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SubjectRe: printk: Add process name information to printk() output.
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On Fri, 2020-09-04 at 12:35 +0200, Greg KH wrote:
> On Fri, Sep 04, 2020 at 11:53:42AM +0206, John Ogness wrote:
> > On 2020-09-04, Changki Kim <changki.kim@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.

__func__ too please so that it could optionally be enabled per
subsystem using %pS, __builtin_return_address(<appropriate_level>)

That way a lot of %s:..., __func__ could be removed from
specific printk instances.



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