linux-kernel - Re: [PATCH] printk: inject caller information into the body of message

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Message-ID: <20180913122625.6ieyexpcmlc5z2it@pathway.suse.cz>
Date:   Thu, 13 Sep 2018 14:26:25 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Alexander Potapenko <glider@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        penguin-kernel@...ove.sakura.ne.jp,
        kbuild test robot <fengguang.wu@...el.com>,
        syzkaller <syzkaller@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] printk: inject caller information into the body of
 message

On Thu 2018-09-13 16:12:54, Sergey Senozhatsky wrote:
> On (09/12/18 12:05), Steven Rostedt wrote:
> > > : Introduce a few helper functions for it:
> > > : 
> > > :  init_line_buffer(&buf);
> > > :  print_line(&buf, fmt, args);
> > > :  vprint_line(&buf, fmt, vararg);
> > > :  finish_line(&buf);
> > > : 
> > 
> --- a/lib/seq_buf.c
> +++ b/lib/seq_buf.c
> @@ -324,3 +324,49 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
>  	s->readpos += cnt;
>  	return cnt;
>  }
> +
> +int vpr_line(struct pr_line *pl, const char *fmt, va_list args)
> +{
> +	struct seq_buf *s = &pl->sb;
> +	int ret, len;
> +
> +	if (fmt[0] == '\n') {
> +		pr_line_flush(pl);
> +		return 0;
> +	}

You would need to check if fmt[1] == '\0'. But then you would need
to be careful about a possible buffer overflow. I would personally
avoid this optimization.


> +	ret = seq_buf_vprintf(s, fmt, args);
> +
> +	len = seq_buf_used(s);
> +	if (len && s->buffer[len - 1] == '\n')
> +		pr_line_flush(pl);

This would cause that pr_line_flush() won't be strictly needed.
Also it would encourage people to use this feature a more
complicated way (for more lines). Do we really want this?


In general, I like this approach more than any attemps to handle
continuous lines transpatently. The other attemps were much more
complicated or were not reliable.

Best Regards,
Petr