typedef struct fs<Type,Impl> {
    __code readsb(Impl* fs, uint dev, struct superblock* sb, __code next(...));
    __code iinit(Impl* fs, __code next(...));
    __code ialloc(Impl* fs, uint dev, short type, __code next(...));
    __code iupdate(Impl* fs, struct inode* ip, __code next(...));
    __code idup(Impl* fs, struct inode* ip, __code next(...));
    __code ilock(Impl* fs, struct inode* ip, __code next(...));
    __code iunlock(Impl* fs, struct inode* ip, __code next(...));
    __code iput(Impl* fs, struct inode* ip, __code next(...));
    __code iunlockput(Impl* fs, struct inode* ip, __code next(...));
    __code stati(Impl* fs , struct inode* ip, struct stat* st, __code next(...));
    __code readi(Impl* fs, struct inode* ip, char* dst, uint off, uint tot, uint n, __code next(int ret, ...));
    __code writei(Impl* fs, struct inode* ip, char* src, uint off, uint tot, uint n, __code next(int ret, ...));
    __code namecmp(Impl* fs, const char* s, const char* t, __code next(int strncmp_val, ...));
    __code dirlookup(Impl* fs, struct inode* dp, char* name, uint off, uint* poff, struct dirent* de, __code next(int ret, ...));
    __code dirlink(Impl* fs, struct inode* ip, struct dirent* de, struct inode* dp, char* name, uint off, uint inum, __code next(...));
    __code namei(Impl* fs, char* path, __code next(int namex_val, ...));
    __code nameiparent(Impl* fs, char* path, char* name, __code next(int namex_val, ...));
    __code next(...);
} fs;