[PATCH 01/01] staging: replace open-coded ARRAY_SIZEs

[Jim Cromie]

hi Dan,


On Wed, Apr 11, 2012 at 12:54 AM, Dan Carpenter
<dan.carpenter at oracle.com> wrote:
> On Tue, Apr 10, 2012 at 04:06:41PM -0600, Jim Cromie wrote:
>> --- a/drivers/staging/media/as102/as102_usb_drv.c
>> +++ b/drivers/staging/media/as102/as102_usb_drv.c
>> @@ -367,7 +367,7 @@ static int as102_usb_probe(struct usb_interface *intf,
>>       ENTER();
>>
>>       /* This should never actually happen */
>> -     if ((sizeof(as102_usb_id_table) / sizeof(struct usb_device_id)) !=
>> +     if (ARRAY_SIZE(as102_usb_id_table) !=
>>           (sizeof(as102_device_names) / sizeof(const char *))) {
>             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> I wonder why it missed this one?
>
> If you wanted to send a follow on patch you could just change this
> to:
>        BUILD_BUG_ON(ARRAY_SIZE(as102_usb_id_table) !=
>                        ARRAY_SIZE(as102_device_names));
>
>>               pr_err("Device names table invalid size");
>>               return -EINVAL;
>
> regards,
> dan carpenter
>

My larger goal was to find use-cases for this:
(sent to LKML a day or 2 ago)

+/**
+ * BUILD_BUG_DECL - check declared objects
+ * @name: distinguishes multiple uses at same scope.
+ * @cond: false expr, typically like sizeof(a) != sizeof(b)
+ *
+ * This works at file-scope too, and supports checks like:
+ * BUILD_BUG_DECL(foo, sizeof(a) != sizeof(b));
+ * BUILD_BUG_DECL(id_strings, ARRAY_SIZE(id_strings) != ARRAY_SIZE(id_vals));
+ */
+#define BUILD_BUG_DECL(name, cond)                             \
+       static __initdata struct {                              \
+               int BUILD_BUG_DECL_ ## name[1 - 2*!!(cond)];    \
+       } BUILD_BUG_DECL_ ##name[0] __attribute__((unused))
+

It lets you check array consistency at compile-time,
rather than waiting til run-time.

Julia Lawall worked up a spatch script that patched
a bunch of cases, all for file-scope static arrays.
As such, it didnt find your case.

Glancing at the context you quoted, it might be useful there ?
Are there others too ?

thanks
Jim