Messages in this thread | ![/](/images/icornerl.gif) | | From | Allen <> | Date | Fri, 28 Aug 2020 12:37:11 +0530 | Subject | Re: [PATCH] linux/kernel.h: add container_from() |
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> > I don't see that kind of redundancy being a _problem_, though. "So > much redundancy" is just over-stating the issue completely. > > In fact, we often encourage people to split declaration from > initialization exactly because it results in simpler expressions and > more legible code, even if that name is now redundant. So it's a small > extra typing of the type. Big deal. > > The above is also a common pattern that once you know how > container_of() works, it's very legible. > > Sure, if you're new to the kernel, and haven't seen "container_of()" > in other projects, it might initially be a bit of an odd pattern, but > that's the advantage of having one single standardized model: it > becomes a pattern, and you don't have to think about it. > > And particularly with that argument-type pattern, you really have to > work at making over-long lines, since the indentation level will by > definition be just one. > > Looking around, I do see a lot of people doing line-breaks, but that > tends to be when they insist on putting the variable initialization in > the declaration. And even then, it often seems pointless (eg > > struct idp_led *led = container_of(cdev, > struct idp_led, cdev); > > was split for no good reason I can see, but it seems to be a pattern > in that file). > > You really have to pick some pretty excessive type names (or variable > names) to get close to 80 characters. Again, to pick an example: > > struct timer_group_priv *priv = container_of(handle, > struct timer_group_priv, timer[handle->num]); > > ends up being long even if you were to split it, but that funky > container_from() wouldn't have helped the real problem - the fact that > the above is complex and nasty. >
An example with a really long member name is
+struct nokia_modem_device *modem = from_tasklet(modem, t, + nokia_modem_rst_ind_tasklet);
With container_of() one can imagine how long it would end up. And am sure we have many more examples in the kernel.
I agree, It would have been simpler to use container_of() as it's been widely used, but as mentioned by Kees, for 1-to-many conversions it does not work well.
I guess container_from() is a NAK, if you would want us to just use container_of() to keep the code clean and simple instead of using wrappers, or any other method, we are open to suggestions.
Thanks, - Allen
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