savela");
MODULE_DESCRIPTION("Just fooling around");

  reply	other threads:[~2007-01-25 13:11 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-25  7:35 Markku Savela
2007-01-25  8:25 ` Greg KH
2007-01-25 13:11   ` Markku Savela [this message]
2007-01-25 13:17     ` Markku Savela
2007-01-25 13:37     ` Jiri Kosina
2007-01-25 15:51     ` Greg KH

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