linux-kernel - Re: [PATCH printk v4 7/8 v2] printk: use printk

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Message-ID: <87pmbospe4.fsf@jogness.linutronix.de>
Date:   Sun, 08 Jan 2023 22:17:15 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v4 7/8 v2] printk: use printk_buffers for devkmsg

On 2023-01-06, Petr Mladek <pmladek@...e.com> wrote:
>> -	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
>> +	while (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true)) {
>
> A problem is that printk_get_next_message() does not format the
> message when it shoud get supressed on the console.

Nice catch. I missed that.

> I would solve it be adding a parameter to printk_get_next_message()
> that will tell whether to suppress or not, e.g. @can_suppress.

OK.

>>  		if (file->f_flags & O_NONBLOCK) {
>>  			ret = -EAGAIN;
>>  			goto out;
>> @@ -814,36 +814,31 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
>>  		 * This pairs with __wake_up_klogd:A.
>>  		 */
>>  		ret = wait_event_interruptible(log_wait,
>> -				prb_read_valid(prb,
>> -					atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
>> +					       prb_read_valid(prb, atomic64_read(&user->seq),
>> +							      NULL)); /* LMM(devkmsg_read:A) */
>
> The above change from "if" to "while" could be avoided if we use
> printk_get_next_message() here as well. It looks slightly more
> strightfoward to me.

Yes, that is better. A loop is overkill here.

John