Re: [PATCH 5/5] tracing: New functions for kernel access to Ftrace instances
From: Divya Indi
Date: Wed Oct 16 2019 - 19:53:37 EST
Hi Steven,
Please find my comments inline -
On 10/15/19 4:19 PM, Steven Rostedt wrote:
On Wed, 14 Aug 2019 10:55:27 -0700
Divya Indi <divya.indi@xxxxxxxxxx> wrote:
Adding 2 new functions -
1) trace_array_lookup : Look up and return a trace array, given its
name.
2) trace_array_set_clr_event : Enable/disable event recording to the
given trace array.
NOTE: trace_array_lookup returns a trace array and also increments the
reference counter associated with the returned trace array. Make sure to
call trace_array_put() once the use is done so that the instance can be
removed at a later time.
Example use:
tr = trace_array_lookup("foo-bar");
Should probably be renamed to: trace_array_get_by_name("foo-bar")
As the name should show that it adds a ref count.
Makes sense! Will make this change.
But if we make the change I suggested before, where we do not need to
do the put before calling the destroy, we should have:
if (!tr)
{
tr = trace_array_create("foo-bar");
trace_array_get(tr);
This would need a corresponding trace_array_put(?).
Additionally, this would again traverse the list of instances, So I
went with incrementing the ref ctr inside the function.
}
// Log to tr
// Enable/disable events to tr
trace_array_set_clr_event(tr, _THIS_IP,"system","event",1);
What's with the __THIS_IP?
My bad! Maybe remnants from a trace_array_printk copy-paste.
Will correct this.
// Done using tr
trace_array_put(tr);
..
Also, use trace_array_set_clr_event to enable/disable events to a trace array.
So now we no longer need to have ftrace_set_clr_event as an exported
API.
Signed-off-by: Divya Indi <divya.indi@xxxxxxxxxx>
---
include/linux/trace.h | 2 ++
include/linux/trace_events.h | 3 ++-
kernel/trace/trace.c | 28 ++++++++++++++++++++++++++++
kernel/trace/trace_events.c | 23 ++++++++++++++++++++++-
4 files changed, 54 insertions(+), 2 deletions(-)
diff --git a/include/linux/trace.h b/include/linux/trace.h
index 2c782d5..05164bb 100644
--- a/include/linux/trace.h
+++ b/include/linux/trace.h
@@ -32,6 +32,8 @@ int trace_array_printk(struct trace_array *tr, unsigned long ip,
struct trace_array *trace_array_create(const char *name);
int trace_array_destroy(struct trace_array *tr);
void trace_array_put(struct trace_array *tr);
+struct trace_array *trace_array_lookup(const char *name);
+
#endif /* CONFIG_TRACING */
#endif /* _LINUX_TRACE_H */
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 8a62731..05a7514 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -540,7 +540,8 @@ extern int trace_define_field(struct trace_event_call *call, const char *type,
#define is_signed_type(type) (((type)(-1)) < (type)1)
int trace_set_clr_event(const char *system, const char *event, int set);
-
+int trace_array_set_clr_event(struct trace_array *tr, const char *system,
+ const char *event, int set);
/*
* The double __builtin_constant_p is because gcc will give us an error
* if we try to allocate the static variable to fmt if it is not a
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7b6a37a..e394d55 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8514,6 +8514,34 @@ static int instance_rmdir(const char *name)
return ret;
}
+/**
+ * trace_array_lookup - Lookup the trace array, given its name.
+ * @name: The name of the trace array to be looked up.
+ *
+ * Lookup and return the trace array associated with @name.
+ *
+ * NOTE: The reference counter associated with the returned trace array is
+ * incremented to ensure it is not freed when in use. Make sure to call
+ * "trace_array_put" for this trace array when its use is done.
+ */
+struct trace_array *trace_array_lookup(const char *name)
+{
+ struct trace_array *tr;
+
+ mutex_lock(&trace_types_lock);
+
+ list_for_each_entry(tr, &ftrace_trace_arrays, list) {
+ if (tr->name && strcmp(tr->name, name) == 0) {
+ tr->ref++;
+ mutex_unlock(&trace_types_lock);
+ return tr;
+ }
+ }
+ mutex_unlock(&trace_types_lock);
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(trace_array_lookup);
+
static __init void create_trace_instances(struct dentry *d_tracer)
{
trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 2621995..96dd997 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -834,7 +834,6 @@ static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
return ret;
}
-EXPORT_SYMBOL_GPL(ftrace_set_clr_event);
/**
* trace_set_clr_event - enable or disable an event
@@ -859,6 +858,28 @@ int trace_set_clr_event(const char *system, const char *event, int set)
}
EXPORT_SYMBOL_GPL(trace_set_clr_event);
+/**
+ * trace_array_set_clr_event - enable or disable an event for a trace array
+ * @system: system name to match (NULL for any system)
+ * @event: event name to match (NULL for all events, within system)
+ * @set: 1 to enable, 0 to disable
We probably should make this a boolean.
This would internally call ftrace_set_clr_event which would expect 0/1.
But I agree making it boolean would be more intuitive.
Thanks,
Divya
-- Steve
+ *
+ * This is a way for other parts of the kernel to enable or disable
+ * event recording to instances.
+ *
+ * Returns 0 on success, -EINVAL if the parameters do not match any
+ * registered events.
+ */
+int trace_array_set_clr_event(struct trace_array *tr, const char *system,
+ const char *event, int set)
+{
+ if (!tr)
+ return -ENOENT;
+
+ return __ftrace_set_clr_event(tr, NULL, system, event, set);
+}
+EXPORT_SYMBOL_GPL(trace_array_set_clr_event);
+
/* 128 should be much more than enough */
#define EVENT_BUF_SIZE 127