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

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Message-ID: <SN1PR0201MB18700901B51BE24AE75EC18D81140@SN1PR0201MB1870.namprd02.prod.outlook.com>
Date:	Wed, 17 Aug 2016 01:19:39 +0000
From:	Bart Van Assche <Bart.VanAssche@...disk.com>
To:	Joe Perches <joe@...ches.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 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. Many drivers define their own logging macros and export a bitmask
>> that allows to enable and disable logging messages per category. These
>> bitmask control mechanisms are annoying because figuring out what bit
>> controls which message category requires a search through the driver
>> source code. I'd like to see all these custom logging macros disappear
>> and being replaced by a single mechanism. The "dynamic debug" mechanism
>> e.g. is in my opinion much easier to use than the different custom
>> logging mechanisms.
>
> Dynamic debug doesn't have a bitmask function and
> still requires looking through the code for lines
> and format strings.
>
> I think you are looking for a system wide equivalent
> for the ethtool/netif_<level> mechanism.
>
> Nothing like that exists currently.
>
> Some code uses a bitmask/and, other code uses a
> level/comparison.
>
> Care to propose something?

Hello Joe,

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.

Anyway, this is just a proposal. Anyone is welcome to come up with an 
alternative proposal.

Bart.