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Re: [libvirt] [PATCH] virCommand: Properly handle POLLHUP



On 01/03/2012 10:58 AM, Michal Privoznik wrote:
> It is a good practise to set revents to zero before doing any poll().
> Moreover, we should check if event we waited for really occurred or
> if any of fds we were polling on didn't encountered hangup.

Looks like this also solves:

https://bugzilla.redhat.com/show_bug.cgi?id=770788

> ---
>  src/util/command.c |   21 +++++++++++++++++----
>  1 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/src/util/command.c b/src/util/command.c
> index f5effdf..9b553f0 100644
> --- a/src/util/command.c
> +++ b/src/util/command.c
> @@ -1620,16 +1620,19 @@ virCommandProcessIO(virCommandPtr cmd)
>          if (infd != -1) {
>              fds[nfds].fd = infd;
>              fds[nfds].events = POLLOUT;
> +            fds[nfds].revents = 0;

Oh my - you're right - we stack-allocated struct pollfd fds[3]; without
initialization earlier on.

> @@ -1708,8 +1711,18 @@ virCommandProcessIO(virCommandPtr cmd)
>                              VIR_DEBUG("ignoring failed close on fd %d", tmpfd);
>                      }
>                  }
> +            } else if (fds[i].revents & POLLHUP) {
> +                if (fds[i].fd == errfd) {
> +                    VIR_DEBUG("hangup on stderr");
> +                    errfd = -1;
> +                } else if (fds[i].fd == outfd) {
> +                    VIR_DEBUG("hangup on stdout");
> +                    outfd = -1;
> +                } else {
> +                    VIR_DEBUG("hangup on stdin");
> +                    infd = -1;
> +                }

Should we also be probing for POLLERR?  (POLLNVAL shouldn't ever be
present, because it would indicate a bigger bug in our code).

ACK - what you have is a strict improvement, even if we further decide
to check for POLLERR.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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