Allow read-only VFD registration (#257)

* Removes no-op callback stubs from read-only VFDs

Also changes VFD registration to allow read-only VFDs with no
write callback to be registered.

* Adds a RELEASE.txt note for HDFFV-11205

For the read-only VFD registration change

1 files changed, 7 insertions, 3 deletions

diff --git a/src/H5FD.c b/src/H5FD.c
index d12bb57..5498644 100644
--- a/src/H5FD.c
+++ b/src/H5FD.c
@@ -231,9 +231,9 @@ H5FDregister(const H5FD_class_t *cls)
                     "'get_eoa' and/or 'set_eoa' methods are not defined")
     if (!cls->get_eof)
         HGOTO_ERROR(H5E_ARGS, H5E_UNINITIALIZED, H5I_INVALID_HID, "'get_eof' method is not defined")
-    if (!cls->read || !cls->write)
+    if (!cls->read)
         HGOTO_ERROR(H5E_ARGS, H5E_UNINITIALIZED, H5I_INVALID_HID,
-                    "'read' and/or 'write' method is not defined")
+                    "'read' method is not defined")
     for (type = H5FD_MEM_DEFAULT; type < H5FD_MEM_NTYPES; type++)
         if (cls->fl_map[type] < H5FD_MEM_NOLIST || cls->fl_map[type] >= H5FD_MEM_NTYPES)
             HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, H5I_INVALID_HID, "invalid free-list mapping")
@@ -277,7 +277,7 @@ H5FD_register(const void *_cls, size_t size, hbool_t app_ref)
     HDassert(cls->open && cls->close);
     HDassert(cls->get_eoa && cls->set_eoa);
     HDassert(cls->get_eof);
-    HDassert(cls->read && cls->write);
+    HDassert(cls->read);
     for (type = H5FD_MEM_DEFAULT; type < H5FD_MEM_NTYPES; type++) {
         HDassert(cls->fl_map[type] >= H5FD_MEM_NOLIST && cls->fl_map[type] < H5FD_MEM_NTYPES);
     }
@@ -1417,6 +1417,10 @@ H5FDwrite(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t siz
     if (!buf)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "result buffer parameter can't be NULL")
 
+    /* Make sure this isn't being called on a read-only VFD */
+    if (!file->cls->write)
+        HGOTO_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "write request made to read-only VFD")
+
     /* Get the default dataset transfer property list if the user didn't provide one */
     if (H5P_DEFAULT == dxpl_id)
         dxpl_id = H5P_DATASET_XFER_DEFAULT;