Re: [PATCH] fs: inode: Reduce volatile inode wraparound risk when ino_t is 64 bit

[J. Bruce Fields]

On Sat, Dec 21, 2019 at 10:16:52AM +0000, Chris Down wrote:
> Darrick J. Wong writes:
> >On Fri, Dec 20, 2019 at 02:49:36AM +0000, Chris Down wrote:
> >>In general, userspace applications expect that (device, inodenum) should
> >>be enough to be uniquely point to one inode, which seems fair enough.
> >
> >Except that it's not.  (dev, inum, generation) uniquely points to an
> >instance of an inode from creation to the last unlink.

I thought that (dev, inum) was supposed to be unique from creation to
last unlink (and last close), and (dev, inum, generation) was supposed
to be unique for all time.

> I didn't mention generation because, even though it's set on tmpfs
> (to prandom_u32()), it's not possible to evaluate it from userspace
> since `ioctl` returns ENOTTY. We can't ask userspace applications to
> introspect on an inode attribute that they can't even access :-)

Is there any reason not to add IOC_GETVERSION support to tmpfs?

I wonder if statx should return it too?

--b.