| Kyle Swenson | 8d8f654 | 2021-03-15 11:02:55 -0600 | [diff] [blame] | 1 | To decode a hex IOCTL code: |
| 2 | |
| 3 | Most architectures use this generic format, but check |
| 4 | include/ARCH/ioctl.h for specifics, e.g. powerpc |
| 5 | uses 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, |
| 22 | character 'r' function 1. Grepping the source reveals this is: |
| 23 | |
| 24 | #define VFAT_IOCTL_READDIR_BOTH _IOR('r', 1, struct dirent [2]) |