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/Documentation/ioctl/ioctl-decoding.txt

https://bitbucket.org/sammyz/iscream_thunderc-2.6.35-rebase
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Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0 
    

  1. To decode a hex IOCTL code:
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  3. Most architectures use this generic format, but check
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  4. include/ARCH/ioctl.h for specifics, e.g. powerpc
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  5. uses 3 bits to encode read/write and 13 bits for size.
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  6. 

  7.  bits    meaning
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  8.  31-30	00 - no parameters: uses _IO macro
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  9. 	10 - read: _IOR
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  10. 	01 - write: _IOW
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  11. 	11 - read/write: _IOWR
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  12. 

  13.  29-16	size of arguments
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  15.  15-8	ascii character supposedly
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  16. 	unique to each driver
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  18.  7-0	function #
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  21. So for example 0x82187201 is a read with arg length of 0x218,
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  22. character 'r' function 1. Grepping the source reveals this is:
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  23. 

  24. #define VFAT_IOCTL_READDIR_BOTH         _IOR('r', 1, struct dirent [2])
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  25.