[Gumstix-users] copy_to_user problems

[Kyle S. <ksc...@fo...>]

I'm writing a driver to run on the gumstix and I'm running into problems
copying data from kernel space to user space.  I can successfully print
out the correct data in the driver using printk, and then read it back
from the user space buffer and print it out again correctly.  

My problem is that I cannot see the correct data from user space.  Below
I show the short snippets of driver code, unit test code, and unit test
output.  Any help is appreciated.


Here's my test "read" implementation for my char device driver that only
copies 4 bytes:

ssize_t i2s_read 
(struct file *filep, char __user *buff, size_t count, loff_t *offp) {

    char bufCheck[4];
    unsigned int sample = SADR;

    printk(KERN_NOTICE "i2s: entering i2s_read!\n");
    printk(KERN_NOTICE "i2s: read %X from SADR\n", sample);

    if( copy_to_user(buff, &sample, 4) ) {
        printk(KERN_ERR "i2s: error copying data to userspace\n");
        return -EFAULT;
    } else {
        printk(KERN_NOTICE "i2s: data copied to userspace!\n");
        if( copy_from_user(bufCheck, buff, 4) ) {
            printk(KERN_ERR "i2s: error copying data from userspace\n");
            return -EFAULT;
        } else {
            printk(KERN_NOTICE "i2s: data copied back from userspace.");
            printk("  Data is: %X\n", *(unsigned int *)bufCheck);
        }
    }

    printk(KERN_NOTICE "i2s: leaving i2s_read!\n");
    return 0;
}


Here's my user space unit tester:

  unsigned int data = 0;
  FILE *adc = fopen("/dev/i2s0", "r");
  if(!adc) {
      printf("run 'mknod /dev/i2s0 c 50 0' on gumstix\n");
      return 1;
  }
  fread(&data, 4, 1, adc);
  printf("data = %X\n", data);



And here's the unit test output:

i2s: entering i2s_read!
i2s: read 64BCF212 from SADR
i2s: data copied to userspace!
i2s: data copied back from userspace.  Data is: 64BCF212
i2s: leaving i2s_read!
data = 0



Anyone see something out of place?


Thanks!

--
Kyle