typedef struct fs_impl<Type, Isa> impl fs{
    union Data* fs_impl;
    struct superblock* sb;
    uint dev;
    short type;
    struct buf* bp;
    struct dinode* dip;
    int inum;

    __code allocinode(Type* fs_impl, uint dev, short type, __code next(...));
    __code allocinode_loop(Type* fs_impl, int inum, uint dev, struct superblock* sb, struct buf* bp, struct dinode* dip, __code next(...));
    __code next(...);
} fs_impl;