Re: [PATCH for-4.5] tools/oxenstored: Fix | vs & error in fd event handling

[Zheng Li <dev@zheng.li>]

On 26/11/2014 15:09, Andrew Cooper wrote:
> This makes fields 0 and 1 true more often than they should be, resulting
> problems when handling events.

Indeed, looks like a mistake I made when rewriting the logic terms lately. The result is POLLUP or POLLERR events being returned in more categories than we'd interest. Thanks for fixing this!

Acked-by: Zheng Li <dev@zheng.li>


Cheers,
Zheng


> ---
>
> This was discovered with XenServers internal Coverity instance.  I have yet to
> work out why the issue is not identified by the upstream coverity scanning.
>
> Konrad: This is a bug in the default event handling used by oxenstored in 4.5,
> as the default switched from select() to poll() in the 4.5 timeframe.  It
> would appear that the negative side effects are limited to just logspam about
> certain clients attempting invalid actions, but I can't rule out anything more
> problematic.
> ---
>   tools/ocaml/xenstored/select_stubs.c |    4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/ocaml/xenstored/select_stubs.c b/tools/ocaml/xenstored/select_stubs.c
> index 4a8edb5..af72b84 100644
> --- a/tools/ocaml/xenstored/select_stubs.c
> +++ b/tools/ocaml/xenstored/select_stubs.c
> @@ -56,8 +56,8 @@ CAMLprim value stub_select_on_poll(value fd_events, value timeo) {
>   			events = Field(Field(fd_events, i), 1);
>
>   			if (c_fds[i].revents & POLLNVAL) unix_error(EBADF, "select", Nothing);
> -			Field(events, 0) = Val_bool(c_fds[i].events | POLLIN  && c_fds[i].revents & (POLLIN |POLLHUP|POLLERR));
> -			Field(events, 1) = Val_bool(c_fds[i].events | POLLOUT && c_fds[i].revents & (POLLOUT|POLLHUP|POLLERR));
> +			Field(events, 0) = Val_bool(c_fds[i].events & POLLIN  && c_fds[i].revents & (POLLIN |POLLHUP|POLLERR));
> +			Field(events, 1) = Val_bool(c_fds[i].events & POLLOUT && c_fds[i].revents & (POLLOUT|POLLHUP|POLLERR));
>   			Field(events, 2) = Val_bool(c_fds[i].revents & POLLPRI);
>
>   		}
>