Add linearSpaceFree() for retrieving the free space in the linear heap

libctru/include/3ds/linear.h

@@ -4,3 +4,4 @@
 void* linearAlloc(size_t size);
 void* linearRealloc(void* mem, size_t size);
 void linearFree(void* mem);
+u32 linearSpaceFree(); // get free linear space in bytes

libctru/source/allocator/linear.cpp

@@ -48,3 +48,8 @@ void linearFree(void* mem)
 	auto pChunk = (MemChunk*)((u8*)mem - 16);
 	sLinearPool.Deallocate(*pChunk);
 }
+
+u32 linearSpaceFree()
+{
+	return sLinearPool.GetFreeSpace();
+}

libctru/source/allocator/mem_pool.cpp

@@ -123,3 +123,11 @@ void MemPool::Dump(const char* title)
 		printf("  - %p (%u bytes)\n", b->base, b->size);
 }
 */
+
+u32 MemPool::GetFreeSpace()
+{
+	u32 acc = 0;
+	for (auto b = first; b; b = b->next)
+		acc += b->size;
+	return acc;
+}

libctru/source/allocator/mem_pool.h

@@ -85,4 +85,5 @@ struct MemPool
 	}
 
 	//void Dump(const char* title);
+	u32 GetFreeSpace();
 };