[PATCH] printk: Warn about dropped messages also on extended consoles

[PATCH] printk: Warn about dropped messages also on extended consoles

[Petr Mladek]

The commit #6fe29354befe4c ("printk: implement support for extended console
drivers") added an extra buffer to format messages for extended consoles.
We need to put there also the warning about dropped messages, so it appears
on these consoles.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index cf8c24203368..77d3d3698283 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2254,8 +2254,15 @@ again:
 		}
 
 		if (console_seq < log_first_seq) {
-			len = sprintf(text, "** %u printk messages dropped ** ",
-				      (unsigned)(log_first_seq - console_seq));
+			static const char dropped_msg[] =
+				"** %u printk messages dropped ** ";
+			unsigned int dropped_count =
+				(unsigned int)(log_first_seq - console_seq);
+
+			len = sprintf(text, dropped_msg, dropped_count);
+			if (nr_ext_console_drivers)
+				ext_len = sprintf(ext_text, dropped_msg,
+						  dropped_count);
 
 			/* messages are gone, move to first one */
 			console_seq = log_first_seq;
@@ -2290,8 +2297,8 @@ skip:
 		len += msg_print_text(msg, console_prev, false,
 				      text + len, sizeof(text) - len);
 		if (nr_ext_console_drivers) {
-			ext_len = msg_print_ext_header(ext_text,
-						sizeof(ext_text),
+			ext_len += msg_print_ext_header(ext_text + ext_len,
+						sizeof(ext_text) - ext_len,
 						msg, console_seq, console_prev);
 			ext_len += msg_print_ext_body(ext_text + ext_len,
 						sizeof(ext_text) - ext_len,
-- 
1.8.5.6

Re: [PATCH] printk: Warn about dropped messages also on extended consoles

[Joe Perches]

On Thu, 2015-07-30 at 13:28 +0200, Petr Mladek wrote:
> The commit #6fe29354befe4c ("printk: implement support for extended console
> drivers") added an extra buffer to format messages for extended consoles.
> We need to put there also the warning about dropped messages, so it appears
> on these consoles.
[]
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
[]
> @@ -2254,8 +2254,15 @@ again:
>  		}
>  
>  		if (console_seq < log_first_seq) {
> -			len = sprintf(text, "** %u printk messages dropped ** ",
> -				      (unsigned)(log_first_seq - console_seq));
> +			static const char dropped_msg[] =
> +				"** %u printk messages dropped ** ";

I don't see any value in dropped_msg as a
const char array instead of just using it directly
as a format in sprintf.  The linker will still use
a single format string in any case.

memcpy might be faster.

	if (nr_ext_console_drivers)
		memcpy(ext_text, text, len + 1);

> +			unsigned int dropped_count =
> +				(unsigned int)(log_first_seq - console_seq);
> +
> +			len = sprintf(text, dropped_msg, dropped_count);
> +			if (nr_ext_console_drivers)
> +				ext_len = sprintf(ext_text, dropped_msg,
> +						  dropped_count);
>  

Re: [PATCH] printk: Warn about dropped messages also on extended consoles

[Tejun Heo]

Hello,

On Thu, Jul 30, 2015 at 01:28:52PM +0200, Petr Mladek wrote:
> The commit #6fe29354befe4c ("printk: implement support for extended console
> drivers") added an extra buffer to format messages for extended consoles.
> We need to put there also the warning about dropped messages, so it appears
> on these consoles.

I don't get it.  Extended messages are all stamped with sequence
number and the gap in sequence number is a clear sign of missing
messages.

> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index cf8c24203368..77d3d3698283 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2254,8 +2254,15 @@ again:
>  		}
>  
>  		if (console_seq < log_first_seq) {
> -			len = sprintf(text, "** %u printk messages dropped ** ",
> -				      (unsigned)(log_first_seq - console_seq));
> +			static const char dropped_msg[] =
> +				"** %u printk messages dropped ** ";
> +			unsigned int dropped_count =
> +				(unsigned int)(log_first_seq - console_seq);
> +
> +			len = sprintf(text, dropped_msg, dropped_count);
> +			if (nr_ext_console_drivers)
> +				ext_len = sprintf(ext_text, dropped_msg,
> +						  dropped_count);

And you can't shove random message in front of the header.

Nacked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

Re: [PATCH] printk: Warn about dropped messages also on extended consoles

[Petr Mladek]

On Thu 2015-07-30 09:39:01, Tejun Heo wrote:
> Hello,
> 
> On Thu, Jul 30, 2015 at 01:28:52PM +0200, Petr Mladek wrote:
> > The commit #6fe29354befe4c ("printk: implement support for extended console
> > drivers") added an extra buffer to format messages for extended consoles.
> > We need to put there also the warning about dropped messages, so it appears
> > on these consoles.
> 
> I don't get it.  Extended messages are all stamped with sequence
> number and the gap in sequence number is a clear sign of missing
> messages.

Grr, I misconfigured netconsole and did not see the extended
information. You are right, the patch is not needed.

Best Regards,
Petr