read()

• ssize_t foo_read ( struct file *f, __user char *buf, size_t sz, loff_t *off)

• Called when user-space uses the read() system call on the device.
• Must read data from the device, write at most sz bytes in the user-space buffer buf, and update the current position in the file off. f is a pointer to the same file structure that was passed in the open() operation
• Must return the number of bytes read.
• On Unix, read() operations typically block when there isn't enough data to read from the device