linux-kernel - [PATCH] Generalize asm-generic/ioctl.h to allow overriding values.

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Date:	Tue, 26 Feb 2008 04:26:09 -0500 (EST)
From:	"Robert P. J. Day" <rpjday@...shcourse.ca>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
cc:	Andrew Morton <akpm@...l.org>
Subject: [PATCH] Generalize asm-generic/ioctl.h to allow overriding values.


In the spirit of a number of other asm-generic header files,
generalize asm-generic/ioctl.h to allow arch-specific ioctl.h headers
to simply override _IOC_SIZEBITS and/or _IOC_DIRBITS before including
this header file, allowing a number of ioctl.h header files to be
shortened considerably.

Signed-off-by: Robert P. J. Day <rpjday@...shcourse.ca>

---

  i'm not sure what kernel subsystem this falls under.  this change
should not affect anything in the kernel, and the corresponding
ioctl.h headers can be tweaked sometime down the road.


diff --git a/include/asm-generic/ioctl.h b/include/asm-generic/ioctl.h
index cd02729..4fb087a 100644
--- a/include/asm-generic/ioctl.h
+++ b/include/asm-generic/ioctl.h
@@ -21,8 +21,19 @@
  */
 #define _IOC_NRBITS	8
 #define _IOC_TYPEBITS	8
-#define _IOC_SIZEBITS	14
-#define _IOC_DIRBITS	2
+
+/*
+ * Let any architecture override either of the following before
+ * including this file.
+ */
+
+#ifndef _IOC_SIZEBITS
+# define _IOC_SIZEBITS	14
+#endif
+
+#ifndef _IOC_DIRBITS
+# define _IOC_DIRBITS	2
+#endif

 #define _IOC_NRMASK	((1 << _IOC_NRBITS)-1)
 #define _IOC_TYPEMASK	((1 << _IOC_TYPEBITS)-1)
@@ -35,11 +46,21 @@
 #define _IOC_DIRSHIFT	(_IOC_SIZESHIFT+_IOC_SIZEBITS)

 /*
- * Direction bits.
+ * Direction bits, which any architecture can choose to override
+ * before including this file.
  */
-#define _IOC_NONE	0U
-#define _IOC_WRITE	1U
-#define _IOC_READ	2U
+
+#ifndef _IOC_NONE
+# define _IOC_NONE	0U
+#endif
+
+#ifndef _IOC_WRITE
+# define _IOC_WRITE	1U
+#endif
+
+#ifndef _IOC_READ
+# define _IOC_READ	2U
+#endif

 #define _IOC(dir,type,nr,size) \
 	(((dir)  << _IOC_DIRSHIFT) | \
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry:
    Have classroom, will lecture.

http://crashcourse.ca                          Waterloo, Ontario, CANADA
========================================================================
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