On Fri, Sep 04, 2020 at 11:53:42AM +0206, John Ogness wrote:
> On 2020-09-04, Changki Kim <changki....@samsung.com> wrote:
> > Printk() meesages are the most basic and useful debug method.
> > However, additional information needs in multi-processor.
> > If we add messages with processor id and process name, we can find
> > a problem only with messages when the problem occurs with H/W IP or CPU.
> > This is very useful in narrowing down the scope of the problems.
>
> [...]
>
> > diff --git a/kernel/printk/printk_ringbuffer.h
> > b/kernel/printk/printk_ringbuffer.h
> > index e6302da041f9..fcefe9516606 100644
> > --- a/kernel/printk/printk_ringbuffer.h
> > +++ b/kernel/printk/printk_ringbuffer.h
> > @@ -21,6 +22,12 @@ struct printk_info {
> > u8 flags:5; /* internal record flags */
> > u8 level:3; /* syslog level */
> > u32 caller_id; /* thread id or processor id */
> > +#ifdef CONFIG_PRINTK_PROCESS
> > + int pid; /* process id */
> > + u8 cpu_id; /* processor id */
> > + u8 in_interrupt; /* interrupt conext */
> > + char process[TASK_COMM_LEN]; /* process name */
> > +#endif
> > };
>
> I can understand the desire to have more information with messages. But
> IMHO adding it to the ringbuffer descriptor is the wrong place for
> it. The descriptor should really be limited to data that the printk
> subsystem needs for _itself_. With respect to LOG_CONT, I think we can
> agree that @caller_id is not enough. But there has been discussions [0]
> of having @caller_id provide a better context representation.
>
> If we want to support adding more meta information to messages, I would
> prefer that the information is either prepended directly to the message
> text string or appended to the dictionary text string. We could even go
> so far as providing a boot argument where a list of information could be
> specified, what should be automatically added to the text/dict strings
> of each message. That would not require any ringbuffer changes and would
> allow new types of information to be added later.
>
> Something like:
>
> printk.format=ts,cpu,comm,pid,in_atomic
>
> John Ogness
>
> [0] https://lkml.kernel.org/r/20200719143527.GA566@jagdpanzerIV.localdomain
Ah, finally a good use of the "dictionary" that we all can agree makes
sense :)
This does seem like a better solution overall, thanks.
greg k-h
