linux-kernel - Re: [patch 1/3] kmsg: Kernel message catalog macros.

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Date:	Sun, 10 Aug 2008 02:08:22 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Greg KH <gregkh@...e.de>, Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	lf_kernel_messages@...ts.linux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Holzheu <holzheu@...ibm.com>,
	Gerrit Huizenga <gh@...ibm.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Jan Kara <jack@...e.cz>, Pavel Machek <pavel@....cz>,
	Sam Ravnborg <sam@...nborg.org>,
	Jochen Voß <jochen.voss@...glemail.com>,
	Kunai Takashi <kunai@...ux-foundation.jp>,
	Tim Bird <tim.bird@...sony.com>
Subject: Re: [patch 1/3] kmsg: Kernel message catalog macros.

On Thu, 2008-08-07 at 08:59 -0700, Joe Perches wrote:
> On Thu, 2008-08-07 at 10:31 +0200, Martin Schwidefsky wrote:
> > On Wed, 2008-08-06 at 13:07 -0700, Greg KH wrote:
> > > No, I mean use dev_printk() as the base for your logging macro.  Add
> > > your message tag as the first field after the dev_printk() information.
> > Hmm, you are proposing to introduce a second format for the kmsg
> > messages to avoid the need for some more printk wrapper macros. To me it
> > seems that this has two problems:
> > 1) The message tag is for the user of the system. If it does not have a
> > fixed position it gets confusing.
> 
> I think the message tag today is not useful for a user.
> 
> It seems a barely useful maintainer value.
> 
> Perhaps the message tag allows for run-time language
> translation and maybe a bit better selective logging.

Aehhm, .. what ? If a user does not understand a message directly
how can he NOT be interested in the kmsg tag? As a random example
consider the situation when the user gets the message

	monwriter.1: Writing monitor data failed with rc=5

Usually a user will go "Huh?" except if he is a z/VM expert. Looking
at the source code won't help too much either:

static int monwrite_diag(struct monwrite_hdr *myhdr, char *buffer, int fcn)
{
        struct appldata_product_id id;
        int rc;

        strcpy(id.prod_nr, "LNXAPPL");
        id.prod_fn = myhdr->applid;
        id.record_nr = myhdr->record_num;
        id.version_nr = myhdr->version;
        id.release_nr = myhdr->release;
        id.mod_lvl = myhdr->mod_level;
        rc = appldata_asm(&id, fcn, (void *) buffer, myhdr->datalen);
        if (rc <= 0)
                return rc;
        if (rc == 5)
                return -EPERM;
        kmsg_err(1,"Writing monitor data failed with rc=%i\n", rc);
        return -EINVAL;
}

What the user should do is to cut-copy-paste the kmsg tag monwriter.1
and pass it to man:

# man monwriter.1

What the user will then get is the man page that has been generated
from the kmsg comment with "make D=2":

--- snip
monwriter.1(9)                                                  monwriter.1(9)

Message
       monwriter.1: Writing monitor data failed with rc=%i

Severity
       Error

Parameters
       @1: return code

Description
       The  monitor  stream  application  device driver used the z/VM diagnose
       call DIAG X'DC' to start writing monitor data. z/VM returned  an  error
       and  the  monitor data cannot be written. If the return code is 5, your
       z/VM guest virtual machine is not authorized to write monitor data.

User action
       If the return code is 5, ensure that your z/VM guest virtual  machine's
       entry in the z/VM directory includes the OPTION APPLMON statement.  For
       other return codes see the section about DIAGNOSE Code X'DC'  in  "z/VM
       CP Programming Services".

LINUX                           Linux Messages                  monwriter.1(9)
--- snip

Now the user actually gets help: the description tells him that rc=5
probably is because the virtual machine is not authorized. The key to
be able to get to the description associated to a message is the kmsg
tag.

By the way the kmsg comment for monwriter.1 is as follows just in case
you are wondering:

/*?
 * Tag: monwriter.1
 * Text: "Writing monitor data failed with rc=%i"
 * Severity: Error
 * Parameter:
 *   @1: return code
 * Description:
 * The monitor stream application device driver used the z/VM diagnose call
 * DIAG X'DC' to start writing monitor data. z/VM returned an error and the
 * monitor data cannot be written. If the return code is 5, your z/VM guest
 * virtual machine is not authorized to write monitor data.
 * User action:
 * If the return code is 5, ensure that your z/VM guest virtual machine's
 * entry in the z/VM directory includes the OPTION APPLMON statement.
 * For other return codes see the section about DIAGNOSE Code X'DC'
 * in "z/VM CP Programming Services".
 */

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.

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