lkml.org 
[lkml]   [2015]   [Dec]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/4] list: introduce list_is_first()
From
Date
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



\
 
 \ /
  Last update: 2015-12-10 17:01    [W:0.058 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site