modules: rename packages/kernel_modules to packages/lkmc

Then inside, split packages/lkmc into kernel_modules and userland,
to keep userland out of the kernel_modules parent path, which makes no
sense.

Copy built modules and userland to the output rootfs overlay.

Document Linux distro tradeoffs.

packages/lkmc/userland/bst_vs_heap.cpp

@@ -0,0 +1,44 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#bst-vs-heap */
+
+#include <algorithm>
+#include <iostream>
+#include <queue>
+#include <random>
+#include <set>
+
+#include "m5ops.h"
+
+int main(int argc, char **argv) {
+    typedef uint64_t I;
+    std::vector<I> randoms;
+    size_t i, n;
+    std::priority_queue<I> heap;
+    std::set<I> bst;
+    unsigned int seed = std::random_device()();
+
+    // CLI arguments.
+    if (argc > 1) {
+        n = std::stoi(argv[1]);
+    } else {
+        n = 1000;
+    }
+
+    // Action.
+    for (i = 0; i < n; ++i) {
+        randoms.push_back(i);
+    }
+    std::shuffle(randoms.begin(), randoms.end(), std::mt19937(seed));
+    for (i = 0; i < n; ++i) {
+    	auto random = randoms[i];
+
+        // Heap.
+		m5_resetstats();
+		heap.emplace(random);
+		m5_dumpstats();
+
+        // BST.
+		m5_resetstats();
+		bst.insert(random);
+		m5_dumpstats();
+    }
+}