realloc(): move mempool internal knowledge out of generic lib code

The realloc function was a bit too intimate with the mempool accounting.
Abstract that knowledge away and move it where it belongs.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

include/sys/mempool.h

@@ -99,4 +99,17 @@ void *sys_mem_pool_alloc(struct sys_mem_pool *p, size_t size);
  */
 void sys_mem_pool_free(void *ptr);
 
+/**
+ * @brief Try to perform in-place expansion of memory allocated from a pool
+ *
+ * Return 0 if memory previously allocated by sys_mem_pool_alloc()
+ * can accommodate a new size, otherwise return the size of data that
+ * needs to be copied over to new memory.
+ *
+ * @param ptr Pointer to previously allocated memory
+ * @param new_size New size requested for the memory block
+ * @return A 0 if OK, or size of data to copy elsewhere
+ */
+size_t sys_mem_pool_try_expand_inplace(void *ptr, size_t new_size);
+
 #endif

lib/libc/minimal/source/stdlib/malloc.c

@@ -87,10 +87,8 @@ void *calloc(size_t nmemb, size_t size)
 
 void *realloc(void *ptr, size_t requested_size)
 {
-	struct sys_mem_pool_block *blk;
-	size_t struct_blk_size = WB_UP(sizeof(struct sys_mem_pool_block));
-	size_t block_size, total_requested_size;
 	void *new_ptr;
+	size_t copy_size;
 
 	if (ptr == NULL) {
 		return malloc(requested_size);
@@ -101,22 +99,9 @@ void *realloc(void *ptr, size_t requested_size)
 		return NULL;
 	}
 
-	/* Stored right before the pointer passed to the user */
-	blk = (struct sys_mem_pool_block *)((char *)ptr - struct_blk_size);
-
-	/* Determine size of previously allocated block by its level.
-	 * Most likely a bit larger than the original allocation
-	 */
-	block_size = blk->pool->base.max_sz;
-	for (int i = 1; i <= blk->level; i++) {
-		block_size = WB_DN(block_size / 4);
-	}
-
-	/* We really need this much memory */
-	total_requested_size = requested_size + struct_blk_size;
-
-	if (block_size >= total_requested_size) {
-		/* Existing block large enough, nothing to do */
+	copy_size = sys_mem_pool_try_expand_inplace(ptr, requested_size);
+	if (copy_size == 0) {
+		/* Existing block large enough, nothing else to do */
 		return ptr;
 	}
 
@@ -125,7 +110,7 @@ void *realloc(void *ptr, size_t requested_size)
 		return NULL;
 	}
 
-	memcpy(new_ptr, ptr, block_size - struct_blk_size);
+	memcpy(new_ptr, ptr, copy_size);
 	free(ptr);
 
 	return new_ptr;

lib/os/mempool.c

@@ -354,3 +354,30 @@ void sys_mem_pool_free(void *ptr)
 	sys_mutex_unlock(&p->mutex);
 }
 
+size_t sys_mem_pool_try_expand_inplace(void *ptr, size_t requested_size)
+{
+	struct sys_mem_pool_block *blk;
+	size_t struct_blk_size = WB_UP(sizeof(struct sys_mem_pool_block));
+	size_t block_size, total_requested_size;
+
+	ptr = (char *)ptr - struct_blk_size;
+	blk = (struct sys_mem_pool_block *)ptr;
+
+	/*
+	 * Determine size of previously allocated block by its level.
+	 * Most likely a bit larger than the original allocation
+	 */
+	block_size = blk->pool->base.max_sz;
+	for (int i = 1; i <= blk->level; i++) {
+		block_size = WB_DN(block_size / 4);
+	}
+
+	/* We really need this much memory */
+	total_requested_size = requested_size + struct_blk_size;
+
+	if (block_size >= total_requested_size) {
+		/* size adjustment can occur in-place */
+		return 0;
+	}
+	return block_size - struct_blk_size;
+}