tracing: Print trace_bprintk() formats for modules too
The file debugfs/tracing/printk_formats maps the addresses
to the formats that are used by trace_bprintk() so that userspace
tools can read the buffer and be able to decode trace_bprintk events
to get the format saved when reading the ring buffer directly.
This is because trace_bprintk() does not store the format into the
buffer, but just the address of the format, which is hidden in
the kernel memory.
But currently it only exports trace_bprintk()s from the kernel core
and not for modules. The modules need their formats exported
as well.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
index b8b2681..dff763b 100644
--- a/kernel/trace/trace_printk.c
+++ b/kernel/trace/trace_printk.c
@@ -89,6 +89,76 @@
return 0;
}
+/*
+ * The debugfs/tracing/printk_formats file maps the addresses with
+ * the ASCII formats that are used in the bprintk events in the
+ * buffer. For userspace tools to be able to decode the events from
+ * the buffer, they need to be able to map the address with the format.
+ *
+ * The addresses of the bprintk formats are in their own section
+ * __trace_printk_fmt. But for modules we copy them into a link list.
+ * The code to print the formats and their addresses passes around the
+ * address of the fmt string. If the fmt address passed into the seq
+ * functions is within the kernel core __trace_printk_fmt section, then
+ * it simply uses the next pointer in the list.
+ *
+ * When the fmt pointer is outside the kernel core __trace_printk_fmt
+ * section, then we need to read the link list pointers. The trick is
+ * we pass the address of the string to the seq function just like
+ * we do for the kernel core formats. To get back the structure that
+ * holds the format, we simply use containerof() and then go to the
+ * next format in the list.
+ */
+static const char **
+find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
+{
+ struct trace_bprintk_fmt *mod_fmt;
+
+ if (list_empty(&trace_bprintk_fmt_list))
+ return NULL;
+
+ /*
+ * v will point to the address of the fmt record from t_next
+ * v will be NULL from t_start.
+ * If this is the first pointer or called from start
+ * then we need to walk the list.
+ */
+ if (!v || start_index == *pos) {
+ struct trace_bprintk_fmt *p;
+
+ /* search the module list */
+ list_for_each_entry(p, &trace_bprintk_fmt_list, list) {
+ if (start_index == *pos)
+ return &p->fmt;
+ start_index++;
+ }
+ /* pos > index */
+ return NULL;
+ }
+
+ /*
+ * v points to the address of the fmt field in the mod list
+ * structure that holds the module print format.
+ */
+ mod_fmt = container_of(v, typeof(*mod_fmt), fmt);
+ if (mod_fmt->list.next == &trace_bprintk_fmt_list)
+ return NULL;
+
+ mod_fmt = container_of(mod_fmt->list.next, typeof(*mod_fmt), list);
+
+ return &mod_fmt->fmt;
+}
+
+static void format_mod_start(void)
+{
+ mutex_lock(&btrace_mutex);
+}
+
+static void format_mod_stop(void)
+{
+ mutex_unlock(&btrace_mutex);
+}
+
#else /* !CONFIG_MODULES */
__init static int
module_trace_bprintk_format_notify(struct notifier_block *self,
@@ -96,6 +166,13 @@
{
return 0;
}
+static inline const char **
+find_next_mod_format(int start_index, void *v, const char **fmt, loff_t *pos)
+{
+ return NULL;
+}
+static inline void format_mod_start(void) { }
+static inline void format_mod_stop(void) { }
#endif /* CONFIG_MODULES */
@@ -158,20 +235,33 @@
}
EXPORT_SYMBOL_GPL(__ftrace_vprintk);
+static const char **find_next(void *v, loff_t *pos)
+{
+ const char **fmt = v;
+ int start_index;
+
+ if (!fmt)
+ fmt = __start___trace_bprintk_fmt + *pos;
+
+ start_index = __stop___trace_bprintk_fmt - __start___trace_bprintk_fmt;
+
+ if (*pos < start_index)
+ return fmt;
+
+ return find_next_mod_format(start_index, v, fmt, pos);
+}
+
static void *
t_start(struct seq_file *m, loff_t *pos)
{
- const char **fmt = __start___trace_bprintk_fmt + *pos;
-
- if ((unsigned long)fmt >= (unsigned long)__stop___trace_bprintk_fmt)
- return NULL;
- return fmt;
+ format_mod_start();
+ return find_next(NULL, pos);
}
static void *t_next(struct seq_file *m, void * v, loff_t *pos)
{
(*pos)++;
- return t_start(m, pos);
+ return find_next(v, pos);
}
static int t_show(struct seq_file *m, void *v)
@@ -210,6 +300,7 @@
static void t_stop(struct seq_file *m, void *p)
{
+ format_mod_stop();
}
static const struct seq_operations show_format_seq_ops = {