On 8/31/20 6:05 PM, Chris Angelico wrote: > On Tue, Sep 1, 2020 at 5:08 AM Richard Damon <rich...@damon-family.org> wrote: >> The file descriptor could remember the path used to get to it. chroot >> shows that .. needs to be somewhat special, as it needs to go away for >> anyone that . is their current root. > But my point is that there might not actually *be* a valid path that > gets you to a file descriptor. It can't remember something that > doesn't exist. (And it's pretty impractical to do that even if it > does.)
Remember, we are talking about a hypothetical OS that handles hardlinks to directories, and defines that .. will point to the parent used to come to it, NOT just having current *NIX allowing hardlinks to directories with no remediation of the issues cause. One result of the definition, is that when you open a file/directory, if it might be a directory, the system WILL need to remember the path to it (so as to provide a value for ..) and that memory will provide a 'reference' for the directories so they can't go away (just like an unlinked file stays around will someone has it open). The normal way to get a file descriptor starts from a path, so the path had to exist in the first place, and since we are assuming that to get .., it keep a reference to that path, it can't truly go away. > >> I see no problem with it being a hardlink, and in fact, executables know >> the name they were executed by, so directories knowing the path isn't >> that different. > Actually no, they don't. They are all taught, and being taught, > believe, that their first argument is their name. > >> The key differnce between a hardlink and a symlink is >> that hardlinks maintain existance, and always point to something that >> exists (things know how many hardlinks refer to them). symlinks don't >> reference the actual file object, but the symbolic path to it, which may >> or may not actually exist, and who doesn't know such a link exists. > Symlinks refer to a path, which may be relative. Hardlinks refer to an > inode (or whatever other way you choose to identify an actual file's > contents). It's entirely possible to have an open file or directory > that no longer has any actual path referring to it; in fact, things > don't know how many hardlinks refer to them, just how many references > there are. > > ChrisA -- Richard Damon -- https://mail.python.org/mailman/listinfo/python-list
