tracing: add saved_cmdlines file to show cached task comms

Export the cached task comms to userspace. This allows user apps to translate
the pids from a trace into their respective task command lines.

[ Impact: let userspace apps reading binary buffer know comm's of pids ]

Signed-off-by: Avadh Patel <avadh4all@gmail.com>
[ added error checking and use of buf pointer to index file_buf ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2d69b26b3cc9fb9bf907849adf7cf2fd4ff90af6..031c46f11bb96de20e6dacdad2929b28c6bb863c 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2421,6 +2421,56 @@ static const struct file_operations tracing_readme_fops = {
        .read           = tracing_readme_read,
 };
 
+static ssize_t
+tracing_saved_cmdlines_read(struct file *file, char __user *ubuf,
+                               size_t cnt, loff_t *ppos)
+{
+       char *buf_comm;
+       char *file_buf;
+       char *buf;
+       int len = 0;
+       int pid;
+       int i;
+
+       file_buf = kmalloc(SAVED_CMDLINES*(16+TASK_COMM_LEN), GFP_KERNEL);
+       if (!file_buf)
+               return -ENOMEM;
+
+       buf_comm = kmalloc(TASK_COMM_LEN, GFP_KERNEL);
+       if (!buf_comm) {
+               kfree(file_buf);
+               return -ENOMEM;
+       }
+
+       buf = file_buf;
+
+       for (i = 0; i < SAVED_CMDLINES; i++) {
+               int r;
+
+               pid = map_cmdline_to_pid[i];
+               if (pid == -1 || pid == NO_CMDLINE_MAP)
+                       continue;
+
+               trace_find_cmdline(pid, buf_comm);
+               r = sprintf(buf, "%d %s\n", pid, buf_comm);
+               buf += r;
+               len += r;
+       }
+
+       len = simple_read_from_buffer(ubuf, cnt, ppos,
+                                     file_buf, len);
+
+       kfree(file_buf);
+       kfree(buf_comm);
+
+       return len;
+}
+
+static const struct file_operations tracing_saved_cmdlines_fops = {
+    .open       = tracing_open_generic,
+    .read       = tracing_saved_cmdlines_read,
+};
+
 static ssize_t
 tracing_ctrl_read(struct file *filp, char __user *ubuf,
                  size_t cnt, loff_t *ppos)
@@ -3973,6 +4023,9 @@ static __init int tracer_init_debugfs(void)
        trace_create_file("trace_marker", 0220, d_tracer,
                        NULL, &tracing_mark_fops);
 
+       trace_create_file("saved_cmdlines", 0444, d_tracer,
+                       NULL, &tracing_saved_cmdlines_fops);
+
 #ifdef CONFIG_DYNAMIC_FTRACE
        trace_create_file("dyn_ftrace_total_info", 0444, d_tracer,
                        &ftrace_update_tot_cnt, &tracing_dyn_info_fops);