linux-kernel - Re: [RFC PATCH v1 04/25] printk-rb: add writer interface

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Date:   Fri, 15 Feb 2019 02:19:50 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Wang <wonderfly@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Feiner <pfeiner@...gle.com>,
        linux-serial@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH v1 04/25] printk-rb: add writer interface

On 2019-02-15, John Ogness <john.ogness@...utronix.de> wrote:
> prb_commit() does not actually care what is in the handle. It is going
> to commit everything up to the reserve.

After thinking about what I wrote here, I realized that the struct
prb_handle has no purpose in this ringbuffer implementation. We really
could simplify the writer interface to:

    char *prb_reserve(struct printk_ringbuffer *rb, unsigned int size);

    void prb_commit(struct printk_ringbuffer *rb);

That probably feels really strange because the writer doesn't specify
_what_ to commit. But this ringbuffer implementation doesn't need to
know that.

The only reason I can think of for having a handle is if there should be
any statistics, debugging, or sanity checking added. (For example if a
writer tried to commit something it did not reserve.)

John Ogness