From 56fdbe77b3513704d0c6b121e915846d6b226a78 Mon Sep 17 00:00:00 2001
From: sbosse <sbosse@uni-bremen.de>
Date: Mon, 14 Oct 2024 23:09:14 +0200
Subject: [PATCH] Mon 14 Oct 23:06:38 CEST 2024

---
 kernel/page.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 kernel/page.c

diff --git a/kernel/page.c b/kernel/page.c
new file mode 100644
index 0000000..1d80a6f
--- /dev/null
+++ b/kernel/page.c
@@ -0,0 +1,107 @@
+/*
+Copyright (C) 2015-2019 The University of Notre Dame
+This software is distributed under the GNU General Public License.
+See the file LICENSE for details.
+*/
+
+#include "console.h"
+#include "kernel/types.h"
+#include "page.h"
+#include "string.h"
+#include "memorylayout.h"
+#include "kernelcore.h"
+
+static uint32_t pages_free = 0;
+static uint32_t pages_total = 0;
+
+static uint32_t *freemap = 0;
+static uint32_t freemap_bits = 0;
+static uint32_t freemap_bytes = 0;
+static uint32_t freemap_cells = 0;
+static uint32_t freemap_pages = 0;
+
+static void *main_memory_start = (void *) MAIN_MEMORY_START;
+
+#define CELL_BITS (8*sizeof(*freemap))
+
+void page_init()
+{
+	int i;
+
+	pages_total = (total_memory * 1024 * 1024 - MAIN_MEMORY_START) / PAGE_SIZE;
+	pages_free = pages_total;
+	printf("memory: %d MB (%d KB) total\n", (pages_free * PAGE_SIZE) / MEGA, (pages_free * PAGE_SIZE) / KILO);
+
+	freemap = main_memory_start;
+	freemap_bits = pages_total;
+	freemap_bytes = 1 + freemap_bits / 8;
+	freemap_cells = 1 + freemap_bits / CELL_BITS;
+	freemap_pages = 1 + freemap_bytes / PAGE_SIZE;
+
+	printf("memory: %d bits %d bytes %d cells %d pages\n", freemap_bits, freemap_bytes, freemap_cells, freemap_pages);
+
+	memset(freemap, 0xff, freemap_bytes);
+	for(i = 0; i < freemap_pages; i++)
+		page_alloc(0);
+
+	// This is ahack that I don't understand yet.
+	// vmware doesn't like the use of a particular page
+	// close to 1MB, but what it is used for I don't know.
+
+	freemap[0] = 0x0;
+
+	printf("memory: %d MB (%d KB) available\n", (pages_free * PAGE_SIZE) / MEGA, (pages_free * PAGE_SIZE) / KILO);
+}
+
+void page_stats( uint32_t *nfree, uint32_t *ntotal )
+{
+	*nfree = pages_free;
+	*ntotal = pages_total;
+}
+
+void *page_alloc(bool zeroit)
+{
+	uint32_t i, j;
+	uint32_t cellmask;
+	uint32_t pagenumber;
+	void *pageaddr;
+
+	if(!freemap) {
+		printf("memory: not initialized yet!\n");
+		return 0;
+	}
+
+	for(i = 0; i < freemap_cells; i++) {
+		if(freemap[i] != 0) {
+			for(j = 0; j < CELL_BITS; j++) {
+				cellmask = (1 << j);
+				if(freemap[i] & cellmask) {
+					freemap[i] &= ~cellmask;
+					pagenumber = i * CELL_BITS + j;
+					pageaddr = (pagenumber << PAGE_BITS) + main_memory_start;
+					if(zeroit)
+						memset(pageaddr, 0, PAGE_SIZE);
+					pages_free--;
+					//printf("page: alloc %d\n",pages_free);
+					return pageaddr;
+				}
+			}
+		}
+	}
+
+	printf("memory: WARNING: everything allocated\n");
+	halt();
+
+	return 0;
+}
+
+void page_free(void *pageaddr)
+{
+	uint32_t pagenumber = (pageaddr - main_memory_start) >> PAGE_BITS;
+	uint32_t cellnumber = pagenumber / CELL_BITS;
+	uint32_t celloffset = pagenumber % CELL_BITS;
+	uint32_t cellmask = (1 << celloffset);
+	freemap[cellnumber] |= cellmask;
+	pages_free++;
+	//printf("page: free %d\n",pages_free);
+}