tracing: Have saved_cmdlines use the seq_read infrastructure

Current tracing_saved_cmdlines_read() implementation is naive; It allocates
a large buffer, constructs output data to that buffer for each read
operation, and then copies a portion of the buffer to the user space
buffer. This has several issues such as slow memory allocation, high
CPU usage, and even corruption of the output data.

The seq_read infrastructure is made to handle this type of work.
By converting it to use seq_read() the code becomes smaller, simplified,
as well as correct.

Link: http://lkml.kernel.org/p/20140220084431.3839.51793.stgit@yunodevel
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index eb228b9de17095418e738d5e5f1ec664d3f2caa1..1855dae73f346ad0e1f781940a57cc156dd49360 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3699,55 +3699,74 @@ static const struct file_operations tracing_readme_fops = {
        .llseek         = generic_file_llseek,
 };
 
-static ssize_t
-tracing_saved_cmdlines_read(struct file *file, char __user *ubuf,
-                               size_t cnt, loff_t *ppos)
+static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
 {
-       char *buf_comm;
-       char *file_buf;
-       char *buf;
-       int len = 0;
-       int pid;
-       int i;
+       unsigned int *ptr = v;
 
-       file_buf = kmalloc(SAVED_CMDLINES*(16+TASK_COMM_LEN), GFP_KERNEL);
-       if (!file_buf)
-               return -ENOMEM;
+       if (*pos || m->count)
+               ptr++;
 
-       buf_comm = kmalloc(TASK_COMM_LEN, GFP_KERNEL);
-       if (!buf_comm) {
-               kfree(file_buf);
-               return -ENOMEM;
-       }
+       (*pos)++;
+
+       for (; ptr < &map_cmdline_to_pid[SAVED_CMDLINES]; ptr++) {
+               if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
+                       continue;
 
-       buf = file_buf;
+               return ptr;
+       }
 
-       for (i = 0; i < SAVED_CMDLINES; i++) {
-               int r;
+       return NULL;
+}
 
-               pid = map_cmdline_to_pid[i];
-               if (pid == -1 || pid == NO_CMDLINE_MAP)
-                       continue;
+static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
+{
+       void *v;
+       loff_t l = 0;
 
-               trace_find_cmdline(pid, buf_comm);
-               r = sprintf(buf, "%d %s\n", pid, buf_comm);
-               buf += r;
-               len += r;
+       v = &map_cmdline_to_pid[0];
+       while (l <= *pos) {
+               v = saved_cmdlines_next(m, v, &l);
+               if (!v)
+                       return NULL;
        }
 
-       len = simple_read_from_buffer(ubuf, cnt, ppos,
-                                     file_buf, len);
+       return v;
+}
 
-       kfree(file_buf);
-       kfree(buf_comm);
+static void saved_cmdlines_stop(struct seq_file *m, void *v)
+{
+}
 
-       return len;
+static int saved_cmdlines_show(struct seq_file *m, void *v)
+{
+       char buf[TASK_COMM_LEN];
+       unsigned int *pid = v;
+
+       trace_find_cmdline(*pid, buf);
+       seq_printf(m, "%d %s\n", *pid, buf);
+       return 0;
+}
+
+static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
+       .start          = saved_cmdlines_start,
+       .next           = saved_cmdlines_next,
+       .stop           = saved_cmdlines_stop,
+       .show           = saved_cmdlines_show,
+};
+
+static int tracing_saved_cmdlines_open(struct inode *inode, struct file *filp)
+{
+       if (tracing_disabled)
+               return -ENODEV;
+
+       return seq_open(filp, &tracing_saved_cmdlines_seq_ops);
 }
 
 static const struct file_operations tracing_saved_cmdlines_fops = {
-    .open       = tracing_open_generic,
-    .read       = tracing_saved_cmdlines_read,
-    .llseek    = generic_file_llseek,
+       .open           = tracing_saved_cmdlines_open,
+       .read           = seq_read,
+       .llseek         = seq_lseek,
+       .release        = seq_release,
 };
 
 static ssize_t