[rfc] 64-bit inode numbers

[Kostik Belousov]

On Thu, Jun 23, 2011 at 08:23:50PM -0400, Rick Macklem wrote:
> Kostik Belousov wrote:
> > On Thu, Jun 23, 2011 at 06:05:56PM -0400, Garance A Drosehn wrote:
> > > On 6/23/11 4:11 AM, Kostik Belousov wrote:
> > > >On Thu, Jun 23, 2011 at 09:43:33AM +0300, Gleb Kurtsou wrote:
> > > >
> > > >>On (22/06/2011 19:19), Garance A Drosehn wrote:
> > > >>
> > > >>>Sorry for replying to an older message, but a reply made in a
> > > >>>different
> > > >>>thread reminded me about this project...
> > > >>>
> > > >>>Also, I may have asked this before. In fact, I'm almost sure that
> > > >>>I
> > > >>>started
> > > >>>a reply to this back in Jan/Feb, but my email client claims I
> > > >>>never
> > > >>>replied
> > > >>>to this topic...
> > > >>>
> > > >>>Are you increasing only the size of ino_t, or could you also look
> > > >>>at
> > > >>>increasing the size of dev_t? (just curious...)
> > > >>>
> > > >>Sure. Incorporating as much of similar changes as possible is
> > > >>good.
> > > >>I've added Kostik and Matthew to CC list, it's for them to decide.
> > > >>
> > > >>dev_t on other OSes:
> > > >>	NetBSD - uint64_t
> > > >>	DragonFly - uint32_t
> > > >>	Darwin - __int32_t
> > > >>	OpenSolaris - ulong_t
> > > >>	Linux - __u32
> > > >>
> > > >>Considering this I think 3rd party software is not ready for such
> > > >>change.
> > > >>
> > > >>Major/minor mapping to dev_t will get more complicated.
> > > >>
> > > >>And the most important question: what would you want it for? [...]
> > > >>
> > > >Indeed, this is the right question.
> > > >
> > > Consider the thread "Increasing the size of dev_t and ino_t" from
> > > freebsd-arch in 2002:
> > >
> > > http://docs.freebsd.org/mail/archive/2002/freebsd-arch/20020317.freebsd-arch.html
> > >
> > > In particular, this message by Robert Watson:
> > >
> > > http://docs.freebsd.org/cgi/getmsg.cgi?fetch=139853+0+archive/2002/freebsd-arch/20020317.freebsd-arch
> > >
> > > I just participated in an online conference for OpenAFS, and while
> > > it
> > > isn't exactly taking the world by storm, I keep thinking it would be
> > > useful if FreeBSD could map individual AFS volumes to unique dev_t
> > > identifiers. And given the way AFS is implemented (as a global
> > > filesystem
> > > with many cells all reachable at the same time), and given the way
> > > most
> > > sites deploy AFS (with thousands or tens-of-thousands of individual
> > > AFS
> > > volumes *per site*), that adds up to a lot of values for dev_t.
> > >
> > > The upcoming release of OpenAFS should include a working and pretty
> > > stable AFS client for FreeBSD, so having a larger dev_t would have a
> > > more immediate application than it did back in 2002.
> > Am I right that the issue is the uniqueness of the dev_t for each
> > AFS volume, as reported by stat(2) ?
> > 
> > Shouldn't the AFS client synthesize the dev_t for each new volume
> > mounted ? It seems that the current 32bit dev_t would be enough,
> > since I do not expect to see hundreds of thousands of mounts
> > on an single system.
> > 
> I think the main concern is making sure that the value is not the
> same as what another mount already has. That's why mnt_stat.f_fsid
> is synthesized for NFS, I think?
We have quite useful unit number allocator that guarantees uniqueness,
see sys/systm.h, look for unrhdr. In fact, it is used by devfs to
maintain dev_t values, see struct cdev_priv member cdp_inode, which
value typically ends up in the st_dev.

If needed, the devfs inode allocator can be exported.

> 
> > Please note that we do not guarantee dev_t stability across reboots
> > even
> > for real devices.
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