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Subject[PATCH V4 2/5] trace-cmd/msg: Use poll(2) to wait for a message
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Use poll(2) to wait for a message. If a client/server cannot send a message for
any reasons, the current server/client will wait in a blocking read operation.
So, we use poll(2) for avoiding remaining in a blocking state.

Changes in V4: Change the argument of tracecmd_msg_recv_wait()
Fix some typos

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
---
trace-msg.c | 42 ++++++++++++++++++++++++++++++++++++------
1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/trace-msg.c b/trace-msg.c
index 08fa2a6..db48365 100644
--- a/trace-msg.c
+++ b/trace-msg.c
@@ -395,6 +395,27 @@ error:
return -ENOMSG;
}

+#define MSG_WAIT_MSEC 5000
+
+/*
+ * A return value of 0 indicates time-out
+ */
+static int tracecmd_msg_recv_wait(int fd, struct tracecmd_msg *msg)
+{
+ struct pollfd pfd;
+ int ret;
+
+ pfd.fd = fd;
+ pfd.events = POLLIN;
+ ret = poll(&pfd, 1, MSG_WAIT_MSEC);
+ if (ret < 0)
+ return -errno;
+ else if (ret == 0)
+ return -ETIMEDOUT;
+
+ return tracecmd_msg_recv(fd, msg);
+}
+
static void *tracecmd_msg_buf_access(struct tracecmd_msg *msg, int offset)
{
return (void *)msg + offset;
@@ -405,9 +426,12 @@ static int tracecmd_msg_wait_for_msg(int fd, struct tracecmd_msg *msg)
u32 cmd;
int ret;

- ret = tracecmd_msg_recv(fd, msg);
- if (ret < 0)
+ ret = tracecmd_msg_recv_wait(fd, msg);
+ if (ret < 0) {
+ if (ret == -ETIMEDOUT)
+ warning("Connection timed out\n");
return ret;
+ }

cmd = ntohl(msg->cmd);
if (cmd == MSG_CLOSE)
@@ -487,9 +511,12 @@ int tracecmd_msg_initial_setting(int fd, int *cpus, int *pagesize)
u32 cmd;

msg = (struct tracecmd_msg *)buf;
- ret = tracecmd_msg_recv(fd, msg);
- if (ret < 0)
+ ret = tracecmd_msg_recv_wait(fd, msg);
+ if (ret < 0) {
+ if (ret == -ETIMEDOUT)
+ warning("Connection timed out\n");
return ret;
+ }

cmd = ntohl(msg->cmd);
if (cmd != MSG_TINIT) {
@@ -627,9 +654,12 @@ int tracecmd_msg_collect_metadata(int ifd, int ofd)
msg = (struct tracecmd_msg *)buf;

do {
- ret = tracecmd_msg_recv(ifd, msg);
+ ret = tracecmd_msg_recv_wait(ifd, msg);
if (ret < 0) {
- warning("reading client");
+ if (ret == -ETIMEDOUT)
+ warning("Connection timed out\n");
+ else
+ warning("reading client");
return ret;
}



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