Kernel/LibC: add free function for FixedWidthAllocator

I have to rework the syscall API and allocators in process. For
now this works well enough :)

kernel/include/kernel/Memory/FixedWidthAllocator.h

@@ -17,7 +17,7 @@ namespace Kernel
 		~FixedWidthAllocator();
 
 		vaddr_t allocate();
-		void deallocate(vaddr_t);
+		bool deallocate(vaddr_t);
 
 		uint32_t allocation_size() const { return m_allocation_size; }
 
@@ -26,8 +26,10 @@ namespace Kernel
 		{
 			node* prev { nullptr };
 			node* next { nullptr };
+			bool allocated { false };
 		};
-		vaddr_t address_of(const node*) const;
+		vaddr_t address_of_node(const node*) const;
+		node* node_from_address(vaddr_t) const;
 		void allocate_page_for_node_if_needed(const node*);
 
 	private:

kernel/include/kernel/Process.h

@@ -57,6 +57,7 @@ namespace Kernel
 		BAN::ErrorOr<void> set_working_directory(BAN::StringView);
 
 		BAN::ErrorOr<void*> allocate(size_t);
+		void free(void*);
 
 		void termid(char*) const;
 

kernel/include/kernel/Syscall.h

@@ -8,6 +8,7 @@
 #define SYS_SEEK 6
 #define SYS_OPEN 7
 #define SYS_ALLOC 8
+#define SYS_FREE 9
 
 #include <stdint.h>
 

kernel/kernel/Memory/FixedWidthAllocator.cpp

@@ -87,6 +87,9 @@ namespace Kernel
 
 		node* node = m_free_list;
 
+		ASSERT(!node->allocated);
+		node->allocated = true;
+
 		m_free_list = node->next;
 		if (m_free_list)
 			m_free_list->prev = nullptr;
@@ -100,23 +103,50 @@ namespace Kernel
 
 		m_allocated++;
 		allocate_page_for_node_if_needed(node);
-		return address_of(node);
+		return address_of_node(node);
 	}
 
-	void FixedWidthAllocator::deallocate(paddr_t addr)
+	bool FixedWidthAllocator::deallocate(vaddr_t address)
 	{
-		(void)addr;
-		ASSERT_NOT_REACHED();
+		if (address % m_allocation_size)
+			return false;
+		
+		node* node = node_from_address(address);
+		if (node == nullptr)
+			return false;
+
+
+		if (!node->allocated)
+		{
+			dwarnln("deallocate called on unallocated address");
+			return true;
+		}
+		node->allocated = false;
+
+		if (node->prev)
+			node->prev->next = node->next;
+		if (node->next)
+			node->next->prev = node->prev;
+
+		node->next = m_free_list;
+		node->prev = nullptr;
+
+		if (m_free_list)
+			m_free_list->prev = node;
+		m_free_list = node;
+
+		m_allocated--;
+		return true;
 	}
 
-	vaddr_t FixedWidthAllocator::address_of(const node* node) const
+	vaddr_t FixedWidthAllocator::address_of_node(const node* node) const
 	{
 		uint32_t index = node - (struct node*)m_nodes_page;
 
-		uint32_t page_index = index / (PAGE_SIZE / sizeof(struct node));
+		uint32_t page_index = index / (PAGE_SIZE / m_allocation_size);
 		ASSERT(page_index < PAGE_SIZE / sizeof(vaddr_t));
 
-		uint32_t offset = index % (PAGE_SIZE / sizeof(struct node));
+		uint32_t offset = index % (PAGE_SIZE / m_allocation_size);
 
 		vaddr_t page_begin = ((vaddr_t*)m_allocated_pages)[page_index];
 		ASSERT(page_begin);
@@ -124,11 +154,38 @@ namespace Kernel
 		return page_begin + offset * m_allocation_size;
 	}
 
+	FixedWidthAllocator::node* FixedWidthAllocator::node_from_address(vaddr_t address) const
+	{
+		// TODO: This probably should be optimized from O(n) preferably to O(1) but I
+		//       don't want to think about performance now.
+		
+		ASSERT(address % m_allocation_size == 0);
+
+		vaddr_t page_begin = address / PAGE_SIZE * PAGE_SIZE;
+
+		for (uint32_t page_index = 0; page_index < PAGE_SIZE / sizeof(vaddr_t); page_index++)
+		{
+			vaddr_t vaddr = ((vaddr_t*)m_allocated_pages)[page_index];
+			if (vaddr != page_begin)
+				continue;
+			
+			uint32_t offset = (address - page_begin) / m_allocation_size;
+
+			node* result = (node*)m_nodes_page;
+			result += page_index * PAGE_SIZE / m_allocation_size;
+			result += offset;
+			ASSERT(address_of_node(result) == address);
+			return result;
+		}
+
+		return nullptr;
+	}
+
 	void FixedWidthAllocator::allocate_page_for_node_if_needed(const node* node)
 	{
 		uint32_t index = node - (struct node*)m_nodes_page;
 
-		uint32_t page_index = index / (PAGE_SIZE / sizeof(struct node));
+		uint32_t page_index = index / (PAGE_SIZE / m_allocation_size);
 		ASSERT(page_index < PAGE_SIZE / sizeof(vaddr_t));
 
 		vaddr_t& page_vaddr = ((vaddr_t*)m_allocated_pages)[page_index];

kernel/kernel/Process.cpp

@@ -386,6 +386,14 @@ namespace Kernel
 		return BAN::Error::from_errno(ENOMEM);
 	}
 
+	void Process::free(void* ptr)
+	{
+		for (auto& allocator : m_fixed_width_allocators)
+			if (allocator.deallocate((vaddr_t)ptr))
+				return;
+		dwarnln("free called on pointer that was not allocated");	
+	}
+
 	void Process::termid(char* buffer) const
 	{
 		if (m_tty == nullptr)

kernel/kernel/Syscall.cpp

@@ -63,6 +63,11 @@ namespace Kernel
 		return (long)res.value();
 	}
 
+	void sys_free(void* ptr)
+	{
+		Process::current().free(ptr);
+	}
+
 	extern "C" long cpp_syscall_handler(int syscall, void* arg1, void* arg2, void* arg3)
 	{
 		Thread::current().set_in_syscall(true);
@@ -96,6 +101,9 @@ namespace Kernel
 		case SYS_ALLOC:
 			ret = sys_alloc((size_t)arg1);
 			break;
+		case SYS_FREE:
+			sys_free(arg1);
+			break;
 		default:
 			Kernel::panic("Unknown syscall {}", syscall);
 		}

libc/stdlib.cpp

@@ -79,7 +79,9 @@ void* calloc(size_t nmemb, size_t size)
 	return ptr;
 }
 
-void free(void*)
+void free(void* ptr)
 {
-
+	if (ptr == nullptr)
+		return;
+	syscall(SYS_FREE, ptr);
 }

libc/unistd.cpp

@@ -74,6 +74,12 @@ long syscall(long syscall, ...)
 			ret = Kernel::syscall(SYS_ALLOC, bytes);
 			break;
 		}
+		case SYS_FREE:
+		{
+			void* ptr = va_arg(args, void*);
+			ret = Kernel::syscall(SYS_FREE, ptr);
+			break;
+		}
 		default:
 			puts("LibC: Unhandeled syscall");
 	}

userspace/test.c

@@ -3,42 +3,24 @@
 
 int main()
 {
-	void* ptr = malloc(10);
-	if (ptr == NULL)
+	for (int i = 0; i < 10; i++)
 	{
-		perror("malloc");
-		return 1;
-	}
-	*(int*)ptr = 5;
-	putc('0' + *(int*)ptr, stdout);
-	return 0;
-
-	FILE* fp = fopen("/boot/grub/grub.cfg", "r");
-	if (fp == NULL)
-	{
-		perror("fopen");
-		return 1;
-	}
-
-	for (;;)
-	{
-		char buffer[128];
-		size_t nread = fread(buffer, 1, sizeof(buffer) - 1, fp);
-		if (nread == 0)
+		int* ptrs[10];
+		for (int j = 0; j < 10; j++)
 		{
-			if (ferror(fp))
-				perror("fread");
-			break;
+			ptrs[j] = malloc(10);
+			if (ptrs[j] == NULL)
+			{
+				perror("malloc");
+				return 1;
+			}
+			*ptrs[j] = j;
+			putc('0' + *ptrs[j], stdout);
 		}
-		buffer[nread] = '\0';
-		fputs(buffer, stdout);
+		for (int j = 0; j < 10; j++)
+			free(ptrs[j]);
+		putc('\n', stdout);
 	}
-
-	if (fclose(fp) == EOF)
-	{
-		perror("fclose");
-		return 1;
-	}
-
+	
 	return 0;
 }