From: David Goulet <dgoulet@efficios.com>
Date: Tue, 27 Aug 2013 19:11:40 +0000 (-0400)
Subject: Get the maximum TCP timeout in sessiond
X-Git-Tag: v2.3.0-rc3~17
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=d831c2497e9e8b2360cbe2026fdb2d736fa07641;p=lttng-tools.git

Get the maximum TCP timeout in sessiond

This actually just open some /proc files when calling
lttcomm_init_inet() and computes the maximum value a TCP timeout for
every possible operations (send/recv/connect).

This is the first patch to fix the health check issue of having a
smaller delta than the TCP maximum possible timeout.

Signed-off-by: David Goulet <dgoulet@efficios.com>
---

diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index 195174a4e..627560f49 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -4652,6 +4652,8 @@ int main(int argc, char **argv)
 
 	/* Initialize communication library */
 	lttcomm_init();
+	/* This is to get the TCP timeout value. */
+	lttcomm_inet_init();
 
 	/* Create thread to manage the client socket */
 	ret = pthread_create(&ht_cleanup_thread, NULL,
diff --git a/src/common/defaults.h b/src/common/defaults.h
index 7bb10c2af..c115491ec 100644
--- a/src/common/defaults.h
+++ b/src/common/defaults.h
@@ -198,6 +198,13 @@
  */
 #define DEFAULT_METADATA_AVAILABILITY_WAIT_TIME 200000  /* usec */
 
+/*
+ * The usual value for the maximum TCP SYN retries time and TCP FIN timeout is
+ * 180 and 60 seconds on most Linux system and the default value since kernel
+ * 2.2 thus using the highest value. See tcp(7) for more details.
+ */
+#define DEFAULT_INET_TCP_TIMEOUT			180	/* sec */
+
 /*
  * Default receiving and sending timeout for an application socket.
  */
diff --git a/src/common/sessiond-comm/inet.c b/src/common/sessiond-comm/inet.c
index eb0c4fde3..b5a016e6f 100644
--- a/src/common/sessiond-comm/inet.c
+++ b/src/common/sessiond-comm/inet.c
@@ -50,6 +50,8 @@ static const struct lttcomm_proto_ops inet_ops = {
 	.sendmsg = lttcomm_sendmsg_inet_sock,
 };
 
+unsigned long lttcomm_inet_tcp_timeout;
+
 /*
  * Creates an PF_INET socket.
  */
@@ -448,3 +450,68 @@ int lttcomm_close_inet_sock(struct lttcomm_sock *sock)
 
 	return ret;
 }
+
+/*
+ * Return value read from /proc or else 0 if value is not found.
+ */
+static unsigned long read_proc_value(const char *path)
+{
+	int ret, fd;
+	long r_val;
+	unsigned long val = 0;
+	char buf[64];
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0) {
+		goto error;
+	}
+
+	ret = read(fd, buf, sizeof(buf));
+	if (ret < 0) {
+		PERROR("read proc failed");
+		goto error_close;
+	}
+
+	errno = 0;
+	r_val = strtol(buf, NULL, 10);
+	if (errno != 0 || r_val < -1L) {
+		val = 0;
+		goto error_close;
+	} else {
+		if (r_val > 0) {
+			val = r_val;
+		}
+	}
+
+error_close:
+	ret = close(fd);
+	if (ret) {
+		PERROR("close /proc value");
+	}
+error:
+	return val;
+}
+
+LTTNG_HIDDEN
+void lttcomm_inet_init(void)
+{
+	unsigned long syn_retries, fin_timeout, syn_timeout;
+
+	/* Assign default value and see if we can change it. */
+	lttcomm_inet_tcp_timeout = DEFAULT_INET_TCP_TIMEOUT;
+
+	syn_retries = read_proc_value(LTTCOMM_INET_PROC_SYN_RETRIES_PATH);
+	fin_timeout = read_proc_value(LTTCOMM_INET_PROC_FIN_TIMEOUT_PATH);
+
+	syn_timeout = syn_retries * LTTCOMM_INET_SYN_TIMEOUT_FACTOR;
+
+	/*
+	 * Get the maximum between the two possible timeout value and use that to
+	 * get the maximum with the default timeout.
+	 */
+	lttcomm_inet_tcp_timeout = max_t(unsigned long,
+			max_t(unsigned long, syn_timeout, fin_timeout),
+			lttcomm_inet_tcp_timeout);
+
+	DBG("TCP inet operation timeout set to %lu sec", lttcomm_inet_tcp_timeout);
+}
diff --git a/src/common/sessiond-comm/inet.h b/src/common/sessiond-comm/inet.h
index 89716b8ba..83209bb71 100644
--- a/src/common/sessiond-comm/inet.h
+++ b/src/common/sessiond-comm/inet.h
@@ -23,6 +23,26 @@
 
 #include "sessiond-comm.h"
 
+/* See man tcp(7) for more detail about this value. */
+#define LTTCOMM_INET_PROC_SYN_RETRIES_PATH "/proc/sys/net/ipv4/tcp_syn_retries"
+#define LTTCOMM_INET_PROC_FIN_TIMEOUT_PATH "/proc/sys/net/ipv4/tcp_fin_timeout"
+
+/*
+ * The timeout value of a connect() is computed with an algorithm inside the
+ * kernel using the defined TCP SYN retries so the end value in time is
+ * approximative. According to tcp(7) man page, a value of 5 is roughly 180
+ * seconds of timeout. With that information, we've computed a factor of 36
+ * (180/5) by considering that it grows linearly. This is of course uncertain
+ * but this is the best approximation we can do at runtime.
+ */
+#define LTTCOMM_INET_SYN_TIMEOUT_FACTOR		36
+
+/*
+ * Maximum timeout value in seconds of a TCP connection for both send/recv and
+ * connect operations.
+ */
+extern unsigned long lttcomm_inet_tcp_timeout;
+
 /* Stub */
 struct lttcomm_sock;
 
@@ -41,4 +61,7 @@ extern ssize_t lttcomm_recvmsg_inet_sock(struct lttcomm_sock *sock, void *buf,
 extern ssize_t lttcomm_sendmsg_inet_sock(struct lttcomm_sock *sock, void *buf,
 		size_t len, int flags);
 
+/* Initialize inet communication layer. */
+extern void lttcomm_inet_init(void);
+
 #endif	/* _LTTCOMM_INET_H */