lkml.org 
[lkml]   [2007]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[patch 5/6] Linux Kernel Markers - Documentation
    Here is some documentation explaining what is/how to use the Linux
    Kernel Markers.

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    ---

    Documentation/marker.txt | 253 +++++++++++++++++++++++++++++++++++++++++++++++
    1 file changed, 253 insertions(+)

    Index: linux-2.6-lttng/Documentation/marker.txt
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-2.6-lttng/Documentation/marker.txt 2007-05-29 14:08:27.000000000 -0400
    @@ -0,0 +1,253 @@
    + Using the Linux Kernel Markers
    +
    + Mathieu Desnoyers
    +
    +
    +This document introduces Linux Kernel Markers and their use. It provides
    +examples of how to insert markers in the kernel and connect probe functions to
    +them and provides some examples of probe functions.
    +
    +
    +* Purpose of markers
    +
    +A marker placed in your code provides a hook to call a function (probe) that
    +you can provide at runtime. A marker can be "on" (a probe is connected to it)
    +or "off" (no probe is attached). When a marker is "off" it has no
    +effect. When a marker is "on", the function you provide is called each
    +time the marker is executed, in the execution context of the
    +caller. When the function provided ends its execution, it returns to the
    +caller (continuing from the marker site).
    +
    +You can put markers at important locations in the code. Markers are
    +lightweight hooks that can pass an arbitrary number of parameters,
    +described in a printk-like format string, to the attached probe function.
    +
    +They can be used for tracing and performance accounting.
    +
    +
    +* Usage
    +
    +In order to use the macro trace_mark, you should include linux/marker.h.
    +
    +#include <linux/marker.h>
    +
    +Add, in your code :
    +
    +trace_mark(subsystem_event, "%d %s", someint, somestring);
    +Where :
    +- subsystem_event is an identifier unique to your event
    + - subsystem is the name of your subsystem.
    + - event is the name of the event to mark.
    +- "%d %s" is the formatted string for the serializer.
    +- someint is an integer.
    +- somestring is a char pointer.
    +
    +Connecting a function (probe) to a marker is done by providing a probe
    +(function to call) for the specific marker through marker_arm_probe(). It will
    +automatically connect the function and enable the marker site. Removing a probe
    +is done through marker_disarm_probe(). Probe removal is preempt-safe because
    +preemption is disabled around the probe call. See the "Probe example" section
    +below for a sample probe module.
    +
    +The marker mechanism supports inserting multiple instances of the same marker.
    +Markers can be put in inline functions, inlined static functions, and
    +unrolled loops.
    +
    +Note: It is safe to put markers within preempt-safe code : preempt_enable()
    +will not call the scheduler due to the tests in preempt_schedule().
    +
    +
    +* Optimization for a given architecture
    +
    +One can implement optimized markers for a given architecture by replacing
    +asm-$ARCH/marker.h.
    +
    +The CF_* flags can be used to control the type of marker. See the
    +include/linux/condcall.h header for the list of flags. They can be specified as
    +the first parameter of the _trace_mark() macro, as in the following example,
    +which is safe with respect to lockdep.c (useful for marking lockdep.c and printk
    +functions).
    +
    +_trace_mark(CF_DEFAULT | ~CF_LOCKDEP, subsystem_eventb, MARK_NOARGS);
    +
    +Another example is to specify that a specific marker must never call printk:
    +_trace_mark(CF_DEFAULT | ~CF_PRINTK, subsystem_eventc,
    + "%d %s", someint, somestring);
    +
    +Flag compatibility is checked before connecting the probe to the marker: the
    +right flags must be given to _marker_arm_probe().
    +
    +
    +* Probe example
    +
    +You can build the kernel modules, probe-example.ko and marker-example.ko,
    +using the following Makefile:
    +------------------------------ CUT -------------------------------------
    +obj-m := probe-example.o marker-example.o
    +KDIR := /lib/modules/$(shell uname -r)/build
    +PWD := $(shell pwd)
    +default:
    + $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
    +clean:
    + rm -f *.mod.c *.ko *.o
    +------------------------------ CUT -------------------------------------
    +/* probe-example.c
    + *
    + * Connects two functions to marker call sites.
    + *
    + * (C) Copyright 2007 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    + *
    + * This file is released under the GPLv2.
    + * See the file COPYING for more details.
    + */
    +
    +#include <linux/sched.h>
    +#include <linux/kernel.h>
    +#include <linux/module.h>
    +#include <linux/marker.h>
    +#include <asm/atomic.h>
    +
    +struct probe_data {
    + const char *name;
    + const char *format;
    + marker_probe_func *probe_func;
    +};
    +
    +void probe_subsystem_event(const struct __mark_marker_c *mdata,
    + const char *format, ...)
    +{
    + va_list ap;
    + /* Declare args */
    + unsigned int value;
    + const char *mystr;
    +
    + /* Assign args */
    + va_start(ap, format);
    + value = va_arg(ap, typeof(value));
    + mystr = va_arg(ap, typeof(mystr));
    +
    + /* Call printk */
    + printk("Value %u, string %s\n", value, mystr);
    +
    + /* or count, check rights, serialize data in a buffer */
    +
    + va_end(ap);
    +}
    +
    +atomic_t eventb_count = ATOMIC_INIT(0);
    +
    +void probe_subsystem_eventb(const struct __mark_marker_c *mdata,
    + const char *format, ...)
    +{
    + /* Increment counter */
    + atomic_inc(&eventb_count);
    +}
    +
    +static struct probe_data probe_array[] =
    +{
    + { .name = "subsystem_event",
    + .format = "%d %s",
    + .probe_func = probe_subsystem_event },
    + { .name = "subsystem_eventb",
    + .format = MARK_NOARGS,
    + .probe_func = probe_subsystem_eventb },
    +};
    +
    +static int __init probe_init(void)
    +{
    + int result;
    + int i;
    +
    + for (i = 0; i < ARRAY_SIZE(probe_array); i++) {
    + result = marker_arm_probe(probe_array[i].name,
    + probe_array[i].format,
    + probe_array[i].probe_func, &probe_array[i]);
    + if (result)
    + printk(KERN_INFO "Unable to register probe %s\n",
    + probe_array[i].name);
    + }
    + return 0;
    +}
    +
    +static void __exit probe_fini(void)
    +{
    + int i;
    +
    + for (i = 0; i < ARRAY_SIZE(probe_array); i++) {
    + marker_disarm_probe(probe_array[i].name);
    + }
    + printk("Number of event b : %u\n", atomic_read(&eventb_count));
    +}
    +
    +module_init(probe_init);
    +module_exit(probe_fini);
    +
    +MODULE_LICENSE("GPL");
    +MODULE_AUTHOR("Mathieu Desnoyers");
    +MODULE_DESCRIPTION("SUBSYSTEM Probe");
    +------------------------------ CUT -------------------------------------
    +/* marker-example.c
    + *
    + * Executes a marker when /proc/marker-example is opened.
    + *
    + * (C) Copyright 2007 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    + *
    + * This file is released under the GPLv2.
    + * See the file COPYING for more details.
    + */
    +
    +#include <linux/module.h>
    +#include <linux/marker.h>
    +#include <linux/sched.h>
    +#include <linux/proc_fs.h>
    +
    +struct proc_dir_entry *pentry_example = NULL;
    +
    +static int my_open(struct inode *inode, struct file *file)
    +{
    + int i;
    +
    + trace_mark(subsystem_event, "%d %s", 123, "example string");
    + for (i=0; i<10; i++) {
    + trace_mark(subsystem_eventb, MARK_NOARGS);
    + }
    + return -EPERM;
    +}
    +
    +static struct file_operations mark_ops = {
    + .open = my_open,
    +};
    +
    +static int example_init(void)
    +{
    + printk(KERN_ALERT "example init\n");
    + pentry_example = create_proc_entry("marker-example", 0444, NULL);
    + if (pentry_example)
    + pentry_example->proc_fops = &mark_ops;
    + else
    + return -EPERM;
    + return 0;
    +}
    +
    +static void example_exit(void)
    +{
    + printk(KERN_ALERT "example exit\n");
    + remove_proc_entry("marker-example", NULL);
    +}
    +
    +module_init(example_init)
    +module_exit(example_exit)
    +
    +MODULE_LICENSE("GPL");
    +MODULE_AUTHOR("Mathieu Desnoyers");
    +MODULE_DESCRIPTION("Linux Trace Toolkit example");
    +------------------------------ CUT -------------------------------------
    +Sequence of operations : (as root)
    +make
    +insmod marker-example.ko
    +insmod probe-example.ko
    + (it is important to load the probe after the marked code)
    +cat /proc/marker-example (returns an expected error)
    +rmmod marker-example probe-example
    +dmesg
    +------------------------------ CUT -------------------------------------
    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-05-29 20:45    [W:0.035 / U:93.136 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site