Re: [RFC Patch] Trace - Samples

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

* Randy Dunlap (randy.dunlap@oracle.com) wrote:
> On Tue, 25 Sep 2007 13:35:47 -0700 David J. Wilder wrote:
> 
> > This patch Moves the trace example into the new samples/ infrastructure
> > 
> > Requires: [patch 3/5] Add samples subdir  (http://lkml.org/lkml/2007/9/25/157)
> > and create samples/Makefile or apply: 
> > [patch 4/5] Linux Kernel Markers - Samples (http://lkml.org/lkml/2007/9/25/166) 
> > 
> > Signed-off-by: David Wilder <dwilder@us.ibm.com>
> 
> Looks good.  Thanks.
> 
> Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
> 
> Andrew, Mathieu is making changes to patch 3/5 referenced above.
> When that is done, do you need a resend of all of these samples/
> patches or do you have them straight?
> 
> Basically we have:
> a.  add samples/ infrastructure  (new coming from Mathieu)
> b.  add markers to samples/  (Mathieu)
Mine is correct as is. (with the new samples infrastructure)

Mathieu

> c.  add trace/ to samples/  (this patch from David)
> d.  add kprobes/ to samples  (move some from Documentation)
> 
> 
> > ---
> >  samples/Kbuild             |    2 -
> >  samples/Kconfig            |    5 ++
> >  samples/Makefile           |    3 +
> >  samples/trace/Makefile     |    4 +
> >  samples/trace/fork_trace.c |  132 ++++++++++++++++++++++++++++++++++++++++++++
> >  5 files changed, 144 insertions(+), 2 deletions(-)
> > 
> > diff --git a/samples/Kbuild b/samples/Kbuild
> > deleted file mode 100644
> > index 8af00e9..0000000
> > --- a/samples/Kbuild
> > +++ /dev/null
> > @@ -1,2 +0,0 @@
> > -# Makefile for Linux samples code
> > -
> > diff --git a/samples/Kconfig b/samples/Kconfig
> > index b46b4cf..e5c6963 100644
> > --- a/samples/Kconfig
> > +++ b/samples/Kconfig
> > @@ -7,5 +7,10 @@ menuconfig SAMPLES
> >  
> >  if SAMPLES
> >  
> > +config SAMPLE_TRACE
> > +	tristate "Build trace example -- loadable modules only"
> > +	depends on TRACE && m
> > +	help
> > +	  This builds a trace example module.
> >  
> >  endif # SAMPLES
> > diff --git a/samples/Makefile b/samples/Makefile
> > new file mode 100644
> > index 0000000..07a32e6
> > --- /dev/null
> > +++ b/samples/Makefile
> > @@ -0,0 +1,3 @@
> > +# Makefile for Linux samples code
> > +
> > +obj-$(CONFIG_SAMPLES) += trace/
> > diff --git a/samples/trace/Makefile b/samples/trace/Makefile
> > new file mode 100644
> > index 0000000..a2da8af
> > --- /dev/null
> > +++ b/samples/trace/Makefile
> > @@ -0,0 +1,4 @@
> > +# builds the trace example kernel modules;
> > +# then to use (as root):  insmod <fork_trace.ko>
> > +
> > +obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
> > diff --git a/samples/trace/fork_trace.c b/samples/trace/fork_trace.c
> > new file mode 100644
> > index 0000000..71c04c7
> > --- /dev/null
> > +++ b/samples/trace/fork_trace.c
> > @@ -0,0 +1,132 @@
> > +/*
> > + * An example of using trace in a kprobes module
> > + *
> > + * Copyright (C) 2007 IBM Inc.
> > + *
> > + * David Wilder <dwilder@us.ibm.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program; if not, write to the Free Software
> > + * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
> > + *
> > + * -------
> > + * This module creates a trace channel and places a kprobe
> > + * on the function do_fork(). The value of current->pid is written to
> > + * the trace channel each time the kprobe is hit..
> > + *
> > + * How to run the example:
> > + * $ mount -t debugfs /debug
> > + * $ insmod fork_trace.ko
> > + *
> > + * To view the data produced by the module:
> > + * $ cat /debug/trace_example/do_fork/trace0
> > + *
> > + */
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/kprobes.h>
> > +#include <linux/trace.h>
> > +
> > +#define USE_GLOBAL_BUFFERS 1
> > +#define USE_FLIGHT 1
> > +
> > +#define PROBE_POINT "do_fork"
> > +
> > +static struct kprobe kp;
> > +static struct trace_info *kprobes_trace;
> > +
> > +#ifdef USE_GLOBAL_BUFFERS
> > +static DEFINE_SPINLOCK(trace_lock);
> > +#endif
> > +
> > +/*
> > + * Send formatted trace data to trace channel.
> > + * @note Preemption must be disabled to use this.
> > + */
> > +static void trace_printf(struct trace_info *trace, const char *format, ...)
> > +{
> > +	va_list ap, aq;
> > +	char *record;
> > +	unsigned long flags;
> > +	int len;
> > +
> > +	if (!trace)
> > +		return;
> > +
> > +#ifdef USE_GLOBAL_BUFFERS
> > +	spin_lock_irqsave(&trace_lock, flags);
> > +#endif
> > +	if (trace_running(trace)) {
> > +		va_start(ap, format);
> > +		va_copy(aq, ap);
> > +		len = vsnprintf(NULL, 0, format, aq);
> > +		va_end(aq);
> > +		record = relay_reserve(trace->rchan, ++len);
> > +		if (record)
> > +			vsnprintf(record, len, format, ap);
> > +		va_end(ap);
> > +	}
> > +#ifdef USE_GLOBAL_BUFFERS
> > +	spin_unlock_irqrestore(&trace_lock, flags);
> > +#endif
> > +}
> > +
> > +static int handler_pre(struct kprobe *p, struct pt_regs *regs)
> > +{
> > +	rcu_read_lock();
> > +	trace_printf(kprobes_trace, "%d\n", current->pid);
> > +	rcu_read_unlock();
> > +	return 0;
> > +}
> > +
> > +int init_module(void)
> > +{
> > +	int ret;
> > +	u32 flags = 0;
> > +
> > +#ifdef USE_GLOBAL_BUFFERS
> > +	flags |= TRACE_GLOBAL_CHANNEL;
> > +#endif
> > +
> > +#ifdef USE_FLIGHT
> > +	flags |= TRACE_FLIGHT_CHANNEL;
> > +#endif
> > +
> > +	/* setup the trace */
> > +	kprobes_trace = trace_setup("trace_example", PROBE_POINT,
> > +				     1024, 8, flags);
> > +	if (IS_ERR(kprobes_trace))
> > +		return PTR_ERR(kprobes_trace);
> > +
> > +	trace_start(kprobes_trace);
> > +
> > +	/* setup the kprobe */
> > +	kp.pre_handler = handler_pre;
> > +	kp.post_handler = NULL;
> > +	kp.fault_handler = NULL;
> > +	kp.symbol_name = PROBE_POINT;
> > +	ret = register_kprobe(&kp);
> > +	if (ret) {
> > +		printk(KERN_ERR "fork_trace: register_kprobe failed\n");
> > +		return ret;
> > +	}
> > +	return 0;
> > +}
> > +
> > +void cleanup_module(void)
> > +{
> > +	unregister_kprobe(&kp);
> > +	trace_stop(kprobes_trace);
> > +	trace_cleanup(kprobes_trace);
> > +}
> > +MODULE_LICENSE("GPL");
> > 
> > 
> > -
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> > 
> 
> 
> ---
> ~Randy
> Phaedrus says that Quality is about caring.

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68