lttng-ctl: notifications: use epoll()/poll() instead of select()

The select(2) system call is an ancient ABI limited to processes
containing at most FD_SETSIZE file descriptors overall (typically
1024).

Those notification APIs will fail if the target file descriptor
is above FD_SETSIZE in a process containing many file descriptors.

Never use select, use the lttng epoll/poll wrapper instead.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/lib/lttng-ctl/channel.c b/src/lib/lttng-ctl/channel.c
index 5271aa13fbd76218fca47b8984c6a055fc84b35f..bcecc65fbbb281d6466b6805c88f28ca1cac448e 100644 (file)
--- a/src/lib/lttng-ctl/channel.c
+++ b/src/lib/lttng-ctl/channel.c
@@ -26,8 +26,7 @@
 #include <common/defaults.h>
 #include <assert.h>
 #include "lttng-ctl-helper.h"
-#include <sys/select.h>
-#include <sys/time.h>
+#include <common/compat/poll.h>
 
 static
 int handshake(struct lttng_notification_channel *channel);
@@ -211,7 +210,7 @@ lttng_notification_channel_get_next_notification(
        struct lttng_notification *notification = NULL;
        enum lttng_notification_channel_status status =
                        LTTNG_NOTIFICATION_CHANNEL_STATUS_OK;
-       fd_set read_fds;
+       struct lttng_poll_event events;
 
        if (!channel || !_notification) {
                status = LTTNG_NOTIFICATION_CHANNEL_STATUS_INVALID;
@@ -241,9 +240,9 @@ lttng_notification_channel_get_next_notification(
        }
 
        /*
-        * Block on select() instead of the message reception itself as the
-        * recvmsg() wrappers always restard on EINTR. We choose to wait
-        * using select() in order to:
+        * Block on interruptible epoll/poll() instead of the message reception
+        * itself as the recvmsg() wrappers always restart on EINTR. We choose
+        * to wait using interruptible epoll/poll() in order to:
         *   1) Return if a signal occurs,
         *   2) Not deal with partially received messages.
         *
@@ -252,20 +251,28 @@ lttng_notification_channel_get_next_notification(
         * announced length, receive_message() will block on recvmsg()
         * and never return (even if a signal is received).
         */
-       FD_ZERO(&read_fds);
-       FD_SET(channel->socket, &read_fds);
-       ret = select(channel->socket + 1, &read_fds, NULL, NULL, NULL);
-       if (ret == -1) {
-               status = errno == EINTR ?
+       ret = lttng_poll_create(&events, 1, LTTNG_CLOEXEC);
+       if (ret < 0) {
+               status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
+               goto end_unlock;
+       }
+       ret = lttng_poll_add(&events, channel->socket, LPOLLIN | LPOLLERR);
+       if (ret < 0) {
+               status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
+               goto end_clean_poll;
+       }
+       ret = lttng_poll_wait_interruptible(&events, -1);
+       if (ret <= 0) {
+               status = (ret == -1 && errno == EINTR) ?
                        LTTNG_NOTIFICATION_CHANNEL_STATUS_INTERRUPTED :
                        LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
-               goto end_unlock;
+               goto end_clean_poll;
        }
 
        ret = receive_message(channel);
        if (ret) {
                status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
-               goto end_unlock;
+               goto end_clean_poll;
        }
 
        switch (get_current_message_type(channel)) {
@@ -274,7 +281,7 @@ lttng_notification_channel_get_next_notification(
                                channel);
                if (!notification) {
                        status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
-                       goto end_unlock;
+                       goto end_clean_poll;
                }
                break;
        case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION_DROPPED:
@@ -284,9 +291,11 @@ lttng_notification_channel_get_next_notification(
        default:
                /* Protocol error. */
                status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
-               goto end_unlock;
+               goto end_clean_poll;
        }
 
+end_clean_poll:
+       lttng_poll_clean(&events);
 end_unlock:
        pthread_mutex_unlock(&channel->lock);
        *_notification = notification;
@@ -387,11 +396,7 @@ lttng_notification_channel_has_pending_notification(
        int ret;
        enum lttng_notification_channel_status status =
                        LTTNG_NOTIFICATION_CHANNEL_STATUS_OK;
-       fd_set read_fds;
-       struct timeval timeout;
-
-       FD_ZERO(&read_fds);
-       memset(&timeout, 0, sizeof(timeout));
+       struct lttng_poll_event events;
 
        if (!channel || !_notification_pending) {
                status = LTTNG_NOTIFICATION_CHANNEL_STATUS_INVALID;
@@ -426,48 +431,57 @@ lttng_notification_channel_has_pending_notification(
         * message if we see data available on the socket. If the peer does
         * not respect the protocol, this may block indefinitely.
         */
-       FD_SET(channel->socket, &read_fds);
-       do {
-               ret = select(channel->socket + 1, &read_fds, NULL, NULL, &timeout);
-       } while (ret < 0 && errno == EINTR);
-
+       ret = lttng_poll_create(&events, 1, LTTNG_CLOEXEC);
+       if (ret < 0) {
+               status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
+               goto end_unlock;
+       }
+       ret = lttng_poll_add(&events, channel->socket, LPOLLIN | LPOLLERR);
+       if (ret < 0) {
+               status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
+               goto end_clean_poll;
+       }
+       /* timeout = 0: return immediately. */
+       ret = lttng_poll_wait_interruptible(&events, 0);
        if (ret == 0) {
                /* No data available. */
                *_notification_pending = false;
-               goto end_unlock;
+               goto end_clean_poll;
        } else if (ret < 0) {
                status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
-               goto end_unlock;
+               goto end_clean_poll;
        }
 
        /* Data available on socket. */
        ret = receive_message(channel);
        if (ret) {
                status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
-               goto end_unlock;
+               goto end_clean_poll;
        }
 
        switch (get_current_message_type(channel)) {
        case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION:
                ret = enqueue_notification_from_current_message(channel);
                if (ret) {
-                       goto end_unlock;
+                       goto end_clean_poll;
                }
                *_notification_pending = true;
                break;
        case LTTNG_NOTIFICATION_CHANNEL_MESSAGE_TYPE_NOTIFICATION_DROPPED:
                ret = enqueue_dropped_notification(channel);
                if (ret) {
-                       goto end_unlock;
+                       goto end_clean_poll;
                }
                *_notification_pending = true;
                break;
        default:
                /* Protocol error. */
                status = LTTNG_NOTIFICATION_CHANNEL_STATUS_ERROR;
-               goto end_unlock;
+               goto end_clean_poll;
        }
 
+end_clean_poll:
+       lttng_poll_clean(&events);
 end_unlock:
        pthread_mutex_unlock(&channel->lock);
 end: