Low-level bindings to libsystemd (and similar) libraries
Items in this module correspond to systemd functions/types that are documented by the systemd
sd_*) man pages.
Helper type to mark functions systemd functions that promise not to modify the underlying iovec data. There is no corresponding type in libc, so their function signatures take *const iovec, which technically allow iov_base to be modified. However, const_iovec provides the same ABI, so it can be used to make the function interface easier to work with.