aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/ioctl/ioctl-decoding.txt
diff options
context:
space:
mode:
authorChuck Ebbert <76306.1226@compuserve.com>2006-12-10 05:18:57 -0500
committerLinus Torvalds <torvalds@woody.osdl.org>2006-12-10 12:55:40 -0500
commitcf1b939e41c28a31f2052e5c0a6619b5711ad7d0 (patch)
treed8ab99d8381b6b3b441f4e2cee545779e7cee24a /Documentation/ioctl/ioctl-decoding.txt
parent0dd4e5b8e197f9d10e171e9f4aa9ed72e4a6d00c (diff)
[PATCH] Document how to decode an IOCTL number
Document how to decode a binary IOCTL number. Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/ioctl/ioctl-decoding.txt')
-rw-r--r--Documentation/ioctl/ioctl-decoding.txt24
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/ioctl/ioctl-decoding.txt b/Documentation/ioctl/ioctl-decoding.txt
new file mode 100644
index 000000000000..bfdf7f3ee4f0
--- /dev/null
+++ b/Documentation/ioctl/ioctl-decoding.txt
@@ -0,0 +1,24 @@
1To decode a hex IOCTL code:
2
3Most architecures use this generic format, but check
4include/ARCH/ioctl.h for specifics, e.g. powerpc
5uses 3 bits to encode read/write and 13 bits for size.
6
7 bits meaning
8 31-30 00 - no parameters: uses _IO macro
9 10 - read: _IOR
10 01 - write: _IOW
11 11 - read/write: _IOWR
12
13 29-16 size of arguments
14
15 15-8 ascii character supposedly
16 unique to each driver
17
18 7-0 function #
19
20
21 So for example 0x82187201 is a read with arg length of 0x218,
22character 'r' function 1. Grepping the source reveals this is:
23
24#define VFAT_IOCTL_READDIR_BOTH _IOR('r', 1, struct dirent [2])