printk or pr_<level>?

[Arlie Stephens]

Thank-you Greg

On Jul 23 2014, Greg KH wrote:
> 
> On Wed, Jul 23, 2014 at 02:45:05PM -0700, Arlie Stephens wrote:
> > On Jul 23 2014, Kristofer Hallin wrote:
> > 
> > > 1. No. Depending on what subsystem your are printing logs from you
> > > should use different functions for logging. In the networking
> > > subsystem netdev_dbg is suitable and so on. Otherwise pr_debug will
> > > always work and is always preferred over printk.
> > 
> > Why?  

[snip]

> Ok, here's the rule in one sentance:
> 	Be as _descriptive_ as you can with the device that is emitting
> 	the message.
> 
> So what does that mean in reality?
> 
> Use the subsystem's logging macros for your messages.  If you are not in
> a subsystem, then fall back to the "default" pr_* messages.
> 
> So, if you are a network driver, then use netdev_dbg().  Other
> subsystems of "class" devices have their own form of logging macros, and
> they should be easy to find.
> 
> If you aren't in a class driver, but are a driver, then use dev_dbg(),
> because you do have a device pointer accessable to you (if you don't,
> either you are in your module init or exit function, and you shouldn't
> be printing messages then anyway.)
> 
> If you are not in a driver, and you do not have _any_ 'struct device'
> accessable to you, reconsider if you really want to be printing
> anything, as the use of it to a user is going to be really low.  But if
> you have to, then fall back to the pr_* functions, as those tie into the
> dynamic debugging logic of the kernel, and provide a format that is
> unified that userspace tools can use to hopefully search and find things
> properly.
> 
> So there is a method to this madness, and it is pretty simple if you
> think about it this way.
> 
> Does that help out?

Yes it does. Thank you. 

And I think I see why I needed help - I'm mentally a "core kernel"
person, whatever I may happen to be working on at the moment ;-) 

So my archetypal kernel message would be something like the ones
generated by BUG_ON() ;-)  

> 
> greg k-h

-- 
Arlie

(Arlie Stephens					arlie at worldash.org)