1 ============================== 1 ==============================
2 Decoding an IOCTL Magic Number 2 Decoding an IOCTL Magic Number
3 ============================== 3 ==============================
4 4
5 To decode a hex IOCTL code: 5 To decode a hex IOCTL code:
6 6
7 Most architectures use this generic format, bu 7 Most architectures use this generic format, but check
8 include/ARCH/ioctl.h for specifics, e.g. power 8 include/ARCH/ioctl.h for specifics, e.g. powerpc
9 uses 3 bits to encode read/write and 13 bits f 9 uses 3 bits to encode read/write and 13 bits for size.
10 10
11 ====== ================================== 11 ====== ==================================
12 bits meaning 12 bits meaning
13 ====== ================================== 13 ====== ==================================
14 31-30 00 - no parameters: uses _IO macro 14 31-30 00 - no parameters: uses _IO macro
15 10 - read: _IOR 15 10 - read: _IOR
16 01 - write: _IOW 16 01 - write: _IOW
17 11 - read/write: _IOWR 17 11 - read/write: _IOWR
18 18
19 29-16 size of arguments 19 29-16 size of arguments
20 20
21 15-8 ascii character supposedly 21 15-8 ascii character supposedly
22 unique to each driver 22 unique to each driver
23 23
24 7-0 function # 24 7-0 function #
25 ====== ================================== 25 ====== ==================================
26 26
27 27
28 So for example 0x82187201 is a read with arg l 28 So for example 0x82187201 is a read with arg length of 0x218,
29 character 'r' function 1. Grepping the source 29 character 'r' function 1. Grepping the source reveals this is::
30 30
31 #define VFAT_IOCTL_READDIR_BOTH 31 #define VFAT_IOCTL_READDIR_BOTH _IOR('r', 1, struct dirent [2])
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.