kdev_t.h old major/minor numbers

kdev_t.h old major/minor numbers

[Corey Richardson]

While reading through some of the kernel stuff I noticed that the macros
at the end of include/linux/kdev_t.h were out-of-sync with the macros at
the top. I'm not certain when/if they would ever be defined and not the
other ones (I'm very new to the kernel), but I would assume that they
shouldn't be using the old 255-number system.

Was this just an oversight or is there something else going on?

Patch:

--- linux/include/linux/kdev_t.h	2011-05-19 00:06:34.000000000 -0400
+++ git/include/linux/kdev_t.h.	2011-08-10 03:19:10.228987057 -0400
@@ -93,8 +93,11 @@
 Some programs want their definitions of MAJOR and MINOR and MKDEV
 from the kernel sources. These must be the externally visible ones.
 */
-#define MAJOR(dev)	((dev)>>8)
-#define MINOR(dev)	((dev) & 0xff)
-#define MKDEV(ma,mi)	((ma)<<8 | (mi))
+#define MINORBITS	20
+#define MINORMASK	((1U << MINORBITS) - 1)
+
+#define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
+#define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
+#define MKDEV(ma,mi)	(((ma) << MINORBITS) | (mi))
 #endif /* __KERNEL__ */
 #endif
-- 
Corey Richardson
  "Those who deny freedom to others, deserve it not for themselves"
     -- Abraham Lincoln

Re: kdev_t.h old major/minor numbers

[Greg KH]

On Wed, Aug 10, 2011 at 04:21:15AM -0400, Corey Richardson wrote:
> 
> While reading through some of the kernel stuff I noticed that the macros
> at the end of include/linux/kdev_t.h were out-of-sync with the macros at
> the top. I'm not certain when/if they would ever be defined and not the
> other ones (I'm very new to the kernel), but I would assume that they
> shouldn't be using the old 255-number system.
> 
> Was this just an oversight or is there something else going on?

No, it is done this way on purpose, please read the comment right before
the code you just changed.

greg k-h