Function resource_unset_value

freebsd/kern/subr_hints.c:496–517

* Clear a value associated with a device by removing it from * the kernel environment. This only removes a hint for an * exact unit. */

 * exact unit.
 */
int
resource_unset_value(const char *name, int unit, const char *resname)
{
	char varname[128];
	const char *retname, *retvalue;
	int error, line;
	size_t len;

	line = 0;
	error = resource_find(&line, NULL, name, &unit, resname, NULL,
	    &retname, NULL, NULL, NULL, NULL, &retvalue);
	if (error)
		return (error);

	retname -= strlen("hint.");
	len = retvalue - retname - 1;
	if (len > sizeof(varname) - 1)
		return (ENAMETOOLONG);
	memcpy(varname, retname, len);
	varname[len] = '\0';
	return (kern_unsetenv(varname));
}