api: status: graceful-degrade when a datastore lookup fails

This can happen if the underlying storage failed, in which case we do
not want to fail the whole API call, as it should report the status
of all datastores. So rather add the error inline to the related
store entry and continue.

Allows to nicely visualize those stores in the gui.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/api2/status.rs

@@ -55,6 +55,7 @@ use crate::config::acl::{
                 },
                 history: {
                     type: Array,
+                    optional: true,
                     description: "A list of usages of the past (last Month).",
                     items: {
                         type: Number,
@@ -69,6 +70,11 @@ use crate::config::acl::{
                         of RRD data of the last Month. Missing if there are not enough data points yet.\
                         If the estimate lies in the past, the usage is decreasing.",
                 },
+                "error": {
+                    type: String,
+                    optional: true,
+                    description: "An error description, for example, when the datastore could not be looked up.",
+                },
             },
         },
     },
@@ -97,7 +103,19 @@ pub fn datastore_status(
             continue;
         }
 
-        let datastore = DataStore::lookup_datastore(&store)?;
+        let datastore = match DataStore::lookup_datastore(&store) {
+            Ok(datastore) => datastore,
+            Err(err) => {
+                list.push(json!({
+                    "store": store,
+                    "total": -1,
+                    "used": -1,
+                    "avail": -1,
+                    "error": err.to_string()
+                }));
+                continue;
+            }
+        };
         let status = crate::tools::disks::disk_usage(&datastore.base_path())?;
 
         let mut entry = json!({