[AFS3-std] Re: A call for consensus on draft-deason-afs3-type-time-02

[Matt W. Benjamin]

Interesting data points.

----- "Steven Jenkins" <steven.jenkins@gmail.com> wrote:

> On Fri, Jul 29, 2011 at 12:22 PM, Andrew Deason
> <adeason@sinenomine.net> wrote:
> > On Thu, 28 Jul 2011 10:09:39 -0400
> > Jeffrey Altman <jaltman@secure-endpoints.com> wrote:
> >
> >> File systems do not copy this information to each other directly.
> =C2=A0All
> >> metadata is copied through an operating system VFS layer. =C2=A0Are
> there
> >> any VFS layers that actually provide better than 100ns resolution?
> >
> > I've been told verbally (informally) that z/OS offers ns-granular
> > timestamp information. I can't find documentation confirming that,
> but
> > I'm not really sure where to look, either.
> >
> > It's also not strictly true that we always go through a VFS layer,
> since
> > we could be translating directly to/from NFS, or there could be a
> > userspace application that speaks those protocols directly. Going
> > through an OS VFS is certainly the vast vast majority of cases,
> though.
> >
> > I'm not saying that means we care, but I believe those are some
> cases
> > where we would lose precision.
> >
>=20
> I agree that most accesses are done via the VFS layer. However,
> filesystems are starting to appear that have higher resolution time,
> and it is only natural for applications to take advantage of this
> infromation.
>=20
> As an additional example beyond NFSv4 and z/OS,  Btrfs, which has
> been
> shipping with Linux kernels for over a year, defines the following
> for
> times (i.e., ctime, atime, mtime)
>=20
> struct btrfs_timespec {
>   __le64 sec;
>   __le32 nsec;
> } __attribute__ ((__packed__));
>=20
> Since we are going to the effort now to define hi-resolution time for
> OpenAFS, it seems better to do this once, rather than do a
> specification for 100ns time resolution now, and another higher
> resolution specification in the future which will then leave us with
> two high-res times, or a need to do a migration.
>=20
> Steven
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--=20

Matt Benjamin

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