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.Dd October 1, 2009
.Dt ISNS 3
.Os
.Sh NAME
.Nm isns
.Nd iSNS protocol support library
.Sh LIBRARY
.Lb libisns
.Sh SYNOPSIS
.In isns.h
.Ft int
.Fn isns_init "ISNS_HANDLE *h" "int is_server"
.Ft void
.Fn isns_stop "ISNS_HANDLE h"
.Ft int
.Fn isns_add_servercon "ISNS_HANDLE h" "int fd" "struct addrinfo *ai"
.Ft int
.Fn isns_init_reg_refresh "ISNS_HANDLE h" "const char *node" "int interval"
.Ft ISNS_TRANS
.Fn isns_new_trans "ISNS_HANDLE h" "uint16_t func_id" "uint16_t pdu_flags"
.Ft int
.Fn isns_add_tlv "ISNS_TRANS t" "uint32_t tag" "int data_len" "const void *data_p"
.Ft int
.Fn isns_add_string "ISNS_TRANS t" "uint32_t tag" "const char *s"
.Ft int
.Fn isns_send_trans "ISNS_TRANS t" "const struct timespec *timeout_p" "uint32_t *status_p"
.Ft int
.Fn isns_get_tlv "ISNS_TRANS t" "int which_tlv" "uint32_t *tag_p" "int data_len_p" "void **data_pp"
.Ft void
.Fn isns_free_trans "ISNS_TRANS t"
.Sh DESCRIPTION
The
.Nm
library exports an API that simplifies Internet Storage Name
Service (iSNS) client implementations.
The API defines a transactional model in support of:
.Pp
.Bl -bullet -width 3n -offset indent -compact
.It
generating iSNS messages composed of iSNS attributes expressed in
Tag-Length-Value (TLV) data format
.It
submitting iSNS Protocol (iSNSP) messages
.It
optionally waiting for iSNSP responses
.El
.Pp
.Nm
does not currently support receipt of iSNS Heartbeat messages, State Change
Notification (SCN) messages, or Entity Status Inquiry (ESI) messages.
.Sh INITIALIZATION
An iSNS client that uses
.Nm
must call
.Fn isns_init
to initialize the iSNS environment.
This call will create a thread to handle client-server communication, and
as such should only be called when thread creation is appropriate (such
as after a daemonized program forks).
.Pp
The value passed as
.Ar is_server
is used to set iSNSP message format Flags
"Sender is the iSNS client" (bit position 16) and "Sender is the iSNS server"
(bit position 17).
For now the value 0 (zero) should be passed for
.Ar is_server .
The value returned in
.Ar h
should be considered opaque by the caller.
This value is passed unchanged to
.Fn isns_add_servercon ,
.Fn isns_init_reg_refresh ,
.Fn isns_stop ,
and
.Fn isns_new_trans .
.Pp
.Fn isns_stop
should be called when the iSNS environment is no longer needed.
This call will kill any threads created by
.Fn isns_init .
.Sh CONFIGURATION
Following initialization,
.Fn isns_add_servercon
should be used to make the iSNS environment aware of the iSNS
server to which iSNSP queries and requests are to be sent.
This routine should not be called by a program acting as an iSNS server.
.Pp
A connected TCP socket descriptor is passed as parameter
.Ar fd .
Parameter
.Ar ai
is the address of the remote TCP endpoint.
It is included so that reconnection may be attempted by
.Nm
in the event that the TCP connection is broken.
.Pp
Certain iSNS servers will limit registration lifetimes, and will
refresh registrations after any request from a given iSNS entity.
The
.Fn isns_init_reg_refresh
function offers a way for
.Nm
to refresh registrations on behalf of the iSNS client.
.Pp
Parameter
.Ar node
is the
.Dq iSCSI Name
attribute used for the periodic queries.
It should be the name of an iSCSI node within the registered iSNS entity.
The desired refresh interval, in seconds, is passed in parameter
.Ar interval .
.Sh TRANSACTIONS
.Fn isns_new_trans
creates new iSNS transactions.
.Pp
Parameter
.Ar func_id
is used as the iSNSP message id.
Parameter
.Ar pdu_flags
is used to set iSNSP message format Flags and is
exposed to allow callers to set flag "Replace flag" (bit position 19).
This provides callers with a way
to specify whether a Device Attribute Registration Request is intended to
update or replace an existing registration.
This is currently the only use defined for parameter
.Ar pdu_flags .
.Pp
Once a new transaction has been created, callers can specify iSNS attributes
used for registration and query requests.
TLV data may be added using either
.Fn isns_add_tlv
or
.Fn isns_add_string .
.Pp
Parameter
.Ar tag
is the iSNS Tag corresponding to the attribute being added.
Parameter
.Ar data_len
is the length of the attribute value.
Parameter
.Ar data_p
references the attribute value.
The caller does not need to handle iSNS attribute 4-byte alignment requirements.
This is handled by the iSNS environment on behalf of the caller.
.Fn isns_add_string
may be used if the attribute value is a NUL terminated C string.
.Pp
Once a transaction has been populated with any required TLV data,
.Fn isns_send_trans
can be used to submit an iSNSP registration or query message.
.Pp
Callers that submit iSNSP query messages may need to wait for returned data.
.Fn isns_send_trans
supports bounded waits.
Successful waits, those that do not time out, return the iSNSP response
status code received in the iSNSP response message.
If a wait does time out, the value of
.Ar status_p
is undefined.
Callers that do not need to wait for returned data can simply
pass
.Dv NULL
for parameter
.Ar timeout_p .
Callers should set parameter
.Ar status_p
to
.Dv NULL
if not waiting.
.Pp
.Fn isns_get_tlv
is used to retrieve TLV data returned in a transaction.
The first call to
.Fn isns_get_tlv
should pass the value
.Dv ISNS_TLV_FIRST
for parameter
.Ar which_tlv .
Each subsequent TLV can be retrieved by passing in
.Dv ISNS_TLV_NEXT
in place of
.Dv ISNS_TLV_FIRST .
.Pp
When a caller is done with a transaction, having submitted either a
registration or a query message and retrieved any returned TLV data,
.Fn isns_free_trans
should be used to release resources used by the transaction.
.Sh RETURN VALUES
.Fn isns_init ,
.Fn isns_add_servercon ,
.Fn isns_init_reg_refresh ,
.Fn isns_add_tlv ,
.Fn isns_add_string ,
and
.Fn isns_send_trans
return 0 on success, or \-1 on failure.
.Fn isns_new_trans
returns 0 on success, or
.Dv ISNS_INVALID_TRANS
on failure.
.Fn isns_get_tlv
returns 0 on success, or
.Er ENOENT
if there are no TLVs to retrieve.
.Sh HISTORY
.Nm
first appeared in
.Nx 6.0 .
The
.Nm
implementation was contributed to the
.Nx
Foundation by Wasabi Systems, Inc.