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Date:   Mon, 23 Sep 2019 19:05:13 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     zhe.he@windriver.com
Cc:     pmladek@suse.com, sergey.senozhatsky@gmail.com,
        rostedt@goodmis.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] printk: Fix unnecessary returning broken pipe error from
 devkmsg_read
Message-ID: <20190923100513.GA51932@jagdpanzerIV>
References: <1568813503-420025-1-git-send-email-zhe.he@windriver.com>
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On (09/18/19 21:31), zhe.he@windriver.com wrote:
> 
> When users read the buffer from start, there is no need to return -EPIPE
> since the possible overflows will not affect the output.
>
[..]
> -	if (user->seq < log_first_seq) {
> +	if (user->seq == 0) {
> +		user->seq = log_first_seq;
> +	} else 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;

A tough call.

User-space wants to read messages which are gone: log_first_seq > user->seq.

I think returning EPIPE is sort of appropriate; user-space, possibly,
can printf(stderr, "Some /dev/kmsg messages are gone\n"); or something
like that.

	-ss