From 500f08f0ccd79c49f038c3cf815561e44610d64c Mon Sep 17 00:00:00 2001 From: Yannick Lamarre Date: Thu, 25 Apr 2019 18:23:32 -0400 Subject: [PATCH] Change lttng_poll_wait behaviour of compat-poll to match compat-epoll MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This removes the need to verify for idle file descriptors and mitigates risks of bug due to behaviour mismatch. Signed-off-by: Yannick Lamarre Signed-off-by: Jérémie Galarneau --- src/common/compat/compat-poll.c | 38 +++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) diff --git a/src/common/compat/compat-poll.c b/src/common/compat/compat-poll.c index 2318920ae..0220b2785 100644 --- a/src/common/compat/compat-poll.c +++ b/src/common/compat/compat-poll.c @@ -293,7 +293,9 @@ error: */ int compat_poll_wait(struct lttng_poll_event *events, int timeout) { - int ret; + int ret, active_fd_count; + int idle_pfd_index = 0; + size_t i; if (events == NULL || events->current.events == NULL) { ERR("poll wait arguments error"); @@ -325,11 +327,39 @@ int compat_poll_wait(struct lttng_poll_event *events, int timeout) goto error; } + active_fd_count = ret; + /* - * poll() should always iterate on all FDs since we handle the pollset in - * user space and after poll returns, we have to try every fd for a match. + * Swap all active pollfd structs to the beginning of the + * array to emulate compat-epoll behaviour. This algorithm takes + * advantage of poll's returned value and the burst nature of active + * events on the file descriptors. The while loop guarantees that + * idle_pfd will always point to an idle fd. */ - return events->wait.nb_fd; + if (active_fd_count == events->wait.nb_fd) { + goto end; + } + while (idle_pfd_index < active_fd_count && + events->wait.events[idle_pfd_index].revents != 0) { + idle_pfd_index++; + } + + for (i = idle_pfd_index + 1; idle_pfd_index < active_fd_count; + i++) { + struct pollfd swap_pfd; + struct pollfd *idle_pfd = &events->wait.events[idle_pfd_index]; + struct pollfd *current_pfd = &events->wait.events[i]; + + if (ipfd->revents != 0) { + swap_pfd = *current_pfd; + *current_pfd = *idle_pfd; + *idle_pfd = swap_pfd; + idle_pfd_index++; + } + } + +end: + return ret; error: return -1; -- 2.34.1