linux-kernel - Re: [PATCH 0/2] be2iscsi: Logging neatening

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Date:	Tue, 16 Aug 2016 20:39:02 -0700
From:	Joe Perches <joe@...ches.com>
To:	Bart Van Assche <Bart.VanAssche@...disk.com>,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Cc:	Jayamohan Kallickal <jayamohan.kallickal@...gotech.com>,
	Ketan Mukadam <ketan.mukadam@...gotech.com>,
	John Soni Jose <sony.john@...gotech.com>,
	"James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] be2iscsi: Logging neatening

On Wed, 2016-08-17 at 01:19 +0000, Bart Van Assche wrote:
> On 08/14/16 10:29, Joe Perches wrote:
> > On Sun, 2016-08-14 at 17:09 +0000, Bart Van Assche wrote:
> > > My primary concern is how to enable and disable log messages from user
> > > space.
[]
> > I think you are looking for a system wide equivalent
> > for the ethtool/netif_ mechanism.
> > 
> > Nothing like that exists currently.
> > 
> > Some code uses a bitmask/and, other code uses a
> > level/comparison.
[]
> As far as I can see all that the ethtool msglevel API implements is a 
> mechanism to query and set the log level from user space. What various 
> SCSI drivers implement is not a log level but a log mask mechanism. How 
> about the following approach to associate a name with each bit in a log 
> mask, to export these names to user space and to make it possible to 
> enable/disable messages per log category:
> * Introduce a variant of pr_debug() that allows to specify a textual
>    representation of the log category (a short string without spaces).
> * Make the log category names available in
>    /sys/kernel/debug/dynamic_debug/...
> * Today dynamic debug allows to enable/disable log messages by
>    specifying the source file name, function name, line number, module
>    name and/or format string. My proposal is to make it also possible to
>    enable/disable log messages based on the log category name.

Many of these logging mechanisms are not just debug
facilities.

Perhaps a dynamic_debug control would be inappropriate.

There have also been various custom scsi log level
facilities like the blogic_msg for the very old
BusLogic blogic_msg.

These functions also sometimes write into some
device-specific buffer.

Perhaps the largest problem, if this is to be scsi only
rather than system wide, is finding out what and how
the various bits in a mask should be used.