On Tue, Oct 10, 2017 at 10:17:09AM +1100, Tobin C. Harding wrote:
> Hi,
>
> I would like to create a boot time variable i.e a variable that is set once at boot time. Variable
> does not need to be globally accessible. (actually I am using two variables).
static foo = 42;
should be all you need, right?
If not, what exactly do you mean by "boot time variable"?
> Could any one point me to examples of this already intree please?
>
> I have tried the following but it has a race condition on the zero check and assignment of randval/oddval.
>
> /* Maps a pointer to a unique identifier. */
> static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
> {
> long hashval;
> static long randval = 0;
> static long oddval = 0;
>
> if (oddval == 0 && randval == 0) {
> randval = get_random_long();
> oddval = get_random_odd_long();
> }
>
> hashval = ptr_obfuscate((unsigned long)ptr, randval, oddval);
> spec.base = 16;
>
> return number(buf, end, hashval, spec);
> }
What's wrong with this code?
> And the compiler doesn't like
>
> static long randval = get_random_long();
> static long oddval = get_random_odd_long();
Yeah, that will not work, static initializers are at link/load time, not
runtime.
> I thought of wrapping oddval/randval in a struct and protecting it with a lock but I don't know
> how/where to initialize the lock in a race free manner?
Put a local lock in the function when testing if the variables are == 0,
if you are worried that two different callers will enter it at the same
time.
hope this helps,
greg k-h
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