diff options
| author | Chuck Ebbert <76306.1226@compuserve.com> | 2006-12-10 02:18:57 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.osdl.org> | 2006-12-10 09:55:40 -0800 |
| commit | cf1b939e41c28a31f2052e5c0a6619b5711ad7d0 (patch) | |
| tree | d8ab99d8381b6b3b441f4e2cee545779e7cee24a | |
| parent | 0dd4e5b8e197f9d10e171e9f4aa9ed72e4a6d00c (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>
| -rw-r--r-- | Documentation/ioctl/ioctl-decoding.txt | 24 |
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 00000000000..bfdf7f3ee4f --- /dev/null +++ b/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]) |