Signed-off-by: Ian Jackson <ian.jack...@eu.citrix.com>
CC: Anthony PERARD <anthony.per...@citrix.com>
---
tools/libxl/libxl_internal.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 43947b1b07..153566acd0 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -232,6 +232,14 @@ typedef void libxl__ev_fd_callback(libxl__egc *egc,
libxl__ev_fd *ev,
* It is not permitted to listen for the same or overlapping events
* on the same fd using multiple different libxl__ev_fd's.
*
+ * Note that (depending on the underlying event loop implementation)
+ * it is possible that a the fd callback system is `level triggered'
+ * or `event triggered'. That is, the callback may be called only
+ * once for each transition from not ready to ready. So the
+ * callback must generally contain a loop which exhausts the fd,
+ * rather than relying on being called again if the fd is still
+ * ready.
+ *
* (Spurious wakeups, and spurious bits set in revents, are
* suppressed by the libxl event core.)
*/
--
2.11.0
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