optimize the system call fork

- add a function to copy a physical page
=> reduce the using of vm_alloc and vm_free

arch/x86/include/asm/string.h

@@ -18,8 +18,13 @@
 extern "C" {
 #endif
 
+/* 
+ * This function copies a physical page to its new physical destination.
+ */
+void copy_page_physical(void* dest, const void * src);
+
 #ifdef HAVE_ARCH_MEMCPY
-inline static void *memcpy(void *dest, const void *src, size_t count)
+inline static void *memcpy(void* dest, const void *src, size_t count)
 {
 	int32_t i, j, k;
 
@@ -39,7 +44,7 @@ inline static void *memcpy(void *dest, const void *src, size_t count)
 #endif
 
 #ifdef HAVE_ARCH_MEMSET
-inline static void *memset(void *dest, int val, size_t count)
+inline static void *memset(void* dest, int val, size_t count)
 {
 	int32_t i, j;
 
@@ -55,7 +60,7 @@ inline static void *memset(void *dest, int val, size_t count)
 #endif
 
 #ifdef HAVE_ARCH_STRLEN
-inline static size_t strlen(const char *str)
+inline static size_t strlen(const char* str)
 {
 	size_t len = 0;
 	uint32_t i, j;
@@ -73,11 +78,11 @@ inline static size_t strlen(const char *str)
 #endif
 
 #ifdef HAVE_ARCH_STRNCPY
-char* strncpy(char *dest, const char *src, size_t n);
+char* strncpy(char* dest, const char* src, size_t n);
 #endif
 
 #ifdef HAVE_ARCH_STRCPY
-char* strcpy(char *dest, const char *src);
+char* strcpy(char* dest, const char* src);
 #endif
 
 #ifdef __cplusplus

arch/x86/kernel/string.asm

@@ -60,4 +60,39 @@ L3:
    pop ebp
    ret
 
+; The following function based on JamesM's kernel development tutorials
+; (http://www.jamesmolloy.co.uk/tutorial_html/)
+global copy_page_physical
+copy_page_physical:
+    push ebx              ; According to __cdecl, we must preserve the contents of EBX.
+    pushf                 ; push EFLAGS, so we can pop it and reenable interrupts
+                          ; later, if they were enabled anyway.
+    cli                   ; Disable interrupts, so we aren't interrupted.
+                          ; Load these in BEFORE we disable paging!
+
+    mov ebx, [esp+16]     ; Source address
+    mov ecx, [esp+12]     ; Destination address
+  
+    mov edx, cr0          ; Get the control register...
+    and edx, 0x7fffffff   ; and...
+    mov cr0, edx          ; Disable paging.
+  
+    mov edx, 1024         ; 1024*4bytes = 4096 bytes
+  
+.loop:
+    mov eax, [ebx]        ; Get the word at the source address
+    mov [ecx], eax        ; Store it at the dest address
+    add ebx, 4            ; Source address += sizeof(word)
+    add ecx, 4            ; Dest address += sizeof(word)
+    dec edx               ; One less word to do
+    jnz .loop             
+  
+    mov edx, cr0          ; Get the control register again
+    or  edx, 0x80000000   ; and...
+    mov cr0, edx          ; Enable paging.
+
+    popf                  ; Pop EFLAGS back.  
+    pop ebx               ; Get the original value of EBX back.
+    ret
+
 SECTION .note.GNU-stack noalloc noexec nowrite progbits

arch/x86/mm/page.c

@@ -84,27 +84,19 @@ inline static size_t copy_page_table(uint32_t pgd_index, page_table_t* pgt, int*
 		(*counter)++;
 
 	for(i=0; i<1024; i++) {
-		if (pgt->entries[i]) {
+		if (pgt->entries[i] & 0xFFFFF000) {
 			phyaddr = get_page();
 			if (!phyaddr)
 				continue;
 			if (counter)
 				(*counter)++;
 
-			viraddr = map_region(0, phyaddr, 1, MAP_KERNEL_SPACE);
-			if (!viraddr) {
-				put_page(phyaddr);
-				continue;
-			}
-
-			memcpy((void*) viraddr, (void*) ((pgd_index << 22) | (i << 12)), PAGE_SIZE);
+			copy_page_physical((void*)phyaddr, (void*) (pgt->entries[i] & 0xFFFFF000));
 
 			new_pgt->entries[i] = phyaddr | (pgt->entries[i] & 0xFFF); 
 
-			// only the child use the copy => unmap copy
-			if (!vm_free(viraddr, 1))
-				atomic_int32_sub(&curr_task->mem_usage, 1);
-
+			// only the child use the copy
+			atomic_int32_sub(&curr_task->mem_usage, 1);
 		}
 	}