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

[Marco Elver]

On Mon, Jul 20, 2020 at 04:07PM +0206, 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
> Signed-off-by: John Ogness <john.ogness at linutronix.de>
> ---
>  based on next-20200720
> 
>  kernel/printk/printk_ringbuffer.c | 58 ++++++++++++++-----------------
>  kernel/printk/printk_ringbuffer.h | 15 ++++----
>  2 files changed, 35 insertions(+), 38 deletions(-)

Thanks! Ran a couple tests and sanitizer report blank lines are back
where they're expected.

Tested-by: Marco Elver <elver at google.com>