tracing: Use seq file for trace_clock

The buffer for the output is as small as 64 bytes, so it'll
overflow if we add more clock type. Use seq file instead.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4B1DC4FB.5030407@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 15 insertions, 9 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a6c41cc63285..886268e0d8ee 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3366,21 +3366,18 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
         return cnt;
 }
 
-static ssize_t tracing_clock_read(struct file *filp, char __user *ubuf,
-                                  size_t cnt, loff_t *ppos)
+static int tracing_clock_show(struct seq_file *m, void *v)
 {
-        char buf[64];
-        int bufiter = 0;
         int i;
 
         for (i = 0; i < ARRAY_SIZE(trace_clocks); i++)
-                bufiter += snprintf(buf + bufiter, sizeof(buf) - bufiter,
+                seq_printf(m,
                         "%s%s%s%s", i ? " " : "",
                         i == trace_clock_id ? "[" : "", trace_clocks[i].name,
                         i == trace_clock_id ? "]" : "");
-        bufiter += snprintf(buf + bufiter, sizeof(buf) - bufiter, "\n");
+        seq_putc(m, '\n');
 
-        return simple_read_from_buffer(ubuf, cnt, ppos, buf, bufiter);
+        return 0;
 }
 
 static ssize_t tracing_clock_write(struct file *filp, const char __user *ubuf,
@@ -3422,6 +3419,13 @@ static ssize_t tracing_clock_write(struct file *filp, const char __user *ubuf,
         return cnt;
 }
 
+static int tracing_clock_open(struct inode *inode, struct file *file)
+{
+        if (tracing_disabled)
+                return -ENODEV;
+        return single_open(file, tracing_clock_show, NULL);
+}
+
 static const struct file_operations tracing_max_lat_fops = {
         .open           = tracing_open_generic,
         .read           = tracing_max_lat_read,
@@ -3460,8 +3464,10 @@ static const struct file_operations tracing_mark_fops = {
 };
 
 static const struct file_operations trace_clock_fops = {
-        .open           = tracing_open_generic,
-        .read           = tracing_clock_read,
+        .open           = tracing_clock_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = single_release,
         .write          = tracing_clock_write,
 };