Merge branch 'docs-3.19' into docs-next

2 files changed, 62 insertions, 11 deletions

diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index 3171822c22a5..9f28b140dc89 100644
--- a/Documentation/CodingStyle
+++ b/Documentation/CodingStyle
@@ -845,6 +845,49 @@ next instruction in the assembly output:
              : /* outputs */ : /* inputs */ : /* clobbers */);
 
 
+                Chapter 20: Conditional Compilation
+
+Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .c
+files; doing so makes code harder to read and logic harder to follow.  Instead,
+use such conditionals in a header file defining functions for use in those .c
+files, providing no-op stub versions in the #else case, and then call those
+functions unconditionally from .c files.  The compiler will avoid generating
+any code for the stub calls, producing identical results, but the logic will
+remain easy to follow.
+
+Prefer to compile out entire functions, rather than portions of functions or
+portions of expressions.  Rather than putting an ifdef in an expression, factor
+out part or all of the expression into a separate helper function and apply the
+conditional to that function.
+
+If you have a function or variable which may potentially go unused in a
+particular configuration, and the compiler would warn about its definition
+going unused, mark the definition as __maybe_unused rather than wrapping it in
+a preprocessor conditional.  (However, if a function or variable *always* goes
+unused, delete it.)
+
+Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
+symbol into a C boolean expression, and use it in a normal C conditional:
+
+        if (IS_ENABLED(CONFIG_SOMETHING)) {
+                ...
+        }
+
+The compiler will constant-fold the conditional away, and include or exclude
+the block of code just as with an #ifdef, so this will not add any runtime
+overhead.  However, this approach still allows the C compiler to see the code
+inside the block, and check it for correctness (syntax, types, symbol
+references, etc).  Thus, you still have to use an #ifdef if the code inside the
+block references symbols that will not exist if the condition is not met.
+
+At the end of any non-trivial #if or #ifdef block (more than a few lines),
+place a comment after the #endif on the same line, noting the conditional
+expression used.  For instance:
+
+#ifdef CONFIG_SOMETHING
+...
+#endif /* CONFIG_SOMETHING */
+
 
                 Appendix I: References
 
diff --git a/tools/testing/selftests/README.txt b/Documentation/kselftest.txt
index 2660d5ff9179..a87d840bacfe 100644
--- a/tools/testing/selftests/README.txt
+++ b/Documentation/kselftest.txt
@@ -15,37 +15,45 @@ Running the selftests (hotplug tests are run in limited mode)
 =============================================================
 
 To build the tests:
-
   $ make -C tools/testing/selftests
 
 
 To run the tests:
-
   $ make -C tools/testing/selftests run_tests
 
+To build and run the tests with a single command, use:
+  $ make kselftest
+
 - note that some tests will require root privileges.
 
-To run only tests targeted for a single subsystem: (including
-hotplug targets in limited mode)
 
-  $  make -C tools/testing/selftests TARGETS=cpu-hotplug run_tests
+Running a subset of selftests
+========================================
+You can use the "TARGETS" variable on the make command line to specify
+single test to run, or a list of tests to run.
+
+To run only tests targeted for a single subsystem:
+  $  make -C tools/testing/selftests TARGETS=ptrace run_tests
+
+You can specify multiple tests to build and run:
+  $  make TARGETS="size timers" kselftest
+
+See the top-level tools/testing/selftests/Makefile for the list of all
+possible targets.
 
-See the top-level tools/testing/selftests/Makefile for the list of all possible
-targets.
 
 Running the full range hotplug selftests
 ========================================
 
-To build the tests:
-
+To build the hotplug tests:
   $ make -C tools/testing/selftests hotplug
 
-To run the tests:
-
+To run the hotplug tests:
   $ make -C tools/testing/selftests run_hotplug
 
 - note that some tests will require root privileges.
 
+
 Contributing new tests
 ======================