linux-kernel - [PATCH 5/5] trace-cmd: Use polling function

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Date:	Wed, 22 Aug 2012 17:43:43 +0900
From:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Amit Shah <amit.shah@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...64.org>,
	"Franch Ch. Eigler" <fche@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ingo Molnar <mingo@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, qemu-devel@...gnu.org,
	yrl.pp-manager.tt@...achi.com,
	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Subject: [PATCH 5/5] trace-cmd: Use polling function

Use poll() for avoiding a busy loop to read trace data of a guest from FIFO.

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
---

 trace-recorder.c |   42 ++++++++++++++++++++++++++++++++++++------
 1 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/trace-recorder.c b/trace-recorder.c
index 6577fe8..bdf9798 100644
--- a/trace-recorder.c
+++ b/trace-recorder.c
@@ -34,9 +34,12 @@
 #include <ctype.h>
 #include <errno.h>
 #include <stdbool.h>
+#include <poll.h>
 
 #include "trace-cmd.h"
 
+#define WAIT_MSEC 1
+
 struct tracecmd_recorder {
 	int		fd;
 	int		trace_fd;
@@ -235,9 +238,37 @@ static void stop_operation_to_trace_agent(int ctl_fd)
 	operation_to_trace_agent(ctl_fd, false);
 }
 
-int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long sleep)
+static int wait_data(struct tracecmd_recorder *recorder, unsigned long sleep)
 {
+	struct pollfd poll_fd;
 	struct timespec req;
+	int ret = 0;
+
+	if (recorder->agent_existing) {
+		poll_fd.fd = recorder->trace_fd;
+		poll_fd.events = POLLIN;
+		while (1) {
+			ret = poll(&poll_fd, 1, WAIT_MSEC);
+
+			if(ret < 0) {
+				warning("polling error");
+				return ret;
+			}
+
+			if (ret)
+				break;
+		}
+	} else if (sleep) {
+		req.tv_sec = sleep / 1000000;
+		req.tv_nsec = (sleep % 1000000) * 1000;
+		nanosleep(&req, NULL);
+	}
+
+	return ret;
+}
+
+int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long sleep)
+{
 	long ret;
 
 	recorder->stop = 0;
@@ -246,11 +277,10 @@ int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long s
 		run_operation_to_trace_agent(recorder->ctl_fd);
 	
 	do {
-		if (sleep) {
-			req.tv_sec = sleep / 1000000;
-			req.tv_nsec = (sleep % 1000000) * 1000;
-			nanosleep(&req, NULL);
-		}
+		ret = wait_data(recorder, sleep);
+		if (ret < 0)
+			return ret;
+
 		ret = splice_data(recorder);
 		if (ret < 0)
 			return ret;


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