Re: [PATCH v3 1/7] Documentation: dynamic-debug: Add description of level bitmask

From: Joe Perches <joe@perches.com>
To: Edward Cree <ecree@solarflare.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Stanimir Varbanov <stanimir.varbanov@linaro.org>
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-acpi@vger.kernel.org,
	netdev@vger.kernel.org, Jason Baron <jbaron@akamai.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Jim Cromie <jim.cromie@gmail.com>
Subject: Re: [PATCH v3 1/7] Documentation: dynamic-debug: Add description of level bitmask
Date: Tue, 09 Jun 2020 10:56:19 -0700	[thread overview]
Message-ID: <2b291c34e10b3b3d9d6e01f8201ec0942e39575f.camel@perches.com> (raw)
In-Reply-To: <727b31a0-543b-3dc5-aa91-0d78dc77df9c@solarflare.com>

On Tue, 2020-06-09 at 18:42 +0100, Edward Cree wrote:
> On 09/06/2020 17:58, Joe Perches wrote:
> > On Tue, 2020-06-09 at 13:16 +0200, Greg Kroah-Hartman wrote:
> > > What is wrong with the existing control of dynamic
> > > debug messages that you want to add another type of arbitrary grouping
> > > to it? 
> > There is no existing grouping mechanism.
> > 
> > Many drivers and some subsystems used an internal one
> > before dynamic debug.
> > 
> > $ git grep "MODULE_PARM.*\bdebug\b"|wc -l
> > 501
> > 
> > This is an attempt to unify those homebrew mechanisms.
> In network drivers, this is probablyusing the existing groupings
>  defined by netif_level() - see NETIF_MSG_DRV and friends.  Note
>  that those groups are orthogonal to the level, i.e. they control
>  netif_err() etc. as well, not just debug messages.

These are _not_ netif_<level> control flags.  Some are though.

For instance:

$ git grep "MODULE_PARM.*\bdebug\b" drivers/net | head -10
drivers/net/ethernet/3com/3c509.c:MODULE_PARM_DESC(debug, "debug level (0-6)");
drivers/net/ethernet/3com/3c515.c:MODULE_PARM_DESC(debug, "3c515 debug level (0-6)");
drivers/net/ethernet/3com/3c59x.c:MODULE_PARM_DESC(debug, "3c59x debug level (0-6)");
drivers/net/ethernet/adaptec/starfire.c:MODULE_PARM_DESC(debug, "Debug level (0-6)");
drivers/net/ethernet/allwinner/sun4i-emac.c:MODULE_PARM_DESC(debug, "debug message flags");
drivers/net/ethernet/altera/altera_tse_main.c:MODULE_PARM_DESC(debug, "Message Level (-1: default, 0: no output, 16: all)");
drivers/net/ethernet/amazon/ena/ena_netdev.c:MODULE_PARM_DESC(debug, "Debug level (0=none,...,16=all)");
drivers/net/ethernet/amd/atarilance.c:MODULE_PARM_DESC(lance_debug, "atarilance debug level (0-3)");
drivers/net/ethernet/amd/lance.c:MODULE_PARM_DESC(lance_debug, "LANCE/PCnet debug level (0-7)");
drivers/net/ethernet/amd/pcnet32.c:MODULE_PARM_DESC(debug, DRV_NAME " debug level");

These are all level/class output controls.

> Certainly in the case of sfc, and I'd imagine for many other net
>  drivers too, the 'debug' modparam is setting the default for
>  net_dev->msg_enable, which can be changed after probe with
>  ethtool.

True.

> It doesn't look like the proposed mechanism subsumes that (we have
>  rather more than 5 groups, and it's not clear how you'd connect
>  it to the existing msg_enable (which uapi must be maintained); if
>  you don't have a way to do this, better exclude drivers/net/ from
>  your grep|wc because you won't be unifying those - in my tree
>  that's 119 hits.

Likely not.

I agree it'd be useful to attach the modparam control flag
to the dynamic debug use somehow.

cheers, Joe