libxl: handle POLLERR, POLLHUP, POLLNVAL properly

Pass POLLERR and POLLHUP to fd callbacks, as is necessary.
Crash on POLLNVAL since that means our fds are messed up.

Document the behaviour (including the fact that poll sometimes sets
POLLHUP or POLLERR even if only POLLIN was requested.

Fix the one current fd callback to do something with POLLERR|POLLHUP.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index e11a4e7603..5046938fd8 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -339,6 +339,9 @@ static void watchfd_callback(libxl__egc *egc, libxl__ev_fd *ev,
 {
     EGC_GC;
 
+    if (revents & (POLLERR|POLLHUP))
+        LIBXL__EVENT_DISASTER(egc, "unexpected poll event on watch fd", 0, 0);
+
     for (;;) {
         char **event = xs_check_watch(CTX->xsh);
         if (!event) {
@@ -743,7 +746,9 @@ static int afterpoll_check_fd(libxl__poller *poller,
         /* again, stale slot entry */
         return 0;
 
-    int revents = fds[slot].revents & events;
+    assert(!(fds[slot].revents & POLLNVAL));
+
+    int revents = fds[slot].revents & (events | POLLERR | POLLHUP);
     /* we mask in case requested events have changed */
 
     return revents;