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

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Date:   Thu, 13 Sep 2018 16:12:54 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        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>, pmladek@...e.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

Hi, Steven

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);
> > : 
> 
> This sounds like seq_buf to me.

Correct.

> > +struct pr_line {
> > +	char			*buffer;
> > +	int			size;
> > +	int			len;
> > +	char			*level;
> > +};
> 
> Can you look at implementing this with using a seq_buf?

Certainly, attached.

It doesn't seem to save us that much code, tho. It looks smaller just
because I dropped "truncated" print out and didn't include !CONFIG_PRINTK
noise this time around. And the OK thing about previous version was that
it didn't introduce any new dependencies to printk.

Making pr_line available via printk.h -- #include seq_buf.h in printk.h - at
glance looks like some fun. printk.h is getting included very early, before
we have all the stuff that seq_buf.h wants - we can remove fs.h from
seq_buf.h and add a bunch of forward declarations for path and seq_file;
but all those BUG_ON/WARN_ON/etc is another story (unless we want every
pr_line user to include seq_buf.h).

... maybe I can change API. But I sort of like that implicit buffer case:

	DEFINE_PR_LINE(KERN_ERR, pl);

	pr_line(&pl, "Hello, ");
	pr_line(&pl, "%s.\n", "Steven");

And, looking at potential users of pr_line, I'd say that we better
have DEFINE_PR_LINE_BUF, because some of them do print messages longer
than 80 chars.

===

From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [PATCH] lib/seq_buf: add pr_line buffering API

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 include/linux/seq_buf.h | 35 +++++++++++++++++++++++++++++++
 lib/seq_buf.c           | 46 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index aa5deb041c25..5e9a5ff9a440 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -23,6 +23,36 @@ struct seq_buf {
 	loff_t			readpos;
 };
 
+#define __SEQ_BUF_INITIALIZER(buf, length) {				\
+	.buffer			= (buf),				\
+	.size			= (length),				\
+	.len			= 0,					\
+	.readpos		= 0, }
+
+#ifdef CONFIG_PRINTK
+#define __PR_LINE_BUF_SZ	80
+#else
+#define __PR_LINE_BUF_SZ	0
+#endif
+
+struct pr_line {
+	struct seq_buf		sb;
+	char			*level;
+};
+
+#define DEFINE_PR_LINE(lev, name)					\
+	char		__line[__PR_LINE_BUF_SZ];			\
+	struct pr_line	name = {					\
+		.sb = __SEQ_BUF_INITIALIZER(__line, __PR_LINE_BUF_SZ),	\
+		.level	= lev,						\
+	}
+
+#define DEFINE_PR_LINE_BUF(lev, name, buf, sz)				\
+	struct pr_line	name = {					\
+		.sb = __SEQ_BUF_INITIALIZER(buf, (sz)),		\
+		.level	= lev,						\
+	}
+
 static inline void seq_buf_clear(struct seq_buf *s)
 {
 	s->len = 0;
@@ -131,4 +161,9 @@ extern int
 seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
 #endif
 
+extern __printf(2, 0)
+int vpr_line(struct pr_line *pl, const char *fmt, va_list args);
+extern __printf(2, 3)
+int pr_line(struct pr_line *pl, const char *fmt, ...);
+extern void pr_line_flush(struct pr_line *pl);
 #endif /* _LINUX_SEQ_BUF_H */
diff --git a/lib/seq_buf.c b/lib/seq_buf.c
index 11f2ae0f9099..29bc4f24b83e 100644
--- 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;
+	}
+
+	ret = seq_buf_vprintf(s, fmt, args);
+
+	len = seq_buf_used(s);
+	if (len && s->buffer[len - 1] == '\n')
+		pr_line_flush(pl);
+
+	return ret;
+}
+EXPORT_SYMBOL(vpr_line);
+
+int pr_line(struct pr_line *pl, const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	va_start(ap, fmt);
+	ret = vpr_line(pl, fmt, ap);
+	va_end(ap);
+
+	return ret;
+}
+EXPORT_SYMBOL(pr_line);
+
+void pr_line_flush(struct pr_line *pl)
+{
+	struct seq_buf *s = &pl->sb;
+	int len = seq_buf_used(s);
+
+	if (!len)
+		return;
+
+	printk("%s%.*s", pl->level, len, s->buffer);
+	seq_buf_clear(s);
+}
+EXPORT_SYMBOL(pr_line_flush);
-- 
2.19.0