[PATCH v2][next] printk: ringbuffer: support dataless records

[Sergey Senozhatsky]

On (20/07/21 15:31), John Ogness wrote:
> With commit ("printk: use the lockless ringbuffer"), printk()
> started silently dropping messages without text because such
> records are not supported by the new printk ringbuffer.
> 
> Add support for such records.
> 
> Currently dataless records are denoted by INVALID_LPOS in order
> to recognize failed prb_reserve() calls. Change the ringbuffer
> to instead use two different identifiers (FAILED_LPOS and
> NO_LPOS) to distinguish between failed prb_reserve() records and
> successful dataless records, respectively.
> 
> Fixes: ("printk: use the lockless ringbuffer")
> Fixes: https://lkml.kernel.org/r/20200718121053.GA691245@elver.google.com
> Reported-by: Marco Elver <elver at google.com>
> Signed-off-by: John Ogness <john.ogness at linutronix.de>

Applied to printk-rework, thanks.

	-ss