loff_t (*llseek) (struct file *, loff_t,int);
This just says that llseek
is a pointer to a function that returns a loff_t
and takes three parameters. The first parameter is a pointer to a struct file
. The second is a loff_t
. The third is an int
.
However, if you look closely, you'll see it appears inside the declaration for struct file_operations
. This means that struct file_operations
contains a member called llseek
that is a pointer to a function that returns a loff_t
and takes those three parameters.
By the way, if you don't understand how to do OOP programming in C by using things like structures that contain pointers to functions, you really have no business going anywhere near a kernel device driver. (If you're familiar with C++, then just understand that a structure with pointers to functions is basically the way you fake a class in C.)