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>

1 files changed, 53 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2d69b26b3cc9..031c46f11bb9 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2422,6 +2422,56 @@ static const struct file_operations tracing_readme_fops = {
 };
 
 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);