Document that fileno is the same for all handles (#3965)

* Document that fileno is same for all handles

* Mention filesystem requirement

1 files changed, 7 insertions, 0 deletions

diff --git a/src/H5Fpublic.h b/src/H5Fpublic.h
index ec4097c..551a345 100644
--- a/src/H5Fpublic.h
+++ b/src/H5Fpublic.h
@@ -740,6 +740,13 @@ H5_DLL herr_t H5Fget_intent(hid_t file_id, unsigned *intent);
  *          file identifier \p file_id and the pointer \p fnumber to the file
  *          number.
  *
+ *          This file number is the same for all open instances of the same
+ *          file, as long as 1. The active VFD implements the file comparison operator,
+ *          and 2. The current filesystem is able to determine if the same file is opened more
+ *          than once. If these conditions are not met, it is the application's
+ *          responsibility to avoid opening multiple handles into the same file,
+ *          which results in undefined behavior.
+ *
  * \since 1.12.0
  *
  */