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(upbeat music)

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- [Instructor] Alright, the moment of truth.

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Did you get it to work?

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You got to have those header files, got to have make

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and GCC installed and so forth.

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So there's a little bit of background work maybe you had

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to do, but let's see what happens with mine.

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Here's my lab.c.

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Really only needed these two includes

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for this particular module.

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And just like the example, we've got the prototypes,

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we've got a init function, we've got a cleanup function,

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we register 'em with the module in it and module exit macros

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and we've got a module license and then we have a makefile.

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I did Makefile

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and obj-m = lab.o.

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So you got, you know,

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a little bit different colon equals or equals.

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That's pretty much the same.

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And then we'll do our make here.

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So as before we're making modules.

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Got a little bit of extra help, we got a warning

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that the compiler is different than the one used

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to build the kernel.

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So that's a little bit of a scary situation.

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It's actually more hygienic

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to make sure you're using exactly the same compiler

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to build your modules that were used to build a kernel.

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What if the compiler lays out structs differently

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than the kernel compiler did?

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Then you'll have misalignment.

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So this is a little bit dangerous,

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but unfortunately it's kind of a common practice,

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but heads up for that, using exactly the same compiler

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is a good idea.

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So we got some extra files there,

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but we got our lab.ko

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so we should be able to load that insmod.

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And let's look if we got our message, we got the hello.

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You can see I had done it before,

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so I got the cleanup and all it before.

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But the last line is the hello.

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And if we do an lsmod,

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we can see the top one there is lab.

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That's the most recently loaded module.

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So our module's loaded.

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Now let's do an RM mod lab, lsmod.

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Is it gone?

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It's gone.

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And we do our dmesg

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and it says cleaning up.

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Alright, now we want to edit our code instead

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of returning zero return minus one,

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that indicates some sort of error, negative value.

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And then we do the make again.

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All right, then we insmod that

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and we got this operation not permitted.

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Well, we didn't really get operation not permitted.

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Minus one means operation not permitted.

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You put minus two, you'll get a different error message.

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So that's kind of misleading.

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If we do lsmod, it's not loaded.

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If we look at dmesg,

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it did do the hello

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because that happened before the return.