tracing: Convert trace_printk() formats for module to const char *

The trace_printk() formats for modules do not show up in the
debugfs/tracing/printk_formats file. Only the formats that are
for trace_printk()s that are in the kernel core.

To facilitate the change to add trace_printk() formats from modules
into that file as well, we need to convert the structure that
holds the formats from char fmt[], into const char *fmt,
and allocate them separately.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_printk.c

@@ -32,7 +32,7 @@ static DEFINE_MUTEX(btrace_mutex);
 
 struct trace_bprintk_fmt {
 	struct list_head list;
-	char fmt[0];
+	const char *fmt;
 };
 
 static inline struct trace_bprintk_fmt *lookup_format(const char *fmt)
@@ -49,6 +49,7 @@ static
 void hold_module_trace_bprintk_format(const char **start, const char **end)
 {
 	const char **iter;
+	char *fmt;
 
 	mutex_lock(&btrace_mutex);
 	for (iter = start; iter < end; iter++) {
@@ -58,15 +59,19 @@ void hold_module_trace_bprintk_format(const char **start, const char **end)
 			continue;
 		}
 
-		tb_fmt = kmalloc(offsetof(struct trace_bprintk_fmt, fmt)
-				+ strlen(*iter) + 1, GFP_KERNEL);
-		if (tb_fmt) {
+		tb_fmt = kmalloc(sizeof(*tb_fmt), GFP_KERNEL);
+		if (tb_fmt)
+			fmt = kmalloc(strlen(*iter) + 1, GFP_KERNEL);
+		if (tb_fmt && fmt) {
 			list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
-			strcpy(tb_fmt->fmt, *iter);
+			strcpy(fmt, *iter);
+			tb_fmt->fmt = fmt;
 			*iter = tb_fmt->fmt;
-		} else
+		} else {
+			kfree(tb_fmt);
 			*iter = NULL;
 		}
+	}
 	mutex_unlock(&btrace_mutex);
 }