Kernel: Add SYS_OPENAT

kernel/include/kernel/Process.h

@@ -58,6 +58,7 @@ namespace Kernel
 		BAN::ErrorOr<void> setenvp(char** envp);
 
 		BAN::ErrorOr<int> open(BAN::StringView, int);
+		BAN::ErrorOr<int> openat(int, BAN::StringView, int);
 		BAN::ErrorOr<void> close(int fd);
 		BAN::ErrorOr<size_t> read(int fd, void* buffer, size_t count);
 		BAN::ErrorOr<size_t> write(int fd, const void* buffer, size_t count);

kernel/kernel/Process.cpp

@@ -469,6 +469,22 @@ namespace Kernel
 		return fd;
 	}
 
+	BAN::ErrorOr<int> Process::openat(int fd, BAN::StringView path, int flags)
+	{
+		BAN::String absolute_path;
+		
+		{
+			LockGuard _(m_lock);
+			TRY(validate_fd(fd));
+			TRY(absolute_path.append(open_file_description(fd).path));
+		}
+		
+		TRY(absolute_path.push_back('/'));
+		TRY(absolute_path.append(path));
+
+		return open(absolute_path, flags);
+	}
+
 	BAN::ErrorOr<void> Process::close(int fd)
 	{
 		LockGuard _(m_lock);

kernel/kernel/Syscall.cpp

@@ -48,6 +48,14 @@ namespace Kernel
 			return -res.error().get_error_code();
 		return res.value();
 	}
+	
+	int sys_openat(int fd, const char* path, int oflags)
+	{
+		auto res = Process::current().openat(fd, path, oflags);
+		if (res.is_error())
+			return -res.error().get_error_code();
+		return res.value();
+	}
 
 	long sys_alloc(size_t bytes)
 	{
@@ -187,6 +195,9 @@ namespace Kernel
 		case SYS_OPEN:
 			ret = sys_open((const char*)arg1, (int)arg2);
 			break;
+		case SYS_OPENAT:
+			ret = sys_openat((int)arg1, (const char*)arg2, (int)arg3);
+			break;
 		case SYS_ALLOC:
 			ret = sys_alloc((size_t)arg1);
 			break;