linux-kernel - [PATCH next v3 07/15] printk: introduce CONSOLE_LOG

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Date:   Thu, 25 Feb 2021 21:24:30 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH next v3 07/15] printk: introduce CONSOLE_LOG_MAX for improved multi-line support

Instead of using "LOG_LINE_MAX + PREFIX_MAX" for temporary buffer
sizes, introduce CONSOLE_LOG_MAX. This represents the maximum size
that is allowed to be printed to the console for a single record.

Rather than setting CONSOLE_LOG_MAX to "LOG_LINE_MAX + PREFIX_MAX"
(1024), increase it to 4096. With a larger buffer size, multi-line
records that are nearly LOG_LINE_MAX in length will have a better
chance of being fully printed. (When formatting a record for the
console, each line of a multi-line record is prepended with a copy
of the prefix.)

Signed-off-by: John Ogness <john.ogness@...utronix.de>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
 kernel/printk/printk.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9a5f9ccc46ea..a60f709896dd 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -410,8 +410,13 @@ static u64 clear_seq;
 #else
 #define PREFIX_MAX		32
 #endif
+
+/* the maximum size allowed to be reserved for a record */
 #define LOG_LINE_MAX		(1024 - PREFIX_MAX)
 
+/* the maximum size of a formatted record (i.e. with prefix added per line) */
+#define CONSOLE_LOG_MAX		4096
+
 #define LOG_LEVEL(v)		((v) & 0x07)
 #define LOG_FACILITY(v)		((v) >> 3 & 0xff)
 
@@ -1472,11 +1477,11 @@ static int syslog_print(char __user *buf, int size)
 	char *text;
 	int len = 0;
 
-	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
+	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
-	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
+	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
 	while (size > 0) {
 		size_t n;
@@ -1542,7 +1547,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	u64 seq;
 	bool time;
 
-	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
+	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
@@ -1554,7 +1559,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	 */
 	seq = find_first_fitting_seq(clear_seq, -1, size, true, time);
 
-	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
+	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
@@ -2187,8 +2192,7 @@ EXPORT_SYMBOL(printk);
 
 #else /* CONFIG_PRINTK */
 
-#define LOG_LINE_MAX		0
-#define PREFIX_MAX		0
+#define CONSOLE_LOG_MAX		0
 #define printk_time		false
 
 #define prb_read_valid(rb, seq, r)	false
@@ -2506,7 +2510,7 @@ static inline int can_use_console(void)
 void console_unlock(void)
 {
 	static char ext_text[CONSOLE_EXT_LOG_MAX];
-	static char text[LOG_LINE_MAX + PREFIX_MAX];
+	static char text[CONSOLE_LOG_MAX];
 	unsigned long flags;
 	bool do_cond_resched, retry;
 	struct printk_info info;
-- 
2.20.1