Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   John Ogness <john.ogness@linutronix.de>
To:     Petr Mladek <pmladek@suse.com>
Cc:     Andrea Parri <andrea.parri@amarulasolutions.com>,
        Andrea Parri <parri.andrea@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Brendan Higgins <brendanhiggins@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: numlist API Re: [RFC PATCH v4 1/9] printk-rb: add a new printk ringbuffer implementation
References: <20190807222634.1723-1-john.ogness@linutronix.de>
        <20190807222634.1723-2-john.ogness@linutronix.de>
        <20190823171802.eo2chwyktibeub7a@pathway.suse.cz>
        <20190823171802.eo2chwyktibeub7a@pathway.suse.cz>
        <87sgpnmqdo.fsf@linutronix.de>
        <20190827130349.6mrnhdlqyqokgsfk@pathway.suse.cz>
        <20190827130349.6mrnhdlqyqokgsfk@pathway.suse.cz>
        <87o909lq3g.fsf@linutronix.de>
        <20190828085845.5k7ewfshbfed7txh@pathway.suse.cz>
Date:   Wed, 28 Aug 2019 16:03:38 +0200
In-Reply-To: <20190828085845.5k7ewfshbfed7txh@pathway.suse.cz> (Petr Mladek's
        message of "Wed, 28 Aug 2019 10:58:45 +0200")
Message-ID: <87k1axjsjp.fsf@linutronix.de>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2019-08-28, Petr Mladek <pmladek@suse.com> wrote:
> I only think that, especially, numlist API is too generic in v4.
> It is not selfcontained. The consistency depends on external barriers.
>
> I believe that it might become fully self-contained and consistent
> if we reduce possibilities of the generic usage. In particular,
> the numlist should allow only linking of reusable structures
> stored in an array.

OK. I will make the numlist the master of the ID-to-node mapping. To
implement the getdesc() callback of the dataring, the printk_ringbuffer
can call a numlist mapping function. Also, numlist will need to provide
a function to bump the descriptor version (as your previous idea already
showed).

I plan to change the array to be numlist nodes. The ID would move into
the numlist node structure and a void-pointer private would be added so
that the numlist user can add private data (for printk_ringbuffer that
would just be a pointer to the dataring structure). When the
printk_ringbuffer gets a never-used numlist node, it can set the private
field.

This has the added benefit of making it easy to detect accidental
never-used descriptor usage when reading dataring garbage. This was
non-trivial and I'm still not sure I solved it correctly. (I've already
spent a week working on a definitive answer to your email[0] asking
about this.)

John Ogness

[0] https://lkml.kernel.org/r/20190820151239.yzdqz56yeldlknln@pathway.suse.cz