linux-kernel - Re: [PATCH] linux/kernel.h: add container

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Message-ID: <1598553133.4237.8.camel@HansenPartnership.com>
Date:   Thu, 27 Aug 2020 11:32:13 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Allen Pais <allen.lkml@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] linux/kernel.h: add container_from()

On Thu, 2020-08-27 at 11:04 -0700, Linus Torvalds wrote:
> On Wed, Aug 26, 2020 at 6:36 PM Allen Pais <allen.lkml@...il.com>
> wrote:
> > 
> > Introduce container_from() as a generic helper instead of
> > sub-systems defining a private from_
> 
> NAK.
> 
> This seems completely broken.
> 
> The documentation comment doesn't even match the macro, and claims
> that "container" is a type.
> 
> Which it isn't. That's what container_of()" already takes.
> 
> And if the argument is that a broken commit introduced a broken
> macro,
> then that's not a great argument. Yes, we have that broken
> "from_tasklet()" macro, but it's not even *USED* anywhere.
> 
> So instead of adding a broken new concept that adds absolutely no
> value, let's just remove the broken macro that isn't even used.

The argument is more over the tasklet rework adding from_tasklet that
was effectively completely generic.

https://lore.kernel.org/dri-devel/20200817091617.28119-1-allen.cryptic@gmail.com/

The tasklet rework people don't want to use container_of, which was our
first suggestion, because it produces lines which are "too long".  So
container_from is a compromise that takes the actual structure pointer
as a second argument instead of the structure type, thus being
completely generic and suitable for line length reduction in the
tasklet rework code.

James