Messages in this thread Patch in this message | | | Date | Thu, 7 Dec 2006 23:02:04 -0500 | From | Chuck Ebbert <> | Subject | [patch] Document how to decode an IOCTL number |
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Document how to decode a binary IOCTL number.
Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com> --- Documentation/ioctl/ioctl-decoding.txt | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)
--- /dev/null +++ 2.6.19.0.5-32smp/Documentation/ioctl/ioctl-decoding.txt @@ -0,0 +1,24 @@ +To decode a hex IOCTL code: + +Most architecures 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]) -- Chuck "Even supernovas have their duller moments." - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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