admin: add connected Mount Clients page and dashboard section (#9968)

* admin: add connected mount clients page and dashboard section

The filer is the authority on who is subscribed to its metadata stream
(FUSE/VFS mounts, S3, peer filers, ...), but its in-memory listener
registry only tracked clientId->epoch and was not exposed.

- Enrich the filer subscriber registry with name/type/address/path/
  connected-time, populated in addClient and cleared in deleteClient so
  it reflects currently-connected clients only.
- Add a ListMetadataSubscribers filer gRPC (optional client-type filter).
- Admin server fans out to every filer, filters to mount types
  ("mount" Go weed mount, "sw-vfs" Rust VFS), and renders a new
  Cluster > Mount Clients page plus a Mount Clients dashboard section.

Read-only; no behavior change to the subscribe hot path.

* admin: address review — parallelize filer fan-out, guard nil map, robust CSV

- GetMountClients now queries filers concurrently, each under a 5s
  timeout, so a slow/unreachable filer can't stall the admin dashboard.
- Defensively initialize fs.subscribers before first write.
- Mount Clients CSV export uses a Blob with quote-escaping instead of a
  data: URI, so special characters in paths export correctly.

weed/admin/dash/admin_data.go

@@ -38,6 +38,9 @@ type AdminData struct {
 	TotalEcVolumes int `json:"total_ec_volumes"` // Total number of EC volumes across all servers
 	TotalEcShards  int `json:"total_ec_shards"`  // Total number of EC shards across all servers
 
+	// TotalMountClients is the number of connected FUSE/VFS mount clients across filers.
+	TotalMountClients int `json:"total_mount_clients"`
+
 	// Trends holds at-a-glance sparklines built from the admin's own recent
 	// cluster snapshots (no Prometheus required).
 	Trends DashboardTrends `json:"trends"`
@@ -186,6 +189,12 @@ func (s *AdminServer) GetAdminData(username string) (AdminData, error) {
 	}
 	totalEcVolumes = len(ecVolumeSet)
 
+	// Count connected FUSE/VFS mount clients (best-effort; don't fail the dashboard)
+	totalMountClients := 0
+	if mountData, mountErr := s.GetMountClients(); mountErr == nil {
+		totalMountClients = mountData.TotalMountClients
+	}
+
 	// Prepare admin data
 	adminData := AdminData{
 		Username:          username,
@@ -202,6 +211,7 @@ func (s *AdminServer) GetAdminData(username string) (AdminData, error) {
 		LastUpdated:       topology.UpdatedAt,
 		TotalEcVolumes:    totalEcVolumes,
 		TotalEcShards:     totalEcShards,
+		TotalMountClients: totalMountClients,
 		Trends:            s.GetDashboardTrends(),
 	}
 

weed/admin/dash/mount_clients.go

@@ -0,0 +1,80 @@
+package dash
+
+import (
+	"context"
+	"sort"
+	"sync"
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/glog"
+	"github.com/seaweedfs/seaweedfs/weed/pb"
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+)
+
+// mountClientTypes are the metadata-subscriber client types that represent a
+// FUSE/VFS mount: the Go `weed mount` ("mount") and the Rust VFS ("sw-vfs").
+var mountClientTypes = []string{"mount", "sw-vfs"}
+
+// mountClientsFilerTimeout bounds each per-filer ListMetadataSubscribers call so
+// a slow or unreachable filer can't stall the admin dashboard.
+const mountClientsFilerTimeout = 5 * time.Second
+
+// GetMountClients queries every filer for its connected mount subscribers and
+// aggregates them. Each filer only knows the clients connected to itself, so a
+// cluster-wide view requires fanning out. The filers are queried concurrently,
+// each under a short timeout, and an unreachable filer is skipped.
+func (s *AdminServer) GetMountClients() (*MountClientsData, error) {
+	var (
+		mu      sync.Mutex
+		clients []MountClient
+		wg      sync.WaitGroup
+	)
+
+	for _, filerAddr := range s.GetAllFilers() {
+		wg.Add(1)
+		go func(filerAddr string) {
+			defer wg.Done()
+			ctx, cancel := context.WithTimeout(context.Background(), mountClientsFilerTimeout)
+			defer cancel()
+			err := pb.WithGrpcFilerClient(false, 0, pb.ServerAddress(filerAddr), s.grpcDialOption, func(client filer_pb.SeaweedFilerClient) error {
+				resp, err := client.ListMetadataSubscribers(ctx, &filer_pb.ListMetadataSubscribersRequest{
+					ClientTypes: mountClientTypes,
+				})
+				if err != nil {
+					return err
+				}
+				mu.Lock()
+				for _, sub := range resp.Subscribers {
+					clients = append(clients, MountClient{
+						ClientName:   sub.ClientName,
+						ClientType:   sub.ClientType,
+						Address:      sub.Address,
+						PathPrefix:   sub.PathPrefix,
+						ClientId:     sub.ClientId,
+						ConnectedAt:  time.Unix(0, sub.ConnectedAtNs),
+						FilerAddress: sub.FilerAddress,
+					})
+				}
+				mu.Unlock()
+				return nil
+			})
+			if err != nil {
+				glog.Warningf("list mount clients from filer %s: %v", filerAddr, err)
+			}
+		}(filerAddr)
+	}
+	wg.Wait()
+
+	sort.Slice(clients, func(i, j int) bool {
+		if clients[i].Address != clients[j].Address {
+			return clients[i].Address < clients[j].Address
+		}
+		return clients[i].PathPrefix < clients[j].PathPrefix
+	})
+
+	return &MountClientsData{
+		MountClients:      clients,
+		TotalMountClients: len(clients),
+		LastUpdated:       time.Now(),
+	}, nil
+}

weed/admin/dash/types.go

@@ -295,6 +295,25 @@ type ClusterFilersData struct {
 	LastUpdated time.Time   `json:"last_updated"`
 }
 
+// MountClient is one connected FUSE/VFS mount as reported by a filer's
+// metadata-subscriber registry.
+type MountClient struct {
+	ClientName   string    `json:"client_name"`
+	ClientType   string    `json:"client_type"` // "mount" (Go) or "sw-vfs" (Rust VFS)
+	Address      string    `json:"address"`
+	PathPrefix   string    `json:"path_prefix"`
+	ClientId     int32     `json:"client_id"`
+	ConnectedAt  time.Time `json:"connected_at"`
+	FilerAddress string    `json:"filer_address"`
+}
+
+type MountClientsData struct {
+	Username          string        `json:"username"`
+	MountClients      []MountClient `json:"mount_clients"`
+	TotalMountClients int           `json:"total_mount_clients"`
+	LastUpdated       time.Time     `json:"last_updated"`
+}
+
 type MessageBrokerInfo struct {
 	Address    string    `json:"address"`
 	DataCenter string    `json:"datacenter"`