tracing: add run-time field descriptions for event filtering

This patch makes the field descriptions defined for event tracing
available at run-time, for the event-filtering mechanism introduced
in a subsequent patch.

The common event fields are prepended with 'common_' in the format
display, allowing them to be distinguished from the other fields
that might internally have same name and can therefore be
unambiguously used in filters.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237710639.7703.46.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 39 insertions, 1 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 3047b56f6637..961b057da28b 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -19,6 +19,34 @@
 
 static DEFINE_MUTEX(event_mutex);
 
+int trace_define_field(struct ftrace_event_call *call, char *type,
+                       char *name, int offset, int size)
+{
+        struct ftrace_event_field *field;
+
+        field = kmalloc(sizeof(*field), GFP_KERNEL);
+        if (!field)
+                goto err;
+        field->name = kstrdup(name, GFP_KERNEL);
+        if (!field->name)
+                goto err;
+        field->type = kstrdup(type, GFP_KERNEL);
+        if (!field->type)
+                goto err;
+        field->offset = offset;
+        field->size = size;
+        list_add(&field->link, &call->fields);
+
+        return 0;
+err:
+        if (field) {
+                kfree(field->name);
+                kfree(field->type);
+        }
+        kfree(field);
+        return -ENOMEM;
+}
+
 static void ftrace_clear_events(void)
 {
         struct ftrace_event_call *call = (void *)__start_ftrace_events;
@@ -343,7 +371,8 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
 #undef FIELD
 #define FIELD(type, name)                                               \
-        #type, #name, offsetof(typeof(field), name), sizeof(field.name)
+        #type, "common_" #name, offsetof(typeof(field), name),          \
+                sizeof(field.name)
 
 static int trace_write_header(struct trace_seq *s)
 {
@@ -581,6 +610,15 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
                                         call->name);
         }
 
+        if (call->define_fields) {
+                ret = call->define_fields();
+                if (ret < 0) {
+                        pr_warning("Could not initialize trace point"
+                                   " events/%s\n", call->name);
+                        return ret;
+                }
+        }
+
         /* A trace may not want to export its format */
         if (!call->show_format)
                 return 0;