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| author | Olof Johansson <olof@lixom.net> | 2019-12-05 13:16:58 -0800 |
|---|---|---|
| committer | Olof Johansson <olof@lixom.net> | 2019-12-05 13:18:54 -0800 |
| commit | 942e6f8a8314e5550e254519dfba4ccd5170421d (patch) | |
| tree | 75ec655b440fbc1c454247af38b5596dd8c78de9 /Documentation/userspace-api/ioctl/ioctl-decoding.rst | |
| parent | 336bab731be76a90291697e51d2aed0ad67d7cb5 (diff) | |
| parent | b08baef02b26cf7c2123e4a24a2fa1fb7a593ffb (diff) | |
Merge mainline/master into arm/fixes
This brings in the mainline tree right after armsoc contents was merged
this release cycle, so that we can re-run savedefconfig, etc.
Signed-off-by: Olof Johansson <olof@lixom.net>
Diffstat (limited to 'Documentation/userspace-api/ioctl/ioctl-decoding.rst')
| -rw-r--r-- | Documentation/userspace-api/ioctl/ioctl-decoding.rst | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/Documentation/userspace-api/ioctl/ioctl-decoding.rst b/Documentation/userspace-api/ioctl/ioctl-decoding.rst new file mode 100644 index 000000000000..380d6bb3e3ea --- /dev/null +++ b/Documentation/userspace-api/ioctl/ioctl-decoding.rst @@ -0,0 +1,31 @@ +============================== +Decoding an IOCTL Magic Number +============================== + +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]) |