How can I uniquely identify users trying to open() a kernel module?

Question

I'm working on a kernel module and I'm trying to uniquely identify each one of the users trying to open() the module (can be either processes or threads).

What is the best way to identify them? Is there an ID I can get from a system call?

I wish to get all users in a list that specifies whether they're trying to open the module for read/write, and I need to know which one tried acting.

Answer 1

When your open method is called, current will point at the task_struct of the task (~= thread) that is calling it.

This is seldom the right approach, though.

Answer 2

I'm assuming that you are creating a simple Linux character device, to be created in a location such as /dev/mydev. If this is the case then the following should give you a good example of how to do it. However, if you have a different meaning for open a device, then this won't be applicable.

Your char device file operations

struct file_operations mydev_fops = {
    .open = mydev_open,
};

Your mydev_open()

static int mydev_open(struct inode *inode, struct file *filp)
{
    pid_t pid;
    int user_id;

    /* This is the thread-ID, traditional PID is found in current->pgid */
    pid = current->pid;

    /* The current user-id (as of 2.6.29) */
    user_id = current_uid();
}

For more information about what you can find out about the current process, then check out the header file include/linux/cred.h.