It only opens dotdot once at the start, though, and calls creat(dotdot) later.
It looks like the code opens dotdot, and then scans through it for something (match for dir?).
The creat call might mean "open for writing", and possibly the flags mean append. It appears dir is appended to the dotdot directory file.
So maybe, add this "dir" entry to dotdot if it isn't there already?
I can't guess what initializes dir; maybe it somehow comes as an argument from the command line or whatever.
c1 = -8;
*9 = tbuf - 1;
do {
*(++(*8)) = *(++(*9));
} while(++c1 != 0);
goto 1b; // b for backwards?
[0] PDP7 manual, big PDF: http://bitsavers.trailing-edge.com/pdf/dec/pdp7/F-75P_PDP7pr...
I think ‘dotdot’ is what is called ‘dd’ there (the corresponding symbol in ls is still named ‘dd'). I don't think the concept of a parent directory existed yet. Maybe ‘pd’ is something like ‘prepare directory’, constructing the dd/dotdot entry.
I think this is on the right track - it looks like the write call is to the newly created .., with df being used to hold the file descriptor.
I am leaning toward Pete_D's ‘pack directory’ idea.
¹ https://github.com/DoctorWkt/pdp7-unix/blob/e94417092a2980e7...