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;
    int iget_val;

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