cgofuse: don't inline lookup tables / alloc once

Truthfully, I didn't benchmark this or look at the assembly.
But I remember this pattern being a concern in the past.

Unless the compiler has changed to optimize this out, things like the
map literal would be initialized each call.
Now we should do that only once on init.

Metrics would be nice to see on this though.
Does the compiler actually still act that way, and does the stack
climbing cost us more than doing that anyway?
Should these be lazy and initialized on the first call rather than at
init time?

internal/filesystem/cgofuse/translate.go

@@ -82,12 +82,8 @@ func goToFuseFileType(m fs.FileMode) fileType {
 }
 
 // TODO: better names
-func goToFusePermissions(m fs.FileMode) filePermissions {
-	var (
-		goPermissions   = m.Perm()
-		fusePermissions filePermissions
-	)
-	for _, bit := range []struct {
+var (
+	goToFusePermissionsTable = [...]struct {
 		golang fs.FileMode
 		fuse   filePermissions
 	}{
@@ -100,7 +96,36 @@ func goToFusePermissions(m fs.FileMode) filePermissions {
 		{golang: filesystem.ExecuteUser, fuse: executeUser},
 		{golang: filesystem.WriteUser, fuse: writeUser},
 		{golang: filesystem.ReadUser, fuse: readUser},
-	} {
+	}
+	goFlagsFromFuseTable = [...]struct {
+		fuse, golang int
+	}{
+		{fuse: fuse.O_APPEND, golang: os.O_APPEND},
+		{fuse: fuse.O_CREAT, golang: os.O_CREATE},
+		{fuse: fuse.O_EXCL, golang: os.O_EXCL},
+		{fuse: fuse.O_TRUNC, golang: os.O_TRUNC},
+	}
+	fsErrorsTable = map[fserrors.Kind]errNo{
+		fserrors.Other:            -fuse.EIO,
+		fserrors.InvalidItem:      -fuse.EINVAL,
+		fserrors.InvalidOperation: -fuse.ENOSYS,
+		fserrors.Permission:       -fuse.EACCES,
+		fserrors.IO:               -fuse.EIO,
+		fserrors.Exist:            -fuse.EEXIST,
+		fserrors.NotExist:         -fuse.ENOENT,
+		fserrors.IsDir:            -fuse.EISDIR,
+		fserrors.NotDir:           -fuse.ENOTDIR,
+		fserrors.NotEmpty:         -fuse.ENOTEMPTY,
+	}
+)
+
+// TODO: better names
+func goToFusePermissions(m fs.FileMode) filePermissions {
+	var (
+		goPermissions   = m.Perm()
+		fusePermissions filePermissions
+	)
+	for _, bit := range goToFusePermissionsTable {
 		if goPermissions&bit.golang != 0 {
 			fusePermissions |= bit.fuse
 		}
@@ -119,14 +144,7 @@ func goFlagsFromFuse(fuseFlags int) int {
 	case fuse.O_RDWR:
 		goFlags = os.O_RDWR
 	}
-	for _, bit := range []struct {
-		fuse, golang int
-	}{
-		{fuse: fuse.O_APPEND, golang: os.O_APPEND},
-		{fuse: fuse.O_CREAT, golang: os.O_CREATE},
-		{fuse: fuse.O_EXCL, golang: os.O_EXCL},
-		{fuse: fuse.O_TRUNC, golang: os.O_TRUNC},
-	} {
+	for _, bit := range goFlagsFromFuseTable {
 		if fuseFlags&bit.fuse != 0 {
 			goFlags |= bit.golang
 		}
@@ -138,19 +156,7 @@ func goFlagsFromFuse(fuseFlags int) int {
 func interpretError(err error) errNo {
 	var fsErr *fserrors.Error
 	if errors.As(err, &fsErr) {
-		// Translation table for interface.Error -> FUSE error
-		return map[fserrors.Kind]errNo{
-			fserrors.Other:            -fuse.EIO,
-			fserrors.InvalidItem:      -fuse.EINVAL,
-			fserrors.InvalidOperation: -fuse.ENOSYS,
-			fserrors.Permission:       -fuse.EACCES,
-			fserrors.IO:               -fuse.EIO,
-			fserrors.Exist:            -fuse.EEXIST,
-			fserrors.NotExist:         -fuse.ENOENT,
-			fserrors.IsDir:            -fuse.EISDIR,
-			fserrors.NotDir:           -fuse.ENOTDIR,
-			fserrors.NotEmpty:         -fuse.ENOTEMPTY,
-		}[fsErr.Kind]
+		return fsErrorsTable[fsErr.Kind]
 	}
 	panic(fmt.Sprintf("provided error is not translatable to POSIX error %#v", err))
 }