Re: Can we avoid chdir'ing in resolve_symlinks() ?

On Thu, 1 Sept 2022 at 19:39, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

This code was mine originally (336969e49), but I sure don't
> remember why I wrote it like that. I know we didn't have a
> robust version of canonicalize_path() then, and that may have
> been the main issue, but that offhand comment about mount
> points bothers me. But I can't reconstruct precisely what
> I was worried about there. The only contemporaneous discussion
> thread I can find is [2], which doesn't go into coding details.
>

Does this happen in a context where we need to worried about the directory
structure changing under us, either accidentally or maliciously?

I'm wondering because I understand cd'ing through the structure can avoid
some of the related problems and might be the reason for doing it that way
originally. My impression is that the modern equivalent would be to use
openat() with O_PATH to step through the hierarchy. But then I'm not clear
on how to get back to the absolute path, given a file descriptor for the
final directory.