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

[Dave Scott <Dave.Scott@xxxxxxxxxx>]

> On 26 Nov 2014, at 15:38, Zheng Li <dev@xxxxxxxx> wrote:
> 
> 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@xxxxxxxx>

This also looks fine to me

Acked-by: David Scott <dave.scott@xxxxxxxxxx>

Cheers,
Dave

> 
> 
> 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);
>> 
>>              }
>> 


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