This commit enhances the stub resolver to reload the configuration
in the per-thread _res object if the /etc/resolv.conf file has
changed. The resolver checks whether the application has modified
_res and will not overwrite the _res object in that case.
The struct resolv_context mechanism is used to check the
configuration file only once per name lookup.
This commit adds the remaining unchanging members (which are loaded
from /etc/resolv.conf) to struct resolv_conf.
The extended name server list is currently not used by the stub
resolver. The switch depends on a cleanup: The _u._ext.nssocks
array stores just a single socket, and needs to be replaced with
a single socket value.
(The compatibility gethostname implementation does not use the
extended addres sort list, either. Updating the compat code is
not worthwhile.)
This change uses the extended resolver state in struct resolv_conf to
store the search list. If applications have not patched the _res
object directly, this extended search list will be used by the stub
resolver during name resolution.
This change provides additional resolver configuration state which
is not exposed through the _res ABI. It reuses the existing
initstamp field in the supposedly-private part of _res. Some effort
is undertaken to avoid memory safety issues introduced by applications
which directly patch the _res object.
With this commit, only the initstamp field is moved into struct
resolv_conf. Additional members will be added later, eventually
migrating the entire resolver configuration.
