tracing: Use seq file for trace_options

Code simplification for reading trace_options.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
LKML-reference: <4B1DC4EF.3090106@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

kernel/trace/trace.c

@@ -2316,67 +2316,32 @@ static const struct file_operations tracing_cpumask_fops = {
 	.write		= tracing_cpumask_write,
 };
 
-static ssize_t
-tracing_trace_options_read(struct file *filp, char __user *ubuf,
-		       size_t cnt, loff_t *ppos)
+static int tracing_trace_options_show(struct seq_file *m, void *v)
 {
 	struct tracer_opt *trace_opts;
 	u32 tracer_flags;
-	int len = 0;
-	char *buf;
-	int r = 0;
 	int i;
 
-
-	/* calculate max size */
-	for (i = 0; trace_options[i]; i++) {
-		len += strlen(trace_options[i]);
-		len += 3; /* "no" and newline */
-	}
-
 	mutex_lock(&trace_types_lock);
 	tracer_flags = current_trace->flags->val;
 	trace_opts = current_trace->flags->opts;
 
-	/*
-	 * Increase the size with names of options specific
-	 * of the current tracer.
-	 */
-	for (i = 0; trace_opts[i].name; i++) {
-		len += strlen(trace_opts[i].name);
-		len += 3; /* "no" and newline */
-	}
-
-	/* +1 for \0 */
-	buf = kmalloc(len + 1, GFP_KERNEL);
-	if (!buf) {
-		mutex_unlock(&trace_types_lock);
-		return -ENOMEM;
-	}
-
 	for (i = 0; trace_options[i]; i++) {
 		if (trace_flags & (1 << i))
-			r += sprintf(buf + r, "%s\n", trace_options[i]);
+			seq_printf(m, "%s\n", trace_options[i]);
 		else
-			r += sprintf(buf + r, "no%s\n", trace_options[i]);
+			seq_printf(m, "no%s\n", trace_options[i]);
 	}
 
 	for (i = 0; trace_opts[i].name; i++) {
 		if (tracer_flags & trace_opts[i].bit)
-			r += sprintf(buf + r, "%s\n",
-				trace_opts[i].name);
+			seq_printf(m, "%s\n", trace_opts[i].name);
 		else
-			r += sprintf(buf + r, "no%s\n",
-				trace_opts[i].name);
+			seq_printf(m, "no%s\n", trace_opts[i].name);
 	}
 	mutex_unlock(&trace_types_lock);
 
-	WARN_ON(r >= len + 1);
-
-	r = simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
-
-	kfree(buf);
-	return r;
+	return 0;
 }
 
 /* Try to assign a tracer specific option */
@@ -2471,9 +2436,18 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 	return cnt;
 }
 
+static int tracing_trace_options_open(struct inode *inode, struct file *file)
+{
+	if (tracing_disabled)
+		return -ENODEV;
+	return single_open(file, tracing_trace_options_show, NULL);
+}
+
 static const struct file_operations tracing_iter_fops = {
-	.open		= tracing_open_generic,
-	.read		= tracing_trace_options_read,
+	.open		= tracing_trace_options_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
 	.write		= tracing_trace_options_write,
 };