The Kernel Template Library is a curated subset of the C++ standard library API using the ktl namespace rather than the std namespace. When a specific interface is deemed useful, safe, and appropriate for use in the kernel, it can be added here. No std APIs are ever used directly in the kernel, only ktl.
The API is a strict subset of the standard C++ library API aside from the namespace. The header file names are mostly directly mapped as well:
<foo> -> <ktl/foo.h>
There are some exceptions. For example, and are very broad collections of APIs and the ktl subset is more focussed. So instead of <ktl/memory.h> and <ktl/utility.h> there are specific headers for the standard APIs from and that are included, such as <ktl/move.h> for ktl::move (std::move in ) and <ktl/unique_ptr.h> for ktl::unique_ptr (std::unique_ptr in ).
The implementation here simply leverages the libc++ implementation and defines using aliases in the ktl namespace. It's expected that ktl will only ever provide “header only” APIs.
The <ktl/enforce.h> header file should be used in most .cc files (but not .h) files meant only for the kernel environment. That is, in .cc files that use the <ktl/*.h> headers or use kernel-only headers that use them.
This file must appear last in the #include list and clang-format will arrange that automatically.
After this #include any use of the std identifier in C++ code will cause a compile-time error. When such errors are encountered, the kernel code should be checked for use of C++ standard library headers (with no .h in the name, like <memory>, etc.) that should be replaced with <ktl/*.h>headers and forstd::names that should be replaced withktl::` names.