[Xen-devel] [PATCH 11/13] libxl: correct some comments regarding event API and fds

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

* libxl may indeed register more than one callback for the same fd,
  with some restrictions.  The allowable range of responses to this by
  the application means that this should pose no problems for users.
  But the documentation comment should be fixed.

* Document the relaxed synchronicity semantics of the fd_modify
  registration callback.

* A couple of comments referred to old names for functions.

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 tools/libxl/libxl_event.h |   17 ++++++++++++++---
 1 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/tools/libxl/libxl_event.h b/tools/libxl/libxl_event.h
index 3344bc8..cead71b 100644
--- a/tools/libxl/libxl_event.h
+++ b/tools/libxl/libxl_event.h
@@ -320,13 +320,24 @@ typedef struct libxl_osevent_hooks {
  * *for_registration_update is honoured by libxl and will be passed
  * to future modify or deregister calls.
  *
- * libxl will only attempt to register one callback for any one fd.
+ * libxl may want to register more than one callback for any one fd;
+ * in that case: (i) each such registration will have at least one bit
+ * set in revents which is unique to that registration; (ii) if an
+ * event occurs which is relevant for multiple registrations the
+ * application's event system is may call libxl_osevent_occurred_fd
+ * for one, some, or all of those registrations.
+ *
+ * If fd_modify is used, it is permitted for the application's event
+ * system to still make calls to libxl_osevent_occurred_fd for the
+ * "old" set of requested events; these will be safely ignored by
+ * libxl.
+ *
  * libxl will remember the value stored in *for_app_registration_out
  * (or *for_app_registration_update) by a successful call to
  * register (or modify), and pass it to subsequent calls to modify
  * or deregister.
  *
- * register_fd_hooks may be called only once for each libxl_ctx.
+ * osevent_register_hooks may be called only once for each libxl_ctx.
  * libxl may make calls to register/modify/deregister from within
  * any libxl function (indeed, it will usually call register from
  * register_event_hooks).  Conversely, the application MUST NOT make
@@ -357,7 +368,7 @@ void libxl_osevent_register_hooks(libxl_ctx *ctx,
 /* It is NOT legal to call _occurred_ reentrantly within any libxl
  * function.  Specifically it is NOT legal to call it from within
  * a register callback.  Conversely, libxl MAY call register/deregister
- * from within libxl_event_registered_call_*.
+ * from within libxl_event_occurred_call_*.
  */
 
 void libxl_osevent_occurred_fd(libxl_ctx *ctx, void *for_libxl,
-- 
1.7.2.5


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