linux-kernel - Re: [PATCH 2/2] printk: use the lockless ringbuffer

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Message-ID: <20200213090757.GA36551@google.com>
Date:   Thu, 13 Feb 2020 18:07:57 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] printk: use the lockless ringbuffer

On (20/01/28 17:25), John Ogness wrote:
[..]
> -	while (user->seq == log_next_seq) {
> +	if (!prb_read_valid(prb, user->seq, r)) {
>  		if (file->f_flags & O_NONBLOCK) {
>  			ret = -EAGAIN;
>  			logbuf_unlock_irq();
> @@ -890,30 +758,26 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
>  
>  		logbuf_unlock_irq();
>  		ret = wait_event_interruptible(log_wait,
> -					       user->seq != log_next_seq);
> +					prb_read_valid(prb, user->seq, r));
>  		if (ret)
>  			goto out;
>  		logbuf_lock_irq();
>  	}
>  
> -	if (user->seq < log_first_seq) {
> -		/* our last seen message is gone, return error and reset */
> -		user->idx = log_first_idx;
> -		user->seq = log_first_seq;
> +	if (user->seq < r->info->seq) {
> +		/* the expected message is gone, return error and reset */
> +		user->seq = r->info->seq;
>  		ret = -EPIPE;
>  		logbuf_unlock_irq();
>  		goto out;
>  	}

Sorry, why doesn't this do something like

	if (user->seq < prb_first_seq(prb)) {
		/* the expected message is gone, return error and reset */
		user->seq = prb_first_seq(prb);
		ret = -EPIPE;
		...
	}

?

	-ss