Add physical page (frame) allocator.

1 files changed, 73 insertions, 0 deletions

diff --git a/kernel/l0/frame.c b/kernel/l0/frame.c
new file mode 100644
index 0000000..1f16eaf
--- /dev/null
+++ b/kernel/l0/frame.c
@@ -0,0 +1,73 @@
+#include <frame.h>
+#include <dbglog.h>
+
+// TODO: buddy allocator
+// this is a simple bitmap allocator
+	
+#define INDEX_FROM_BIT(a) (a/(8*4))
+#define OFFSET_FROM_BIT(a) (a%(8*4))
+
+static uint32_t *frame_bitset;
+static uint32_t nframes, nused_frames;
+static uint32_t begin_search_at;
+
+void frame_init_allocator(size_t total_ram, void** kernel_data_end) {
+	nframes = PAGE_ID(total_ram);
+
+	frame_bitset = (uint32_t*)ALIGN4_UP((size_t)*kernel_data_end);
+	*kernel_data_end = (void*)frame_bitset + ALIGN4_UP(nframes / 8);
+
+	for (size_t i = 0; i < ALIGN4_UP(nframes / 8)/4; i++)
+		frame_bitset[i] = 0;
+
+	nused_frames = 0;
+
+	size_t kernel_pages = PAGE_ALIGN_UP((size_t)*kernel_data_end - K_HIGHHALF_ADDR)/PAGE_SIZE;
+	for (size_t i = 0; i < kernel_pages; i++) {
+		size_t idx = INDEX_FROM_BIT(i);
+		size_t ofs = OFFSET_FROM_BIT(i);
+		frame_bitset[idx] |= (0x1 << ofs);
+		nused_frames++;
+	}
+	begin_search_at = INDEX_FROM_BIT(kernel_pages);
+}
+
+uint32_t frame_alloc(size_t n) {
+	if (n > 32) return 0;
+
+	for (uint32_t i = begin_search_at; i < INDEX_FROM_BIT(nframes); i++) {
+		if (frame_bitset[i] == 0xFFFFFFFF) {
+			if (i == begin_search_at) begin_search_at++;
+			continue;
+		}
+
+		for (uint32_t j = 0; j < 32 - n + 1; j++) {
+			uint32_t to_test = (0xFFFFFFFF >> (32 - n)) << j;
+			if (!(frame_bitset[i]&to_test)) {
+				frame_bitset[i] |= to_test;
+				nused_frames += n;
+				return i * 32 + j;
+			}
+		}
+	}
+	return 0;
+}
+
+void frame_free(uint32_t base, size_t n) {
+	for (size_t x = 0; x < n; x++) {
+		uint32_t idx = INDEX_FROM_BIT(base + n);
+		uint32_t ofs = OFFSET_FROM_BIT(base + n);
+		if (frame_bitset[idx] & (0x1 << ofs)) {
+			frame_bitset[idx] &= ~(0x1 << ofs);
+			nused_frames--;
+		}
+	}
+	if (INDEX_FROM_BIT(base) < begin_search_at)
+		begin_search_at = INDEX_FROM_BIT(base);
+}
+
+void dbg_print_frame_stats() {
+	dbg_printf("Used frames: %d/%d\n", nused_frames, nframes);
+}
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/