On Mon, Apr 01, 2019 at 01:59:23PM -0400, Yannick Lamarre wrote:
> This removes the need to verify for idle file descriptors and mitigates
> risks of bug due to behaviour mismatch.
>
> Signed-off-by: Yannick Lamarre <ylama...@efficios.com>
> ---
>
> The assert in the for loop is removed.
>
> src/common/compat/compat-poll.c | 37 +++++++++++++++++++++++++++++++++----
> 1 file changed, 33 insertions(+), 4 deletions(-)
>
> diff --git a/src/common/compat/compat-poll.c b/src/common/compat/compat-poll.c
> index be655728..5b752a28 100644
> --- a/src/common/compat/compat-poll.c
> +++ b/src/common/compat/compat-poll.c
> @@ -293,7 +293,8 @@ error:
> */
> int compat_poll_wait(struct lttng_poll_event *events, int timeout)
> {
> - int ret;
> + int ret, active_fd_count;
> + int idle_pfd_index = 0;
>
> if (events == NULL || events->current.events == NULL) {
> ERR("poll wait arguments error");
> @@ -325,11 +326,39 @@ 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 (int i = idle_pfd_index + 1; idle_pfd_index < active_fd_count;
> + i++) {
Declare 'i' at the beginning of the function.
Thanks!
Jérémie
> + 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
>
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