Format specifier for printk loff_t types?

Question

I am working on a Linux character device driver for a school assignment and am not sure how to print the *ppos passed into my read function which is of type loff_t.

I know I must use printk rather than the standard library printf from within the kernel but I can't seem to figure out the proper format specifier.

Answer 1

loff_t is just a typedef. To determine which format specifier to use, you should look for its definition:

• typedef __kernel_loff_t loff_t
• typedef long long __kernel_loff_t

Then you can refer to the Kernel's documentation to see how to format a "long long" (%lld).