Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) ==============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) Decoding an IOCTL Magic Number
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) ==============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) To decode a hex IOCTL code:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7) Most architectures use this generic format, but check
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8) include/ARCH/ioctl.h for specifics, e.g. powerpc
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) uses 3 bits to encode read/write and 13 bits for size.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)  ====== ==================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12)  bits   meaning
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13)  ====== ==================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14)  31-30	00 - no parameters: uses _IO macro
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) 	10 - read: _IOR
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) 	01 - write: _IOW
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) 	11 - read/write: _IOWR
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19)  29-16	size of arguments
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21)  15-8	ascii character supposedly
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) 	unique to each driver
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24)  7-0	function #
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25)  ====== ==================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) So for example 0x82187201 is a read with arg length of 0x218,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) character 'r' function 1. Grepping the source reveals this is::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) 	#define VFAT_IOCTL_READDIR_BOTH         _IOR('r', 1, struct dirent [2])