Add isConstant and isVolatile to LSET

src/ioc/db/dbAccess.c

@@ -1048,23 +1048,12 @@ static long dbPutFieldLink(DBADDR *paddr,
         }
     }
 
-    switch (plink->type) { /* Old link type */
-    case DB_LINK:
-    case CA_LINK:
-    case CONSTANT:
-        dbRemoveLink(&locker, plink);   /* link type becomes PV_LINK */
-        break;
-
-    case PV_LINK:
-    case MACRO_LINK:
-        break;  /* should never get here */
-
-    default: /* Hardware address */
-        if (!isDevLink) {
-            status = S_db_badHWaddr;
-            goto restoreScan;
-        }
-        break;
+    if (dbLinkIsDefined(plink)) {
+        dbRemoveLink(&locker, plink);   /* Clear out old link */
+    }
+    else if (!isDevLink) {
+        status = S_db_badHWaddr;
+        goto restoreScan;
     }
 
     if (special) status = dbPutSpecial(paddr, 0);
@@ -1097,6 +1086,7 @@ static long dbPutFieldLink(DBADDR *paddr,
     switch (plink->type) { /* New link type */
     case PV_LINK:
     case CONSTANT:
+    case JSON_LINK:
         dbAddLink(&locker, plink, pfldDes->field_type, pdbaddr);
         break;
 

src/ioc/db/dbCa.c

@@ -713,6 +713,7 @@ static void scanLinkOnce(dbCommon *prec, caLink *pca) {
 }
 
 static lset dbCa_lset = {
+    0, 1, /* not Constant, Volatile */
     dbCaRemoveLink,
     NULL, NULL,
     isConnected,

src/ioc/db/dbConstLink.c

@@ -85,6 +85,7 @@ static long dbConstGetValue(struct link *plink, short dbrType, void *pbuffer,
 }
 
 static lset dbConst_lset = {
+    1, 0, /* Constant, not Volatile */
     NULL,
     dbConstLoadScalar,
     dbConstLoadArray,

src/ioc/db/dbDbLink.c

@@ -336,6 +336,7 @@ static void dbDbScanFwdLink(struct link *plink)
 }
 
 static lset dbDb_lset = {
+    0, 0, /* not Constant, not Volatile */
     dbDbRemoveLink,
     NULL, NULL,
     dbDbIsConnected,

src/ioc/db/dbLink.c

@@ -120,6 +120,9 @@ void dbAddLink(struct dbLocker *locker, struct link *plink, short dbfType,
         return;
     }
 
+    if (plink->type != PV_LINK)
+        return;
+
     if (plink == &precord->tsel)
         recGblTSELwasModified(plink);
 
@@ -142,10 +145,45 @@ void dbAddLink(struct dbLocker *locker, struct link *plink, short dbfType,
     }
 }
 
-long dbLoadLink(struct link *plink, short dbrType, void *pbuffer)
+void dbRemoveLink(struct dbLocker *locker, struct link *plink)
 {
     lset *plset = plink->lset;
 
+    if (plset) {
+        if (plset->removeLink)
+            plset->removeLink(locker, plink);
+        plink->lset = NULL;
+    }
+}
+
+int dbLinkIsDefined(const struct link *plink)
+{
+    return (plink->lset != 0);
+}
+
+int dbLinkIsConstant(const struct link *plink)
+{
+    lset *plset = plink->lset;
+
+    if (plset)
+        return plset->isConstant;
+
+    return -1;
+}
+
+int dbLinkIsVolatile(const struct link *plink)
+{
+    lset *plset = plink->lset;
+
+    if (plset)
+        return plset->isVolatile;
+
+    return -1;
+}
+
+long dbLoadLink(struct link *plink, short dbrType, void *pbuffer)
+{
+    lset *plset = plink->lset;
 
     if (plset && plset->loadScalar)
         return plset->loadScalar(plink, dbrType, pbuffer);
@@ -164,17 +202,6 @@ long dbLoadLinkArray(struct link *plink, short dbrType, void *pbuffer,
     return S_db_noLSET;
 }
 
-void dbRemoveLink(struct dbLocker *locker, struct link *plink)
-{
-    lset *plset = plink->lset;
-
-    if (plset) {
-        if (plset->removeLink)
-            plset->removeLink(locker, plink);
-        plink->lset = NULL;
-    }
-}
-
 int dbIsLinkConnected(const struct link *plink)
 {
     lset *plset = plink->lset;

src/ioc/db/dbLink.h

@@ -28,13 +28,24 @@ extern "C" {
 struct dbLocker;
 
 typedef struct lset {
+    /* Characteristics of the link type */
+    const unsigned isConstant:1;
+    const unsigned isVolatile:1;
+
+    /* Destructor */
     void (*removeLink)(struct dbLocker *locker, struct link *plink);
+
+    /* Const init, data type hinting */
     long (*loadScalar)(struct link *plink, short dbrType, void *pbuffer);
     long (*loadArray)(struct link *plink, short dbrType, void *pbuffer,
             long *pnRequest);
+
+    /* Metadata */
     int (*isConnected)(const struct link *plink);
     int (*getDBFtype)(const struct link *plink);
     long (*getElements)(const struct link *plink, long *nelements);
+
+    /* Get data */
     long (*getValue)(struct link *plink, short dbrType, void *pbuffer,
             epicsEnum16 *pstat, epicsEnum16 *psevr, long *pnRequest);
     long (*getControlLimits)(const struct link *plink, double *lo, double *hi);
@@ -46,10 +57,14 @@ typedef struct lset {
     long (*getAlarm)(const struct link *plink, epicsEnum16 *status,
             epicsEnum16 *severity);
     long (*getTimeStamp)(const struct link *plink, epicsTimeStamp *pstamp);
+
+    /* Put data */
     long (*putValue)(struct link *plink, short dbrType,
             const void *pbuffer, long nRequest);
     long (*putAsync)(struct link *plink, short dbrType,
             const void *pbuffer, long nRequest);
+
+    /* Process */
     void (*scanForward)(struct link *plink);
 } lset;
 
@@ -60,6 +75,11 @@ epicsShareFunc void dbInitLink(struct link *plink, short dbfType);
 epicsShareFunc void dbAddLink(struct dbLocker *locker, struct link *plink,
         short dbfType, DBADDR *ptarget);
 epicsShareFunc void dbRemoveLink(struct dbLocker *locker, struct link *plink);
+
+epicsShareFunc int dbLinkIsDefined(const struct link *plink);  /* 0 or 1 */
+epicsShareFunc int dbLinkIsConstant(const struct link *plink); /* -1, 0 or 1 */
+epicsShareFunc int dbLinkIsVolatile(const struct link *plink); /* -1, 0 or 1 */
+
 epicsShareFunc long dbLoadLink(struct link *plink, short dbrType,
         void *pbuffer);
 epicsShareFunc long dbLoadLinkArray(struct link *, short dbrType, void *pbuffer,

src/ioc/db/recGbl.c

@@ -256,7 +256,7 @@ void recGblGetTimeStamp(void *pvoid)
     dbCommon* prec = (dbCommon*)pvoid;
     struct link *plink = &prec->tsel;
 
-    if (plink->type != CONSTANT) {
+    if (!dbLinkIsConstant(plink)) {
         struct pv_link *ppv_link = &plink->value.pv_link;
 
         if (ppv_link->pvlMask & pvlOptTSELisTime) {