From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v2 6/6] tools/libxl: Adjust datacopiers POLLHUP handling when the fd is also readable Date: Wed, 11 Mar 2015 12:21:36 +0000 Message-ID: <1426076496.21353.221.camel@citrix.com> References: <1425668741-28003-1-git-send-email-andrew.cooper3@citrix.com> <1425668741-28003-7-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1425668741-28003-7-git-send-email-andrew.cooper3@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andrew Cooper Cc: Wei Liu , Ian Jackson , Xen-devel List-Id: xen-devel@lists.xenproject.org On Fri, 2015-03-06 at 19:05 +0000, Andrew Cooper wrote: > POLLHUP|POLLIN is a valid revent to receive when there is readable data in a > pipe, but the writable fd has been closed. This occurs in migration v2 when > the legacy conversion process (which transforms the data inline) completes and > exits successfully. > > In the case that there is data to read, suppress the POLLHUP. POSIX states > that the hangup state is latched[1], which means it will reoccur on subsequent > poll() calls. The datacopier is thus provided the opportunity to read until > EOF, if possible. > > A POLLHUP on its own is treated exactly as before, indicating a different > error with the fd. > > [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/poll.html > > Signed-off-by: Andrew Cooper > CC: Ian Campbell > CC: Ian Jackson > CC: Wei Liu Having looked at the previous thread I'm satisfied that this matches what was discussed there, but I think the final ack needs to come from Ian. > > --- > v2: Rework solution from scratch > --- > tools/libxl/libxl_aoutils.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c > index a402e5c..a5ad3e5 100644 > --- a/tools/libxl/libxl_aoutils.c > +++ b/tools/libxl/libxl_aoutils.c > @@ -204,6 +204,9 @@ static void datacopier_readable(libxl__egc *egc, libxl__ev_fd *ev, > libxl__datacopier_state *dc = CONTAINER_OF(ev, *dc, toread); > STATE_AO_GC(dc->ao); > > + if ((revents & (POLLHUP|POLLIN)) == (POLLHUP|POLLIN)) > + revents &= ~POLLHUP; > + > if (datacopier_pollhup_handled(egc, dc, revents, 0)) > return; >