tracing/events: add support for modules to TRACE_EVENT

Impact: allow modules to add TRACE_EVENTS on load

This patch adds the final hooks to allow modules to use the TRACE_EVENT
macro. A notifier and a data structure are used to link the TRACE_EVENTs
defined in the module to connect them with the ftrace event tracing system.

It also adds the necessary automated clean ups to the trace events when a
module is removed.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 103 insertions, 32 deletions

diff --git a/kernel/module.c b/kernel/module.c
index e797812a4d95..a0394706f10c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -18,6 +18,7 @@
 */
 #include <linux/module.h>
 #include <linux/moduleloader.h>
+#include <linux/ftrace_event.h>
 #include <linux/init.h>
 #include <linux/kallsyms.h>
 #include <linux/fs.h>
@@ -2172,6 +2173,12 @@ static noinline struct module *load_module(void __user *umod,
                                         sizeof(*mod->tracepoints),
                                         &mod->num_tracepoints);
 #endif
+#ifdef CONFIG_EVENT_TRACING
+        mod->trace_events = section_objs(hdr, sechdrs, secstrings,
+                                         "_ftrace_events",
+                                         sizeof(*mod->trace_events),
+                                         &mod->num_trace_events);
+#endif
 
 #ifdef CONFIG_MODVERSIONS
         if ((mod->num_syms && !mod->crcs)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 8b9e621b80b4..a4b177720a6c 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -713,7 +713,13 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
                 return d_events;
         }
 
-        system->name = name;
+        system->name = kstrdup(name, GFP_KERNEL);
+        if (!system->name) {
+                debugfs_remove(system->entry);
+                kfree(system);
+                return d_events;
+        }
+
         list_add(&system->list, &event_subsystems);
 
         system->preds = NULL;
@@ -738,7 +744,7 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
          * If the trace point header did not define TRACE_SYSTEM
          * then the system would be called "TRACE_SYSTEM".
          */
-        if (strcmp(call->system, "TRACE_SYSTEM") != 0)
+        if (strcmp(call->system, TRACE_SYSTEM) != 0)
                 d_events = event_subsystem_dir(call->system, d_events);
 
         if (call->raw_init) {
@@ -757,21 +763,13 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
                 return -1;
         }
 
-        if (call->regfunc) {
-                entry = debugfs_create_file("enable", 0644, call->dir, call,
-                                            &ftrace_enable_fops);
-                if (!entry)
-                        pr_warning("Could not create debugfs "
-                                   "'%s/enable' entry\n", call->name);
-        }
+        if (call->regfunc)
+                entry = trace_create_file("enable", 0644, call->dir, call,
+                                          &ftrace_enable_fops);
 
-        if (call->id) {
-                entry = debugfs_create_file("id", 0444, call->dir, call,
-                                &ftrace_event_id_fops);
-                if (!entry)
-                        pr_warning("Could not create debugfs '%s/id' entry\n",
-                                        call->name);
-        }
+        if (call->id)
+                entry = trace_create_file("id", 0444, call->dir, call,
+                                          &ftrace_event_id_fops);
 
         if (call->define_fields) {
                 ret = call->define_fields();
@@ -780,40 +778,102 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
                                    " events/%s\n", call->name);
                         return ret;
                 }
-                entry = debugfs_create_file("filter", 0644, call->dir, call,
-                                            &ftrace_event_filter_fops);
-                if (!entry)
-                        pr_warning("Could not create debugfs "
-                                   "'%s/filter' entry\n", call->name);
+                entry = trace_create_file("filter", 0644, call->dir, call,
+                                          &ftrace_event_filter_fops);
         }
 
         /* A trace may not want to export its format */
         if (!call->show_format)
                 return 0;
 
-        entry = debugfs_create_file("format", 0444, call->dir, call,
-                                    &ftrace_event_format_fops);
-        if (!entry)
-                pr_warning("Could not create debugfs "
-                           "'%s/format' entry\n", call->name);
+        entry = trace_create_file("format", 0444, call->dir, call,
+                                  &ftrace_event_format_fops);
+
+        return 0;
+}
+
+#define for_each_event(event, start, end)                       \
+        for (event = start;                                     \
+             (unsigned long)event < (unsigned long)end;         \
+             event++)
+
+static void trace_module_add_events(struct module *mod)
+{
+        struct ftrace_event_call *call, *start, *end;
+        struct dentry *d_events;
+
+        start = mod->trace_events;
+        end = mod->trace_events + mod->num_trace_events;
+
+        if (start == end)
+                return;
+
+        d_events = event_trace_events_dir();
+        if (!d_events)
+                return;
+
+        for_each_event(call, start, end) {
+                /* The linker may leave blanks */
+                if (!call->name)
+                        continue;
+                call->mod = mod;
+                list_add(&call->list, &ftrace_events);
+                event_create_dir(call, d_events);
+        }
+}
+
+static void trace_module_remove_events(struct module *mod)
+{
+        struct ftrace_event_call *call, *p;
+
+        list_for_each_entry_safe(call, p, &ftrace_events, list) {
+                if (call->mod == mod) {
+                        if (call->enabled) {
+                                call->enabled = 0;
+                                call->unregfunc();
+                        }
+                        if (call->event)
+                                unregister_ftrace_event(call->event);
+                        debugfs_remove_recursive(call->dir);
+                        list_del(&call->list);
+                }
+        }
+}
+
+int trace_module_notify(struct notifier_block *self,
+                        unsigned long val, void *data)
+{
+        struct module *mod = data;
+
+        mutex_lock(&event_mutex);
+        switch (val) {
+        case MODULE_STATE_COMING:
+                trace_module_add_events(mod);
+                break;
+        case MODULE_STATE_GOING:
+                trace_module_remove_events(mod);
+                break;
+        }
+        mutex_unlock(&event_mutex);
 
         return 0;
 }
 
+struct notifier_block trace_module_nb = {
+        .notifier_call = trace_module_notify,
+        .priority = 0,
+};
+
 extern struct ftrace_event_call __start_ftrace_events[];
 extern struct ftrace_event_call __stop_ftrace_events[];
 
-#define for_each_event(event)                                           \
-        for (event = __start_ftrace_events;                             \
-             (unsigned long)event < (unsigned long)__stop_ftrace_events; \
-             event++)
-
 static __init int event_trace_init(void)
 {
         struct ftrace_event_call *call;
         struct dentry *d_tracer;
         struct dentry *entry;
         struct dentry *d_events;
+        int ret;
 
         d_tracer = tracing_init_dentry();
         if (!d_tracer)
@@ -837,7 +897,7 @@ static __init int event_trace_init(void)
         if (!d_events)
                 return 0;
 
-        for_each_event(call) {
+        for_each_event(call, __start_ftrace_events, __stop_ftrace_events) {
                 /* The linker may leave blanks */
                 if (!call->name)
                         continue;
@@ -845,6 +905,10 @@ static __init int event_trace_init(void)
                 event_create_dir(call, d_events);
         }
 
+        ret = register_module_notifier(&trace_module_nb);
+        if (!ret)
+                pr_warning("Failed to register trace events module notifier\n");
+
         return 0;
 }
 fs_initcall(event_trace_init);