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

[patchbot@xxxxxxx]

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

    libxl: libxl__ev_fd_callback: Document perhaps-no-retry semantics
    
    Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
    CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 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

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