Record networking and DMA development progress

Add the current OS source tree, build scripts, system image layout, and development notes covering DMA page allocation, e1000 bring-up, net API dispatch, and DHCP work in progress.

CODE/UTSM/mm/arena.c

@@ -0,0 +1,38 @@
+#include <utsm/arena.h>
+#include <utsm/config.h>
+#include <utsm/log.h>
+
+static u8 arena[UTSM_ARENA_SIZE] __attribute__((aligned(UTSM_PAGE_SIZE)));
+static u64 arena_offset;
+
+void arena_init(void) {
+    arena_offset = 0;
+}
+
+void *kmem_alloc_aligned(u64 size, u64 alignment) {
+    u64 current = (u64)&arena[0] + arena_offset;
+    u64 aligned = utsm_align_up_u64(current, alignment);
+    u64 new_offset = (aligned - (u64)&arena[0]) + size;
+    if (new_offset > UTSM_ARENA_SIZE) {
+        log_error("[UTSM] arena out of memory");
+        return NULL;
+    }
+    arena_offset = new_offset;
+    return (void *)aligned;
+}
+
+void *kmem_alloc(u64 size) {
+    return kmem_alloc_aligned(size, 16);
+}
+
+void *kmem_alloc_page(u64 page_count) {
+    return kmem_alloc_aligned(page_count * UTSM_PAGE_SIZE, UTSM_PAGE_SIZE);
+}
+
+u64 kmem_arena_virtual_base(void) {
+    return (u64)&arena[0];
+}
+
+u64 kmem_arena_virtual_end(void) {
+    return (u64)&arena[0] + UTSM_ARENA_SIZE;
+}