printk or pr_<level>?

printk or pr_<level>?

[Raphael Silva]

Hello guys,

1)
If I use printk(KERN_<LEVEL>...) the checkpatch warns me:
WARNING: Prefer [subsystem eg: netdev]_dbg([subsystem]dev, ... then 
dev_dbg(dev, ... then pr_debug(...  to printk(KERN_DEBUG ...

So, pr_devel() is the correct way to print a debug level msg?

2)
if pr_<level> is the correct way, what about KERN_DEFAULT ?

If I don't put the kern_level (printk("Hello");)
WARNING: printk() should include KERN_ facility level

if I put KERN_DEFAULT:
WARNING: Prefer [subsystem eg: netdev]_default([subsystem]dev, ... then 
dev_default(dev, ... then pr_default(...  to printk(KERN_DEFAULT ...

But for KERN_DEFAULT, there isn't a macro pr_<level> like pr_devel().

Can anyone show me the correct way?

tks

printk or pr_<level>?

[Kristofer Hallin]

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.

2. Use pr_debug.

On Wed, Jul 23, 2014 at 8:16 PM, Raphael Silva
<raphaelcampos.rp@gmail.com> wrote:
> Hello guys,
>
> 1)
> If I use printk(KERN_<LEVEL>...) the checkpatch warns me:
> WARNING: Prefer [subsystem eg: netdev]_dbg([subsystem]dev, ... then
> dev_dbg(dev, ... then pr_debug(...  to printk(KERN_DEBUG ...
>
> So, pr_devel() is the correct way to print a debug level msg?
>
> 2)
> if pr_<level> is the correct way, what about KERN_DEFAULT ?
>
> If I don't put the kern_level (printk("Hello");)
> WARNING: printk() should include KERN_ facility level
>
> if I put KERN_DEFAULT:
> WARNING: Prefer [subsystem eg: netdev]_default([subsystem]dev, ... then
> dev_default(dev, ... then pr_default(...  to printk(KERN_DEFAULT ...
>
> But for KERN_DEFAULT, there isn't a macro pr_<level> like pr_devel().
>
> Can anyone show me the correct way?
>
> tks
>
>
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

printk or pr_<level>?

[Fernando Apesteguía]

On Wed, Jul 23, 2014 at 8:34 PM, Kristofer Hallin <
kristofer.hallin@gmail.com> 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.
>

By default, pr_debug is an empty macro unless you add -DDEBUG to CFLAGS. So
in addition to what Kristofer said, be sure you compile your module/kernel
with that flag enabled.

Cheers.


>
> 2. Use pr_debug.
>
> On Wed, Jul 23, 2014 at 8:16 PM, Raphael Silva
> <raphaelcampos.rp@gmail.com> wrote:
> > Hello guys,
> >
> > 1)
> > If I use printk(KERN_<LEVEL>...) the checkpatch warns me:
> > WARNING: Prefer [subsystem eg: netdev]_dbg([subsystem]dev, ... then
> > dev_dbg(dev, ... then pr_debug(...  to printk(KERN_DEBUG ...
> >
> > So, pr_devel() is the correct way to print a debug level msg?
> >
> > 2)
> > if pr_<level> is the correct way, what about KERN_DEFAULT ?
> >
> > If I don't put the kern_level (printk("Hello");)
> > WARNING: printk() should include KERN_ facility level
> >
> > if I put KERN_DEFAULT:
> > WARNING: Prefer [subsystem eg: netdev]_default([subsystem]dev, ... then
> > dev_default(dev, ... then pr_default(...  to printk(KERN_DEFAULT ...
> >
> > But for KERN_DEFAULT, there isn't a macro pr_<level> like pr_devel().
> >
> > Can anyone show me the correct way?
> >
> > tks
> >
> >
> >
> >
> > _______________________________________________
> > Kernelnewbies mailing list
> > Kernelnewbies at kernelnewbies.org
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
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printk or pr_<level>?

[Kristofer Hallin]

Yes.

https://www.kernel.org/doc/local/pr_debug.txt

On Wed, Jul 23, 2014 at 8:39 PM, Fernando Apestegu?a
<fernando.apesteguia@gmail.com> wrote:
>
>
>
> On Wed, Jul 23, 2014 at 8:34 PM, Kristofer Hallin
> <kristofer.hallin@gmail.com> 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.
>
>
> By default, pr_debug is an empty macro unless you add -DDEBUG to CFLAGS. So
> in addition to what Kristofer said, be sure you compile your module/kernel
> with that flag enabled.
>
> Cheers.
>
>>
>>
>> 2. Use pr_debug.
>>
>> On Wed, Jul 23, 2014 at 8:16 PM, Raphael Silva
>> <raphaelcampos.rp@gmail.com> wrote:
>> > Hello guys,
>> >
>> > 1)
>> > If I use printk(KERN_<LEVEL>...) the checkpatch warns me:
>> > WARNING: Prefer [subsystem eg: netdev]_dbg([subsystem]dev, ... then
>> > dev_dbg(dev, ... then pr_debug(...  to printk(KERN_DEBUG ...
>> >
>> > So, pr_devel() is the correct way to print a debug level msg?
>> >
>> > 2)
>> > if pr_<level> is the correct way, what about KERN_DEFAULT ?
>> >
>> > If I don't put the kern_level (printk("Hello");)
>> > WARNING: printk() should include KERN_ facility level
>> >
>> > if I put KERN_DEFAULT:
>> > WARNING: Prefer [subsystem eg: netdev]_default([subsystem]dev, ... then
>> > dev_default(dev, ... then pr_default(...  to printk(KERN_DEFAULT ...
>> >
>> > But for KERN_DEFAULT, there isn't a macro pr_<level> like pr_devel().
>> >
>> > Can anyone show me the correct way?
>> >
>> > tks
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > Kernelnewbies mailing list
>> > Kernelnewbies at kernelnewbies.org
>> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>

printk or pr_<level>?

[Greg KH]

On Wed, Jul 23, 2014 at 08:40:04PM +0200, Kristofer Hallin wrote:
> Yes.
> 
> https://www.kernel.org/doc/local/pr_debug.txt

No, that isn't true if CONFIG_DYNAMIC_DEBUG is enabled, which you really
should enable all the time.  If that option is enabled, then you can
enable the debugging messages after the code is loaded, or from the
module load command line, through that interface, which is much more
useful than just "enable/disable at build time".

Hope this helps,

greg k-h

printk or pr_<level>?

[Arlie Stephens]

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?  

No snark intended here, just confused curiousity. 

It would seem to me that one common method of printing would be better
than a different one for each subsystem, each needing to be
individually remembered, and potentially having its own
bugs\b\b\b\bquirks. 

The kernel is complex enough, without adding uneeded extra.



And yes, this begs the question of why you want to print messages
from the kernel, whether they ought to be conditional and/or rate
limited, etc. etc.   Clearly the recommendation of pr_debug() suggests
someone thinks they should be at least somewhat conditional...

> 
> 2. Use pr_debug.
> 
> On Wed, Jul 23, 2014 at 8:16 PM, Raphael Silva
> <raphaelcampos.rp@gmail.com> wrote:
> > Hello guys,
> >
> > 1)
> > If I use printk(KERN_<LEVEL>...) the checkpatch warns me:
> > WARNING: Prefer [subsystem eg: netdev]_dbg([subsystem]dev, ... then
> > dev_dbg(dev, ... then pr_debug(...  to printk(KERN_DEBUG ...
> >
> > So, pr_devel() is the correct way to print a debug level msg?
> >
> > 2)
> > if pr_<level> is the correct way, what about KERN_DEFAULT ?
> >
> > If I don't put the kern_level (printk("Hello");)
> > WARNING: printk() should include KERN_ facility level
> >
> > if I put KERN_DEFAULT:
> > WARNING: Prefer [subsystem eg: netdev]_default([subsystem]dev, ... then
> > dev_default(dev, ... then pr_default(...  to printk(KERN_DEFAULT ...
> >
> > But for KERN_DEFAULT, there isn't a macro pr_<level> like pr_devel().
> >
> > Can anyone show me the correct way?
> >
> > tks

-- 
Arlie

(Arlie Stephens					arlie at worldash.org)

printk or pr_<level>?

[Greg KH]

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?  
> 
> No snark intended here, just confused curiousity. 
> 
> It would seem to me that one common method of printing would be better
> than a different one for each subsystem, each needing to be
> individually remembered, and potentially having its own
> bugs\b\b\b\bquirks. 
> 
> The kernel is complex enough, without adding uneeded extra.

Yes it is, but it's "layered", in that normally you only deal with one
specific layer.  Very rarely are you touching code everywhere in the
kernel.

> And yes, this begs the question of why you want to print messages
> from the kernel, whether they ought to be conditional and/or rate
> limited, etc. etc.   Clearly the recommendation of pr_debug() suggests
> someone thinks they should be at least somewhat conditional...

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?

greg k-h

printk or pr_<level>?

[Greg KH]

On Wed, Jul 23, 2014 at 04:00:04PM -0700, 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?  
> > 
> > No snark intended here, just confused curiousity. 
> > 
> > It would seem to me that one common method of printing would be better
> > than a different one for each subsystem, each needing to be
> > individually remembered, and potentially having its own
> > bugs\b\b\b\bquirks. 
> > 
> > The kernel is complex enough, without adding uneeded extra.
> 
> Yes it is, but it's "layered", in that normally you only deal with one
> specific layer.  Very rarely are you touching code everywhere in the
> kernel.
> 
> > And yes, this begs the question of why you want to print messages
> > from the kernel, whether they ought to be conditional and/or rate
> > limited, etc. etc.   Clearly the recommendation of pr_debug() suggests
> > someone thinks they should be at least somewhat conditional...
> 
> 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.

Oh, and never use a "raw" printk() call anymore, someone will just come
along behind you and fix it up to use the "proper" macro, if you happen
to get it accepted into the kernel tree.

greg k-h

printk or pr_<level>?

[Raphael Silva]

Hi guys,

Thanks for the help, I learned a lot of new things.

On 7/23/14, 8:00 PM, Greg KH wrote:
> On Wed, Jul 23, 2014 at 04:00:04PM -0700, 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?
>>>
>>> No snark intended here, just confused curiousity.
>>>
>>> It would seem to me that one common method of printing would be better
>>> than a different one for each subsystem, each needing to be
>>> individually remembered, and potentially having its own
>>> bugs\b\b\b\bquirks.
>>>
>>> The kernel is complex enough, without adding uneeded extra.
>> Yes it is, but it's "layered", in that normally you only deal with one
>> specific layer.  Very rarely are you touching code everywhere in the
>> kernel.
>>
>>> And yes, this begs the question of why you want to print messages
>>> from the kernel, whether they ought to be conditional and/or rate
>>> limited, etc. etc.   Clearly the recommendation of pr_debug() suggests
>>> someone thinks they should be at least somewhat conditional...
>> 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.
> Oh, and never use a "raw" printk() call anymore, someone will just come
> along behind you and fix it up to use the "proper" macro, if you happen
> to get it accepted into the kernel tree.
>
> greg k-h

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)