linkfile
error = linkfile(xc, fileid_targ_dir, pcn_targ->pcn_name, fileid_src);
error = linkfile(xc, dir_fileid, pcn->pcn_name, targ_fileid);
error = linkfile(xc, parent, name, fileid);
int linkfile(struct Xconn *, fileid_t, const char *, fileid_t);