Question

I am trying to get some message from kernel space to userspace, when a condition fails!

Here’s my kernel code:

#define MESSAGTOUSER 1

int ret_val;
struct siginfo sinfo;
pid_t id;
struct task_struct *task;

unsigned char msgBuffer[20];
unsigned char buf1[20]= "HI";

static int major_no;
static struct class *safe_class;

static long device_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
static int device_open(struct inode *inode, struct file *file);
static int device_write(struct file *file, const char *gdata, size_t len, loff_t *off);
static int device_read(struct file *file, char *buf, size_t len, loff_t *off);
static int device_release(struct inode *inode, struct file *file);


int failureDetection (char* faultMsg) {
    strcpy (msgBuffer, faultMsg);
    printk(KERN_ALERT"\nMessage from HBM %s\n", msgBuffer);
    printk(KERN_ALERT".......... RETURN VALUE ...... : %d", ret_val);

    int Reg_Dev(void);
    memset (&sinfo, 0, sizeof(struct siginfo));
    sinfo.si_signo = SIGUSR1;
    sinfo.si_code  = SI_USER;

    if (id == 0) {
        printk("\ncan't find User PID: %d\n", id);
    }else {
    //task = pid_task(find_vpid(pid), PIDTYPE_PID);
    task = find_task_by_vpid(id);
    send_sig_info(SIGUSR1, &sinfo, task);
    }
    return 0;
}

static int device_open(struct inode *inode, struct file *file){
    /*sucess*/
    return 0;
}

void strPrint(void) {
    printk("value of msgBuffer: %s", msgBuffer);
}

static int device_write(struct file *file, const char *gdata, size_t len, loff_t *off){
    get_user (id,(int *)gdata);
    if(id <0)
        printk(KERN_ALERT"Cann't find PID from userspace its : %i", id);
    else
        printk(KERN_ALERT"Successfully received the PID of userspace %i", id);
    return len;
}

static int
device_read(struct file *file, char *buf, size_t len, loff_t *off){
    /*success*/
    return 0;
}

static int device_release(struct inode *inode, struct file *file){
    /*success*/
    return 0;
}


static long device_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {


    switch (cmd) {
        case MESSAGTOUSER:
            ret_val = copy_to_user((char *)arg, msgBuffer, sizeof(arg));
            printk("Msg of Kernel %s", msgBuffer);
            break;
        default:
            break;
    }
    return 0;

}



static struct file_operations fops = {
    .open = device_open,
    .write = device_write,
    .read = device_read,
    .release = device_release,
    .unlocked_ioctl = device_ioctl
};


int Reg_Dev(void) {

    major_no = register_chrdev(0, "safe_dev", &fops);
    safe_class = class_create(THIS_MODULE, "safe_dev");
    device_create(safe_class,NULL, MKDEV(major_no, 0), "safe_dev");
    printk("\n Device Registered and Created \n");
    return 0;
}

void UnReg_dev (void) {
    printk("\nUser PID : %d\n", id);
    unregister_chrdev(major_no, "safe_dev");
    device_destroy(safe_class, MKDEV(major_no,0));
    class_unregister(safe_class);
    class_destroy(safe_class);
    printk("\n Device Un-Registered and Destroyed \n");
}

extern int Reg_Dev(void);

for he userspace i have this code:

#define PORT 9930
#define G_IP "192.168.10.71"
#define BUFLEN 512

#define MESSAGTOUSER 0

unsigned char *str[20];
char b1[BUFLEN], b2[BUFLEN];
struct sockaddr_in me,client;
int s, i, n=sizeof(me);
int fd;



void error_handler(char *s) {
  perror(s);
  exit(1);
}



void signal_handler (int signum) {

  if(signum == SIGUSR1)
  {
    printf("\n%s\n",str);

    if((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))  == -1)
       error_handler("\nERROR: in Socket\n");

    memset((char *) &me, 0, sizeof(me));
    me.sin_family = AF_INET;
    me.sin_port = PORT;

    if (inet_aton(G_IP, &me.sin_addr)==0) 
    {
       fprintf(stderr, "inet_aton() failed\n");
       exit(1);
    }
    printf("Message from Kernel : %s", &str);
    //strcpy (str, newStr);


    int cntr =0;    sprintf(b2, "\nFailure Message: %s\n",str);
    printf("\nsending Fault to PMN Group : Tick - %d\n", cntr++);


    if(sendto(s, str, sizeof(str),0,(struct sockaddr *) &me,n)==-1)
        error_handler("\nERROR: in sendto()\n");
    close (s);
//    counter ++;
 //   sendAndReceiveOverUDP();
    return;
  }
}

int main() {
   pid_t u_id;
   u_id = getpid();
   int i = 1;

   fd = open("/dev/safe_dev",O_RDWR);
   write(fd, &u_id, 4);
   ioctl (fd, MESSAGTOUSER, &str);
   printf("\n PID sent to device successfully: %d \n", u_id);
   close(fd);

   signal(SIGUSR1, signal_handler);
   printf("\nMy PID is: %d\n",u_id);
   //printf("Subnet 1 working fine.. Tick - %d", tv.tv_sec);

   while (1)
   sleep(1);
   return 0;
}

Now what I am expecting to receive on Userspace:

Message from Kernel: A<->B
Sending Fault o PMN Group : tick - 0

Message from Kernel: B<->B
Sending Fault o PMN Group : tick - 1
....
...

but what is the output:

Message from Kernel:
Sending Fault o PMN Group : tick - 0

Message from Kernel:
Sending Fault o PMN Group : tick - 1
....
...

It seems that copy_to_user is not working, while in simple program just copying a string from kernel to user is working fine, but while i am using in this scenario then its not working, its compiling without any warning,

• Some other Details:
• failureDetection() is getting a string like A<->B mentioned in output from rest of the programs..
• the same message from failureDetection is printing on kernel level but not transferring at the user level.
• I have also tried to create an own string in this and tried to transfer that, but it is also not working! suppose msgBuffer = HI, then I should receive HI on to the userspace. but its not happening! can anyone please please make me correct whats wrong with this code? how can i get updates onto the userspace!!??

Sindhu..

Answer 1

The copy_to_user() only happens in response to the ioctl(), which only happens once, very early on in your code. Presumably at that point the kernel buffer msgBuffer is empty, because the failureDetection() function has not yet run at that point. It doesn’t matter if failureDetection() runs later and sets msgBuffer then, because your userspace program never calls the ioctl() again so it doesn’t see the new contents of msgBuffer.

You also have a bug in your copy_to_user() call – instead of sizeof(args) (which is a constant 4) you should probably use sizeof msgBuffer.