[PATCH bpf v2 1/2] fprobe: samples: Add use_trace option and show hit/missed counter

["Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Add use_trace option to use trace_printk() instead of pr_info()
so that the handler doesn't involve the RCU operations.
And show the hit and missed counter so that the user can check
how many times the probe handler hit and missed.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 samples/fprobe/fprobe_example.c |   21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/samples/fprobe/fprobe_example.c b/samples/fprobe/fprobe_example.c
index 24d3cf109140..aad5af0278f4 100644
--- a/samples/fprobe/fprobe_example.c
+++ b/samples/fprobe/fprobe_example.c
@@ -21,6 +21,7 @@
 #define BACKTRACE_DEPTH 16
 #define MAX_SYMBOL_LEN 4096
 struct fprobe sample_probe;
+static unsigned long nhit;
 
 static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
 module_param_string(symbol, symbol, sizeof(symbol), 0644);
@@ -28,6 +29,8 @@ static char nosymbol[MAX_SYMBOL_LEN] = "";
 module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
 static bool stackdump = true;
 module_param(stackdump, bool, 0644);
+static bool use_trace = false;
+module_param(use_trace, bool, 0644);
 
 static void show_backtrace(void)
 {
@@ -40,7 +43,11 @@ static void show_backtrace(void)
 
 static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
 {
-	pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
+	if (use_trace)
+		trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
+	else
+		pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
+	nhit++;
 	if (stackdump)
 		show_backtrace();
 }
@@ -49,8 +56,13 @@ static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_r
 {
 	unsigned long rip = instruction_pointer(regs);
 
-	pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
-		(void *)ip, (void *)ip, (void *)rip, (void *)rip);
+	if (use_trace)
+		trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
+			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
+	else
+		pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
+			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
+	nhit++;
 	if (stackdump)
 		show_backtrace();
 }
@@ -112,7 +124,8 @@ static void __exit fprobe_exit(void)
 {
 	unregister_fprobe(&sample_probe);
 
-	pr_info("fprobe at %s unregistered\n", symbol);
+	pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
+		symbol, nhit, sample_probe.nmissed);
 }
 
 module_init(fprobe_init)