[Xen-changelog] [xen-unstable] libxl: handle POLLERR, POLLHUP, POLLNVAL properly

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
# Date 1336759135 -3600
# Node ID b675568d14b8f40b75a0db4dd8762c42c188961a
# Parent  01d64a3dea717134d9387a1b39745bdc2eb8cf59
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@xxxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Committed-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
---


diff -r 01d64a3dea71 -r b675568d14b8 tools/libxl/libxl_event.c
--- a/tools/libxl/libxl_event.c Fri May 11 18:30:29 2012 +0100
+++ b/tools/libxl/libxl_event.c Fri May 11 18:58:55 2012 +0100
@@ -339,6 +339,9 @@ static void watchfd_callback(libxl__egc 
 {
     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__pol
         /* 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;
diff -r 01d64a3dea71 -r b675568d14b8 tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h      Fri May 11 18:30:29 2012 +0100
+++ b/tools/libxl/libxl_internal.h      Fri May 11 18:58:55 2012 +0100
@@ -128,6 +128,11 @@ _hidden void libxl__alloc_failed(libxl_c
 typedef struct libxl__ev_fd libxl__ev_fd;
 typedef void libxl__ev_fd_callback(libxl__egc *egc, libxl__ev_fd *ev,
                                    int fd, short events, short revents);
+  /* Note that revents may contain POLLERR or POLLHUP regardless of
+   * events; otherwise revents contains only bits in events.  Contrary
+   * to the documentation for poll(2), POLLERR and POLLHUP can occur
+   * even if only POLLIN was set in events.  (POLLNVAL is a fatal
+   * error and will cause libxl event machinery to fail an assertion.) */
 struct libxl__ev_fd {
     /* caller should include this in their own struct */
     /* read-only for caller, who may read only when registered: */

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog