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Subject[patch 2/5] Linux Kernel Markers
The marker activation functions sits in kernel/marker.c. A hash table is used
to keep track of the registered probes and armed markers, so the markers within
a newly loaded module that should be active can be activated at module load
time.

marker_query has been removed. marker_get_first, marker_get_next and
marker_release should be used as iterators on the markers.

Changelog:
- markers_mutex now nests inside module_mutex rather than the opposite.
- Iteration on modules is now done in module.c.
- module_mutex is not exported anymore.
- Don't declare a __markers_strings section.
- Simplified: do not use immediate values, just a simple variable read.
(removed dependency on immediate values).
- Removed the args field in the marker structure : it was not used.
- Removed the iterators. Will come back with the actual users.
- Merge the markers menu entry.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: "Frank Ch. Eigler" <fche@redhat.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: Rusty Russell <rusty@rustcorp.com.au>
---
include/asm-generic/vmlinux.lds.h | 7
include/linux/marker.h | 130 +++++++++
include/linux/module.h | 12
kernel/Kconfig.instrumentation | 6
kernel/Makefile | 1
kernel/marker.c | 527 ++++++++++++++++++++++++++++++++++++++
kernel/module.c | 30 ++
7 files changed, 711 insertions(+), 2 deletions(-)
Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h 2007-09-25 07:17:49.000000000 -0400
+++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h 2007-09-25 07:18:50.000000000 -0400
@@ -12,7 +12,11 @@
/* .data section */
#define DATA_DATA \
*(.data) \
- *(.data.init.refok)
+ *(.data.init.refok) \
+ . = ALIGN(8); \
+ VMLINUX_SYMBOL(__start___markers) = .; \
+ *(__markers) \
+ VMLINUX_SYMBOL(__stop___markers) = .;

#define RO_DATA(align) \
. = ALIGN((align)); \
@@ -20,6 +24,7 @@
VMLINUX_SYMBOL(__start_rodata) = .; \
*(.rodata) *(.rodata.*) \
*(__vermagic) /* Kernel version magic */ \
+ *(__markers_strings) /* Markers: strings */ \
} \
\
.rodata1 : AT(ADDR(.rodata1) - LOAD_OFFSET) { \
Index: linux-2.6-lttng/include/linux/marker.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/include/linux/marker.h 2007-09-25 07:18:50.000000000 -0400
@@ -0,0 +1,130 @@
+#ifndef _LINUX_MARKER_H
+#define _LINUX_MARKER_H
+
+/*
+ * Code markup for dynamic and static tracing.
+ *
+ * See Documentation/marker.txt.
+ *
+ * (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#include <linux/types.h>
+
+struct module;
+struct __mark_marker;
+
+/**
+ * marker_probe_func - Type of a marker probe function
+ * @mdata: pointer of type struct __mark_marker
+ * @private_data: caller site private data
+ * @fmt: format string
+ * @...: variable argument list
+ *
+ * Type of marker probe functions. They receive the mdata and need to parse the
+ * format string to recover the variable argument list.
+ */
+typedef void marker_probe_func(const struct __mark_marker *mdata,
+ void *private_data, const char *fmt, ...);
+
+struct __mark_marker {
+ const char *name; /* Marker name */
+ const char *format; /* Marker format string, describing the
+ * variable argument list.
+ */
+ char state; /* Marker state. */
+ marker_probe_func *call;/* Probe handler function pointer */
+ void *private; /* Private probe data */
+} __attribute__((aligned(8)));
+
+#ifdef CONFIG_MARKERS
+
+/*
+ * Note : the empty asm volatile with read constraint is used here instead of a
+ * "used" attribute to fix a gcc 4.1.x bug.
+ * Make sure the alignment of the structure in the __markers section will
+ * not add unwanted padding between the beginning of the section and the
+ * structure. Force alignment to the same alignment as the section start.
+ */
+#define __trace_mark(name, call_data, format, args...) \
+ do { \
+ static const char __mstrtab_name_##name[] \
+ __attribute__((section("__markers_strings"))) \
+ = #name; \
+ static const char __mstrtab_format_##name[] \
+ __attribute__((section("__markers_strings"))) \
+ = format; \
+ static struct __mark_marker __mark_##name \
+ __attribute__((section("__markers"))) = \
+ { __mstrtab_name_##name, __mstrtab_format_##name, \
+ 0, __mark_empty_function, NULL }; \
+ asm volatile ( "" : : "i" (&__mark_##name)); \
+ __mark_check_format(format, ## args); \
+ if (unlikely(__mark_##name.state)) { \
+ preempt_disable(); \
+ (*__mark_##name.call) \
+ (&__mark_##name, call_data, \
+ format, ## args); \
+ preempt_enable(); \
+ } \
+ } while (0)
+
+extern void marker_update_probe_range(struct __mark_marker *begin,
+ struct __mark_marker *end, struct module *probe_module, int *refcount);
+#else /* !CONFIG_MARKERS */
+#define __trace_mark(name, call_data, format, args...) \
+ __mark_check_format(format, ## args)
+static inline void marker_update_probe_range(struct __mark_marker *begin,
+ struct __mark_marker *end, struct module *probe_module, int *refcount)
+{ }
+#endif /* CONFIG_MARKERS */
+
+/**
+ * trace_mark - Marker
+ * @name: marker name, not quoted.
+ * @format: format string
+ * @args...: variable argument list
+ *
+ * Places a marker.
+ */
+#define trace_mark(name, format, args...) \
+ __trace_mark(name, NULL, format, ## args)
+
+#define MARK_MAX_FORMAT_LEN 1024
+
+/**
+ * MARK_NOARGS - Format string for a marker with no argument.
+ */
+#define MARK_NOARGS " "
+
+/* To be used for string format validity checking with gcc */
+static inline void __printf(1, 2) __mark_check_format(const char *fmt, ...)
+{
+}
+
+extern marker_probe_func __mark_empty_function;
+
+/*
+ * Connect a probe to a marker.
+ * private data pointer must be a valid allocated memory address, or NULL.
+ */
+extern int marker_probe_register(const char *name, const char *format,
+ marker_probe_func *probe, void *private);
+
+/*
+ * Returns the private data given to marker_probe_register.
+ */
+extern void *marker_probe_unregister(const char *name);
+/*
+ * Unregister a marker by providing the registered private data.
+ */
+extern void *marker_probe_unregister_private_data(void *private);
+
+extern int marker_arm(const char *name);
+extern int marker_disarm(const char *name);
+extern void *marker_get_private_data(const char *name);
+
+#endif
Index: linux-2.6-lttng/include/linux/module.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/module.h 2007-09-25 07:17:49.000000000 -0400
+++ linux-2.6-lttng/include/linux/module.h 2007-09-25 07:18:50.000000000 -0400
@@ -15,6 +15,7 @@
#include <linux/stringify.h>
#include <linux/kobject.h>
#include <linux/moduleparam.h>
+#include <linux/marker.h>
#include <asm/local.h>

#include <asm/module.h>
@@ -370,6 +371,10 @@ struct module
/* The command line arguments (may be mangled). People like
keeping pointers to this stuff */
char *args;
+#ifdef CONFIG_MARKERS
+ struct __mark_marker *markers;
+ unsigned int num_markers;
+#endif
};
#ifndef MODULE_ARCH_INIT
#define MODULE_ARCH_INIT {}
@@ -473,6 +478,8 @@ int unregister_module_notifier(struct no

extern void print_modules(void);

+extern void module_update_markers(struct module *probe_module, int *refcount);
+
#else /* !CONFIG_MODULES... */
#define EXPORT_SYMBOL(sym)
#define EXPORT_SYMBOL_GPL(sym)
@@ -572,6 +579,11 @@ static inline void print_modules(void)
{
}

+static inline void module_update_markers(struct module *probe_module,
+ int *refcount)
+{
+}
+
#endif /* CONFIG_MODULES */

struct device_driver;
Index: linux-2.6-lttng/kernel/module.c
===================================================================
--- linux-2.6-lttng.orig/kernel/module.c 2007-09-25 07:17:49.000000000 -0400
+++ linux-2.6-lttng/kernel/module.c 2007-09-25 07:18:50.000000000 -0400
@@ -1717,6 +1717,8 @@ static struct module *load_module(void _
unsigned int unusedcrcindex;
unsigned int unusedgplindex;
unsigned int unusedgplcrcindex;
+ unsigned int markersindex;
+ unsigned int markersstringsindex;
struct module *mod;
long err = 0;
void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -1982,6 +1984,8 @@ static struct module *load_module(void _
add_taint_module(mod, TAINT_FORCED_MODULE);
}
#endif
+ markersindex = find_sec(hdr, sechdrs, secstrings, "__markers");
+ markersstringsindex = find_sec(hdr, sechdrs, secstrings, "__markers_strings");

/* Now do relocations. */
for (i = 1; i < hdr->e_shnum; i++) {
@@ -2004,6 +2008,11 @@ static struct module *load_module(void _
if (err < 0)
goto cleanup;
}
+#ifdef CONFIG_MARKERS
+ mod->markers = (void *)sechdrs[markersindex].sh_addr;
+ mod->num_markers =
+ sechdrs[markersindex].sh_size / sizeof(*mod->markers);
+#endif

/* Find duplicate symbols */
err = verify_export_symbols(mod);
@@ -2027,7 +2036,11 @@ static struct module *load_module(void _
if (err < 0)
goto nomodsectinfo;
#endif
-
+#ifdef CONFIG_MARKERS
+ if (!mod->taints)
+ marker_update_probe_range(mod->markers,
+ mod->markers + mod->num_markers, NULL, NULL);
+#endif
err = module_finalize(hdr, sechdrs, mod);
if (err < 0)
goto cleanup;
@@ -2629,3 +2642,18 @@ EXPORT_SYMBOL(module_remove_driver);
void struct_module(struct module *mod) { return; }
EXPORT_SYMBOL(struct_module);
#endif
+
+#ifdef CONFIG_MARKERS
+void module_update_markers(struct module *probe_module, int *refcount)
+{
+ struct module *mod;
+
+ mutex_lock(&module_mutex);
+ list_for_each_entry(mod, &modules, list)
+ if (!mod->taints)
+ marker_update_probe_range(mod->markers,
+ mod->markers + mod->num_markers,
+ probe_module, refcount);
+ mutex_unlock(&module_mutex);
+}
+#endif
Index: linux-2.6-lttng/kernel/marker.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/kernel/marker.c 2007-09-25 07:18:50.000000000 -0400
@@ -0,0 +1,527 @@
+/*
+ * Copyright (C) 2007 Mathieu Desnoyers
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+#include <linux/jhash.h>
+#include <linux/list.h>
+#include <linux/rcupdate.h>
+#include <linux/marker.h>
+#include <linux/err.h>
+
+extern struct __mark_marker __start___markers[];
+extern struct __mark_marker __stop___markers[];
+
+/*
+ * module_mutex nests inside markers_mutex. Markers mutex protects the builtin
+ * and module markers, the hash table and deferred_sync.
+ */
+DEFINE_MUTEX(markers_mutex);
+
+/*
+ * Marker deferred synchronization.
+ * Upon marker probe_unregister, we delay call to synchronize_sched() to
+ * accelerate mass unregistration (only when there is no more reference to a
+ * given module do we call synchronize_sched()). However, we need to make sure
+ * every critical region has ended before we re-arm a marker that has been
+ * unregistered and then registered back with a different probe data.
+ */
+static int deferred_sync;
+
+/*
+ * Marker hash table, containing the active markers.
+ * Protected by module_mutex.
+ */
+#define MARKER_HASH_BITS 6
+#define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)
+
+struct marker_entry {
+ struct hlist_node hlist;
+ char *format;
+ marker_probe_func *probe;
+ void *private;
+ int refcount; /* Number of times armed. 0 if disarmed. */
+ char name[0]; /* Contains name'\0'format'\0' */
+};
+
+static struct hlist_head marker_table[MARKER_TABLE_SIZE];
+
+/**
+ * __mark_empty_function - Empty probe callback
+ * @mdata: pointer of type const struct __mark_marker
+ * @fmt: format string
+ * @...: variable argument list
+ *
+ * Empty callback provided as a probe to the markers. By providing this to a
+ * disabled marker, we make sure the execution flow is always valid even
+ * though the function pointer change and the marker enabling are two distinct
+ * operations that modifies the execution flow of preemptible code.
+ */
+void __mark_empty_function(const struct __mark_marker *mdata,
+ void *private_data,
+ const char *fmt, ...)
+{
+}
+EXPORT_SYMBOL_GPL(__mark_empty_function);
+
+/*
+ * Get marker if the marker is present in the marker hash table.
+ * Must be called with markers_mutex held.
+ * Returns NULL if not present.
+ */
+static struct marker_entry *get_marker(const char *name)
+{
+ struct hlist_head *head;
+ struct hlist_node *node;
+ struct marker_entry *e;
+ u32 hash = jhash(name, strlen(name), 0);
+
+ head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
+ hlist_for_each_entry(e, node, head, hlist) {
+ if (!strcmp(name, e->name))
+ return e;
+ }
+ return NULL;
+}
+
+/*
+ * Add the marker to the marker hash table. Must be called with markers_mutex
+ * held.
+ */
+static int add_marker(const char *name, const char *format,
+ marker_probe_func *probe, void *private)
+{
+ struct hlist_head *head;
+ struct hlist_node *node;
+ struct marker_entry *e;
+ size_t name_len = strlen(name) + 1;
+ size_t format_len = 0;
+ u32 hash = jhash(name, name_len-1, 0);
+
+ if (format)
+ format_len = strlen(format) + 1;
+ head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
+ hlist_for_each_entry(e, node, head, hlist) {
+ if (!strcmp(name, e->name)) {
+ printk(KERN_NOTICE
+ "Marker %s busy, probe %p already installed\n",
+ name, e->probe);
+ return -EBUSY; /* Already there */
+ }
+ }
+ /*
+ * Using kmalloc here to allocate a variable length element. Could
+ * cause some memory fragmentation if overused.
+ */
+ e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
+ GFP_KERNEL);
+ if (!e)
+ return -ENOMEM;
+ memcpy(&e->name[0], name, name_len);
+ if (format) {
+ e->format = &e->name[name_len];
+ memcpy(e->format, format, format_len);
+ trace_mark(core_marker_format, "name %s format %s",
+ e->name, e->format);
+ } else
+ e->format = NULL;
+ e->probe = probe;
+ e->private = private;
+ e->refcount = 0;
+ hlist_add_head(&e->hlist, head);
+ return 0;
+}
+
+/*
+ * Remove the marker from the marker hash table. Must be called with mutex_lock
+ * held.
+ */
+static void *remove_marker(const char *name)
+{
+ struct hlist_head *head;
+ struct hlist_node *node;
+ struct marker_entry *e;
+ int found = 0;
+ size_t len = strlen(name) + 1;
+ void *private = NULL;
+ u32 hash = jhash(name, len-1, 0);
+
+ head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
+ hlist_for_each_entry(e, node, head, hlist) {
+ if (!strcmp(name, e->name)) {
+ found = 1;
+ break;
+ }
+ }
+ if (found) {
+ private = e->private;
+ hlist_del(&e->hlist);
+ kfree(e);
+ }
+ return private;
+}
+
+/*
+ * Set the mark_entry format to the format found in the element.
+ */
+static int marker_set_format(struct marker_entry **entry, const char *format)
+{
+ struct marker_entry *e;
+ size_t name_len = strlen((*entry)->name) + 1;
+ size_t format_len = strlen(format) + 1;
+
+ e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
+ GFP_KERNEL);
+ if (!e)
+ return -ENOMEM;
+ memcpy(&e->name[0], (*entry)->name, name_len);
+ e->format = &e->name[name_len];
+ memcpy(e->format, format, format_len);
+ e->probe = (*entry)->probe;
+ e->private = (*entry)->private;
+ e->refcount = (*entry)->refcount;
+ hlist_add_before(&e->hlist, &(*entry)->hlist);
+ hlist_del(&(*entry)->hlist);
+ kfree(*entry);
+ *entry = e;
+ trace_mark(core_marker_format, "name %s format %s",
+ e->name, e->format);
+ return 0;
+}
+
+/*
+ * Sets the probe callback corresponding to one marker.
+ */
+static int set_marker(struct marker_entry **entry,
+ struct __mark_marker *elem)
+{
+ int ret;
+ WARN_ON(strcmp((*entry)->name, elem->name) != 0);
+
+ if ((*entry)->format) {
+ if (strcmp((*entry)->format, elem->format) != 0) {
+ printk(KERN_NOTICE
+ "Format mismatch for probe %s "
+ "(%s), marker (%s)\n",
+ (*entry)->name,
+ (*entry)->format,
+ elem->format);
+ return -EPERM;
+ }
+ } else {
+ ret = marker_set_format(entry, elem->format);
+ if (ret)
+ return ret;
+ }
+ elem->call = (*entry)->probe;
+ elem->private = (*entry)->private;
+ elem->state = 1;
+ return 0;
+}
+
+/*
+ * Disable a marker and its probe callback.
+ * Note: only after a synchronize_sched() issued after setting elem->call to the
+ * empty function insures that the original callback is not used anymore. This
+ * insured by preemption disabling around the call site.
+ */
+static void disable_marker(struct __mark_marker *elem)
+{
+ elem->state = 0;
+ elem->call = __mark_empty_function;
+ /*
+ * Leave the private data and id there, because removal is racy and
+ * should be done only after a synchronize_sched(). These are never used
+ * until the next initialization anyway.
+ */
+}
+
+/**
+ * marker_update_probe_range - Update a probe range
+ * @begin: beginning of the range
+ * @end: end of the range
+ * @probe_module: module address of the probe being updated
+ * @refcount: number of references left to the given probe_module (out)
+ *
+ * Updates the probe callback corresponding to a range of markers.
+ * Must be called with markers_mutex held.
+ */
+void marker_update_probe_range(struct __mark_marker *begin,
+ struct __mark_marker *end, struct module *probe_module,
+ int *refcount)
+{
+ struct __mark_marker *iter;
+ struct marker_entry *mark_entry;
+
+ for (iter = begin; iter < end; iter++) {
+ mark_entry = get_marker(iter->name);
+ if (mark_entry && mark_entry->refcount) {
+ set_marker(&mark_entry, iter);
+ /*
+ * ignore error, continue
+ */
+ if (probe_module)
+ if (probe_module ==
+ __module_text_address((unsigned long)mark_entry->probe))
+ (*refcount)++;
+ } else {
+ disable_marker(iter);
+ }
+ }
+}
+
+/*
+ * Update probes, removing the faulty probes.
+ * Issues a synchronize_sched() when no reference to the module passed
+ * as parameter is found in the probes so the probe module can be
+ * safely unloaded from now on.
+ */
+static void marker_update_probes(struct module *probe_module)
+{
+ int refcount = 0;
+
+ mutex_lock(&markers_mutex);
+ /* Core kernel markers */
+ marker_update_probe_range(__start___markers,
+ __stop___markers, probe_module, &refcount);
+ /* Markers in modules. */
+ module_update_markers(probe_module, &refcount);
+ if (probe_module && refcount == 0) {
+ synchronize_sched();
+ deferred_sync = 0;
+ }
+ mutex_unlock(&markers_mutex);
+}
+
+/**
+ * marker_probe_register - Connect a probe to a marker
+ * @name: marker name
+ * @format: format string
+ * @probe: probe handler
+ * @private: probe private data
+ *
+ * private data must be a valid allocated memory address, or NULL.
+ * Returns 0 if ok, error value on error.
+ */
+int marker_probe_register(const char *name, const char *format,
+ marker_probe_func *probe, void *private)
+{
+ struct marker_entry *entry;
+ int ret = 0, need_update = 0;
+
+ mutex_lock(&markers_mutex);
+ entry = get_marker(name);
+ if (entry && entry->refcount) {
+ ret = -EBUSY;
+ goto end;
+ }
+ if (deferred_sync) {
+ synchronize_sched();
+ deferred_sync = 0;
+ }
+ ret = add_marker(name, format, probe, private);
+ if (ret)
+ goto end;
+ need_update = 1;
+end:
+ mutex_unlock(&markers_mutex);
+ if (need_update)
+ marker_update_probes(NULL);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(marker_probe_register);
+
+/**
+ * marker_probe_unregister - Disconnect a probe from a marker
+ * @name: marker name
+ *
+ * Returns the private data given to marker_probe_register, or an ERR_PTR().
+ */
+void *marker_probe_unregister(const char *name)
+{
+ struct module *probe_module;
+ struct marker_entry *entry;
+ void *private;
+ int need_update = 0;
+
+ mutex_lock(&markers_mutex);
+ entry = get_marker(name);
+ if (!entry) {
+ private = ERR_PTR(-ENOENT);
+ goto end;
+ }
+ entry->refcount = 0;
+ /* In what module is the probe handler ? */
+ probe_module = __module_text_address((unsigned long)entry->probe);
+ private = remove_marker(name);
+ deferred_sync = 1;
+ need_update = 1;
+end:
+ mutex_unlock(&markers_mutex);
+ if (need_update)
+ marker_update_probes(probe_module);
+ return private;
+}
+EXPORT_SYMBOL_GPL(marker_probe_unregister);
+
+/**
+ * marker_probe_unregister_private_data - Disconnect a probe from a marker
+ * @private: probe private data
+ *
+ * Unregister a marker by providing the registered private data.
+ * Returns the private data given to marker_probe_register, or an ERR_PTR().
+ */
+void *marker_probe_unregister_private_data(void *private)
+{
+ struct module *probe_module;
+ struct hlist_head *head;
+ struct hlist_node *node;
+ struct marker_entry *entry;
+ int found = 0;
+ unsigned int i;
+ int need_update = 0;
+
+ mutex_lock(&markers_mutex);
+ for (i = 0; i < MARKER_TABLE_SIZE; i++) {
+ head = &marker_table[i];
+ hlist_for_each_entry(entry, node, head, hlist) {
+ if (entry->private == private) {
+ found = 1;
+ goto iter_end;
+ }
+ }
+ }
+iter_end:
+ if (!found) {
+ private = ERR_PTR(-ENOENT);
+ goto end;
+ }
+ entry->refcount = 0;
+ /* In what module is the probe handler ? */
+ probe_module = __module_text_address((unsigned long)entry->probe);
+ private = remove_marker(entry->name);
+ deferred_sync = 1;
+ need_update = 1;
+end:
+ mutex_unlock(&markers_mutex);
+ if (need_update)
+ marker_update_probes(probe_module);
+ return private;
+}
+EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);
+
+/**
+ * marker_arm - Arm a marker
+ * @name: marker name
+ *
+ * Activate a marker. It keeps a reference count of the number of
+ * arming/disarming done.
+ * Returns 0 if ok, error value on error.
+ */
+int marker_arm(const char *name)
+{
+ struct marker_entry * entry;
+ int ret = 0, need_update = 0;
+
+ mutex_lock(&markers_mutex);
+ entry = get_marker(name);
+ if (!entry) {
+ ret = -ENOENT;
+ goto end;
+ }
+ /*
+ * Only need to update probes when refcount passes from 0 to 1.
+ */
+ if (entry->refcount++)
+ goto end;
+ need_update = 1;
+end:
+ mutex_unlock(&markers_mutex);
+ if (need_update)
+ marker_update_probes(NULL);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(marker_arm);
+
+/**
+ * marker_disarm - Disarm a marker
+ * @name: marker name
+ *
+ * Disarm a marker. It keeps a reference count of the number of arming/disarming
+ * done.
+ * Returns 0 if ok, error value on error.
+ */
+int marker_disarm(const char *name)
+{
+ struct marker_entry * entry;
+ int ret = 0, need_update = 0;
+
+ mutex_lock(&markers_mutex);
+ entry = get_marker(name);
+ if (!entry) {
+ ret = -ENOENT;
+ goto end;
+ }
+ /*
+ * Only permit decrement refcount if higher than 0.
+ * Do probe update only on 1 -> 0 transition.
+ */
+ if (entry->refcount) {
+ if (--entry->refcount)
+ goto end;
+ } else {
+ ret = -EPERM;
+ goto end;
+ }
+ need_update = 1;
+end:
+ mutex_unlock(&markers_mutex);
+ if (need_update)
+ marker_update_probes(NULL);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(marker_disarm);
+
+/**
+ * marker_get_private_data - Get a marker's probe private data
+ * @name: marker name
+ *
+ * Returns the private data pointer, or an ERR_PTR.
+ * The private data pointer should _only_ be dereferenced if the caller is the
+ * owner of the data, or its content could vanish. This is mostly used to
+ * confirm that a caller is the owner of a registered probe.
+ */
+void *marker_get_private_data(const char *name)
+{
+ struct hlist_head *head;
+ struct hlist_node *node;
+ struct marker_entry *e;
+ size_t name_len = strlen(name) + 1;
+ u32 hash = jhash(name, name_len-1, 0);
+ int found = 0;
+
+ head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
+ hlist_for_each_entry(e, node, head, hlist) {
+ if (!strcmp(name, e->name)) {
+ found = 1;
+ return e->private;
+ }
+ }
+ return ERR_PTR(-ENOENT);
+}
+EXPORT_SYMBOL_GPL(marker_get_private_data);
Index: linux-2.6-lttng/kernel/Kconfig.instrumentation
===================================================================
--- linux-2.6-lttng.orig/kernel/Kconfig.instrumentation 2007-09-25 07:18:40.000000000 -0400
+++ linux-2.6-lttng/kernel/Kconfig.instrumentation 2007-09-25 07:18:50.000000000 -0400
@@ -40,4 +40,10 @@ config KPROBES
for kernel debugging, non-intrusive instrumentation and testing.
If in doubt, say "N".

+config MARKERS
+ bool "Activate markers"
+ help
+ Place an empty function call at each marker site. Can be
+ dynamically changed for a probe function.
+
endif # INSTRUMENTATION
Index: linux-2.6-lttng/kernel/Makefile
===================================================================
--- linux-2.6-lttng.orig/kernel/Makefile 2007-09-25 07:17:49.000000000 -0400
+++ linux-2.6-lttng/kernel/Makefile 2007-09-25 07:18:50.000000000 -0400
@@ -61,6 +61,7 @@ obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o
obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o
obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
+obj-$(CONFIG_MARKERS) += marker.o

ifneq ($(CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER),y)
# According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
-
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