Keep Stack usage to a minimum


On i386 user context in kernel is 8k per process - sizeof(struct user) = 5136 bytes deeply nested and/or recursive code is asking for trouble


"I was asked for general rules for stack allocation. Well, here it is:
 You will never, ever change a function in the kernel so that it
 allocates more than 256 bytes on the stack (and even that can be too
 much in some cases). And when all the offenders are fixed, I will
 start checking those that eat more than 100 bytes." - art@

The -Wstack-larger-than-N warning has been added to GCC in base to
help prevent the existance of such code, currently the kernel is
compiled with -Wstack-larger-than-2047.

Use malloc(9) or global declarations in the data segment, not
local variables for large arrays of data.