linux-kernel - Re: [PATCH] printk: remove unnecessary kmalloc() from syslog during clear

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Date:   Mon, 25 Jun 2018 10:37:04 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Namit Gupta <gupta.namit@...sung.com>,
        sergey.senozhatsky@...il.com, linux-kernel@...r.kernel.org,
        pankaj.m@...sung.com, a.sahrawat@...sung.com,
        himanshu.m@...sung.com
Subject: Re: [PATCH] printk: remove unnecessary kmalloc() from syslog during
 clear

On Mon, 25 Jun 2018 15:37:05 +0200
Petr Mladek <pmladek@...e.com> wrote:

> On Wed 2018-06-20 19:26:19, Namit Gupta wrote:
> > When the request is only for clearing logs, there is no need for
> > allocation/deallocation. Only the indexes need to be reset and returned.
> > Rest of the patch is mostly made up of changes because of indention.
> > 
> > Signed-off-by: Namit Gupta <gupta.namit@...sung.com>
> > Signed-off-by: Himanshu Maithani <himanshu.m@...sung.com>  
> 
> > ---
> >  kernel/printk/printk.c | 111 ++++++++++++++++++++++++++-----------------------
> >  1 file changed, 60 insertions(+), 51 deletions(-)
> > 
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index 512f7c2..53952ce 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -1348,71 +1348,80 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
> >  {
> >  	char *text;
> >  	int len = 0;
> > +	u64 next_seq;
> > +	u64 seq;
> > +	u32 idx;
> > +
> > +	if (!buf) {
> > +		if (clear) {
> > +			logbuf_lock_irq();
> > +			clear_seq = log_next_seq;
> > +			clear_idx = log_next_idx;
> > +			logbuf_unlock_irq();  
> 
> I pushed a bit different version into printk.git, branch for-4.19,
> see below. It removes the code duplication. Also it keeps the original
> indentation. IMHO, it helped to better distinguish the code for printing
> and clearing.
> 
> It is rather a cosmetic change, so I do not want you to resend
> Reviewed-by tags. But feel free to disagree and ask me to use
> the original variant.
> 

I actually prefer the original version. It's not really duplicating
much text, and it's cleaner, because it lets you know exactly what is
happening when buf == NULL.

	if (buf)
		text = kmalloc();

	logbuf_lock_irq();

	if (buf) {
		[...]
	}

Is IMHO rather ugly.

And the original patch has one more advantage. If buf and clear are
both NULL/zero, we don't take any locks.

-- Steve