fix(agent): keep every EXTRA_FILESYSTEMS mount when device keys collide

agent/disk.go

@@ -2,6 +2,7 @@ package agent
 
 import (
 	"context"
+	"fmt"
 	"log/slog"
 	"os"
 	"path/filepath"
@@ -95,6 +96,25 @@ func isDockerSpecialMountpoint(mountpoint string) bool {
 	return false
 }
 
+// uniqueFsStatsKey derives a fsStats map key that does not collide with an
+// existing entry by starting from the mountpoint's basename and appending a
+// numeric suffix when necessary. Used when the device-derived key would
+// otherwise overwrite a different mount (e.g. autofs reporting "systemd-1"
+// for every automount target).
+func uniqueFsStatsKey(existing map[string]*system.FsStats, mountpoint string) string {
+	base := filepath.Base(mountpoint)
+	if base == "" || base == "/" || base == "." {
+		base = "fs"
+	}
+	key := base
+	for i := 2; ; i++ {
+		if _, exists := existing[key]; !exists {
+			return key
+		}
+		key = fmt.Sprintf("%s-%d", base, i)
+	}
+}
+
 // registerFilesystemStats resolves the tracked key and stats payload for a
 // filesystem before it is inserted into fsStats.
 func registerFilesystemStats(existing map[string]*system.FsStats, device, mountpoint string, root bool, customName string, ctx fsRegistrationContext) (string, *system.FsStats, bool) {
@@ -140,8 +160,16 @@ func registerFilesystemStats(existing map[string]*system.FsStats, device, mountp
 		}
 	}
 
-	if _, exists := existing[key]; exists {
-		return "", nil, false
+	if existingStats, exists := existing[key]; exists {
+		if existingStats.Mountpoint == mountpoint {
+			return "", nil, false
+		}
+		// Key collides on a different mountpoint. Pseudo-device setups like
+		// systemd-automount report the same device ("systemd-1") for every
+		// mount, which would otherwise drop every entry after the first
+		// (see #1931). Derive a unique key from the mountpoint so each mount
+		// survives.
+		key = uniqueFsStatsKey(existing, mountpoint)
 	}
 
 	fsStats := &system.FsStats{Root: root, Mountpoint: mountpoint}

agent/disk_test.go

@@ -258,9 +258,9 @@ func TestBuildFsStatRegistration(t *testing.T) {
 		assert.Equal(t, `C:`, key)
 	})
 
-	t.Run("skips existing key", func(t *testing.T) {
+	t.Run("skips re-registration of the same mountpoint", func(t *testing.T) {
 		key, stats, ok := registerFilesystemStats(
-			map[string]*system.FsStats{"sda1": {Mountpoint: "/existing"}},
+			map[string]*system.FsStats{"sda1": {Mountpoint: "/mnt/data"}},
 			"/dev/sda1",
 			"/mnt/data",
 			false,
@@ -277,6 +277,52 @@ func TestBuildFsStatRegistration(t *testing.T) {
 		assert.Empty(t, key)
 		assert.Nil(t, stats)
 	})
+
+	t.Run("keeps both mounts when a pseudo-device key collides (issue #1931)", func(t *testing.T) {
+		// systemd-automount reports every mount with device="systemd-1", so
+		// registering the second entry must not silently drop it.
+		existing := map[string]*system.FsStats{
+			"systemd-1": {Mountpoint: "/media/video"},
+		}
+		key, stats, ok := registerFilesystemStats(
+			existing,
+			"systemd-1",
+			"/media/backup",
+			false,
+			"Backup",
+			fsRegistrationContext{
+				isWindows:      false,
+				diskIoCounters: map[string]disk.IOCountersStat{},
+			},
+		)
+
+		assert.True(t, ok)
+		assert.NotEqual(t, "systemd-1", key, "key must differ from the colliding entry")
+		assert.Equal(t, "backup", key)
+		assert.Equal(t, "/media/backup", stats.Mountpoint)
+		assert.Equal(t, "Backup", stats.Name)
+	})
+
+	t.Run("derives a suffixed unique key when the mountpoint basename also collides", func(t *testing.T) {
+		existing := map[string]*system.FsStats{
+			"systemd-1": {Mountpoint: "/srv/backup"},
+			"backup":    {Mountpoint: "/media/backup"},
+		}
+		key, _, ok := registerFilesystemStats(
+			existing,
+			"systemd-1",
+			"/mnt/backup",
+			false,
+			"",
+			fsRegistrationContext{
+				isWindows:      false,
+				diskIoCounters: map[string]disk.IOCountersStat{},
+			},
+		)
+
+		assert.True(t, ok)
+		assert.Equal(t, "backup-2", key)
+	})
 }
 
 func TestAddConfiguredRootFs(t *testing.T) {