From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Andr=C3=A9=20Fabian=20Silva=20Delgado?= Date: Wed, 5 Aug 2015 17:04:01 -0300 Subject: Initial import --- Documentation/ioctl/ioctl-decoding.txt | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) create mode 100644 Documentation/ioctl/ioctl-decoding.txt (limited to 'Documentation/ioctl/ioctl-decoding.txt') diff --git a/Documentation/ioctl/ioctl-decoding.txt b/Documentation/ioctl/ioctl-decoding.txt new file mode 100644 index 000000000..e35efb0ce --- /dev/null +++ b/Documentation/ioctl/ioctl-decoding.txt @@ -0,0 +1,24 @@ +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]) -- cgit v1.2.3