sysfs: add InfiniBand device listing and per-device parsing

sysfs/class_infiniband.go

@@ -136,19 +136,35 @@ type InfiniBandDevice struct {
 // The map keys are the names of the InfiniBand devices.
 type InfiniBandClass map[string]InfiniBandDevice
 
-// InfiniBandClass returns info for all InfiniBand devices read from
-// /sys/class/infiniband.
-func (fs FS) InfiniBandClass() (InfiniBandClass, error) {
+// InfiniBandClassDevices returns the names of the InfiniBand devices found in
+// /sys/class/infiniband without reading any device attributes or counters.
+func (fs FS) InfiniBandClassDevices() ([]string, error) {
 	path := fs.sys.Path(infinibandClassPath)
 
 	dirs, err := os.ReadDir(path)
 	if err != nil {
 		return nil, err
 	}
 
-	ibc := make(InfiniBandClass, len(dirs))
+	devices := make([]string, 0, len(dirs))
 	for _, d := range dirs {
-		device, err := fs.parseInfiniBandDevice(d.Name())
+		devices = append(devices, d.Name())
+	}
+
+	return devices, nil
+}
+
+// InfiniBandClass returns info for all InfiniBand devices read from
+// /sys/class/infiniband.
+func (fs FS) InfiniBandClass() (InfiniBandClass, error) {
+	devices, err := fs.InfiniBandClassDevices()
+	if err != nil {
+		return nil, err
+	}
+
+	ibc := make(InfiniBandClass, len(devices))
+	for _, name := range devices {
+		device, err := fs.InfiniBandDevice(name)
 		if err != nil {
 			return nil, err
 		}
@@ -159,6 +175,12 @@ func (fs FS) InfiniBandClass() (InfiniBandClass, error) {
 	return ibc, nil
 }
 
+// InfiniBandDevice returns info for a single InfiniBand device read from
+// /sys/class/infiniband/<Name>.
+func (fs FS) InfiniBandDevice(name string) (*InfiniBandDevice, error) {
+	return fs.parseInfiniBandDevice(name)
+}
+
 // Parse one InfiniBand device.
 // Refer to https://www.kernel.org/doc/Documentation/ABI/stable/sysfs-class-infiniband
 func (fs FS) parseInfiniBandDevice(name string) (*InfiniBandDevice, error) {

sysfs/class_infiniband_test.go

@@ -16,11 +16,37 @@
 package sysfs
 
 import (
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 )
 
+func TestInfiniBandClassDevicesDoesNotReadDevice(t *testing.T) {
+	sysPath := t.TempDir()
+	for _, name := range []string{"mlx5_6", "mlx5_5"} {
+		if err := os.MkdirAll(filepath.Join(sysPath, "class", "infiniband", name), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	fs, err := NewFS(sysPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := fs.InfiniBandClassDevices()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := []string{"mlx5_5", "mlx5_6"}
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Fatalf("unexpected InfiniBand device names (-want +got):\n%s", diff)
+	}
+}
+
 func TestParseSlowRate(t *testing.T) {
 	tests := []struct {
 		rate string
@@ -344,3 +370,25 @@ func TestInfiniBandClass(t *testing.T) {
 		t.Fatalf("unexpected InfiniBand class (-want +got):\n%s", diff)
 	}
 }
+
+func TestInfiniBandDevice(t *testing.T) {
+	fs, err := NewFS(sysTestFixtures)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	class, err := fs.InfiniBandClass()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := fs.InfiniBandDevice("mlx5_0")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := class["mlx5_0"]
+	if diff := cmp.Diff(want, *got); diff != "" {
+		t.Fatalf("unexpected InfiniBand device (-want +got):\n%s", diff)
+	}
+}