On Thu 22-02-24 06:27:14, Kent Overstreet wrote:
> On Thu, Feb 22, 2024 at 12:01:38PM +0100, Jan Kara wrote:
> > On Thu 22-02-24 04:42:07, Kent Overstreet wrote:
> > > On Thu, Feb 22, 2024 at 10:14:20AM +0100, Miklos Szeredi wrote:
> > > > On Wed, 21 Feb 2024 at 22:08, Josef Bacik <[email protected]> wrote:
> > > > >
> > > > > On Wed, Feb 21, 2024 at 04:06:34PM +0100, Miklos Szeredi wrote:
> > > > > > On Wed, 21 Feb 2024 at 01:51, Kent Overstreet
> > > > > > <[email protected]> wrote:
> > > > > > >
> > > > > > > Recently we had a pretty long discussion on statx extensions,
> > > > > > > which
> > > > > > > eventually got a bit offtopic but nevertheless hashed out all the
> > > > > > > major
> > > > > > > issues.
> > > > > > >
> > > > > > > To summarize:
> > > > > > > - guaranteeing inode number uniqueness is becoming increasingly
> > > > > > > infeasible, we need a bit to tell userspace "inode number is
> > > > > > > not
> > > > > > > unique, use filehandle instead"
> > > > > >
> > > > > > This is a tough one. POSIX says "The st_ino and st_dev fields
> > > > > > taken
> > > > > > together uniquely identify the file within the system."
> > > > > >
> > > > >
> > > > > Which is what btrfs has done forever, and we've gotten yelled at
> > > > > forever for
> > > > > doing it. We have a compromise and a way forward, but it's not a
> > > > > widely held
> > > > > view that changing st_dev to give uniqueness is an acceptable
> > > > > solution. It may
> > > > > have been for overlayfs because you guys are already doing something
> > > > > special,
> > > > > but it's not an option that is afforded the rest of us.
> > > >
> > > > Overlayfs tries hard not to use st_dev to give uniqueness and instead
> > > > partitions the 64bit st_ino space within the same st_dev. There are
> > > > various fallback cases, some involve switching st_dev and some using
> > > > non-persistent st_ino.
> > >
> > > Yeah no, you can't crap multiple 64 bit inode number spaces into 64
> > > bits: pigeonhole principle.
> > >
> > > We need something better than "hacks".
> >
> > I agree we should have a better long-term plan than finding ways how to
> > cram things into 64-bits inos. However I don't see a realistic short-term
> > solution other than that.
> >
> > To explicit: Currently, tar and patch and very likely other less well-known
> > tools are broken on bcachefs due to non-unique inode numbers. If you want
> > ot fix them, either you find ways how bcachefs can cram things into 64-bit
> > ino_t or you go and modify these tools (or prod maintainers or whatever) to
> > not depend on ino_t for uniqueness. The application side of things isn't
> > going to magically fix itself by us telling "bad luck, ino_t isn't unique
> > anymore".
>
> My intent is to make a real effort towards getting better interfaces
> going, prod those maintainers, _then_ look at adding those hacks (that
> will necessarily be short term solutions since 64 bits is already
> looking cramped).
OK, fine by me :) So one thing is still not quite clear to me - how do you
expect the INO_NOT_UNIQUE flag to be used by these apps? Do you expect them
to use st_dev + st_ino by default and fall back to fsid + fhandle only when
INO_NOT_UNIQUE is set?
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
