Our simple kernel timer module – running it

Now, let's test our kernel timer module. On our x86_64 Ubuntu VM, we will use our lkm convenience script to load up the kernel module. The following screenshot shows a partial view of this and the kernel log:

Figure 5.2 – A partial screenshot of running our timer_simple.ko kernel module

Study the dmesg (kernel log) output shown here. Since we've set the initial value of our private structure's data member to 3, the kernel timer expires three times (just as our logic demands). Check out the timestamps in the left-most column; you can see that the second timer expiry occurred at 4234.289334 (sec.us) and the third at 4234.737346; a quick subtraction reveals that the time difference is 448,012 microseconds; that is, about 448 milliseconds. This is reasonable since we asked for a 420 ms timeout (its a bit over that; the overheads of the printks do matter as well).

The PRINT_CTX() macro's...