On Thu, Oct 24, 2024 at 08:30:39PM +0800, Huang, Ying wrote: > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> writes: > > On Wed, Oct 23, 2024 at 02:07:52PM -0700, Dan Williams wrote: > >> Andy Shevchenko wrote: > >> > On Fri, Oct 11, 2024 at 09:06:37AM +0800, Huang, Ying wrote: > >> > > David Hildenbrand <david@xxxxxxxxxx> writes: > >> > > > On 10.10.24 08:55, Huang Ying wrote: ... > >> > > > for ((_p) = (_root)->child; (_p); (_p) = next_resource_XXX(_root, _p)) > >> > > > >> > > Yes. This can improve code readability. > >> > > > >> > > A possible issue is that "_root" will be evaluated twice in above macro > >> > > definition. IMO, this should be avoided. > >> > > >> > Ideally, yes. But how many for_each type of macros you see that really try hard > >> > to achieve that? I believe we shouldn't worry right now about this and rely on > >> > the fact that root is the given variable. Or do you have an example of what you > >> > suggested in the other reply, i.e. where it's an evaluation of the heavy call? > >> > > >> > > Do you have some idea about > >> > > how to do that? Something like below? > >> > > > >> > > #define for_each_resource_XXX(_root, _p) \ > >> > > for (typeof(_root) __root = (_root), __p = (_p) = (__root)->child; \ > >> > > __p && (_p); (_p) = next_resource_XXX(__root, _p)) > >> > > >> > This is a bit ugly :-( I would avoid ugliness as long as we have no problem to > >> > solve (see above). > >> > >> Using a local defined variable to avoid double evaluation is standard > >> practice. I do not understand "avoid ugliness as long as we have no problem to > >> solve", the problem to solve will be if someone accidentally does > >> something like "for_each_resource_descendant(root++, res)". *That* will > >> be a problem when someone finally realizes that the macro is hiding a > >> double evaluation. > > > > Can you explain, why do we need __p and how can we get rid of that? > > I understand the part of the local variable for root. > > If don't use '__p', the macro becomes > > #define for_each_resource_XXX(_root, _p) \ > for (typeof(_root) __root = (_root), (_p) = (__root)->child; \ > (_p); (_p) = next_resource_XXX(__root, _p)) > > Where, '_p' must be a variable name, and it will be a new variable > inside for loop and mask the variable with same name outside of macro. > IIUC, this breaks the macro convention in kernel and has subtle variable > masking semantics. Yep. In property.h nobody cares about evaluation which makes the macro as simple as #define for_each_resource_XXX(_root, _p) \ for (_p = next_resource_XXX(__root, NULL); _p; \ _p = next_resource_XXX(__root, _p)) (Dan, that's what I called to avoid solving issues we don't have and most likely will never have.) but if you want to stick with your variant some improvements can be done: #define for_each_resource_XXX(_root, _p) \ for (typeof(_root) __root = (_root), __p = _p = __root->child; \ __p && _p; _p = next_resource_XXX(__root, _p)) 1) no need to have local variable in parentheses; 2) no need to have iterator in parentheses, otherwise it would be crazy code that has put something really wrong there and still expect the thing to work. > >> So no, this proposal is not "ugly", it is a best practice. See the > >> definition of min_not_zero() for example. > > > > I know that there are a lot of macros that look uglier that this one. -- With Best Regards, Andy Shevchenko
