| ============================== |
| Decoding an IOCTL Magic Number |
| ============================== |
| |
| To decode a hex IOCTL code: |
| |
| Most architectures 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]) |
