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Re: static functions are your friends (Was GPIO revisited)

Am 09.08.2009 um 19:11 schrieb Adam Hoka:

On Sun, 9 Aug 2009 19:03:26 +0200
Marc Balmer <> wrote:

One more comment...

+int    gpio_pinbyname(struct gpio_softc *, char *gp_name);
+/* Old API version */
+int    gpio_ioctl_oapi(struct gpio_softc *, u_long cmd, void
*data, int flag,
+    int pinset);

KNF: no variables names in the declaration.
Also, any reason why these are not static?

While it certainly can make sense to declare functions static in
some userland programs for the sole reason to include a command
in a crunched binary, it does not make sense in kernel code; much
to the contrary, it makes debugging harder.

static functions make great sense in kernel code.  In fact, we
have too many public functions as is and even more of the kernel
should be using static.

When a component only has a relatively small on entry points, it
allows the compiler to treat the component as one single unit to
compiled.  This allows it to inline, follow the scope of
variables, and lots of other thing to generate better code.

The other reason to use static it prevents code from calling your
function that should never have never called it in the first place.

I want to quickly come back to this and explain my reasoning for
not making all functions static in the kernel, although I am
totally aware of all the positive effects of static in general.

I do mostly low-level driver development, something where you see
the ddb prompt more often than you like...  Now with the functions
not being declared static, the trace command is my friend, I see
immediately in which function my driver crashed, this is an immense
debugging aid.

I took the time to write a function that crahses the kernel on
purpose.  Compiled as non static function, ddb showed me the
function name and function call trace with proper function names.
Quite easy to locate the faulty spot.  To complete my test, I
compiled the very same code with all functions declared static.
Now the ddb trace does not show me the function names, making it a
lot harder to locate the faulty spot.

Can you show code which worked and not worked with static function
declarations. I'm pretty sure that this works
for me for a long time.

We can consider this issue solved.  I can declare my functions as
"__noinline static ...." and have both the benefits of a static
declaration and the function name show up in ddb's 'trace' command.

I will slowly convert my code to this idiom, if no one objects.

And later on we could unify this as a macro maybe.

why a macro? well, I know we like macros here, but still?

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