syscallcompat: downgrade DT_UNKNOWN message level on XFS

Old XFS filesystems always return DT_UNKNOWN. Downgrade the message
to "info" level if we are on XFS.

Using the "warning" level means that users on old XFS filesystems
cannot run the test suite as it intentionally aborts on any
warnings.

Fixes https://github.com/rfjakob/gocryptfs/issues/267

1 files changed, 16 insertions, 3 deletions

diff --git a/internal/syscallcompat/getdents_linux.go b/internal/syscallcompat/getdents_linux.go
index 1387023..3853f2d 100644
--- a/internal/syscallcompat/getdents_linux.go
+++ b/internal/syscallcompat/getdents_linux.go
@@ -123,6 +123,21 @@ func getdentsName(s unix.Dirent) (string, error) {
 
 var dtUnknownWarnOnce sync.Once
 
+func dtUnknownWarn(dirfd int) {
+	const XFS_SUPER_MAGIC = 0x58465342 // From man 2 statfs
+	var buf syscall.Statfs_t
+	err := syscall.Fstatfs(dirfd, &buf)
+	if err == nil && buf.Type == XFS_SUPER_MAGIC {
+		// Old XFS filesystems always return DT_UNKNOWN. Downgrade the message
+		// to "info" level if we are on XFS.
+		// https://github.com/rfjakob/gocryptfs/issues/267
+		tlog.Info.Printf("Getdents: convertDType: received DT_UNKNOWN, fstype=xfs, falling back to stat")
+	} else {
+		tlog.Warn.Printf("Getdents: convertDType: received DT_UNKNOWN, fstype=%#x, falling back to stat",
+			buf.Type)
+	}
+}
+
 // convertDType converts a Dirent.Type to at Stat_t.Mode value.
 func convertDType(dirfd int, name string, dtype uint8) (uint32, error) {
 	if dtype != syscall.DT_UNKNOWN {
@@ -130,9 +145,7 @@ func convertDType(dirfd int, name string, dtype uint8) (uint32, error) {
 		return uint32(dtype) << 12, nil
 	}
 	// DT_UNKNOWN: we have to call stat()
-	dtUnknownWarnOnce.Do(func() {
-		tlog.Warn.Printf("Getdents: convertDType: received DT_UNKNOWN, falling back to stat")
-	})
+	dtUnknownWarnOnce.Do(func() { dtUnknownWarn(dirfd) })
 	var st unix.Stat_t
 	err := Fstatat(dirfd, name, &st, unix.AT_SYMLINK_NOFOLLOW)
 	if err != nil {