tracing: add trace_bprintk()

Impact: add a generic printk() for tracing, like trace_printk()

trace_bprintk() uses the infrastructure to record events on ring_buffer.

[ fweisbec@gmail.com: ported to latest -tip, made it work if
  !CONFIG_MODULES, never free the format strings from modules
  because we can't keep track of them and conditionnaly create
  the ftrace format strings section (reported by Steven Rostedt) ]

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1236356510-8381-4-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 77 insertions, 10 deletions

diff --git a/kernel/trace/trace_bprintk.c b/kernel/trace/trace_bprintk.c
index 1f8e532c3fb9..f4c245a5cd33 100644
--- a/kernel/trace/trace_bprintk.c
+++ b/kernel/trace/trace_bprintk.c
@@ -19,9 +19,21 @@
 
 #include "trace.h"
 
+#ifdef CONFIG_MODULES
+
 /* binary printk basic */
 static DEFINE_MUTEX(btrace_mutex);
-static int btrace_metadata_count;
+/*
+ * modules trace_bprintk()'s formats are autosaved in struct trace_bprintk_fmt
+ * which are queued on trace_bprintk_fmt_list.
+ */
+static LIST_HEAD(trace_bprintk_fmt_list);
+
+struct trace_bprintk_fmt {
+        struct list_head list;
+        char fmt[0];
+};
+
 
 static inline void lock_btrace(void)
 {
@@ -33,26 +45,75 @@ static inline void unlock_btrace(void)
         mutex_unlock(&btrace_mutex);
 }
 
-static void get_btrace_metadata(void)
+
+static inline struct trace_bprintk_fmt *lookup_format(const char *fmt)
 {
-        lock_btrace();
-        btrace_metadata_count++;
-        unlock_btrace();
+        struct trace_bprintk_fmt *pos;
+        list_for_each_entry(pos, &trace_bprintk_fmt_list, list) {
+                if (!strcmp(pos->fmt, fmt))
+                        return pos;
+        }
+        return NULL;
 }
 
-static void put_btrace_metadata(void)
+static
+void hold_module_trace_bprintk_format(const char **start, const char **end)
 {
+        const char **iter;
         lock_btrace();
-        btrace_metadata_count--;
+        for (iter = start; iter < end; iter++) {
+                struct trace_bprintk_fmt *tb_fmt = lookup_format(*iter);
+                if (tb_fmt) {
+                        *iter = tb_fmt->fmt;
+                        continue;
+                }
+
+                tb_fmt = kmalloc(offsetof(struct trace_bprintk_fmt, fmt)
+                                + strlen(*iter) + 1, GFP_KERNEL);
+                if (tb_fmt) {
+                        list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
+                        strcpy(tb_fmt->fmt, *iter);
+                        *iter = tb_fmt->fmt;
+                } else
+                        *iter = NULL;
+        }
         unlock_btrace();
 }
 
+static int module_trace_bprintk_format_notify(struct notifier_block *self,
+                unsigned long val, void *data)
+{
+        struct module *mod = data;
+        if (mod->num_trace_bprintk_fmt) {
+                const char **start = mod->trace_bprintk_fmt_start;
+                const char **end = start + mod->num_trace_bprintk_fmt;
+
+                if (val == MODULE_STATE_COMING)
+                        hold_module_trace_bprintk_format(start, end);
+        }
+        return 0;
+}
+
+#else /* !CONFIG_MODULES */
+__init static int
+module_trace_bprintk_format_notify(struct notifier_block *self,
+                unsigned long val, void *data)
+{
+        return 0;
+}
+#endif /* CONFIG_MODULES */
+
+
+__initdata_or_module static
+struct notifier_block module_trace_bprintk_format_nb = {
+        .notifier_call = module_trace_bprintk_format_notify,
+};
+
 /* events tracer */
 int trace_bprintk_enable;
 
 static void start_bprintk_trace(struct trace_array *tr)
 {
-        get_btrace_metadata();
         tracing_reset_online_cpus(tr);
         trace_bprintk_enable = 1;
 }
@@ -61,7 +122,6 @@ static void stop_bprintk_trace(struct trace_array *tr)
 {
         trace_bprintk_enable = 0;
         tracing_reset_online_cpus(tr);
-        put_btrace_metadata();
 }
 
 static int init_bprintk_trace(struct trace_array *tr)
@@ -81,7 +141,14 @@ static struct tracer bprintk_trace __read_mostly =
 
 static __init int init_bprintk(void)
 {
-        return register_tracer(&bprintk_trace);
+        int ret = register_module_notifier(&module_trace_bprintk_format_nb);
+        if (ret)
+                return ret;
+
+        ret = register_tracer(&bprintk_trace);
+        if (ret)
+                unregister_module_notifier(&module_trace_bprintk_format_nb);
+        return ret;
 }
 
 device_initcall(init_bprintk);