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Subject[RFC PATCH 09/11] trace-cmd: 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.

This modification avoids to try to connect to an old-version client. An
old-version network server will send a message "tracecmd" first, and an
old-version client will start to send cpu number, pagesize, and option.
By introducing trace-msg, the new client sends a message "MSG_TCONNECT" first,
so the start point of the connection is different. If the old client tries
to connect to the new network server, the server should make the connection
close. A server applied this patch will die when the predetermined time will
have elapsed.

Note that if a new client tries to connect to an old server, the new client
will automatically die. This is because the new client which received the
inappropriate message "tracecmd" will die.

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
---
trace-msg.c | 50 ++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 42 insertions(+), 8 deletions(-)

diff --git a/trace-msg.c b/trace-msg.c
index 777ea1f..36117cd 100644
--- a/trace-msg.c
+++ b/trace-msg.c
@@ -435,6 +435,27 @@ error:
return -ENOMSG;
}

+#define MSG_WAIT_MSEC 5000
+
+/*
+ * A return value of 0 indicates time-out
+ */
+static int tracecmd_msg_recv_wait(int fd, char *buf, 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, buf);
+}
+
static void *tracecmd_msg_buf_access(struct tracecmd_msg *msg, int offset)
{
return (void *)msg + offset;
@@ -448,9 +469,12 @@ static int tracecmd_msg_wait_for_msg(int fd, struct tracecmd_msg **msg)
u32 cmd;
int ret;

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

*msg = (struct tracecmd_msg *)msg_tmp;
cmd = ntohl((*msg)->cmd);
@@ -549,9 +573,13 @@ int tracecmd_msg_set_connection(int fd)
int ret;

/* wait for connection msg by a client first */
- ret = tracecmd_msg_recv(fd, buf);
+ ret = tracecmd_msg_recv_wait(fd, buf, &msg);
if (ret < 0) {
- warning("Disconnect");
+ if (ret == -ETIMEDOUT)
+ /* network connection will be started soon */
+ warning("No connection message");
+ else
+ warning("Disconnect");
return ret;
}

@@ -586,9 +614,12 @@ int tracecmd_msg_initial_setting(int fd, int *cpus, int *pagesize)
u32 size = 0;
u32 cmd;

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

msg = (struct tracecmd_msg *)buf;
cmd = ntohl(msg->cmd);
@@ -724,9 +755,12 @@ int tracecmd_msg_collect_metadata(int ifd, int ofd)
int ret;

do {
- ret = tracecmd_msg_recv(ifd, buf);
+ ret = tracecmd_msg_recv_wait(ifd, buf, &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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