Messages in this thread | | | Subject | Re: [PATCH 1/4] list: introduce list_is_first() | From | Jens Axboe <> | Date | Thu, 10 Dec 2015 08:35:04 -0700 |
| |
On 12/10/2015 08:23 AM, Josh Poimboeuf wrote: > On Thu, Dec 10, 2015 at 08:10:34AM -0700, Jens Axboe wrote: >> On 12/10/2015 07:17 AM, Geliang Tang wrote: >>> We already have list_is_last(), it makes sense to also add >>> list_is_first() for consistency. This list utility function >>> to check for first element in a list. >> >> Honestly, I think we already have way too many of these kind of helpers. >> IMHO they don't really help, they hurt readability. You should know how the >> list works anyway, and if you do, then it's a no-brainer what's first and >> last. If you don't, then you are bound to screw up in other ways. >> >> Just my 2 cents. > > Personally I would disagree. Something like: > > if (list_is_first(&rq->queuelist, &nd->queue)) > > is much more readable to me than: > > if (rq->queuelist.prev == &nd->queue)
Both the function and your example are backwards, and hence a lot harder to comprehend than they should be. It'd be much clearer as:
if (nd->queue.next == &rq->queuelist)
which is a lot easier to read. Nobody should open-code a 'is this the first entry in the list' by asking 'is the previous link to my node the head', asking 'is the next entry in the list X' makes a lot more sense. I'm assuming this happened because the list_is_last was just copied and modified, instead of thinking about this for a second.
> The first one takes no effort for me -- it's almost English. While the > second one takes me a few seconds (and some precious brain cycles) to > decipher. > > Maybe whether it's readable depends on how many years you've been > looking at the pattern. But IMHO we shouldn't make "having x # of years > staring at kernel code" a prerequisite for being able to read kernel > code.
It's a balance, as we also should not make APIs out of everything. As I said, purely my opinion, but I think the is_last/is_first have jumped the shark.
-- Jens Axboe
| |