Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 3 Jan 2023 17:13:11 +0100
From:   Petr Mladek <pmladek@suse.com>
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk v3 6/6] printk: introduce
 console_prepend_dropped() for dropped messages
Message-ID: <Y7RUF1zhmJEJKWl3@alley>
References: <20221221202704.857925-1-john.ogness@linutronix.de>
 <20221221202704.857925-7-john.ogness@linutronix.de>
 <Y7MEDmP1zqWblj0N@alley>
 <87y1qjdimw.fsf@jogness.linutronix.de>
 <Y7QtusGlIX3AU+TN@alley>
 <87o7rfd96w.fsf@jogness.linutronix.de>
 <Y7Q4u9ICptw0RnXb@alley>
 <87fscrd5os.fsf@jogness.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <87fscrd5os.fsf@jogness.linutronix.de>
Precedence: bulk

On Tue 2023-01-03 16:06:03, John Ogness wrote:
> On 2023-01-03, Petr Mladek <pmladek@suse.com> wrote:
> >> Actually, I would like to rename all of those limit macros to something
> >> that makes more sense for the new code base:
> >> 
> >> CONSOLE_EXT_LOG_MAX -> CONSOLE_MESSAGE_MAX
> >> 
> >> CONSOLE_LOG_MAX     -> SYSLOG_MESSAGE_MAX
> >
> > Heh, we actually do not need this. The size of @scratchbuf
> > might be LOG_LINE_MAX/PRINTK_RECORD_MAX. The scratch buffer
> > is newly used only to read the plain message. The prefixes
> > are added to @outbuf.
> >
> >> LOG_LINE_MAX        -> PRINTK_RECORD_MAX
> 
> The scratch buffer would become PRINTK_RECORD_MAX, but we still need
> SYSLOG_MESSAGE_MAX for the kmalloc's syslog buffers.

I see.

> Unless you think it is OK to kmalloc 8KB instead of 1KB for the
> syslog calls. Then yes, we do not need SYSLOG_MESSAGE_MAX.

IMHO, it is acceptable and even correct. syslog uses the same
prefixes as console. It would make sense to use the same
buffers for formatting.

That said, 8kB looks non-necessary big to me.

It seems that it comes from devkmsg interface, see the commit
d43ff430f434d862db59582 ("printk: guard the amount written
per line by devkmsg_read()"). It was supposed to include
the message, the extended prefix and dictionary, where

   + message is limited by LOG_LINE_MAX
   + prefix includes few well defined fields (should be < 128B)
   + dictionary comes from dev_printk() => ( < 128B as well)

I believe that 2kB or 4kB would be perfectly fine.

Best Regards,
Petr