MPU9150 - Recommended method for reading magnetometer

Hi,
I am developing an application using a MCU that interfaces via I2C with the MPU9150. So I think I have to code the driver that access MPU9150 registers.

I was planning to setup a fixed sample rate to read accelerometer, gyroscope and magnetometer values, but when reading the documentation I am not sure how to read the magnetometer data. I cannot find the register that defines the sample rate for the magnetometer and also I am not sure that registers 0x03-0x08 should be read directly or through an indirect reading via MPU9150 I2C slaves or external sensor data.

What are the available options to read magnetometer and setting a global sample rate for all the measures? Is there any recommendation about the preferred way to do that (i.e: use the FIFO for accel and gyro and configure magnetometer readings through external sensor via I2C slave) ?

Thanks in advance,

malonso