mbb[io].*VL fields unwritable

[Andrew Johnson]

Between 3.16 and 7.0 the mbbi and mbbo record types lost the ability to write to their *VL fields (ZRVL, ONVL etc.)

tux% caput anj:mbbi0.ONVL 123
Old : anj:mbbi0.ONVL 0
CA.Client.Exception...............................................
    Warning: "Channel write request failed"
    Context: "op=1, channel=anj:mbbi0.ONVL, type=DBR_STRING, count=1, ctx="anj:mbbi0""
    Source File: ../oldChannelNotify.cpp line 160
    Current Time: Mon Sep 24 2018 17:14:31.744304921
New : anj:mbbi0.ONVL 0
..................................................................
tux%

epics> dbpf anj:mbbi0.ONVL 123
Error (511,511) PV: anj:mbbi0.ONVL error detected in routine: mbbi: special

DBF_ULONG: 0 = 0x0

[Andrew Johnson (anj)]

Ralph's commit 45415512 seems to be the culprit; the modifications to special() to add the SIMM field look to have been written without realizing that the *VL fields are also marked SPC_MOD in the mbbi and mbbo records. Previously special() returned 0 for these fields, but now it is returning an error.

Patch attached to return the special() routines to doing the right thing. I will apply after Mark Rivers confirms it fixes the problem for him. I haven't checked any other record types.

[Ralph Lange (ralph-lange)]

My bad. Sorry to have broken functionality that I wasn't aware of. Thanks for adding a hint in the comment.

Underlines the fact that we are really and almost completely missing functional tests for the record types.