Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <1597784438.3978.6.camel@HansenPartnership.com>
Subject: Re: [PATCH] block: convert tasklets to use new tasklet_setup() API
From:   James Bottomley <James.Bottomley@HansenPartnership.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Jens Axboe <axboe@kernel.dk>, Allen Pais <allen.cryptic@gmail.com>,
        jdike@addtoit.com, richard@nod.at, anton.ivanov@cambridgegreys.com,
        3chas3@gmail.com, stefanr@s5r6.in-berlin.de, airlied@linux.ie,
        daniel@ffwll.ch, sre@kernel.org, kys@microsoft.com, deller@gmx.de,
        dmitry.torokhov@gmail.com, jassisinghbrar@gmail.com,
        shawnguo@kernel.org, s.hauer@pengutronix.de,
        maximlevitsky@gmail.com, oakad@yahoo.com, ulf.hansson@linaro.org,
        mporter@kernel.crashing.org, alex.bou9@gmail.com,
        broonie@kernel.org, martyn@welchs.me.uk, manohar.vanga@gmail.com,
        mitch@sfgoth.com, davem@davemloft.net, kuba@kernel.org,
        linux-um@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-atm-general@lists.sourceforge.net, netdev@vger.kernel.org,
        linux-block@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        openipmi-developer@lists.sourceforge.net,
        linux1394-devel@lists.sourceforge.net,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-hyperv@vger.kernel.org, linux-parisc@vger.kernel.org,
        linux-input@vger.kernel.org, linux-mmc@vger.kernel.org,
        linux-ntb@googlegroups.com, linux-s390@vger.kernel.org,
        linux-spi@vger.kernel.org, devel@driverdev.osuosl.org,
        Allen Pais <allen.lkml@gmail.com>,
        Romain Perier <romain.perier@gmail.com>
Date:   Tue, 18 Aug 2020 14:00:38 -0700
In-Reply-To: <202008181309.FD3940A2D5@keescook>
References: <20200817091617.28119-1-allen.cryptic@gmail.com>
         <20200817091617.28119-2-allen.cryptic@gmail.com>
         <b5508ca4-0641-7265-2939-5f03cbfab2e2@kernel.dk>
         <202008171228.29E6B3BB@keescook>
         <161b75f1-4e88-dcdf-42e8-b22504d7525c@kernel.dk>
         <202008171246.80287CDCA@keescook>
         <df645c06-c30b-eafa-4d23-826b84f2ff48@kernel.dk>
         <1597780833.3978.3.camel@HansenPartnership.com>
         <202008181309.FD3940A2D5@keescook>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 2020-08-18 at 13:10 -0700, Kees Cook wrote:
> On Tue, Aug 18, 2020 at 01:00:33PM -0700, 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@gmail.com>
> > > > > > > > 
> > > > > > > > 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.
> 
> I like this! Shall I send this to Linus to see if this can land in
> -rc2 for use going forward?

Sure ... he's probably been lurking on this thread anyway ... it's
about time he got off his arse^Wthe fence and made an executive
decision ...

James