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eCos and

eCos and

RedBoot

RedBoot

can both use the DNS package to perform network name lookups.

can both use the DNS package to perform network name lookups.

The DNS client uses the normal BSD API for performing lookups:

The DNS client uses the normal BSD API for performing lookups:

gethostbyname() and

gethostbyname() and

gethostbyaddr().

gethostbyaddr().

There are a few restrictions:

There are a few restrictions:

Only IPv4 is supported, ie IPv6 addresses cannot be looked

Only IPv4 is supported, ie IPv6 addresses cannot be looked

up.

up.

If the DNS server returns multiple authoritive records

If the DNS server returns multiple authoritive records

for a host name, the hostent will only contain a record for the

for a host name, the hostent will only contain a record for the

first entry.

first entry.

The code has been made thread safe. ie multiple threads

The code has been made thread safe. ie multiple threads

may call

may call

gethostbyname()

gethostbyname()

 without causing problems to the hostent structure returned. What

 without causing problems to the hostent structure returned. What

is not safe is one thread using both

is not safe is one thread using both

gethostbyname()

gethostbyname()

 and

 and

gethostbyaddr().

gethostbyaddr().

A call to one will destroy the results from the previous call

A call to one will destroy the results from the previous call

to the other function.

to the other function.

To initialise the DNS client the following function must be

To initialise the DNS client the following function must be

called:

called:

#include <network.h>

#include <network.h>

int cyg_dns_res_init(struct in_addr *dns_server)

int cyg_dns_res_init(struct in_addr *dns_server)

where dns_server is the address of the DNS server

where dns_server is the address of the DNS server

the client should query. On Error this function returns -1, otherwise

the client should query. On Error this function returns -1, otherwise

0 for success. If lookups are attemped before this function has

0 for success. If lookups are attemped before this function has

been called, they will fail and return NULL.

been called, they will fail and return NULL.

A default, hard coded, server may be specified in the CDL option

A default, hard coded, server may be specified in the CDL option

CYGDAT_NS_DNS_DEFAULT_SERVER. The use of this is

CYGDAT_NS_DNS_DEFAULT_SERVER. The use of this is

controlled by CYGPKG_NS_DNS_DEFAULT. If this is

controlled by CYGPKG_NS_DNS_DEFAULT. If this is

enabled, init_all_network_interfaces will

enabled, init_all_network_interfaces will

initialize the resolver with the hard coded address. The DHCP client

initialize the resolver with the hard coded address. The DHCP client

or user code my override this address by calling

or user code my override this address by calling

cyg_dns_res_init again. 

cyg_dns_res_init again. 

The DNS client understands the concepts of the target being

The DNS client understands the concepts of the target being

in a domain. By default no domain will be used. Host name lookups

in a domain. By default no domain will be used. Host name lookups

should be for fully qualified names. The domain name can be set

should be for fully qualified names. The domain name can be set

and retrieved using the functions:

and retrieved using the functions:

    int getdomainname

    int getdomainname

    char *name

    char *name

    size_t len

    size_t len

    int setdomainname

    int setdomainname

    const char *name

    const char *name

    size_t len

    size_t len

Alternatively, a hard coded domain name can be set using CDL.

Alternatively, a hard coded domain name can be set using CDL.

The boolean CYGPKG_NS_DNS_DOMAINNAME enables this

The boolean CYGPKG_NS_DNS_DOMAINNAME enables this

and the domain name is taken from

and the domain name is taken from

CYGPKG_NS_DNS_DOMAINNAME_NAME.

CYGPKG_NS_DNS_DOMAINNAME_NAME.

Once set, the DNS client will first perform a lookup with the domain

Once set, the DNS client will first perform a lookup with the domain

name appended. If this fails it will then perform a second lookup

name appended. If this fails it will then perform a second lookup

without the appended domain name. 

without the appended domain name.