filesystem: Fix mountinfo parsing

Migrate mountinfo parsing to procfs library. This fixes incorrect
parsing introduced by PR #3387.

Fixes: #3450

Signed-off-by: Ben Kochie <superq@gmail.com>

Author: SuperQ

collector/filesystem_linux.go

@@ -17,10 +17,9 @@
 package collector
 
 import (
-	"bufio"
+	"bytes"
 	"errors"
 	"fmt"
-	"io"
 	"log/slog"
 	"os"
 	"slices"
@@ -182,9 +181,9 @@ func stuckMountWatcher(mountPoint string, success chan struct{}, logger *slog.Lo
 
 func mountPointDetails(logger *slog.Logger) ([]filesystemLabels, error) {
 	fs, err := procfs.NewFS(*procPath)
-  if err != nil {
-    return nil, fmt.Errorf("failed to open procfs: %w", err)
-  }
+	if err != nil {
+		return nil, fmt.Errorf("failed to open procfs: %w", err)
+	}
 	mountInfo, err := fs.GetProcMounts(1)
 	if errors.Is(err, os.ErrNotExist) {
 		// Fallback to `/proc/self/mountinfo` if `/proc/1/mountinfo` is missing due hidepid.
@@ -195,48 +194,37 @@ func mountPointDetails(logger *slog.Logger) ([]filesystemLabels, error) {
 		return nil, err
 	}
 
-	return parseFilesystemLabels(file)
+	return parseFilesystemLabels(mountInfo)
 }
 
 func parseFilesystemLabels(mountInfo []*procfs.MountInfo) ([]filesystemLabels, error) {
 	var filesystems []filesystemLabels
 
-	for mount in range mountInfo {
-		parts := strings.Fields(scanner.Text())
-
-		if len(parts) < 11 {
-			return nil, fmt.Errorf("malformed mount point information: %q", scanner.Text())
-		}
-
+	for _, mount := range mountInfo {
 		major, minor := 0, 0
-		_, err := fmt.Sscanf(parts[2], "%d:%d", &major, &minor)
+		_, err := fmt.Sscanf(mount.MajorMinorVer, "%d:%d", &major, &minor)
 		if err != nil {
-			return nil, fmt.Errorf("malformed mount point information: %q", scanner.Text())
-		}
-
-		m := 5
-		for parts[m+1] != "-" {
-			m++
+			return nil, fmt.Errorf("malformed mount point MajorMinorVer: %q", mount.MajorMinorVer)
 		}
 
 		// Ensure we handle the translation of \040 and \011
 		// as per fstab(5).
-		parts[4] = strings.ReplaceAll(parts[4], "\\040", " ")
-		parts[4] = strings.ReplaceAll(parts[4], "\\011", "\t")
+		mount.MountPoint = strings.ReplaceAll(mount.MountPoint, "\\040", " ")
+		mount.MountPoint = strings.ReplaceAll(mount.MountPoint, "\\011", "\t")
 
 		filesystems = append(filesystems, filesystemLabels{
-			device:       parts[m+3],
-			mountPoint:   rootfsStripPrefix(parts[4]),
-			fsType:       parts[m+2],
-			mountOptions: parts[5],
-			superOptions: parts[10],
+			device:       mount.Source,
+			mountPoint:   rootfsStripPrefix(mount.MountPoint),
+			fsType:       mount.FSType,
+			mountOptions: mountOptionsString(mount.Options),
+			superOptions: mountOptionsString(mount.SuperOptions),
 			major:        strconv.Itoa(major),
 			minor:        strconv.Itoa(minor),
 			deviceError:  "",
 		})
 	}
 
-	return filesystems, scanner.Err()
+	return filesystems, nil
 }
 
 // see https://github.com/prometheus/node_exporter/issues/3157#issuecomment-2422761187
@@ -248,3 +236,15 @@ func isFilesystemReadOnly(labels filesystemLabels) bool {
 
 	return false
 }
+
+func mountOptionsString(m map[string]string) string {
+	b := new(bytes.Buffer)
+	for key, value := range m {
+		if value == "" {
+			fmt.Fprintf(b, "%s", key)
+		} else {
+			fmt.Fprintf(b, "%s=%s", key, value)
+		}
+	}
+	return b.String()
+}

collector/filesystem_linux_test.go

@@ -19,26 +19,31 @@ package collector
 import (
 	"io"
 	"log/slog"
-	"strings"
 	"testing"
 
 	"github.com/alecthomas/kingpin/v2"
+
+	"github.com/prometheus/procfs"
 )
 
 func Test_parseFilesystemLabelsError(t *testing.T) {
 	tests := []struct {
 		name string
-		in   string
+		in   []*procfs.MountInfo
 	}{
 		{
-			name: "too few fields",
-			in:   "hello world",
+			name: "malformed Major:Minor",
+			in:   []*procfs.MountInfo{
+				{
+					MajorMinorVer: "nope",
+				},
+			},
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			if _, err := parseFilesystemLabels(strings.NewReader(tt.in)); err == nil {
+			if _, err := parseFilesystemLabels(tt.in); err == nil {
 				t.Fatal("expected an error, but none occurred")
 			}
 		})

go.mod

@@ -25,7 +25,7 @@ require (
 	github.com/prometheus/client_model v0.6.2
 	github.com/prometheus/common v0.67.1
 	github.com/prometheus/exporter-toolkit v0.14.1
-	github.com/prometheus/procfs v0.18.0
+	github.com/prometheus/procfs v0.18.1-0.20251025084418-43b7c7448da2
 	github.com/safchain/ethtool v0.6.2
 	golang.org/x/exp v0.0.0-20250911091902-df9299821621
 	golang.org/x/sys v0.37.0

go.sum

@@ -80,8 +80,12 @@ github.com/prometheus/common v0.67.1 h1:OTSON1P4DNxzTg4hmKCc37o4ZAZDv0cfXLkOt0oE
 github.com/prometheus/common v0.67.1/go.mod h1:RpmT9v35q2Y+lsieQsdOh5sXZ6ajUGC8NjZAmr8vb0Q=
 github.com/prometheus/exporter-toolkit v0.14.1 h1:uKPE4ewweVRWFainwvAcHs3uw15pjw2dk3I7b+aNo9o=
 github.com/prometheus/exporter-toolkit v0.14.1/go.mod h1:di7yaAJiaMkcjcz48f/u4yRPwtyuxTU5Jr4EnM2mhtQ=
+github.com/prometheus/procfs v0.17.1-0.20251025084002-e60b46b3da45 h1:/y4YcGcWAwmgZWxMsVWBZRBbPIJ+sxgXenRUvITCnd8=
+github.com/prometheus/procfs v0.17.1-0.20251025084002-e60b46b3da45/go.mod h1:sMb3/7ihkhO3ZKptrvInZq/aFyCqq7Y1/FJrHCY+hBE=
 github.com/prometheus/procfs v0.18.0 h1:2QTA9cKdznfYJz7EDaa7IiJobHuV7E1WzeBwcrhk0ao=
 github.com/prometheus/procfs v0.18.0/go.mod h1:M0aotyiemPhBCM0z5w87kL22CxfcH05ZpYlu+b4J7mw=
+github.com/prometheus/procfs v0.18.1-0.20251025084418-43b7c7448da2 h1:eHSoxAQdihm9FU0OxMEV4f766bcbS63L8eOYurtNp6E=
+github.com/prometheus/procfs v0.18.1-0.20251025084418-43b7c7448da2/go.mod h1:M0aotyiemPhBCM0z5w87kL22CxfcH05ZpYlu+b4J7mw=
 github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
 github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 github.com/safchain/ethtool v0.6.2 h1:O3ZPFAKEUEfbtE6J/feEe2Ft7dIJ2Sy8t4SdMRiIMHY=