Fix file mode bit handling (#8)

fs.FileMode specifies a number of bits that do not match the
file mode bits defined in the inode, so constructing a valid
fs.FileMode requires translating bits 9-16 into the equivalent
flags defined in fs package vs just casting the filemode bits
from the inode.

In addition, the IsDir method in inode was incorrect - a block device
has the value 0x6000, which means IsDir will return true for block
device nodes.

Author: mpoindexter

xfs/inode.go

@@ -834,19 +834,19 @@ func parseEntry(r io.Reader, i8count bool) (*Dir2SfEntry, error) {
 }
 
 func (ic InodeCore) IsDir() bool {
-	return ic.Mode&0x4000 != 0 && ic.Mode&0x8000 == 0
+	return ic.Mode&0xF000 == 0x4000
 }
 
 func (ic InodeCore) IsRegular() bool {
-	return ic.Mode&0x8000 != 0 && ic.Mode&0x4000 == 0
+	return ic.Mode&0xF000 == 0x8000
 }
 
 func (ic InodeCore) IsSocket() bool {
-	return ic.Mode&0xC000 != 0
+	return ic.Mode&0xF000 == 0xC000
 }
 
 func (ic InodeCore) IsSymlink() bool {
-	return ic.Mode&0xA000 != 0
+	return ic.Mode&0xF000 == 0xA000
 }
 
 func (ic InodeCore) isSupported() bool {

xfs/xfs.go

@@ -148,7 +148,6 @@ func (xfs *FileSystem) ReadDirInfo(name string) (fs.FileInfo, error) {
 		return FileInfo{
 			name:  "/",
 			inode: inode,
-			mode:  fs.FileMode(inode.inodeCore.Mode),
 		}, nil
 	}
 	name = strings.TrimRight(name, string(filepath.Separator))
@@ -334,7 +333,6 @@ func (xfs *FileSystem) listFileInfo(ino uint64) ([]FileInfo, error) {
 			FileInfo{
 				name:  entry.Name(),
 				inode: inode,
-				mode:  fs.FileMode(inode.inodeCore.Mode),
 			},
 		)
 	}
@@ -399,8 +397,6 @@ func (xfs *FileSystem) listEntries(ino uint64) ([]Entry, error) {
 type FileInfo struct {
 	name  string
 	inode *Inode
-
-	mode fs.FileMode
 }
 
 func (i FileInfo) IsDir() bool {
@@ -424,7 +420,42 @@ func (i FileInfo) Sys() interface{} {
 }
 
 func (i FileInfo) Mode() fs.FileMode {
-	return i.mode
+	m := i.inode.inodeCore.Mode
+	// Bottom 9 bits are same in fs.FileMode and XFS inode (unix permission bits)
+	translatedMode := fs.FileMode(m & 0o777)
+
+	// Bits 9-12 in the inode are sticky, setuid, and setgid bits
+	if m&0o1000 != 0 {
+		translatedMode |= fs.ModeSticky
+	}
+	if m&0o2000 != 0 {
+		translatedMode |= fs.ModeSetuid
+	}
+	if m&0o4000 != 0 {
+		translatedMode |= fs.ModeSetgid
+	}
+
+	// bits 13-16 are file type bits, defined in stat.h
+	switch m & 0xF000 {
+	case 0xC000:
+		translatedMode |= fs.ModeSocket
+	case 0xA000:
+		translatedMode |= fs.ModeSymlink
+	case 0x8000:
+		// Regular file, no flags to set
+	case 0x6000:
+		translatedMode |= fs.ModeDevice
+	case 0x4000:
+		translatedMode |= fs.ModeDir
+	case 0x2000:
+		translatedMode |= fs.ModeCharDevice
+	case 0x1000:
+		translatedMode |= fs.ModeNamedPipe
+	default:
+		translatedMode |= fs.ModeIrregular
+	}
+
+	return translatedMode
 }
 
 // dirEntry is implemented io/fs DirEntry interface

xfs/xfs_test.go

@@ -25,19 +25,19 @@ func TestFileSystemCheckFileExtents(t *testing.T) {
 			filesystem:   "testdata/image.xfs",
 			name:         "fmt_extents_file_1024",
 			expectedSize: 1024,
-			mode:         33188,
+			mode:         0o644,
 		},
 		{
 			filesystem:   "testdata/image.xfs",
 			name:         "fmt_extents_file_4096",
 			expectedSize: 4096,
-			mode:         33188,
+			mode:         0o644,
 		},
 		{
 			filesystem:   "testdata/image.xfs",
 			name:         "fmt_extents_file_16384",
 			expectedSize: 16384,
-			mode:         33188,
+			mode:         0o644,
 		},
 		{
 			filesystem:  "testdata/image.xfs",