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- 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])
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