[PATCH printk-rework 05/14] printk: introduce CONSOLE_LOG_MAX for improved multi-line support

John Ogness
2021-02-18T09:40:02Z

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@linutronix.de>
---
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 d6f93ebd7bd0..f79e7515b5f1 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)

@@ -1473,11 +1478,11 @@ 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;
@@ -1543,7 +1548,7 @@ 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;

@@ -1555,7 +1560,7 @@ 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) {
@@ -2188,8 +2193,7 @@ 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
@@ -2500,7 +2504,7 @@ 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