[Xen-changelog] [xen master] libxl: libxl__ev_fd_callback: Document perhaps-no-retry semantics

[p***@xen.org]

commit 65c0bcc47103fe839b959dfdfa61a91f745d78b1
Author: Ian Jackson <***@eu.citrix.com>
AuthorDate: Mon Oct 15 14:58:54 2018 +0100
Commit: Ian Jackson <***@eu.citrix.com>
CommitDate: Tue Oct 30 17:03:27 2018 +0000

libxl: libxl__ev_fd_callback: Document perhaps-no-retry semantics

Signed-off-by: Ian Jackson <***@eu.citrix.com>
CC: Anthony PERARD <***@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.)
*/
--
generated by git-patchbot for /home/xen/git/xen.git#master