infiniband: apply device filters before reading counters

collector/infiniband_linux.go

@@ -158,20 +158,25 @@ func (c *infinibandCollector) pushCounter(ch chan<- prometheus.Metric, name stri
 }
 
 func (c *infinibandCollector) Update(ch chan<- prometheus.Metric) error {
-	devices, err := c.fs.InfiniBandClass()
+	deviceNames, err := c.fs.InfiniBandClassDevices()
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
 			c.logger.Debug("infiniband statistics not found, skipping")
 			return ErrNoData
 		}
-		return fmt.Errorf("error obtaining InfiniBand class info: %w", err)
+		return fmt.Errorf("error obtaining InfiniBand device list: %w", err)
 	}
 
-	for _, device := range devices {
-		if c.deviceFilter.ignored(device.Name) {
+	for _, name := range deviceNames {
+		if c.deviceFilter.ignored(name) {
 			continue
 		}
 
+		device, err := c.fs.InfiniBandDevice(name)
+		if err != nil {
+			return fmt.Errorf("error obtaining InfiniBand device %q info: %w", name, err)
+		}
+
 		infoDesc := prometheus.NewDesc(
 			prometheus.BuildFQName(namespace, c.subsystem, "info"),
 			"Non-numeric data from /sys/class/infiniband/<device>, value is always 1.",

collector/infiniband_linux_test.go

@@ -0,0 +1,68 @@
+// Copyright 2026 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !noinfiniband
+
+package collector
+
+import (
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func TestInfiniBandDeviceFilterBeforeRead(t *testing.T) {
+	sys := t.TempDir()
+	included := filepath.Join(sys, "class", "infiniband", "mlx5_7")
+	excluded := filepath.Join(sys, "class", "infiniband", "mlx5_5")
+
+	if err := os.MkdirAll(filepath.Join(included, "ports"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(included, "fw_ver"), []byte("28.47.1088\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	// The excluded device deliberately lacks fw_ver and ports. Reading it would fail.
+	if err := os.MkdirAll(excluded, 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	oldSysPath := *sysPath
+	oldInclude := *infinibandDeviceInclude
+	oldExclude := *infinibandDeviceExclude
+	t.Cleanup(func() {
+		*sysPath = oldSysPath
+		*infinibandDeviceInclude = oldInclude
+		*infinibandDeviceExclude = oldExclude
+	})
+	*sysPath = sys
+	*infinibandDeviceInclude = ""
+	*infinibandDeviceExclude = "^mlx5_5$"
+
+	collector, err := NewInfiniBandCollector(slog.New(slog.NewTextHandler(io.Discard, nil)))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ch := make(chan prometheus.Metric, 1)
+	if err := collector.Update(ch); err != nil {
+		t.Fatalf("excluded device was read: %v", err)
+	}
+	if len(ch) != 1 {
+		t.Fatalf("expected one metric from the included device, got %d", len(ch))
+	}
+}