From mboxrd@z Thu Jan 1 00:00:00 1970 From: ylamarre@efficios.com (Yannick Lamarre) Date: Thu, 25 Apr 2019 10:36:18 -0400 Subject: [lttng-dev] [PATCH lttng-tools v5 6/8] Change lttng_poll_wait behaviour of compat-poll to match compat-epoll In-Reply-To: <20190425143620.3348-1-ylamarre@efficios.com> References: <20190425143620.3348-1-ylamarre@efficios.com> Message-ID: <20190425143620.3348-7-ylamarre@efficios.com> This removes the need to verify for idle file descriptors and mitigates risks of bug due to behaviour mismatch. Signed-off-by: Yannick Lamarre --- Iterator declaration moved to the begining of function. 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 2318920a..0220b278 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; -- 2.11.0