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Re: [Xen-devel] use xs_watch from userspace and use epoll instead of sel

To: "v.tolstov@xxxxxxxxx" <v.tolstov@xxxxxxxxx>
Subject: Re: [Xen-devel] use xs_watch from userspace and use epoll instead of select
From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Date: Mon, 6 Jun 2011 09:41:48 +0100
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On Fri, 2011-06-03 at 17:07 +0100, Vasiliy G Tolstov wrote:
> On Fri, 2011-06-03 at 16:17 +0400, Vasiliy G Tolstov wrote:
> > On Fri, 2011-06-03 at 13:13 +0100, Ian Campbell wrote:
> > > On Fri, 2011-06-03 at 13:04 +0100, Vasiliy G Tolstov wrote:
> > > > Hello. I have some examples of usage xs_watch in userspace that contains
> > > > loop with select function usage. If i use epoll, no events returned from
> > > > epoll_wait...
> > > > Does it matter to use select from fd that used for watch?
> > > > epoll fd added with ev.events = (EPOLLIN | EPOLLPRI | EPOLLONESHOT);
> > > 
> > > I think you need to provide an example of the code which doesn't work.
> > > 
> > > Ian.
> > > 
> > 
> > This is not work:
> >   if ((err = xs_watch(stats->xs, "data/xenmgm", "xenmgm")) != 0) {
> Ok. I'm investigate, that xs_read can use relative to root path, for
> example i can read domid not provide full path to it
> (/local/domain/XX/domid), but if i want use watch, i need provide full
> path to wathed node.... This is not clear to me after reading
> examples... =)

Which xenstored implementation are you using? In general I would expect
relative watches to work correctly. I looked briefly at the C xenstored
and it appears to (at least be trying to) do the right thing here.

Are you running this code in dom0 or domU?

If it is domU which Xen release is libxenstore you are linking this code
against against from? Which Xen release is your xenstored/dom0 running?

How are you opening your xenstore connection? i.e. which specific
function call, xs_open, xs_daemon_open or xs_domain_open?

Did I understand correctly in your original message that basically the
same code using select() works ok?

In another mail you wrote:
> in stats_in_tfunc i'm use this, but looping2 never happening
>  for (;;) {
>     log_debug("%s", "looping1");
>     if ((nr_events = epoll_wait(epfd, xen_events, 10, -1)) < 0) {
>       log_error("%s", "failed epoll_wait");
>       return NULL;
>     }
>     log_debug("%s", "looping1");
> }

I guess this is a typo in the email rather than the actual code, but
"looping2" never appears in this snippet -- you have "looping1" twice...


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