rrdd: add more comments about its datastructures

Signed-off-by: Pau Ruiz Safont <[email protected]>

ocaml/libs/xapi-rrd/lib/rrd.ml

@@ -621,9 +621,9 @@ let rrd_add_ds_unsafe rrd timestamp newds =
         rrd.rrd_rras
   }
 
-(** Add in a new DS into a pre-existing RRD. Preserves data of all the other archives
-    and fills the new one full of NaNs. Note that this doesn't fill in the CDP values
-    correctly at the moment!
+(** Add in a new DS into a pre-existing RRD. Preserves data of all the other
+    archives and fills the new one full of NaNs. Note that this doesn't fill
+    in the CDP values correctly at the moment!
 *)
 
 let rrd_add_ds rrd timestamp newds =

ocaml/xcp-rrdd/bin/rrdd/rrdd_monitor.ml

@@ -51,10 +51,10 @@ let merge_new_dss rrdi dss =
     !Rrdd_shared.enable_all_dss || ds.ds_default
   in
   let default_dss = StringMap.filter should_enable_ds dss in
-  (* NOTE: It's enough to check if all the default datasources have been added
-     to the RRD_INFO, because if a non-default one has been enabled at runtime,
-     it's added to the RRD immediately and we don't need to bother *)
-  let new_dss =
+  (* NOTE: Only add enabled dss to the live rrd, ignoring non-default ones.
+     This is because non-default ones are added to the RRD when they are
+     enabled. *)
+  let new_enabled_dss =
     StringMap.filter
       (fun ds_name _ -> not (StringMap.mem ds_name rrdi.dss))
       default_dss
@@ -73,7 +73,7 @@ let merge_new_dss rrdi dss =
         rrd_add_ds_unsafe rrd timestamp
           (Rrd.ds_create ds.ds_name ds.Ds.ds_type ~mrhb:300.0 Rrd.VT_Unknown)
       )
-      new_dss rrdi.rrd
+      new_enabled_dss rrdi.rrd
   )
 
 module OwnerMap = Map.Make (struct

ocaml/xcp-rrdd/bin/rrdd/rrdd_server.ml

@@ -347,7 +347,7 @@ let send_host_rrd_to_master master_address =
 let fail_missing name = raise (Rrdd_error (Datasource_missing name))
 
 (** {add_ds rrdi ds_name} creates a new time series (rrd) in {rrdi} with the
-    name {ds_name}. The operation fails if rrdi does not contain any live
+    name {ds_name}. The operation fails if rrdi does not contain any
     datasource with the name {ds_name} *)
 let add_ds ~rrdi ~ds_name =
   match Rrd.StringMap.find_opt ds_name rrdi.dss with

ocaml/xcp-rrdd/bin/rrdd/rrdd_shared.ml

@@ -77,10 +77,13 @@ let mutex = Mutex.create ()
 
 type rrd_info = {
     rrd: Rrd.rrd
+        (** Contains the live metrics, i.e. The datasources that are enabled
+            and being collected .*)
   ; mutable dss: (float * Ds.ds) Rrd.StringMap.t
-        (* Important: this must contain the entire list of datasources associated
-           with the RRD, even the ones disabled by default, as rrd_add_ds calls
-           can enable DSs at runtime *)
+        (** Important: this must contain the entire list of datasources
+           associated with the RRD, even the ones disabled by default, because
+           functions like rrd_add_ds or rrd_remove_ds expect disabled
+           datasources to be present. e.g. to enable DSs at runtime *)
   ; mutable domid: int
 }