IOCTL number differs from kernel space

Jeshwanth Kumar N K Jeshu jeshkumar555 at
Thu Jan 3 13:30:03 EST 2013

Hello All,

I am trying IOCTL example provided in,
both user-space and kernel space using same chardev.h file for IOCTL
number. But the number receiving in kernel is different than number in
kernel. I printed both the received number and defined number in dmesg,
please find it below.

// IOCTL number which is in kernel
[ 6417.807403]  Value of IOCTL_GET_NTH_BYTE: -1073454078
[ 6417.807398]  Value of IOCTL_GET_MSG: -2147195903
[ 6417.807391]  Value of IOCTL_SET_MSG: -2147195904

// IOCTL number which is received by kernel.
[ 6426.691360] Passed IOCTL:number 0
[ 6426.691464] Passed IOCTL:number -1074930088
[ 6426.691537] Passed IOCTL:number 134514878

Can you please tell why this number is getting changed while receiving in
kernel ?

// Here is the definition of numbers.
#define MAJOR_NUM 100
#define IOCTL_SET_MSG _IOR(MAJOR_NUM, 0, char *)
#define IOCTL_GET_MSG _IOR(MAJOR_NUM, 1, char *)

Jeshwanth Kumar N K
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