linux-kernel - [PATCH trace-cmd 2/2] trace-recorder: better error handling during copy

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Date:	Tue, 22 Mar 2016 15:40:42 +0800
From:	Peter Xu <peterx@...hat.com>
To:	linux-kernel@...r.kernel.org, srostedt@...hat.com
Cc:	peterx@...hat.com
Subject: [PATCH trace-cmd 2/2] trace-recorder: better error handling during copy

Currently we have two ways to copy data, one is splice, one is read +
write. For both, dump more information when we got errors during the
copy. Also, when we update_fd(), we should make sure all bytes written,
and update written bytes only.

These information might be important to better diagnose when the copy
got wrong, like no space error, or connection error when copying data to
remote sockets. In the past, we just got silence errors without notice.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 trace-recorder.c | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/trace-recorder.c b/trace-recorder.c
index 49b04ea..7d6feb0 100644
--- a/trace-recorder.c
+++ b/trace-recorder.c
@@ -334,13 +334,14 @@ static inline void update_fd(struct tracecmd_recorder *recorder, int size)
  */
 static long splice_data(struct tracecmd_recorder *recorder)
 {
-	long ret;
+	long ret, written;
 
 	ret = splice(recorder->trace_fd, NULL, recorder->brass[1], NULL,
 		     recorder->page_size, 1 /* SPLICE_F_MOVE */);
 	if (ret < 0) {
 		if (errno != EAGAIN && errno != EINTR) {
-			warning("recorder error in splice input");
+			warning("recorder error in splice input: %s",
+				strerror(errno));
 			return -1;
 		}
 		if (errno == EINTR)
@@ -348,16 +349,23 @@ static long splice_data(struct tracecmd_recorder *recorder)
 	} else if (ret == 0)
 		return 0;
 
-	ret = splice(recorder->brass[0], NULL, recorder->fd, NULL,
-		     recorder->page_size, recorder->fd_flags);
-	if (ret < 0) {
+	written = splice(recorder->brass[0], NULL, recorder->fd, NULL,
+			 recorder->page_size, recorder->fd_flags);
+	if (written < 0) {
 		if (errno != EAGAIN && errno != EINTR) {
-			warning("recorder error in splice output");
+			warning("recorder error in splice output: %s",
+				strerror(errno));
 			return -1;
 		}
 		ret = 0;
-	} else
+	} else {
+		if (written != ret) {
+			warning("recorder written %ld to write %d: %s",
+				written, ret, strerror(errno));
+			return -1;
+		}
 		update_fd(recorder, ret);
+	}
 
 	return ret;
 }
@@ -369,18 +377,24 @@ static long splice_data(struct tracecmd_recorder *recorder)
 static long read_data(struct tracecmd_recorder *recorder)
 {
 	char buf[recorder->page_size];
-	long ret;
+	ssize_t ret, written;
 
 	ret = read(recorder->trace_fd, buf, recorder->page_size);
 	if (ret < 0) {
 		if (errno != EAGAIN && errno != EINTR) {
-			warning("recorder error in read output");
+			warning("recorder error in read output: %s",
+				strerror(errno));
 			return -1;
 		}
 		ret = 0;
 	}
 	if (ret > 0) {
-		write(recorder->fd, buf, ret);
+		written = write(recorder->fd, buf, ret);
+		if (written != ret) {
+			warning("recorder written %ld to write %d: %s",
+				written, ret, strerror(errno));
+			return -1;
+		}
 		update_fd(recorder, ret);
 	}
 
-- 
2.4.3