don't fail if ftrace_enable is not there

We should still be able to do tracing if the kernel was not compiled
with function tracer. Don't fail on failure to read ftrace_enable.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 16 insertions, 3 deletions

diff --git a/trace-cmd.c b/trace-cmd.c
index 22c3df6..77ce277 100644
--- a/trace-cmd.c
+++ b/trace-cmd.c
@@ -289,17 +289,26 @@ static int find_trace_type(const char *type)
         return ret > 0;
 }
 
-static void set_ftrace(int set)
+static int set_ftrace(int set)
 {
+        struct stat buf;
+        char *path = "/proc/sys/kernel/ftrace_enabled";
         int fd;
         char *val = set ? "1" : "0";
 
-        fd = open("/proc/sys/kernel/ftrace_enabled", O_WRONLY);
+        /* if ftace_enable does not exist, simply ignore it */
+        fd = stat(path, &buf);
+        if (fd < 0)
+                return -ENODEV;
+
+        fd = open(path, O_WRONLY);
         if (fd < 0)
                 die ("Can't %s ftrace", set ? "enable" : "disable");
 
         write(fd, val, 1);
         close(fd);
+
+        return 0;
 }
 
 void run_cmd(int argc, char **argv)
@@ -1101,6 +1110,7 @@ int main (int argc, char **argv)
         int plug = 0;
         int events = 0;
         int options = 0;
+        int fset;
 
         int c;
 
@@ -1201,7 +1211,7 @@ int main (int argc, char **argv)
 
         read_tracing_data();
 
-        set_ftrace(!disable);
+        fset = set_ftrace(!disable);
 
         disable_all();
 
@@ -1224,6 +1234,9 @@ int main (int argc, char **argv)
                         latency = 1;
                         stop_threads();
                 }
+                if (fset < 0 && (strcmp(plugin, "function") == 0 ||
+                                 strcmp(plugin, "function_graph") == 0))
+                        die("function tracing not configured on this kernel");
                 set_plugin(plugin);
         }