ioctl-decoding.txt 606 B

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  1. To decode a hex IOCTL code:
  2. Most architecures use this generic format, but check
  3. include/ARCH/ioctl.h for specifics, e.g. powerpc
  4. uses 3 bits to encode read/write and 13 bits for size.
  5. bits meaning
  6. 31-30 00 - no parameters: uses _IO macro
  7. 10 - read: _IOR
  8. 01 - write: _IOW
  9. 11 - read/write: _IOWR
  10. 29-16 size of arguments
  11. 15-8 ascii character supposedly
  12. unique to each driver
  13. 7-0 function #
  14. So for example 0x82187201 is a read with arg length of 0x218,
  15. character 'r' function 1. Grepping the source reveals this is:
  16. #define VFAT_IOCTL_READDIR_BOTH _IOR('r', 1, struct dirent [2])