N/A T. Keiser
Internet-Draft Sine Nomine
Intended status: Informational S. Jenkins
Expires: March 14, 2013
A. Deason, Ed.
Sine Nomine
September 10, 2012
AFS-3 Protocol Capabilities Query Mechanism
draft-keiser-afs3-capabilities-00
Abstract
AFS-3 is a distributed file system based upon prototypes developed at
Carnegie Mellon University during the 1980s. AFS-3 heavily leverages
Remote Procedure Calls (RPCs) as the foundation for its distributed
architecture. In 2003, new RPCs were introduced into AFS-3 that
provide for capability querying between file servers and cache
managers. This memo provides a formal specification for that
functionality, and provides analogous extensions to the volume server
RPC interface.
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.
AFS-3 Document State
This document is in state "draft", as per the document state
definitions set forth in [I-D.wilkinson-afs3-standardisation].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified,
and derivative works of it may not be created, and it may not be
published except as an Internet-Draft.
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
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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 March 14, 2013.
Copyright Notice
Copyright (c) 2012 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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Motivations . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Capability Query Mechanism . . . . . . . . . . . . . . . . . . 6
3.1. Capability Bit Vector (array index 0) . . . . . . . . . . 6
3.2. Interpretation by caller . . . . . . . . . . . . . . . . . 7
4. afsint Capability Query Interface . . . . . . . . . . . . . . 7
4.1. Cache Coherence . . . . . . . . . . . . . . . . . . . . . 8
5. afscbint Capability Query Interface . . . . . . . . . . . . . 8
5.1. Cache Coherence . . . . . . . . . . . . . . . . . . . . . 9
6. volint Capability Query Interface . . . . . . . . . . . . . . 9
6.1. Cache Coherence . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. AFS Assigned Numbers Registrar Considerations . . . . . . . . 10
9.1. AFSVol Capabilities Registry . . . . . . . . . . . . . . . 10
10. Security Considerations . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Sample RPC-L for afsint Capabilities Mechanism . . . 13
Appendix B. Sample RPC-L for afscbint Capabilities Mechanism . . 14
Appendix C. Sample RPC-L for volint Capabilities Mechanism . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
AFS-3 [CMU-ITC-88-062] [CMU-ITC-87-068] is a distributed file system
that has its origins in the VICE project [CMU-ITC-84-020]
[CMU-ITC-85-039] at the Carnegie Mellon University Information
Technology Center [CMU-ITC-83-025], a joint venture between CMU and
IBM. VICE later became AFS when CMU moved development to a new
commercial venture called Transarc Corporation, which later became
IBM Pittsburgh Labs. AFS-3 is a suite of un-standardized network
protocols based on a remote procedure call (RPC) suite known as Rx.
While de jure standards for AFS-3 fail to exist, the various AFS-3
implementations have agreed upon certain de facto standards, largely
helped by the existence of an open source fork called OpenAFS that
has served the role of reference implementation. In addition to
using OpenAFS as a reference, IBM wrote and donated developer
documentation that contains somewhat outdated specifications for the
Rx protocol and all AFS-3 remote procedure calls, as well as a
detailed description of the AFS-3 system architecture.
Unlike most network file systems (e.g., NFS), where protocol updates
are traditionally handled in large batches, AFS-3 aims for
incremental, evolutionary change to its wire protocol. Because of
this lack of RPC interface major versions, it is the responsibility
of calling peers to ascertain what capabilities (i.e., available RPC
interfaces, call semantics, etc.) are supported by the peer.
Naturally, this is a best-effort mechanism since the capabilities are
assumed to be malleable by, e.g., transparent code upgrades at the
remote peer.
To this end, the afsint [AFS3-FSCM] and afscbint Rx RPC service
endpoints--RXAFS (UDP port 7000, Rx service id 1), and RXAFSCB (UDP
port 7001, Rx service id 1), respectively--were (circa 2003) each
extended with a capabilities query RPC. These RPCs return (among
other things) an OUT parameter containing an XDR [RFC4506] variable-
length array of reserved fields, which future extensions could
utilize to advertise support of new protocol extensions.
1.1. Purpose
This memo serves several purposes:
1. it serves as a historical record of the interfaces and semantics
(of the file server and cache manager capabilities query
interfaces), as they were designed and implemented circa 2003,
and informally specified in 2006;
2. it specifies the general data encoding and semantics for all
present AFS-3 capabilities interfaces (thus, hopefully, serving
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as a normative reference for future capability drafts); and
3. specifies a new capabilities interface for the volint Rx RPC
service endpoint--AFSVol (UDP port 7005, Rx service id 4)--in
order to permit future extensions to the AFS-3 volume server.
1.2. Motivations
The legacy method for extending AFS-3 protocols has been to define
new RPCs with prototypes that augment existing RPC interfaces with
additional arguments, or that supplant legacy data structures with
new data structure definitions (and associated new RPCs that
references those definitions). While this solves the XDR decoding
backwards compatibility problem, it does so at the expense of
requiring an O(n) search to find out which RPC version is implemented
on a given endpoint: by iterating backwards from the newest to the
oldest implementation of a given interface--until an invocation does
not return the RXGEN_OPCODE error. Consequently, the "get
capabilities" mechanisms specified in this document reduce the worst-
case capability probing from N round trips to 2--at the potential
expense of 1 additional round-trip, occasionally, to prevent
capabilities cache staleness.
1.3. Abbreviations
AFS - Historically, AFS stood for the Andrew File System; AFS
no longer stands for anything
afscbint - AFS-3 Cache Manager RPC Interface Definition
afsint - AFS-3 File Server RPC Interface Definition
AFSVol - AFS Volume Server Rx RPC Implementation
CM - AFS-3 Cache Manager
FS - AFS-3 File Server
RPC - Remote Procedure Call
RPC-L - Rx RPC Interface Definition Language (fork of ONC RPC
[RFC5531] .x file format)
Rx - The Remote Procedure Call mechanism utilized by AFS-3
[AFS3-RX]
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RXAFS - AFS File Server Rx RPC Implementation
RXAFSCB - AFS Cache Manager Rx RPC Implementation
TTL - Time to Live for cached data
volint - AFS-3 Volume Server RPC Interface Definition
volser - AFS-3 Volume Server
XDR - eXternal Data Representation [RFC4506]
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Capability Query Mechanism
Many AFS-3 services permit evolution by querying the capabilities of
the service that they are contacting. This is accomplished via a
special RPC code point that is defined for many AFS-3 RPC services.
This RPC returns an opaque bit string to the caller. In terms of
RPC-L, this bit string is defined as a variable-length sequence of
32-bit unsigned integers [I-D.keiser-afs3-xdr-primitive-types]:
const AFSCAPABILITIESMAX = 196;
typedef afs_uint32 Capabilities<AFSCAPABILITIESMAX>;
This XDR encoding permits the size of a capabilities payload to grow
quite large, while simultaneously keeping the payload small--until
more elements in the variable-length array are allocated. Moreover,
it allows the semantics of the XDR variable-length array to be
defined gradually. The cost for this flexibility is that the 32-bit
value of all zeroes MUST be treated the same as if the array index
had not been returned at all.
3.1. Capability Bit Vector (array index 0)
The file server and cache manager both define the first array
slot--of their capabilities arrays--to be a bit vector, where each
bit position SHALL be advertised as zero, until such time as a bit
position is:
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1. allocated by the AFS Assigned Numbers Registrar;
2. its semantics are agreed upon by the AFS-3 standardization group
(if applicable); and
3. the attendant functionality is implemented by the callee of the
capability query RPC.
3.2. Interpretation by caller
Interpreting the capabilities bit string returned by a server is
complicated by the fact that the client and/or the server may
implement differing subsets of the AFS-3 protocol. For this reason,
differing subsets of the standardized capability bit vector array
indices may be supported by the caller and callee.
For example: the client may know how to decode the contents of
capability array indices 0, 1, and 3; the server may implement the
encodings of indices 0, 1, and 4. In this example, the server would
return a 20-octet array where indices 2 and 3 are all zero bits. As
noted earlier, the client SHALL interpret the 32-bit value of zero
for indices 2 and 3 to mean that the server does not support the
standardized encodings for these indices, let alone the standards
whose capability metadata is encoded therein. Of course, the client
would ignore the contents of array indices 2 and 4, as it has no
means of decoding those capabilities. Therefore, the client will
decode and interpret the intersection of known capabilities: array
indices 0, and 1.
4. afsint Capability Query Interface
In 2003, the AFS-3 community agreed to define file server and cache
manager capability RPC code points. The RPC-L definition of the file
server's (afsint) code point is as follows:
proc GetCapabilities(
OUT Capabilities *caps
) multi = 65540;
The first array element in this variable-length array was defined as
a 32-bit bit vector of capability flags (See Section 3.1). Four flag
bits were subsequently allocated:
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VICED_CAPABILITY_ERRORTRANS = 1
Advertise support for the UAE error code translation table
mechanism. When this flag is asserted, the server may translate
system errno codes into the UAE namespace to preserve accuracy.
VICED_CAPABILITY_64BITFILES = 2
Advertise support for 64-bit variants of the FetchData and
StoreData RPCs (i.e., RXAFS_FetchData64, and RXAFS_StoreData64).
VICED_CAPABILITY_WRITELOCKACL = 4
Advertise that RXAFS_SetLock and RXAFS_ExtendLock will permit
ViceLockType of LockWrite (1) when the caller only possesses
credentials conferring the PRSFS_INSERT privilege
[afs3-stds-jaltman-2006-08-01].
VICED_CAPABILITY_SANEACLS = 8
Hint to the client that volumes on this file server are, to the
best knowledge of the system administrator, sane with respect to
the lock ("k") permission bit [afs3-stds-jhutz-2006-07-19].
4.1. Cache Coherence
Clients SHOULD issue an RXAFS_GetCapabilities call frequently in
order to limit the capability incoherence time window. It is
RECOMMENDED that clients issue RXAFS_GetCapabilities where they would
have formerly issued RXAFS_GetTime (usually during periodic server
probing, and NAT table entry refreshing).
5. afscbint Capability Query Interface
In 2003, the AFS-3 community agreed to define file server and cache
manager capability RPC code points. The afscbint RPC-L definition is
as follows:
proc TellMeAboutYourself(
OUT struct interfaceAddr *addrs,
OUT Capabilities *caps
) = 65538;
The semantics of the addrs parameter are as defined for
RXAFSCB_WhoAreYou (a multi-home aware evolution beyond RXAFSCB_Probe
[AFS3-FSCM], which was implemented by IBM during the 1990s). The
first array element in the variable-length caps array was defined as
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a 32-bit bit vector of capability flags. One flag was subsequently
allocated and standardized:
CLIENT_CAPABILITY_ERRORTRANS = 1
Advertise support for the UAE error code translation table
mechanism. When this flag is asserted, the server may translate
system errno codes into the UAE namespace to preserve accuracy.
5.1. Cache Coherence
Clients SHOULD issue an RXAFSCB_TellMeAboutYourself call frequently
in order to limit the capability incoherence time window.
6. volint Capability Query Interface
This memo introduces a capabilities namespace, and GetCapabilities
interface to the volint service. The GetCapabilities interface SHALL
be be functionally identical to the previously-defined
RXAFS_GetCapabilities interface (see Section 4). Its RPC-L
definition SHALL be:
proc GetCapabilities(
OUT Capabilities * capabilities
) = XXX;
Figure 1
The "Capabilities" type referenced here is the same one utilized by
the afsint interface. As with that interface, the first index in the
capabilities array MUST be interpreted as a 32-bit bit vector, where
all bits SHALL be set to zero--until such time as they meet the
requirements set forth in Section 3.1.
6.1. Cache Coherence
One important distinction between this capability querying interface
and the ones utilized by afsint is: afsint is a stateful circuit --
file servers can reset the cached state across themselves and clients
via the RXAFSCB_InitCallBackState, RXAFSCB_InitCallBackState2, and
RXAFSCB_InitCallBackState3 RPCs. Because volint is a stateless (with
the exception of rxkad and voltrans) client/server protocol, there is
no means of maintaining volint capabilities cache coherence. It is
RECOMMENDED that clients receiving RPC error codes, or extended union
legs that they cannot decode, perform a new AFSVolGetCapabilities
invocation to ensure that capabilities cache incoherence is detected.
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Clearly, the above technique is open to races; volint clients SHOULD
try to limit race probability by minimizing the time window between
GetCapabilities calls, and invocation of capabilities-dependent RPCs.
All volint clients MUST flush cached capabilities at most two hours
after retrieving them via AFSVolGetCapabilities.
7. Acknowledgements
The author would like to thank, in particular, Jeffrey Altman, and
Jeffrey Hutzelman for their contributions to the 2006 mailing list
discussions regarding the capabilities RPCs; and Derrick Brashear for
the capabilities RPC language he wrote in
[I-D.brashear-afs3-pts-extended-names], which the author found quite
useful while writing this specification.
8. IANA Considerations
This memo includes no request to IANA.
9. AFS Assigned Numbers Registrar Considerations
This memo makes one registry allocation request of the AFS Assigned
Numbers Registrar.
9.1. AFSVol Capabilities Registry
This memo requests the allocation of a new registry with the formal
name "AFSVol Capabilities". This registry will be used to track
allocations of AFSVol capability bits. The capability bit namespace
contains 6272 bits, subdivided into 196 32-bit buckets. Allocation
requests for this namespace MUST be in the form of an RFC.
Furthermore, final approval for allocations SHALL be made by a
Designated Expert [RFC5226] to be nominated by the AFS-3 Working
Group. Should the AFS-3 Working Group be unable to assign a
Designated Expert, the AFS Assigned Numbers Registrar will be free to
appoint one or more Designated Experts to aid the registrar in the
process of vetting requests for this namespace. All allocation
requests for this registry MUST include the following information:
o capability name, and
o RFC section reference to definition of how this capability bit
alters AFSVol protocol semantics.
In addition, an allocation request MAY include any of the following
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optional elements:
o capability description,
o desired capability bucket number and bit position,
o RFC section reference to discussion regarding backwards
compatibility, or
o RFC section reference to relevant security considerations.
10. Security Considerations
Given that these capability querying interfaces may be invoked over
unprotected (e.g., rxnull) connections, application developers should
be extremely careful when utilizing capability data to negotiate
security-related mechanisms. When such functionality is required,
the implementor should make every effort to access the required
capability bits over an Rx connection whose security class guarantees
the capability bits are at least integrity-protected.
11. References
11.1. Normative References
[I-D.keiser-afs3-xdr-primitive-types]
Keiser, T., "AFS-3 Rx RPC XDR Primitive Type Definitions",
draft-keiser-afs3-xdr-primitive-types-00 (work in
progress), June 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
11.2. Informative References
[AFS3-FSCM]
Zayas, E., "AFS-3 Programmer's Reference: File Server/
Cache Manager Interface", Transarc Corp. Tech. Rep. FS-00-
D162, August 1991.
[AFS3-RX] Zayas, E., "AFS-3 Programmer's Reference: Specification
for the Rx Remote Procedure Call Facility", Transarc Corp.
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Tech. Rep. FS-00-D164, August 1991.
[CMU-ITC-83-025]
Morris, J., Van Houweling, D., and K. Slack, "The
Information Technology Center", CMU ITC Tech. Rep. CMU-
ITC-83-025, 1983.
[CMU-ITC-84-020]
West, M., "VICE File System Services", CMU ITC Tech.
Rep. CMU-ITC-84-020, August 1984.
[CMU-ITC-85-039]
Satyanarayanan, M., Howard, J., Nichols, D., Sidebotham,
R., Spector, A., and M. West, "The ITC Distributed File
System: Principles and Design", Proc. 10th ACM Symp.
Operating Sys. Princ. Vol. 19, No. 5, December 1985.
[CMU-ITC-87-068]
Howard, J., Kazar, M., Menees, S., Nichols, D.,
Satyanarayanan, M., Sidebotham, R., and M. West, "Scale
and Performance in a Distributed File System", ACM Trans.
Comp. Sys. Vol. 6, No. 1, pp. 51-81, February 1988.
[CMU-ITC-88-062]
Howard, J., "An Overview of the Andrew File System"",
Proc. 1988 USENIX Winter Tech. Conf. pp. 23-26,
February 1988.
[I-D.brashear-afs3-pts-extended-names]
Brashear, D., "Authentication Name Mapping extension for
AFS-3 Protection Service",
draft-brashear-afs3-pts-extended-names-09 (work in
progress), March 2011.
[I-D.wilkinson-afs3-standardisation]
Wilkinson, S., "Options for AFS Standardisation",
draft-wilkinson-afs3-standardisation-00 (work in
progress), June 2010.
[RFC4506] Eisler, M., "XDR: External Data Representation Standard",
STD 67, RFC 4506, May 2006.
[RFC5531] Thurlow, R., "RPC: Remote Procedure Call Protocol
Specification Version 2", RFC 5531, May 2009.
[afs3-stds-jaltman-2006-08-01]
Altman, J., "Locking, ACLs, and Capabilities", AFS-3 Stds
List 000067, August 2006, <http://lists.openafs.org/
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pipermail/afs3-standardization/2006-August/000067.html>.
[afs3-stds-jhutz-2006-07-19]
Hutzelman, J., "Locking, ACLs, and Capabilities", AFS-3
Stds List 000063, July 2006, <http://lists.openafs.org/
pipermail/afs3-standardization/2006-July/000063.html>.
[openafs-delta-capabilities-20030304]
Brashear, D., "DELTA capabilities-20030304", OpenAFS
Git 2712c1202ab17436ced8b466575c8bebdd9f68b7, March 2003,
<http://git.openafs.org/
?p=openafs.git;a=commitdiff;h=2712c1202ab17436ced8b466575c
8bebdd9f68b7>.
Appendix A. Sample RPC-L for afsint Capabilities Mechanism
The following is excerpted from an OpenAFS change-set implementing
the RXAFS_GetCapabilities functionality
[openafs-delta-capabilities-20030304].
/*
* Copyright 2000, International Business Machines Corporation
* and others. All Rights Reserved.
*
* This software has been released under the terms of the IBM
* Public License. For details, see the LICENSE file in the
* top-level source directory or online at
* http://www.openafs.org/dl/license10.html
*/
const AFSCAPABILITIESMAX = 196;
typedef afs_uint32 Capabilities<AFSCAPABILITIESMAX>;
/* Viced Capability Flags */
const VICED_CAPABILITY_ERRORTRANS = 0x0001;
const VICED_CAPABILITY_64BITFILES = 0x0002;
const VICED_CAPABILITY_WRITELOCKACL = 0x0004;
const VICED_CAPABILITY_SANEACLS = 0x0008;
proc GetCapabilities(
OUT Capabilities *caps
) multi = 65540;
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Appendix B. Sample RPC-L for afscbint Capabilities Mechanism
The following is excerpted from an OpenAFS change-set implementing
the RXAFSCB_TellMeAboutYourself functionality
[openafs-delta-capabilities-20030304].
/*
* Copyright 2000, International Business Machines Corporation
* and others. All Rights Reserved.
*
* This software has been released under the terms of the IBM
* Public License. For details, see the LICENSE file in the
* top-level source directory or online at
* http://www.openafs.org/dl/license10.html
*/
const AFSCAPABILITIESMAX = 196;
typedef afs_uint32 Capabilities<AFSCAPABILITIESMAX>;
/* Cache Manager Capability Flags */
const CLIENT_CAPABILITY_ERRORTRANS = 0x0001;
const AFS_MAX_INTERFACE_ADDR = 32;
struct interfaceAddr {
int numberOfInterfaces;
afsUUID uuid;
afs_int32 addr_in[AFS_MAX_INTERFACE_ADDR];
afs_int32 subnetmask[AFS_MAX_INTERFACE_ADDR];
afs_int32 mtu[AFS_MAX_INTERFACE_ADDR];
};
proc TellMeAboutYourself(
OUT struct interfaceAddr *addrs,
OUT Capabilities *caps
) = 65538;
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Appendix C. Sample RPC-L for volint Capabilities Mechanism
/*
* Copyright 2000, International Business Machines Corporation
* and others. All Rights Reserved.
*
* This software has been released under the terms of the IBM
* Public License. For details, see the LICENSE file in the
* top-level source directory or online at
* http://www.openafs.org/dl/license10.html
*/
const AFSVOL_CAPABILITIES_MAX = 196;
typedef afs_uint32 AFSVolCapabilities<AFSVOL_CAPABILITIES_MAX>;
proc GetCapabilities(
OUT AFSVolCapabilities * caps
) = XXX;
Authors' Addresses
Thomas Keiser
Sine Nomine Associates
43596 Blacksmith Square
Ashburn, VA 20147
USA
Email: tkeiser@gmail.com
Steven Jenkins
Email: steven.jenkins@gmail.com
Andrew Deason (editor)
Sine Nomine Associates
43596 Blacksmith Square
Ashburn, Virginia 20147-4606
USA
Phone: +1 703 723 6673
Email: adeason@sinenomine.net
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