On 8/19/20 6:11 AM, Greg KH wrote: > On Wed, Aug 19, 2020 at 07:00:53AM -0600, Jens Axboe wrote: >> On 8/18/20 1:00 PM, James Bottomley wrote: >>> On Mon, 2020-08-17 at 13:02 -0700, Jens Axboe wrote: >>>> On 8/17/20 12:48 PM, Kees Cook wrote: >>>>> On Mon, Aug 17, 2020 at 12:44:34PM -0700, Jens Axboe wrote: >>>>>> On 8/17/20 12:29 PM, Kees Cook wrote: >>>>>>> On Mon, Aug 17, 2020 at 06:56:47AM -0700, Jens Axboe wrote: >>>>>>>> On 8/17/20 2:15 AM, Allen Pais wrote: >>>>>>>>> From: Allen Pais <allen.lkml@xxxxxxxxx> >>>>>>>>> >>>>>>>>> In preparation for unconditionally passing the >>>>>>>>> struct tasklet_struct pointer to all tasklet >>>>>>>>> callbacks, switch to using the new tasklet_setup() >>>>>>>>> and from_tasklet() to pass the tasklet pointer explicitly. >>>>>>>> >>>>>>>> Who came up with the idea to add a macro 'from_tasklet' that >>>>>>>> is just container_of? container_of in the code would be >>>>>>>> _much_ more readable, and not leave anyone guessing wtf >>>>>>>> from_tasklet is doing. >>>>>>>> >>>>>>>> I'd fix that up now before everything else goes in... >>>>>>> >>>>>>> As I mentioned in the other thread, I think this makes things >>>>>>> much more readable. It's the same thing that the timer_struct >>>>>>> conversion did (added a container_of wrapper) to avoid the >>>>>>> ever-repeating use of typeof(), long lines, etc. >>>>>> >>>>>> But then it should use a generic name, instead of each sub-system >>>>>> using some random name that makes people look up exactly what it >>>>>> does. I'm not huge fan of the container_of() redundancy, but >>>>>> adding private variants of this doesn't seem like the best way >>>>>> forward. Let's have a generic helper that does this, and use it >>>>>> everywhere. >>>>> >>>>> I'm open to suggestions, but as things stand, these kinds of >>>>> treewide >>>> >>>> On naming? Implementation is just as it stands, from_tasklet() is >>>> totally generic which is why I objected to it. from_member()? Not >>>> great with naming... But I can see this going further and then we'll >>>> suddenly have tons of these. It's not good for readability. >>> >>> Since both threads seem to have petered out, let me suggest in >>> kernel.h: >>> >>> #define cast_out(ptr, container, member) \ >>> container_of(ptr, typeof(*container), member) >>> >>> It does what you want, the argument order is the same as container_of >>> with the only difference being you name the containing structure >>> instead of having to specify its type. >> >> Not to incessantly bike shed on the naming, but I don't like cast_out, >> it's not very descriptive. And it has connotations of getting rid of >> something, which isn't really true. > > I agree, if we want to bike shed, I don't like this color either. > >> FWIW, I like the from_ part of the original naming, as it has some clues >> as to what is being done here. Why not just from_container()? That >> should immediately tell people what it does without having to look up >> the implementation, even before this becomes a part of the accepted >> coding norm. > > Why are people hating on the well-known and used container_of()? > > If you really hate to type the type and want a new macro, what about > 'container_from()'? (noun/verb is nicer to sort symbols by...) > > But really, why is this even needed? container_from() or from_container(), either works just fine for me in terms of naming. I think people are hating on it because it makes for _really_ long lines, and it's arguably cleaner/simpler to just pass in the pointer type instead. Then you end up with lines like this: struct request_queue *q = container_of(work, struct request_queue, requeue_work.work); But I'm not the one that started this addition of from_tasklet(), my objection was adding a private macro for something that should be generic functionality. Hence I think we either need to provide that, or tell the from_tasklet() folks that they should just use container_of(). -- Jens Axboe
