Add a VSM_IsOpen API function

include/vapi/vsm.h

@@ -126,6 +126,15 @@ int VSM_Open(struct VSM_data *vd);
 	 *	<0 on failure, VSM_Error() returns diagnostic string
 	 */
 
+int VSM_IsOpen(const struct VSM_data *vd);
+	/*
+	 * Check if the VSM is open.
+	 *
+	 * Returns:
+	 *       1: Is open
+	 *       0: Is closed
+	 */
+
 int VSM_Abandoned(struct VSM_data *vd);
 	/*
 	 * Find out if the VSM file has been abandoned or closed and should

lib/libvarnishapi/libvarnishapi.map

@@ -129,4 +129,5 @@ LIBVARNISHAPI_1.4 {
   global:
 	VNUM;
 	VSLQ_SetCursor;
+	VSM_IsOpen;
 } LIBVARNISHAPI_1.0;

lib/libvarnishapi/vsm.c

@@ -287,6 +287,16 @@ VSM_Open(struct VSM_data *vd)
 
 /*--------------------------------------------------------------------*/
 
+int
+VSM_IsOpen(const struct VSM_data *vd)
+{
+
+	CHECK_OBJ_NOTNULL(vd, VSM_MAGIC);
+	return (vd->head != NULL);
+}
+
+/*--------------------------------------------------------------------*/
+
 void
 VSM_Close(struct VSM_data *vd)
 {