Standards
| Standards / Extensions |
C or C++ |
Dependencies |
|---|
BSD 4.3
|
both |
OS/390 V2R8 |
Format
#define _XOPEN_SOURCE_EXTENDED 1
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
int res_init(void);
struct __res_state _res;
General description
The res_init() function
is the Resolver function that initializes the __res_state structure
for use by other Resolver functions. Initialization normally occurs
on the first call to any of the IP address resolution routines commonly
called the XL C/C++ Runtime
Library Resolver.
The res_init() routine does its initialization
by passing the __res_state structure to the CS for
z/OS® Resolver.
The Resolver reads the "TCPIP.DATA" configuration file and updates
the __res_state structure. The data in the __res_state structure
is filled in based on the contents of the "TCPIP.DATA" configuration
file and can then be referenced in the
_res variable.
Global configuration and state information that is used by the Resolver
routines is kept in the structure
_res.
Most of the values have reasonable defaults and can be left unchanged.
- Value
- Description
- _res.retrans
- Retransmission time interval is taken from the ResolverTimeOut
statement found in the "TCPIP.DATA" configuration file.
- _res.retry
- The number of times to retransmit a request. It is taken from
the ResolverUDPRetries statement found in the "TCPIP.DATA" configuration
file.
- _res.options
- Options stored in _res.options are defined in <resolv.h>
and are listed below. Options are stored as a simple bit mask containing
the bitwise OR of the options enabled.
- Option
- Description
- RES_INIT
- True after the initial name server address and default domain
name are initialized, because res_init() has been called. This option
should only be tested but not set, except by the res_init() function.
- RES_DEBUG
- Print debugging messages.
- RES_AAONLY
- Accept authoritative answers only. With this option, res_send()
should continue until it finds an authoritative answer or finds an
error. Currently this is not implemented.
- RES_USEVC
- Use TCP connections for queries instead of UDP datagrams.
- RES_STAYOPEN
- Used with RES_USEVC to keep the TCP connection open between queries.
This is useful only in programs that regularly do many queries.
UDP should be the normal mode used.
- RES_IGNTC
- Ignore truncation errors, that is, don't retry with TCP. Currently
unused.
- RES_RECURSE
- Set the recursion-desired bit in queries. This is the default.
(res_send() does not do iterative queries and expects the name server
to handle recursion.)
- RES_DEFNAMES
- If set, res_search() will append the default domain name to single-component
names (those that do not contain a dot). This option is enabled by
default.
- RES_DNSRCH
- If this option is set, res_search() will search for host names
in the current domain and in parent domains. This is used by the standard
host lookup routine gethostbyname(). This option is enabled by default.
- RES_NOALIASES
- This option turns off the user level aliasing feature controlled
by the "HOSTALIASES" environment variable. Network daemons should
set this option.
- _res.nscount
- The number of name servers specified in the "TCPIP.DATA" configuration
file.
- _res.*nsaddr_list[0]
- The addresses of name servers specified by the NSINTERADDR or
NameServer statements found in the "TCPIP.DATA" configuration file.
- _res.dnsrch[0]
- The beginning of the list of domains to be searched, as specified
in the SEARCH statement found in the "TCPIP.DATA" configuration file.
The structure will have either a Default DOMAIN or SEARCH.
- _res.defdname[0]
- The Default Domain name, as specified in the Domain or DomainOrigin
statement found in the "TCPIP.DATA" configuration file. The structure
will have either a Default DOMAIN or SEARCH.
- _res.pfcode
- Currently this is not implemented.
- _res.ndots
- The threshold for the number of dots in the domain name, as specified
by the OPTIONS statement value ndots:n found in the "TCPIP.DATA"
configuration file. The default is 1.
- _res.nsort
- The number of elements in sort_list[] as listed in the SORTLIST
statement found in the "TCPIP.DATA" configuration file.
- _res.sort_list[0]
- The network address and subnet mask in the SORTLIST statement
found in the "TCPIP.DATA" configuration file.
Returned value
If successful, res_init()
returns 0.
If unsuccessful, res_init() returns -1 and sets
h_errno to one of the following values:
- Error Code
- Description
- NO_RECOVERY
- An error occurred that will continue to fail if tried again. Storage
could not be obtained for this thread to contain the _res structure.
- TRY_AGAIN
- An error occurred while initializing the __res_state structure
name selected, which can be retried.
If successful, _res returns
the address of __res_state structure.
If unsuccessful,
_res returns
NULL and sets errno to one of the following values:
- Error Code
- Description
- ENOMEM
- The storage needed to define the _res structure
could not be obtained.