linux-kernel - Re: [PATCH v4 2/7] printk: initialize syslog_prev and console

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Message-ID: <53CD018A.3080800@linaro.org>
Date:	Mon, 21 Jul 2014 07:03:22 -0500
From:	Alex Elder <elder@...aro.org>
To:	Petr Mládek <pmladek@...e.cz>
CC:	akpm@...ux-foundation.org, kay@...y.org, bp@...e.de,
	john.stultz@...aro.org, jack@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/7] printk: initialize syslog_prev and console_prev

On 07/21/2014 05:01 AM, Petr Mládek wrote:
> On Fri 2014-07-18 16:28:00, Alex Elder wrote:
>> Two global variables, "syslog_prev" and "console_prev", maintain a
>> copy of the flags value used in the log record most recently
>> formatted for syslog or the console, respectively.
>>
>> Initially there is no previous formatted log record, and these
>> variables simply have an initial value 0.  And occasionally log
>> records can get consumed at a rate such that syslog or the console
>> can't keep up, in which case those variables (along with their
>> corresponding position variables) must be reset.  Here too, they're
>> reset to 0.
>>
>> This patch changes it so the initial value used is LOG_NEWLINE.
>> That is, if we know nothing about the prevously-formatted log
>> record, we can assume it was complete, and ended with a newline.
>>
>> This is being done to support the next patch.  Initializing
>> these variables this way makes LOG_NEWLINE and LOG_CONT be
>> mutually exclusive, and the next patch uses that fact to simplify
>> some logic.
> 
> I have decided to double check it and found more locations where the flags were
> reset to 0:
> 
>       + "prev" variable in syslog_print_all()
>       + "prev" variable in kmsg_dump_get_buffer()

Yes, you're right.  I'm glad you checked.  Some of those
don't matter much (because they're only measuring the size
of the needed buffer) but I'll do it on all of them for
consistency.

> Also I think that we should not reset it to LOG_NEWLINE when the
> message is gone. I would suggest to do
> 
> 	&= (LOG_CONT | LOG_NEWLINE);

What you're saying is that in the case we're resetting
because we couldn't keep up, we *do* in fact know something
about the previously-formatted message, so we should preserve
that.  That's an astute observation.  I like it, and will
implement it.

Thanks.  v5 will be coming out this morning.

					-Alex

> I mean to preserve the status of the last copied/printed piece. Then
> we could put there "\n" when the last proceed piece was continuous and
> the next one starts with prefix.
> 
> The only exception would be "console_prev" in  console_unlock()
> because there we already add "\n" in the "** %u printk messages
> dropped **" warning.
> 
> How does that sound?
> 
> 
> Best Regards,
> Petr
> 
> 
>>
>> Signed-off-by: Alex Elder <elder@...aro.org>
>> Reviewed-by: Petr Mládek <pmladek@...e.cz>
>> ---
>>  kernel/printk/printk.c | 10 +++++-----
>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
>> index ffc9928..4034a88 100644
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -236,7 +236,7 @@ DECLARE_WAIT_QUEUE_HEAD(log_wait);
>>  /* the next printk record to read by syslog(READ) or /proc/kmsg */
>>  static u64 syslog_seq;
>>  static u32 syslog_idx;
>> -static enum log_flags syslog_prev;
>> +static enum log_flags syslog_prev = LOG_NEWLINE;
>>  static size_t syslog_partial;
>>  
>>  /* index and sequence number of the first record stored in the buffer */
>> @@ -250,7 +250,7 @@ static u32 log_next_idx;
>>  /* the next printk record to write to the console */
>>  static u64 console_seq;
>>  static u32 console_idx;
>> -static enum log_flags console_prev;
>> +static enum log_flags console_prev = LOG_NEWLINE;
>>  
>>  /* the next printk record to read after the last 'clear' command */
>>  static u64 clear_seq;
>> @@ -1071,7 +1071,7 @@ static int syslog_print(char __user *buf, int size)
>>  			/* messages are gone, move to first one */
>>  			syslog_seq = log_first_seq;
>>  			syslog_idx = log_first_idx;
>> -			syslog_prev = 0;
>> +			syslog_prev = LOG_NEWLINE;
>>  			syslog_partial = 0;
>>  		}
>>  		if (syslog_seq == log_next_seq) {
>> @@ -1301,7 +1301,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
>>  			/* messages are gone, move to first one */
>>  			syslog_seq = log_first_seq;
>>  			syslog_idx = log_first_idx;
>> -			syslog_prev = 0;
>> +			syslog_prev = LOG_NEWLINE;
>>  			syslog_partial = 0;
>>  		}
>>  		if (from_file) {
>> @@ -2149,7 +2149,7 @@ again:
>>  			/* messages are gone, move to first one */
>>  			console_seq = log_first_seq;
>>  			console_idx = log_first_idx;
>> -			console_prev = 0;
>> +			console_prev = LOG_NEWLINE;
>>  		} else {
>>  			len = 0;
>>  		}
>> -- 
>> 1.9.1
>>

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