linux-kernel - Printk mulitple line message support

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Date:	Mon, 14 Nov 2011 14:58:56 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Joe Perches <joe@...ches.com>,
	William Douglas <william.r.douglas@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Printk mulitple line message support

Hi,

In most cases, printk only guarantees messages from different printk
calling will not be interleaved between each other.  But many printk
users uses multiple line to form a complete message and call printk
for each line.  So the following situation is possible for two printk
users running on two CPUs.

line 1 of message from printk user1
line 1 of message from printk user2
line 2 of message from printk user1
line 2 of message from printk user2

This makes kernel log hard to read.  One possible solution to this
issue is to give a sequence number (or ID) to each complete message.
So the above lines will be:

{1}line 1 of message from printk user1
{2}line 1 of message from printk user2
{1}line 2 of message from printk user1
{2}line 2 of message from printk user2

Then some simple script can be used to group lines together according
to sequence number in lines.

What do you think about that?

A simple patch to implement this is followed.

Best Regards,
Huang Ying

---
 include/linux/printk.h |   24 ++++++++++++++++++++++++
 kernel/printk.c        |    7 +++++++
 2 files changed, 31 insertions(+)

--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -149,6 +149,7 @@ static char *log_buf = __log_buf;
 static int log_buf_len = __LOG_BUF_LEN;
 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 static int saved_console_loglevel = -1;
+static atomic_t printk_seqno;
 
 #ifdef CONFIG_KEXEC
 /*
@@ -970,6 +971,12 @@ out_restore_irqs:
 EXPORT_SYMBOL(printk);
 EXPORT_SYMBOL(vprintk);
 
+unsigned int printk_ml_seqno(void)
+{
+	return atomic_inc_return(&printk_seqno);
+}
+EXPORT_SYMBOL_GPL(printk_ml_seqno);
+
 #else
 
 static void call_console_drivers(unsigned start, unsigned end)
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -116,6 +116,7 @@ extern int kptr_restrict;
 
 void log_buf_kexec_setup(void);
 void __init setup_log_buf(int early);
+unsigned int printk_ml_seqno(void);
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
@@ -144,6 +145,11 @@ static inline void log_buf_kexec_setup(v
 static inline void setup_log_buf(int early)
 {
 }
+
+static unsigned int printk_ml_seqno(void)
+{
+	return 0;
+}
 #endif
 
 extern void dump_stack(void) __cold;
@@ -192,6 +198,24 @@ extern void dump_stack(void) __cold;
 	no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
 #endif
 
+#define PR_ML_FMT	"{%u}"
+
+#define pr_emerg_ml(seqno, fmt, ...)					\
+	printk(KERN_EMERG PR_ML_FMT pr_fmt(fmt), seqno, ##__VA_ARGS__)
+#define pr_alert_ml(seqno, fmt, ...)					\
+	printk(KERN_ALERT PR_ML_FMT pr_fmt(fmt), seqno, ##__VA_ARGS__)
+#define pr_crit_ml(seqno, fmt, ...)					\
+	printk(KERN_CRIT PR_ML_FMT pr_fmt(fmt), seqno, ##__VA_ARGS__)
+#define pr_err_ml(seqno, fmt, ...)					\
+	printk(KERN_ERR PR_ML_FMT pr_fmt(fmt), seqno, ##__VA_ARGS__)
+#define pr_warning_ml(seqno, fmt, ...)					\
+	printk(KERN_WARNING PR_ML_FMT pr_fmt(fmt), seqno, ##__VA_ARGS__)
+#define pr_warn_ml pr_warning_ml
+#define pr_notice_ml(seqno, fmt, ...)					\
+	printk(KERN_NOTICE PR_ML_FMT pr_fmt(fmt), seqno, ##__VA_ARGS__)
+#define pr_info_ml(seqno, fmt, ...)					\
+	printk(KERN_INFO PR_ML_FMT pr_fmt(fmt), seqno, ##__VA_ARGS__)
+
 /*
  * Print a one-time message (analogous to WARN_ONCE() et al):
  */


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