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ISNS(3) Library Functions Manual ISNS(3)


isnsiSNS protocol support library


Internet Storage Name Service Library (libisns, -lisns)


#include <isns.h>

isns_init(ISNS_HANDLE *h, int is_server);

isns_stop(ISNS_HANDLE h);

isns_add_servercon(ISNS_HANDLE h, int fd, struct addrinfo *ai);

isns_init_reg_refresh(ISNS_HANDLE h, const char *node, int interval);

isns_new_trans(ISNS_HANDLE h, uint16_t func_id, uint16_t pdu_flags);

isns_add_tlv(ISNS_TRANS t, uint32_t tag, int data_len, const void *data_p);

isns_add_string(ISNS_TRANS t, uint32_t tag, const char *s);

isns_send_trans(ISNS_TRANS t, const struct timespec *timeout_p, uint32_t *status_p);

isns_get_tlv(ISNS_TRANS t, int which_tlv, uint32_t *tag_p, int data_len_p, void **data_pp);

isns_free_trans(ISNS_TRANS t);


The isns library exports an API that simplifies Internet Storage Name Service (iSNS) client implementations. The API defines a transactional model in support of:

  • generating iSNS messages composed of iSNS attributes expressed in Tag-Length-Value (TLV) data format
  • submitting iSNS Protocol (iSNSP) messages
  • optionally waiting for iSNSP responses

isns does not currently support receipt of iSNS Heartbeat messages, State Change Notification (SCN) messages, or Entity Status Inquiry (ESI) messages.


An iSNS client that uses isns must call 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).

The value passed as 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 is_server. The value returned in h should be considered opaque by the caller. This value is passed unchanged to isns_add_servercon(), isns_init_reg_refresh(), isns_stop(), and isns_new_trans().

isns_stop() should be called when the iSNS environment is no longer needed. This call will kill any threads created by isns_init().


Following initialization, 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.

A connected TCP socket descriptor is passed as parameter fd. Parameter ai is the address of the remote TCP endpoint. It is included so that reconnection may be attempted by isns in the event that the TCP connection is broken.

Certain iSNS servers will limit registration lifetimes, and will refresh registrations after any request from a given iSNS entity. The isns_init_reg_refresh() function offers a way for isns to refresh registrations on behalf of the iSNS client.

Parameter node is the “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 interval.


isns_new_trans() creates new iSNS transactions.

Parameter func_id is used as the iSNSP message id. Parameter 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 pdu_flags.

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 isns_add_tlv() or isns_add_string().

Parameter tag is the iSNS Tag corresponding to the attribute being added. Parameter data_len is the length of the attribute value. Parameter 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. isns_add_string() may be used if the attribute value is a NUL terminated C string.

Once a transaction has been populated with any required TLV data, isns_send_trans() can be used to submit an iSNSP registration or query message.

Callers that submit iSNSP query messages may need to wait for returned data. 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 status_p is undefined. Callers that do not need to wait for returned data can simply pass NULL for parameter timeout_p. Callers should set parameter status_p to NULL if not waiting.

isns_get_tlv() is used to retrieve TLV data returned in a transaction. The first call to isns_get_tlv() should pass the value ISNS_TLV_FIRST for parameter which_tlv. Each subsequent TLV can be retrieved by passing in ISNS_TLV_NEXT in place of ISNS_TLV_FIRST.

When a caller is done with a transaction, having submitted either a registration or a query message and retrieved any returned TLV data, isns_free_trans() should be used to release resources used by the transaction.


isns_init(), isns_add_servercon(), isns_init_reg_refresh(), isns_add_tlv(), isns_add_string(), and isns_send_trans() return 0 on success, or -1 on failure. isns_new_trans() returns 0 on success, or ISNS_INVALID_TRANS on failure. isns_get_tlv() returns 0 on success, or ENOENT if there are no TLVs to retrieve.


isns first appeared in NetBSD 6.0. The isns implementation was contributed to the NetBSD Foundation by Wasabi Systems, Inc.
October 1, 2009 NetBSD 7.0