fat12/16/32: expose attribute flags and timestamps via FileInfo.Sys()

filesystem/fat12/directoryentry.go

@@ -55,9 +55,23 @@ func (de *directoryEntry) Info() (iofs.FileInfo, error) {
 		shortName: de.fullShortName(),
 		size:      int64(de.fileSize),
 		isDir:     de.isSubdirectory,
+		sys:       de.stat(),
 	}, nil
 }
 
+func (de *directoryEntry) stat() *StatT {
+	return &StatT{
+		ReadOnly:    de.isReadOnly,
+		Hidden:      de.isHidden,
+		System:      de.isSystem,
+		Archive:     de.isArchiveDirty,
+		VolumeLabel: de.isVolumeLabel,
+		CreateTime:  de.createTime,
+		AccessTime:  de.accessTime,
+		Cluster:     de.clusterLocation,
+	}
+}
+
 func (de *directoryEntry) nameMatches(name string) bool {
 	return strings.EqualFold(de.filenameLong, name) || strings.EqualFold(de.fullShortName(), name)
 }

filesystem/fat12/fat12_test.go

@@ -408,6 +408,32 @@ func TestFat12Stat(t *testing.T) {
 	}
 }
 
+func TestFat12StatSys(t *testing.T) {
+	_, fs := createFAT12(t, "SYSTEST")
+	writeFile(t, fs, "/sys.txt", []byte("sys"))
+
+	info, err := fs.Stat("sys.txt")
+	if err != nil {
+		t.Fatalf("Stat: %v", err)
+	}
+	stat, ok := info.Sys().(*fat12.StatT)
+	if !ok {
+		t.Fatalf("Sys() did not return *fat12.StatT, got %T", info.Sys())
+	}
+	if stat == nil {
+		t.Fatal("StatT is nil")
+	}
+	if stat.Cluster < 2 {
+		t.Errorf("Cluster = %d, expected >= 2 (data clusters start at 2)", stat.Cluster)
+	}
+	if stat.VolumeLabel {
+		t.Error("regular file should not have VolumeLabel set")
+	}
+	if stat.Hidden || stat.System || stat.ReadOnly {
+		t.Errorf("unexpected attribute bits set: Hidden=%v System=%v ReadOnly=%v", stat.Hidden, stat.System, stat.ReadOnly)
+	}
+}
+
 // ── ReadFile (fs.ReadFileFS) ──────────────────────────────────────────────────
 
 func TestFat12ReadFile(t *testing.T) {

filesystem/fat12/file.go

@@ -30,6 +30,7 @@ func (fl *File) Stat() (iofs.FileInfo, error) {
 		shortName: fl.fullShortName(),
 		size:      int64(fl.fileSize),
 		isDir:     fl.isSubdirectory,
+		sys:       fl.stat(),
 	}, nil
 }
 

filesystem/fat12/fileinfo.go

@@ -14,6 +14,21 @@ type FileInfo struct {
 	shortName string
 	size      int64
 	isDir     bool
+	sys       *StatT
+}
+
+// StatT carries FAT-specific metadata returned by FileInfo.Sys(). FAT12/16/32
+// have no inodes, uid/gid, or POSIX permissions, but they do carry attribute
+// flags and additional timestamps that os.FileMode doesn't represent.
+type StatT struct {
+	ReadOnly    bool
+	Hidden      bool
+	System      bool
+	Archive     bool
+	VolumeLabel bool
+	CreateTime  time.Time
+	AccessTime  time.Time
+	Cluster     uint32
 }
 
 // IsDir abbreviation for Mode().IsDir()
@@ -63,9 +78,9 @@ func (fi FileInfo) Size() int64 {
 	return fi.size
 }
 
-// Sys underlying data source - not supported yet and so will return nil
+// Sys returns *StatT with FAT-specific metadata.
 //
 //nolint:gocritic // we need this to comply with fs.FileInfo
 func (fi FileInfo) Sys() interface{} {
-	return nil
+	return fi.sys
 }

filesystem/fat16/fat16.go

@@ -20,6 +20,9 @@ type FileSystem struct {
 // interface guard
 var _ filesystem.FileSystem = (*FileSystem)(nil)
 
+// StatT is an alias for fat12.StatT, the metadata returned by FileInfo.Sys().
+type StatT = fat12.StatT
+
 // Type returns filesystem.TypeFat16, overriding fat12.FileSystem.Type().
 func (fs *FileSystem) Type() filesystem.Type { return filesystem.TypeFat16 }
 

filesystem/fat32/fat32.go

@@ -28,6 +28,9 @@ const (
 // is directly usable in fat12.Dos20BPB struct literals.
 type SectorSize = fat12.SectorSize
 
+// StatT is an alias for fat12.StatT, the metadata returned by FileInfo.Sys().
+type StatT = fat12.StatT
+
 const (
 	SectorSize512        SectorSize = 512
 	SectorSize4096       SectorSize = 4096