fusefrontend: add quirks for MacOS ExFAT

This also moves the quirks logic into fusefrontend.

Fixes https://github.com/rfjakob/gocryptfs/issues/585

1 files changed, 52 insertions, 0 deletions

diff --git a/internal/fusefrontend/quirks.go b/internal/fusefrontend/quirks.go
new file mode 100644
index 0000000..2979c84
--- /dev/null
+++ b/internal/fusefrontend/quirks.go
@@ -0,0 +1,52 @@
+package fusefrontend
+
+import (
+	"runtime"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+const (
+	quirkBrokenFalloc = uint64(1 << iota)
+	quirkDuplicateIno1
+)
+
+func detectQuirks(cipherdir string) (q uint64) {
+	const (
+		// From Linux' man statfs
+		BTRFS_SUPER_MAGIC = 0x9123683e
+
+		// From https://github.com/rfjakob/gocryptfs/issues/585#issuecomment-887370065
+		DARWIN_EXFAT_MAGIC = 35
+	)
+
+	var st unix.Statfs_t
+	err := unix.Statfs(cipherdir, &st)
+	if err != nil {
+		tlog.Warn.Printf("detectQuirks: Statfs on %q failed: %v", cipherdir, err)
+		return 0
+	}
+
+	logQuirk := func(s string) {
+		tlog.Info.Printf(tlog.ColorYellow + "detectQuirks: " + s + tlog.ColorReset)
+	}
+
+	// Preallocation on Btrfs is broken ( https://github.com/rfjakob/gocryptfs/issues/395 )
+	// and slow ( https://github.com/rfjakob/gocryptfs/issues/63 ).
+	//
+	// Cast to uint32 avoids compile error on arm: "constant 2435016766 overflows int32"
+	if uint32(st.Type) == BTRFS_SUPER_MAGIC {
+		logQuirk("Btrfs detected, forcing -noprealloc. See https://github.com/rfjakob/gocryptfs/issues/395 for why.")
+		q |= quirkBrokenFalloc
+	}
+	// On MacOS ExFAT, all empty files share inode number 1:
+	// https://github.com/rfjakob/gocryptfs/issues/585
+	if runtime.GOOS == "darwin" && st.Type == DARWIN_EXFAT_MAGIC {
+		logQuirk("ExFAT detected, disabling hard links. See https://github.com/rfjakob/gocryptfs/issues/585 for why.")
+		q |= quirkDuplicateIno1
+	}
+
+	return q
+}