alloc: realloc

kernel-src/include/kernel/alloc.h

@@ -5,6 +5,7 @@
 
 void alloc_init();
 void *alloc(size_t s);
+void *realloc(void *addr, size_t s);
 void free(void *addr);
 
 #endif

kernel-src/mm/alloc.c

@@ -3,6 +3,11 @@
 #include <logging.h>
 #include <string.h>
 
+// each allocation has the following structure:
+// ptr: data capacity (allocsizes size)
+// ptr + sizeof(size_t): current size
+// ptr + sizeof(size_t) * 2: data
+
 #define CACHE_COUNT 12
 
 static size_t allocsizes[CACHE_COUNT] = {32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536};
@@ -10,8 +15,8 @@ static scache_t *caches[CACHE_COUNT];
 
 static void initarea(scache_t *cache, void *obj) {
 	size_t *ptr = obj;
-	*ptr = cache->size - sizeof(size_t);
-	memset(ptr + 1, 0, *ptr);
+	*ptr = cache->size - sizeof(size_t) * 2;
+	memset(ptr + 2, 0, *ptr);
 }
 
 static scache_t *getcachefromsize(size_t size) {
@@ -30,22 +35,54 @@ static scache_t *getcachefromsize(size_t size) {
 void *alloc(size_t size) {
 	scache_t *cache = getcachefromsize(size);
 	size_t *ret = slab_allocate(cache);
+	*(ret + 1) = size;
 	if (ret == NULL)
 		return NULL;
-	return ret + 1;
+	return ret + 2;
 }
 
 void free(void *ptr) {
 	size_t *start = ptr;
-	start -= 1;
+	start -= 2;
 	size_t size = *start;
 	scache_t *cache = getcachefromsize(size);
 	slab_free(cache, start);
 }
 
+void *realloc(void *ptr, size_t size) {
+	size_t *start = ptr;
+	start -= 2;
+	size_t currentsize = *(start + 1);
+	if (size <= currentsize) {
+		*(start + 1) = size;
+		return ptr;
+	}
+
+	// grow
+	scache_t *oldcache = getcachefromsize(*start);
+	scache_t *newcache = getcachefromsize(size);
+
+	// same allocation
+	if (oldcache == newcache) {
+		size_t diff = size - currentsize;
+		memset((void *)((uintptr_t)ptr + currentsize), 0, diff);
+		*(start + 1) = size;
+		return ptr;
+	}
+
+	// different allocation
+	size_t *new = slab_allocate(newcache);
+	if (new == NULL)
+		return NULL;
+	*(new + 1) = size;
+	memcpy((new + 2), ptr, currentsize);
+	slab_free(oldcache, start);
+	return new + 2;
+}
+
 void alloc_init() {
 	for (int i = 0; i < CACHE_COUNT; ++i) {
-		caches[i] = slab_newcache(allocsizes[i] + sizeof(size_t), 0, initarea, initarea);
+		caches[i] = slab_newcache(allocsizes[i] + sizeof(size_t) * 2, 0, initarea, initarea);
 		__assert(caches[i]);
 	}
 }