On 2011-01-09, at 07:58, Ted Ts'o wrote:
> Defensive programming would be something like
>
> BUG_ON(sizeof(struct ext4_super_block) != 1024);
>
> (unfortunately #error sizeof(struct ext4_super_block) != 1024 won't
> work since #error is handled by the preprocessor, and I don't think we
> can trigger a compile-time warning for a structure size issue).
We actually use a compile-time assertion in the Lustre code:
/*
* compile-time assertions. @cond has to be constant expression.
* ISO C Standard:
*
* 6.8.4.2 The switch statement
*
* ....
*
* [#3] The expression of each case label shall be an integer
* constant expression and no two of the case constant expressions
* in the same switch statement shall have the same value after
* after conversion...
*/
#define CLASSERT(cond) ({ switch(42) { case (cond): case 0: break; } })
Of course, the "cond" expression must be resolvable at compile time, or
it will turn into a compile error because it is not legal to have a
variable "case".
Cheers, Andreas
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