[Libguestfs] [PATCH libnbd v2 4/5] docs: callbacks: Document that user_data, valid_flag only used by the C API.

[Richard W.M. Jones]

Thanks: Eric Blake.
---
 docs/libnbd.pod | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/docs/libnbd.pod b/docs/libnbd.pod
index 0ce4d32..6c8d962 100644
--- a/docs/libnbd.pod
+++ b/docs/libnbd.pod
@@ -487,7 +487,9 @@ C<nbd_set_debug_callback>, C<nbd_pread_callback>).  Libnbd can call
 these functions while processing.
 
 Callbacks have an opaque C<void *user_data> pointer.  This is passed
-as the second parameter to the callback.
+as the second parameter to the callback.  The opaque pointer is only
+used from the C API, since in other languages you can use closures to
+achieve the same outcome.
 
 =head2 Callback lifetimes
 
@@ -539,6 +541,9 @@ write this:
    // Rest of callback as normal.
  }
 
+The valid flag is only present in the C API.  It is not needed when
+using garbage-collected programming languages.
+
 =head2 Callbacks and locking
 
 The callbacks are invoked at a point where the libnbd lock is held; as
-- 
2.22.0