Bug in dbCa.c's doLocked breaks CA link disconnect detection

[Sebastian Marsching]

There is a bug in the doLocked function of dbCa.c: Due to the use of pcaGetCheck, the supplied callback does not get called when the CA channel is disconnected.

This causes a problem when using a CA link as the input to a soft record: The soft device support for the ai record (and most likely also the ones for the other records) does the following when the record is processed:

// ...
    status = dbLinkDoLocked(&prec->inp, readLocked, &vt);
    if (status == S_db_noLSET)
        status = readLocked(&prec->inp, &vt);
// ...

The readLocked function then calls dbGetLink for actually reading the value. However, when the link is a CA link and the channel is not connected, the implementation of dbLinkDoLocked for CA links does not actually call the callback and simply returns -1. This means that dbGetLink is never called and thus the processed record's alarm severity and status are never set to INVALID_ALARM and LINK_ALARM.

This bug is present in EPICS Base 3.16 (starting with 3.16-rc1) and 7.0. Earlier versions are not affected because the soft device support code in these version does not use dbLinkDoLocked and calls dbGetLink directly.

I attached a patch that fixed the problem in EPICS Base 7.0.1.1. Apart from changes to the path, this patch should also apply to EPICS Base 3.16.

[mdavidsaver (mdavidsaver)]

Reproduced with

cat <<EOF >badlink.db
record(ai, "rec") {
    field(INP, "invalid CA")
    field(UDF, "0")
    field(PINI, "RUNNING")
}
EOF
softIoc -d badlink.db

No alarm is active.

[mdavidsaver (mdavidsaver)]

e78b4e75313788830eea944ac7bcf9eb01d478c3 adds a case to regressTest (with TODO) which demonstrates this issue. The Sebastian's patch makes this test pass.

@anj Please have a look.

[mdavidsaver (mdavidsaver)]

Make that 693c1020f259c287cdf1a408f69238c9cc2211a8

[Andrew Johnson (anj)]

Thanks guys, I applied the patch and removed the testToDo calls.