linux-kernel - Re: kernel.h: add ARRAY_AND_SIZE() macro to complement ARRAY

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Message-ID: <20080919073254.GB7222@lenovo>
Date:	Fri, 19 Sep 2008 11:32:54 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Eric Miao <eric.y.miao@...il.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Ben Dooks <ben-linux@...ff.org>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: kernel.h: add ARRAY_AND_SIZE() macro to complement
	ARRAY_SIZE().

[Eric Miao - Fri, Sep 19, 2008 at 03:22:13PM +0800]
| On Fri, Sep 19, 2008 at 2:54 PM, Cyrill Gorcunov <gorcunov@...il.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@...il.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.
| 

Absolutely agreed with this (ie pass _one_ array name). Would
be a good cleanup.

		- Cyrill -
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