Implement page allocation

core/klibc.c

@@ -9,3 +9,11 @@ void *memcpy(void *dst, const void *src, size_t n)
         }
         return dst;
 }
+
+void *memset(void *src, int c, size_t n)
+{
+        for (char *ptr = (char *)src; n > 0; n--, ptr++) {
+                *ptr = (char)c;
+        }
+        return src;
+}

core/klibc.h

@@ -2,3 +2,4 @@
 #include "stdarg.h"
 
 void *memcpy(void *dest, const void *src, size_t n );
+void *memset(void *s, int c, size_t n);

core/main.c

@@ -4,6 +4,7 @@
 #include "interrupt.h"
 #include "io.h"
 #include "irq.h"
+#include "klibc.h"
 #include "mem.h"
 #include "multiboot.h"
 #include "pit.h"
@@ -16,8 +17,8 @@ void cpuid(int code, uint32_t *a, uint32_t *d)
     asm volatile("cpuid" : "=a"(*a), "=d"(*d) : "0"(code) : "ebx", "ecx");
 }
 
-
+// Multiboot information available here :
-// Multiboot information available here : https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#kernel_002ec
+// https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#kernel_002ec
 void kmain(unsigned long magic, unsigned long addr)
 {
     unsigned long upper_mem = 0;

core/mem.c

@@ -1,7 +1,13 @@
 #include "mem.h"
+#include "list.h"
 #include "vga.h"
 
-struct mem_desc *page_desc = (struct mem_desc *)&__ld_kernel_end;
+static struct mem_desc *page_desc = (struct mem_desc *)&__ld_kernel_end;
+static struct mem_desc *free_page;
+static struct mem_desc *used_page;
+static unsigned long bottom_mem;
+static unsigned long top_mem;
+
 
 int memInit(unsigned long upper_mem)
 {
@@ -10,13 +16,53 @@ int memInit(unsigned long upper_mem)
 	    (unsigned long)page_desc +
 	    ((upper_mem) / (PAGE_SIZE / 1024)) * sizeof(struct mem_desc);
 	uint lastUsed = (memdesc_end >> PAGE_SHIFT) + 1;
+	list_init(free_page);
+	list_init(used_page);
+	bottom_mem = lastUsed;
+	top_mem = upper_mem;
 	for (uint i = 0; i < (upper_mem / (PAGE_SIZE / 1024)); i++) {
 		struct mem_desc *mem = &page_desc[i];
-		if (i < lastUsed)
+		if (i < lastUsed) {
 			mem->ref = 1;
-		else
+			list_add_tail(used_page, mem);
+		} else {
 			mem->ref = 0;
+			list_add_tail(free_page, mem);
+		}
 		mem->phy_addr = i * PAGE_SIZE;
 	}
 	return 0;
 }
+
+struct mem_desc *addr2memDesc(unsigned long addr)
+{
+	if (addr > top_mem || addr < bottom_mem)
+		return NULL;
+	int idx = addr >> PAGE_SHIFT;
+	return page_desc + idx;
+}
+
+
+unsigned long allocPage(void)
+{
+	if (list_is_empty(free_page))
+		return (unsigned long)NULL;
+	struct mem_desc *mem = list_pop_head(free_page);
+	mem->ref             = 1;
+	list_add_tail(used_page, mem);
+	return mem->phy_addr;
+}
+
+int unrefPage(unsigned long addr)
+{
+	struct mem_desc *mem = addr2memDesc(addr);
+	if (!mem) {
+		return -1;
+	}
+	mem->ref--;
+	if (mem->ref == 0) {
+		list_add_tail(free_page, mem);
+	}
+
+	return 0;
+}

core/mem.h

@@ -12,7 +12,10 @@ extern uint32_t __ld_kernel_end;
 struct mem_desc{
 	unsigned long phy_addr;
 	unsigned long ref;
+	struct mem_desc *next, *prev;
 };
 
 
 int memInit(unsigned long upper_mem);
+unsigned long allocPage(void);
+int unrefPage(unsigned long addr);