linux-kernel - [PATCH 4/5] trace-cmd: Add non-blocking option for open() and splice

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Date:	Wed, 22 Aug 2012 17:43:32 +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 4/5] trace-cmd: Add non-blocking option for open() and
 splice_read()

Add non-blocking option for open() and splice_read() for avoiding block to read
trace data of a guest from FIFO.

If SIGINT comes to read/write processes from the parent process in the case
where FIFO as a read I/F is assigned, then reading is normally blocked for
splice_read(). So, we added nonblock option to open() and splice_read().

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

 trace-recorder.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/trace-recorder.c b/trace-recorder.c
index 3b750e9..6577fe8 100644
--- a/trace-recorder.c
+++ b/trace-recorder.c
@@ -124,7 +124,7 @@ struct tracecmd_recorder *tracecmd_create_recorder_fd(int fd, int cpu)
 		goto out_free;
 
 	sprintf(path, "%s/per_cpu/cpu%d/trace_pipe_raw", tracing, cpu);
-	recorder->trace_fd = open(path, O_RDONLY);
+	recorder->trace_fd = open(path, O_RDONLY | O_NONBLOCK);
 	if (recorder->trace_fd < 0)
 		goto out_free;
 
@@ -172,14 +172,17 @@ static long splice_data(struct tracecmd_recorder *recorder)
 	long ret;
 
 	ret = splice(recorder->trace_fd, NULL, recorder->brass[1], NULL,
-		     recorder->page_size, 1 /* SPLICE_F_MOVE */);
+		     recorder->page_size, SPLICE_F_MOVE | SPLICE_F_NONBLOCK);
 	if (ret < 0) {
-		warning("recorder error in splice input");
-		return -1;
+		if (errno != EAGAIN) {
+			warning("recorder error in splice input");
+			return -1;
+		}
+		return 0; /* Buffer is empty */
 	}
 
 	ret = splice(recorder->brass[0], NULL, recorder->fd, NULL,
-		     recorder->page_size, 3 /* and NON_BLOCK */);
+		     recorder->page_size, SPLICE_F_MOVE | SPLICE_F_NONBLOCK);
 	if (ret < 0) {
 		if (errno != EAGAIN) {
 			warning("recorder error in splice output");


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