[bcc tech-userlevel tech-toolchain, followups on tech-kern] Traditionally to avoid problems with repeated inclusion of a header file, you put #include guards around it, say in sys/dev/foo.h:
#ifndef _SYS_DEV_FOO_H_ #define _SYS_DEV_FOO_H_ ... #endif /* _SYS_DEV_FOO_H_ */ With newer compilers this can be replaced by a single line in the header file: #pragma once It's nonstandard, but using #pragma once is maybe a bit less error-prone -- don't have to have to pollute the namespace with have-I-been-included macros, and I've made mistakes with copying & pasting the per-file have-I-been-included macro into the wrong file. That said, clang has a warning these days to detect this mistake so maybe traditional #include guards aren't that error-prone. Thoughts on its use in NetBSD in: (a) purely internal header files? (b) header files exposed to potentially out-of-tree kernel modules? (c) header files exposed to userland? How reliable/consistent is toolchain support for it? Is it worth adopting or is the benefit negligible over continuing to use traditional #include guards? Likely problems with adopting it?
