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Versions: 00 01 02 03                                                   
N/A                                                            A. Deason
Internet-Draft                                               Sine Nomine
Intended status: Informational                             March 7, 2011
Expires: September 8, 2011


                      Base Types for Time in AFS-3
                     draft-deason-afs3-type-time-00

Abstract

   This document defines two types to be used in future AFS-3 Rx Remote
   Procedure Calls (RPCs) to represent time.  Current AFS-3 RPCs
   represent time as 32-bit integers representing seconds.  This is
   insufficient in both granularity and range, so new types to represent
   time are defined in this document to overcome these limitations.

Internet Draft Comments

   Comments regarding this draft are solicited.  Please include the
   AFS-3 protocol standardization mailing list
   (afs3-standardization@openafs.org) as a recipient of any comments.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 8, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Data Types  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  AFSAbsTime  . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.2.  AFSRelTime  . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Informative References  . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6



































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1.  Introduction

   All extant AFS-3 RPCs represent time as a 32-bit integer, as encoded
   by XDR in [RFC4506], which represents a number of seconds.  For RPCs
   that specify an absolute time, this is the number of seconds that
   have passed since since midnight or 0 hour January 1, 1970
   Coordinated Universal Time (UTC), not counting leap seconds.  These
   time structures will be unusable after January 2038, and are already
   insufficient to represent time with more granularity than one second.

   This limited granularity creates inefficiencies in various parts of
   the AFS-3 protocol when it must be determined in what order two
   events have occurred (for example, whether or not a file was changed
   since the last time a volume has been backed up).  When those two
   events have occurred during the same second, implementations must
   take a conservative assumption about which event occurred first,
   often resulting in unnecessary duplication or retransmission of data.
   In addition, metadata can be lost when files are copied to AFS from
   other filesystems that store file modification times with finer
   granularity than one second.

   This document defines a new type, AFSAbsTime, to be used in AFS-3
   RPCs in the future.  This type aims to solve these problems, as it
   supports a much wider range of dates at a much finer granularity.
   Another type, AFSRelTime, is defined to represent times relative to
   some other event, which provides for greater granularity over the
   existing representations via 32-bit integers.

   Both of these new types also provide standard type identifiers to be
   used when specifying relative or absolute time in AFS-3 RPC arguments
   and structures.  Currently, both of these are just specified as
   "afs_int32" types in the XDR language definitions, which can make it
   ambiguous whether or not a field is an absolute time, relative time,
   or something else completely.  Using the standard types AFSAbsTime
   and AFSRelTime will make this unambiguous.


2.  Data Types

   This document defines two new data types: AFSAbsTime and AFSRelTime.
   Both of these are encoded on the wire using the XDR standard
   described in [RFC4506], and are described using the XDR language
   specification therein.

2.1.  AFSAbsTime

   The new AFSAbsTime type is represented as an XDR-encoded structure
   containing a 64-bit unsigned integer as the timestamp, and an



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   unsigned 32-bit integer representing the resolution.  It is defined
   as thus in XDR:

       struct AFSAbsTime {
         unsigned hyper timestamp;
         unsigned int resolution;
       };

   The AFSAbsTime structure represents the amount of time that has
   passed since midnight or 0 hour January 1, 1601 Coordinated Universal
   Time (UTC).  The value of the timestamp field represents this amount
   of time in increments of 100 nanoseconds (ns).  This precision and
   starting date is equivalent to the Microsoft Windows FILETIME
   structure.

   The value of the resolution field represents the resolution of the
   time source from which the timestamp was obtained.  The presence of
   this field is important when calculating the order in which two
   events occurred relative to each other.  If a timestamp is obtained
   from a time source that only has 1-second granularity, the event may
   have occurred anywhere in that second, whereas if it was obtained
   from a source with 100-ns granularity, it is known that it occurred
   before an event that occurred 0.5 seconds later.

   The value of the resolution field is the smallest amount of time
   representable by that time source, in increments of 100 ns.  If the
   value of the timestamp field is X, and the value of the resolution is
   Y, the AFSAbsTime structure describes an event that occurs at or
   after time X, but before time X+Y.

   For example, to represent the time 60 seconds after midnight on
   January 1, 1601, the value of the timestamp field would be 600000000
   (600 million).  If the time source this was obtained from only has
   1-second granularity, the resolution field would have the value
   10000000 (10 million).  In effect, the AFSAbsTime structure then
   represents an event that happened at or after 60 seconds after
   midnight on January 1, 1601, but happened before 61 seconds after
   midnight on January 1, 1601.

   This structure can represent any time from January 1, 1601 up to the
   year 30282 with 100-ns granularity.

2.2.  AFSRelTime

   The new AFSRelTime type has nearly the same representation on the
   wire as AFSAbsTime in Section 2.1:





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       struct AFSRelTime {
         hyper timestamp;
         unsigned int resolution;
       };

   The AFSRelTime structure represents the amount of time that has
   passed since some other event.  The event to which this time is
   relative is unspecified, and can be anything; it must be specified by
   the RPC or structure that defines a field of the AFSRelTime type.

   The value of the timestamp field represents this amount of time in
   increments of 100 ns.  Values greater than 0 represent dates that
   occur after the relative event, and values less than 0 represent
   dates that occur before the relative event.

   The meaning and value of the resolution field is the same as that of
   the resolution field in AFSAbsTime specified in Section 2.1.

   For example, to represent the time 5 seconds before some other event,
   the value of the timestamp field would be -50000000 (negative 50
   million).  If the time source has 1-second granularity, the
   resolution field would have the value 10000000 (10 million).  In
   effect, the AFSRelTime structure then represents an event that
   happens at or after 5 seconds before some other event X, but before 4
   seconds before the event X.


3.  Security Considerations

   This memo raises no security issues.


4.  IANA Considerations

   This document makes no request of the IANA.


5.  Acknowledgements

   The author thanks Simon Wilkinson And Jeffrey Altman for some
   background text and for bringing up the question of varying time
   resolution, and Tom Keiser and David Boyes for input on the problem
   of time resolution.


6.  Informative References

   [RFC4506]  Eisler, M., "XDR: External Data Representation Standard",



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              STD 67, RFC 4506, May 2006.


Author's Address

   Andrew Deason
   Sine Nomine Associates
   43596 Blacksmith Square
   Ashburn, Virginia  20147-4606
   USA

   Phone: +1 703 723 6673
   Email: adeason@sinenomine.net






































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