Did anybody start project 1?
	What sorting algorithm did you use?
	Could also use qsort library function if you want

Let's make a quick macro that does something useful:
	SIZE(), and it gives the number of elements in a local array
	Could it give an error or something if it's not a local array?

Alright, how about a FOREACH that works on local arrays?

void*, since it's in project 1:
	Pointers are 64-bit unsigned integers
	Pointers can point to any type, since it's just a number
	Use size_t for data structure sizes
	ssize_t for signed size_t (why is this ok?)
	sizeof returns the size of variables
	void* can point to anything!
		So you have to cast it to a more useful type
		Can add a variable here if you want (will be optimized out)

Allocating Memory:
	malloc and free
	calloc
	Don't forget to deallocate!
	Arrays vs. Python lists, and realloc
		- Userspace:  C++ vector
		- Kernel:  Kernel linked lists

Notes about linking:
	We'll build, but not link, a file with a C function
	Then later, write a program that uses it
	Does it work if we build with clang on one file, and gcc on another?
	If we compile the library on FreeBSD?
	If we engineer a name conflict?
	Inefficiency of static linking
		Multifunction machines to save space
	Dynamic linking instead with .so files
		kernel will use .ko

Kernel Modules!

A note about versions:
	Review from 253, and what do version numbers mean?

LKM:
	Around since Linux 1.2 (1995)
	Why? (kinda covered it last time)
		- Debugging
		- Recompile less often
		- Reboot less often (reset and update both)
		- Not slower
		- Kernel is smaller
		- Reload a particular driver without rebooting
	Why not?
		- More complicated
		- Management system required for hotplug
		- I used to dislike them
	Used for:
		- Device Drivers (most of the time)
		- Filesystems
		- Can add system calls
		- Network drivers (operate protocol)
		- Executable interpreter (ELF is normal, can add more)
	
Utilities:
	insmod
	rmmod
	depmod
	lsmod 
	modinfo
	modprobe 

Inserting Modules:
	insmod or modprobe
	Unresolved symbols:
		- Symbols are exported from the kernel OR MODULES
		- Dependencies among modules
		- /proc/kallsyms
		- Use count
	remove with rmmod or modprobe -r
	Could not find kernel version
		- Descriptive error messages are sometimes lacking
	How do you tell if it worked?
		- Depends on the module
		- lsmod will tell you if it's there
	Automatic Loading
		- Do you really want this?  Maybe...probably not
		- unload after 1min with autoclean
	Where are LKMs found?
		- Usually /lib/modules

Versions:
	Kernel version must match module version
		- Memory layout, kernel subroutines, etc
		- Did anything important really change?  insmod -f
		- Symbol versioning
		- gcc versions
		- What about multiple kernels?
			+ People do that sometimes...
		- Symbol licensing errors and viral GPL

Boot without device drivers?
	- This is complicated and probably not a good idea
	- Loader can load stuff into RAM before kernel starts
	- Still need to understand FS and run programs

How insmod works:
	init_module system call
	init_module subroutine in module
		- Linking is done at insertion time
	
Debugging is possible with kdb

Memory:
	Linux kernel is not pageable - virtual addresses = real addresses
	Modules can't be paged either, but virtual addresses != real addresses
		- kmalloc

Demo:
	blink.c	

/proc filesystem:
	Demo adding something
	crypto.c
	Let's make read pedantic