Re: [RFC PATCH 2/2] cxl: Add tprintk support for header log hex dump

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 17 Jan 2023 11:08:26 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> On 1/13/23 8:40 AM, Jonathan Cameron wrote:
> > May not make sense in general, but very helpful when writing multiple
> > header logging support.
> > 
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>  
> 
> The user logging software would be retrieving from the log data directly 
> instead of parsing the trace output right? Will people visually inspect 
> the formatted trace output? Useful for debugging?

Rather depends on the use case and rate of expected errors + if you are
trying to debug errors before your logging infrastructure is up.

Sure in production, likely these tracepoints would just get stored to a DB for later
querying.  But in debug, I often just use the kernel parameter
to directly dump them in the main kernel log, or perf's own decoding of a trace.

The nearest equivalent to this is AER which does print the log.
https://elixir.bootlin.com/linux/v6.2-rc4/source/include/ras/ras_event.h#L337

though that uses __print_array so maybe that's a better choice.
Don't get the nice offsets though if we do that though...

I'm not fussed about this patch going upstream or not, it just makes testing
patch 1 a lot easier :)

Jonathan


> 
> > ---
> >   drivers/cxl/core/trace.h | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/cxl/core/trace.h b/drivers/cxl/core/trace.h
> > index 20ca2fe2ca8e..64f6ad13529d 100644
> > --- a/drivers/cxl/core/trace.h
> > +++ b/drivers/cxl/core/trace.h
> > @@ -62,10 +62,13 @@ TRACE_EVENT(cxl_aer_uncorrectable_error,
> >   		 */
> >   		memcpy(__entry->header_log, hl, CXL_HEADERLOG_SIZE);
> >   	),
> > -	TP_printk("%s: status: '%s' first_error: '%s'",
> > +	TP_printk("%s: status: '%s' first_error: '%s' header_log: %s",
> >   		  __get_str(dev_name),
> >   		  show_uc_errs(__entry->status),
> > -		  show_uc_errs(__entry->first_error)
> > +		  show_uc_errs(__entry->first_error),
> > +		__print_hex_dump("", DUMP_PREFIX_OFFSET, 32, 4,
> > +				(char *)__entry->header_log,
> > +				CXL_HEADERLOG_SIZE_U32, false)
> >   	)
> >   );
> >