linux-kernel - Re: [patch 3/4] make pr_debug() dynamic

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Date:	Fri, 8 Feb 2008 10:49:29 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch 3/4] make pr_debug() dynamic - sysctl support

On Thu, Feb 07, 2008 at 04:10:52PM -0800, Stephen Hemminger wrote:
> Jason Baron <jbaron@...hat.com> wrote:
> 
> > 
> > -add /proc/sys/debug/pr_debug, to toggle pr_debug() on/off
> > 
> > Signed-off-by: Jason Baron <jbaron@...hat.com>
> > ---
> > 
> >  kernel/sysctl.c |   41 +++++++++++++++++++++++++++++++++++++++++
> >  1 files changed, 41 insertions(+), 0 deletions(-)
> > 
> > 
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index 7cb1ac3..73508d7 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -155,6 +155,11 @@ static int proc_do_cad_pid(struct ctl_table *table, int write, struct file *filp
> >  static int proc_dointvec_taint(struct ctl_table *table, int write, struct file *filp,
> >  			       void __user *buffer, size_t *lenp, loff_t *ppos);
> >  #endif
> > +#ifdef CONFIG_PR_DEBUG_DYNAMIC
> > +static int proc_pr_debug_handler(struct ctl_table *table, int write,
> > +				 struct file *filp, void __user *buffer,
> > +				 size_t *lenp, loff_t *ppos);
> > +#endif
> >  
> >  static struct ctl_table root_table[];
> >  static struct ctl_table_root sysctl_table_root;
> > @@ -1312,6 +1317,16 @@ static struct ctl_table debug_table[] = {
> >  		.proc_handler	= proc_dointvec
> >  	},
> >  #endif
> > +#ifdef CONFIG_PR_DEBUG_DYNAMIC
> > +	{
> > +		.ctl_name       = CTL_UNNUMBERED,
> > +		.procname       = "pr_debug",
> > +		.data           = NULL,
> > +		.maxlen         = sizeof(int),
> > +		.mode           = 0644,
> > +		.proc_handler   = &proc_pr_debug_handler
> > +	},
> > +#endif
> >  	{ .ctl_name = 0 }
> >  };
> >  
> > @@ -2499,6 +2514,32 @@ static int proc_do_cad_pid(struct ctl_table *table, int write, struct file *filp
> >  	return 0;
> >  }
> >  
> > +#ifdef CONFIG_PR_DEBUG_DYNAMIC
> > +
> > +static int proc_pr_debug_handler(struct ctl_table *table, int write,
> > +				 struct file *filp, void __user *buffer,
> > +				 size_t *lenp, loff_t *ppos)
> > +{
> > +	int tmp, r;
> > +
> > +	if (!write)
> > +		tmp = imv_read(pr_debug_on);
> > +	r = __do_proc_dointvec(&tmp, table, write, filp, buffer,
> > +				lenp, ppos, NULL, NULL);
> > +	if (r)
> > +		return r;
> > +
> > +	if (write) {
> > +		if (tmp)
> > +			imv_set(pr_debug_on, 1);
> > +		else
> > +			imv_set(pr_debug_on, 0);
> > +	}
> > +	return 0;
> > +}
> > +
> > +#endif
> > +
> >  #else /* CONFIG_PROC_FS */
> >  
> >  int proc_dostring(struct ctl_table *table, int write, struct file *filp,
> 
> Please no, there are many pr_debug calls that are only intended for debugging that
> particular subsystem, not a global enable/disable. It also adds to kernel bloat.
> 

Yes, but you are going to have to re-compile your kernel to get at them...the
ability to turn on/off pr_debug() calls, at runtime, seems like a powerful
runtime diagnostic tool...the CONFIG_PR_DEBUG_DYNAMIC can default to 'n',
instead of being automactically set as I've proposed. In terms of bloat, the
vmlinux file goes from 53649330 to 53985478, < %1 increase.

thanks,

-Jason

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