On Fri, Aug 28, 2020 at 08:37:07AM -0400, Hendrik Boom wrote: > > >>>> Is there an establiched word in the Linux/Unix xommunity > > >>>> for something which might be a file or a directory?
> > Therefore it looks to me more like an implementation > > detail than a sensible concept. > > I do miss the ability to identify a directory independent of its name. > It can be important if a directory is renamed and you have active data in it. > > There's one directory that works for -- the current directory. If you > rename that directory you're still in it. > > In the 80's or 90's (I forget) there was a proposal to the ISO from > Japan to establish a standard OS-independent OS interface for > programmers to use. I lost against POSIX. > > But it had a machanism whereby opening a file could be done in two > phases. > > First you get a "lock" on a file. That gives you a connection to that > file. It's not an exclusive kind of lock (unless you ask it to be); > it's just a way of unambiguously identifying the file as long as it > exists and you keep the lock. It hangs on to the file even if someone > renames it. (not sure what happens if the file is deleted, though) _Any_ file descriptor does that. And a deleted file stays there, merely with a 0 link count -- if there's an open descriptor, you can link the file back into the filesystem. That's even the recommended way to create a new file atomically -- instead of the old write+fsync+rename trick that leaves junk upon a crash. And if you don't need to do any I/O on the file, O_PATH won't waste time. > Then afterward you can open it, close it, set exclusive > read/write access, release exclusive access, etc, using the lock instead > of the name. > > I've often regretted there's no such similar feature in Linux. The > assurance that several uses of a file or directory are indeed to the > same file or directory. You can do some of this by keeping a file open, > but I know of nothing like that for directories. man name_to_handle_at, open_by_handle_at. But this interface sucks and is superfluous with regular openat() -- which is also portable. So _always_ use openat() if you suspect something might happen to the underlying directories. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢠⠒⠀⣿⡁ ⢿⡄⠘⠷⠚⠋⠀ It's time to migrate your Imaginary Protocol from version 4i to 6i. ⠈⠳⣄⠀⠀⠀⠀ _______________________________________________ Dng mailing list Dng@lists.dyne.org https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng
