How to get userID when writing Linux kernel module

Question

Here is my function in my kernel module which I insert using insmod command after make at later stages. I am working on goldfish (2.6.29)

Answer 1

After spending two days, I finally figured out how to get uid of the process who made a system call. I will give all the suggestions I found on different links so that if my solution does not work, one of the others may work.

1) As told me Mats,

#include 

 static int getuid()
 {
     return current_uid();
 }

You call this function to get uid but it gave me negative numbers like -943124788 etc.

2)

uid_t credd_uid ;
const struct cred *cred = current_cred();
credd_uid = current->cred->uid; 

Same output like large negative numbers.

3)

uid_t struct_uid;
struct user_struct *u = current_user();

struct_uid = get_uid(u);

4) Worked Solution

It's given here actually.

i) Declare function prototype on the top like

asmlinkage int (*getuid_call)();

ii) Add following line to init_module() function

/* Get the system call for getuid */

  getuid_call = sys_call_table[__NR_getuid];

iii) Call the function in your trapped system call functions to get uid like

uid_t uid = getuid_call();