Messages in this thread | | | Date | Fri, 19 Sep 2008 08:28:45 -0700 | From | "Russ Dill" <> | Subject | Re: kernel.h: add ARRAY_AND_SIZE() macro to complement ARRAY_SIZE(). |
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On Fri, Sep 19, 2008 at 12:22 AM, Eric Miao <eric.y.miao@gmail.com> wrote: > On Fri, Sep 19, 2008 at 2:54 PM, Cyrill Gorcunov <gorcunov@gmail.com> wrote: >> [Eric Miao - Fri, Sep 19, 2008 at 02:38:21AM +0800] >> | On Thu, Sep 18, 2008 at 11:06 PM, Alexey Dobriyan <adobriyan@gmail.com> wrote: >> | > On Thu, Sep 18, 2008 at 02:24:47PM +0100, Ben Dooks wrote: >> | >> Move the ARRAY_AND_SIZE() macro from arch/arm/mach-pxa/generic.h >> | >> to a more useful position in include/linux/kernel.h. This macro >> | >> is very useful to registration functions that take an array and >> | >> the number of array elements in it as consecutive arguments. >> | >> >> | >> The macro also should ensure that mistakes where the wrong array >> | >> is used to the ARRAY_SIZE() macro is passed. It also makes it >> | >> easier to avoid wrapping registration function arguments. >> | > >> | >> --- linux-2.6.27-rc6-quilt4.orig/include/linux/kernel.h >> | >> +++ linux-2.6.27-rc6-quilt4/include/linux/kernel.h >> | >> @@ -43,6 +43,7 @@ extern const char linux_proc_banner[]; >> | >> #define IS_ALIGNED(x, a) (((x) & ((typeof(x))(a) - 1)) == 0) >> | >> >> | >> #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr)) >> | >> +#define ARRAY_AND_SIZE(arr) (arr), ARRAY_SIZE(arr) >> | > >> | > Just like ARRAY_SIZE, it is misnamed. >> | > >> | >> | Any hint about the correct spelling? >> | >> | > And it isn't obvious to what it expands. Hopefully arm people will >> | > remove it. :-) >> | >> | This is handy to use, saving several key strokes and making the line >> | shorter. If it's not obvious to what it expands, there must be some >> | fix for it? >> | >> >> well, it seems it's not that good to use ARRAY_AND_SIZE at all. >> Yes it's short but quite frankly - hiding number of args is not >> that good. >> >> example >> >> static void ssp_send_cmd(uint32_t *cmd, int num); >> >> called as >> >> ssp_send_cmd(ARRAY_AND_SIZE(lcd_panel_on)); >> >> thanks it's not that spreaded across kernel. >> Someday it could lead to ARRAY_AND_SIZE_CHECK_IF_EXIST_AND_PANIC :) > > Probably that not gonna happen. > > without ARRAY_AND_SIZE: > > ssp_send_cmd(lcd_panel_on, ARRAY_SIZE(lcd_panel_on)); > > with: > > ssp_send_cmd(ARRAY_AND_SIZE(lcd_panel_on)); > > where you don't have to repeat the array name. I have to admit > that a macro expanding to something like an argument list instead > of a single variable or something is not a good idea. But, we are > using C, and there's no easy way just to pass the array itself, > otherwise one may come up with: > > ssp_send_cmd(lcd_panel_on); > > ssp_send_cmd(array a) > { > int size = a.length(); > > ........ > } > > I'm not trying to buy anyone anything, just illustrate this, and see > if anyone else is interested in doing so. >
My vote is for ARRAY_AND_SIZE to spread far and wide across the land. ARRAY_SIZE is already very safe, as it has a __must_be_array macro built in. So ARRAY_AND_SIZE is even safer, as it prevents you from mixing up two different arrays. It also reduces line length and makes driver and device (usually platform_device) registration code easier to read.
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