libxl: Comment cleanups

* Add two comments in libxl_remus_disk_drbd documenting buggy handling
  of the hotplug script exit status.

* Add a section heading for async exec in libxl_aoutils.c

* Mention the right function name (libxl__ev_child_fork, not
  libxl__ev_fork) in libxl_internal.h

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Yang Hongyang <yanghy@cn.fujitsu.com>
CC: Wen Congyang <wency@cn.fujitsu.com>
CC: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Yang Hongyang <yanghy@cn.fujitsu.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl_aoutils.c

@@ -478,6 +478,8 @@ int libxl__openptys(libxl__openpty_state *op,
     return rc;
 }
 
+/*----- async exec -----*/
+
 static void async_exec_timeout(libxl__egc *egc,
                                libxl__ev_time *ev,
                                const struct timeval *requested_abs)

tools/libxl/libxl_internal.h

@@ -1413,7 +1413,7 @@ _hidden int libxl__spawn_record_pid(libxl__gc*, libxl__spawn_state*,
  * This is a NOT function for waiting for ordinary child processes.
  * If you want to run (fork/exec/wait) subprocesses from libxl:
  *  - Make your libxl entrypoint use the ao machinery
- *  - Use libxl__ev_fork, and use the callback programming style
+ *  - Use libxl__ev_child_fork, and use the callback programming style
  *
  * This function is intended for interprocess communication with a
  * service process.  If the service process does not respond quickly,

tools/libxl/libxl_remus_disk_drbd.c

@@ -145,6 +145,8 @@ static void match_async_exec_cb(libxl__egc *egc,
 
     if (status) {
         rc = ERROR_REMUS_DEVOPS_DOES_NOT_MATCH;
+        /* BUG: seems to assume that any exit status means `no match' */
+        /* BUG: exit status will have been logged as an error */
         goto out;
     }