From 252fd492b48721806ed8d72b508ea3733bc70845 Mon Sep 17 00:00:00 2001
From: Julien Desfossez <julien.desfossez@polymtl.ca>
Date: Tue, 24 May 2011 22:30:42 +0200
Subject: [PATCH] Remove the timeout on poll

Use a shared pipe to wake the poll thread when new fds arrive.

Signed-off-by: Julien Desfossez <julien.desfossez@polymtl.ca>
---
 kconsumerd/kconsumerd.c | 44 +++++++++++++++++++++++++++++++++++------
 kconsumerd/kconsumerd.h |  3 ---
 2 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/kconsumerd/kconsumerd.c b/kconsumerd/kconsumerd.c
index 66f3877d0..fcd4101a6 100644
--- a/kconsumerd/kconsumerd.c
+++ b/kconsumerd/kconsumerd.c
@@ -61,6 +61,9 @@ static pthread_t threads[2];
 /* communication with splice */
 static int thread_pipe[2];
 
+/* pipe to wake the poll thread when necessary */
+static int poll_pipe[2];
+
 /* socket to communicate errors with sessiond */
 static int error_socket = -1;
 
@@ -404,7 +407,7 @@ static int consumerd_recv_fd(int sfd, int size,
 {
 	struct msghdr msg;
 	struct iovec iov[1];
-	int ret, i;
+	int ret, i, tmp2;
 	struct cmsghdr *cmsg;
 	int nb_fd;
 	char tmp[CMSG_SPACE(size)];
@@ -465,7 +468,8 @@ static int consumerd_recv_fd(int sfd, int size,
 		}
 		/* flag to tell the polling thread to update its fd array */
 		update_fd_array = 1;
-		send_error(KCONSUMERD_SUCCESS_RECV_FD);
+		/* signal the poll thread */
+		tmp2 = write(poll_pipe[1], "4", 1);
 	} else {
 		ERR("Didn't received any fd");
 		send_error(KCONSUMERD_ERROR_RECV_FD);
@@ -561,13 +565,15 @@ static int update_poll_array(struct pollfd **pollfd,
 		*local_kconsumerd_fd = NULL;
 	}
 
-	*pollfd = malloc(fds_count * sizeof(struct pollfd));
+	/* allocate for all fds + 1 for the poll_pipe */
+	*pollfd = malloc((fds_count + 1) * sizeof(struct pollfd));
 	if (*pollfd == NULL) {
 		perror("pollfd malloc");
 		goto error_mem;
 	}
 
-	*local_kconsumerd_fd = malloc(fds_count * sizeof(struct ltt_kconsumerd_fd));
+	/* allocate for all fds + 1 for the poll_pipe */
+	*local_kconsumerd_fd = malloc((fds_count + 1) * sizeof(struct ltt_kconsumerd_fd));
 	if (*local_kconsumerd_fd == NULL) {
 		perror("local_kconsumerd_fd malloc");
 		goto error_mem;
@@ -588,6 +594,13 @@ static int update_poll_array(struct pollfd **pollfd,
 			del_fd(iter);
 		}
 	}
+	/*
+	 * insert the poll_pipe at the end of the array and don't increment i
+	 * so nb_fd is the number of real FD
+	 */
+	(*pollfd)[i].fd = poll_pipe[0];
+	(*pollfd)[i].events = POLLIN;
+
 	update_fd_array = 0;
 	pthread_mutex_unlock(&kconsumerd_lock_fds);
 	return i;
@@ -610,6 +623,8 @@ static void *thread_poll_fds(void *data)
 	struct ltt_kconsumerd_fd **local_kconsumerd_fd = NULL;
 	/* local view of fds_count */
 	int nb_fd = 0;
+	char tmp;
+	int tmp2;
 
 	ret = pipe(thread_pipe);
 	if (ret < 0) {
@@ -638,8 +653,8 @@ static void *thread_poll_fds(void *data)
 		}
 
 		/* poll on the array of fds */
-		DBG("polling on %d fd", nb_fd);
-		num_rdy = poll(pollfd, nb_fd, POLL_TIMEOUT);
+		DBG("polling on %d fd", nb_fd + 1);
+		num_rdy = poll(pollfd, nb_fd + 1, -1);
 		DBG("poll num_rdy : %d", num_rdy);
 		if (num_rdy == -1) {
 			perror("Poll error");
@@ -647,6 +662,16 @@ static void *thread_poll_fds(void *data)
 			goto end;
 		}
 
+		/*
+		 * if only the poll_pipe triggered poll to return just return to the
+		 * beginning of the loop to update the array
+		 */
+		if (num_rdy == 1 && pollfd[nb_fd].revents == POLLIN) {
+			DBG("poll_pipe wake up");
+			tmp2 = read(poll_pipe[0], &tmp, 1);
+			continue;
+		}
+
 		/* Take care of high priority channels first. */
 		for (i = 0; i < nb_fd; i++) {
 			switch(pollfd[i].revents) {
@@ -830,6 +855,13 @@ int main(int argc, char **argv)
 		goto error;
 	}
 
+	/* create the pipe to wake to polling thread when needed */
+	ret = pipe(poll_pipe);
+	if (ret < 0) {
+		perror("Error creating poll pipe");
+		goto end;
+	}
+
 	/* Connect to the socket created by ltt-sessiond to report errors */
 	DBG("Connecting to error socket %s", error_sock_path);
 	error_socket = lttcomm_connect_unix_sock(error_sock_path);
diff --git a/kconsumerd/kconsumerd.h b/kconsumerd/kconsumerd.h
index f5ec288bc..6c78663f5 100644
--- a/kconsumerd/kconsumerd.h
+++ b/kconsumerd/kconsumerd.h
@@ -19,9 +19,6 @@
 #ifndef _LTT_KCONSUMERD_H
 #define _LTT_KCONSUMERD_H
 
-/* timeout of 1s on poll to ensure the fd list is updated when needed */
-#define POLL_TIMEOUT 1000
-
 struct ltt_kconsumerd_fd_list {
 	struct cds_list_head head;
 };
-- 
2.34.1