linux-kernel - Re: [PATCH v3 3/4] driver core: add dev_print_hex

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Message-ID: <20190408120736.GN9224@smile.fi.intel.com>
Date:   Mon, 8 Apr 2019 15:07:36 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     "Life is hard, and then you die" <ronald@...ovation.ch>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Henrik Rydberg <rydberg@...math.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Lukas Wunner <lukas@...ner.de>,
        Federico Lorenzi <federico@...velground.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/4] driver core: add dev_print_hex_dump() logging
 function.

On Sat, Apr 06, 2019 at 06:46:13PM -0700, Life is hard, and then you die wrote:
> > On Mon, Apr 01, 2019 at 07:47:14PM -0700, Life is hard, and then you die wrote:
> > > On Thu, Mar 28, 2019 at 12:29:52PM +0100, Greg Kroah-Hartman wrote:
> > > > On Thu, Mar 28, 2019 at 03:27:55AM -0700, Life is hard, and then you die wrote:
> > > > > On Thu, Mar 28, 2019 at 06:29:17AM +0100, Greg Kroah-Hartman wrote:
> > > > > > On Wed, Mar 27, 2019 at 05:28:17PM -0700, Life is hard, and then you die wrote:
> > > > > > > On Wed, Mar 27, 2019 at 11:37:57AM +0900, Greg Kroah-Hartman wrote:
> > > > > > > > On Tue, Mar 26, 2019 at 06:48:06PM -0700, Ronald Tschalär wrote:

> > You can do dynamic debugging from the kernel command line, if your code
> > is built into the kernel (but why would a tiny driver under testing like
> > this, not be built into the kernel?) what specifically did not work for you?
> 
> This may be part of our disconnect: there's almost no reason (and
> several downsides) to building it into the kernel instead of as a
> module:
> 
> - When developing, being able to just reload the module instead of
>   rebooting is just so much faster and more convenient.

modprobe -r foo
modprobe foo dyndbg=...

Not an argument.

> - For other users, having them build the driver as a dkms managed
>   module is also by far the simplest and least error-prone approach -
>   explaning to users how to rebuild their kernel (something most of
>   them have never done) takes a bunch of time and effort on both
>   sides for essentially no gain.
> 
> - Once the driver is part of the regular kernel, practically all
>   distro's will build it as a module (at least I'm fairly certain
>   about this).

Above seems a sub-items to the first one. So, reloading module with dyndbg
parameter is quite flexible. What else?

> > You can enable/disable logging per-function, which is what you want,
> > right?
> 
> Yes'ish: the problem is that if they are just part of regular
> functions, A) the chances are higher that the function may get renamed
> and hence any existing debug instructions broken, and B) this doesn't
> work if there are multiple debug statements in a function. Hence my
> assertion that for this work well (and yes, it can work well) you
> basically need to create a separate function for each debug statement
> (which that contains just that debug statement) (a sort of stable
> labelling of each debug statement).

I guess you tried and have an examples?

-- 
With Best Regards,
Andy Shevchenko