From: Chuck Ebbert <76306.1226@compuserve.com>
To: linux-kernel <linux-kernel@vger.kernel.org>
Cc: Andrew Morton <akpm@osdl.org>
Subject: [patch] Document how to decode an IOCTL number
Date: Thu, 7 Dec 2006 23:02:04 -0500 [thread overview]
Message-ID: <200612072306_MC3-1-D448-DB6A@compuserve.com> (raw)
Document how to decode a binary IOCTL number.
Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
---
Documentation/ioctl/ioctl-decoding.txt | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
--- /dev/null
+++ 2.6.19.0.5-32smp/Documentation/ioctl/ioctl-decoding.txt
@@ -0,0 +1,24 @@
+To decode a hex IOCTL code:
+
+Most architecures use this generic format, but check
+include/ARCH/ioctl.h for specifics, e.g. powerpc
+uses 3 bits to encode read/write and 13 bits for size.
+
+ bits meaning
+ 31-30 00 - no parameters: uses _IO macro
+ 10 - read: _IOR
+ 01 - write: _IOW
+ 11 - read/write: _IOWR
+
+ 29-16 size of arguments
+
+ 15-8 ascii character supposedly
+ unique to each driver
+
+ 7-0 function #
+
+
+ So for example 0x82187201 is a read with arg length of 0x218,
+character 'r' function 1. Grepping the source reveals this is:
+
+#define VFAT_IOCTL_READDIR_BOTH _IOR('r', 1, struct dirent [2])
--
Chuck
"Even supernovas have their duller moments."
next reply other threads:[~2006-12-08 4:12 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-08 4:02 Chuck Ebbert [this message]
2006-12-08 4:42 ` [patch] Document how to decode an IOCTL number Randy Dunlap
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