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resolv: Automatically reload a changed /etc/resolv.conf file [BZ #984]

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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 is contained in:
Florian Weimer
2017-07-03 21:06:23 +02:00
parent a1c4eb8794
commit aef16cc8a4
11 changed files with 273 additions and 95 deletions
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80
resolv/res_init.c
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@ -106,8 +106,6 @@
static uint32_t net_mask (struct in_addr);
unsigned long long int __res_initstamp;
int
res_ninit (res_state statp)
{
@ -164,6 +162,16 @@ struct resolv_conf_parser
struct resolv_conf template;
};
/* Return true if *PREINIT contains actual preinitialization. */
static bool
has_preinit_values (const struct __res_state *preinit)
{
return (preinit->retrans != 0 && preinit->retrans != RES_TIMEOUT)
|| (preinit->retry != 0 && preinit->retry != RES_DFLRETRY)
|| (preinit->options != 0
&& (preinit->options & ~RES_INIT) != RES_DEFAULT);
}
static void
resolv_conf_parser_init (struct resolv_conf_parser *parser,
const struct __res_state *preinit)
@ -531,14 +539,8 @@ res_vinit_1 (FILE *fp, struct resolv_conf_parser *parser)
return true;
}
/* Set up default settings. If the /etc/resolv.conf configuration
file exist, the values there will have precedence. Otherwise, the
server address is set to INADDR_LOOPBACK and the default domain
name comes from gethostname. The RES_OPTIONS and LOCALDOMAIN
environment variables can be used to override some settings.
Return 0 if completes successfully, -1 on error. */
int
__res_vinit (res_state statp, int preinit)
struct resolv_conf *
__resolv_conf_load (struct __res_state *preinit)
{
/* Ensure that /etc/hosts.conf has been loaded (once). */
_res_hconf_init ();
@ -559,20 +561,14 @@ __res_vinit (res_state statp, int preinit)
default:
/* Other errors refer to resource allocation problems and
need to be handled by the application. */
return -1;
return NULL;
}
struct resolv_conf_parser parser;
if (preinit)
{
resolv_conf_parser_init (&parser, statp);
statp->id = res_randomid ();
}
else
resolv_conf_parser_init (&parser, NULL);
resolv_conf_parser_init (&parser, preinit);
bool ok = res_vinit_1 (fp, &parser);
if (ok)
struct resolv_conf *conf = NULL;
if (res_vinit_1 (fp, &parser))
{
parser.template.nameserver_list
= nameserver_list_begin (&parser.nameserver_list);
@ -583,21 +579,42 @@ __res_vinit (res_state statp, int preinit)
= search_list_size (&parser.search_list);
parser.template.sort_list = sort_list_begin (&parser.sort_list);
parser.template.sort_list_size = sort_list_size (&parser.sort_list);
struct resolv_conf *conf = __resolv_conf_allocate (&parser.template);
if (conf == NULL)
ok = false;
else
{
ok = __resolv_conf_attach (statp, conf);
__resolv_conf_put (conf);
}
conf = __resolv_conf_allocate (&parser.template);
}
resolv_conf_parser_free (&parser);
if (!ok)
return -1;
return conf;
}
/* Set up default settings. If the /etc/resolv.conf configuration
file exist, the values there will have precedence. Otherwise, the
server address is set to INADDR_LOOPBACK and the default domain
name comes from gethostname. The RES_OPTIONS and LOCALDOMAIN
environment variables can be used to override some settings.
Return 0 if completes successfully, -1 on error. */
int
__res_vinit (res_state statp, int preinit)
{
struct resolv_conf *conf;
if (preinit && has_preinit_values (statp))
/* For the preinit case, we cannot use the cached configuration
because some settings could be different. */
conf = __resolv_conf_load (statp);
else
return 0;
conf = __resolv_conf_get_current ();
if (conf == NULL)
return -1;
bool ok = __resolv_conf_attach (statp, conf);
__resolv_conf_put (conf);
if (ok)
{
if (preinit)
statp->id = res_randomid ();
return 0;
}
else
return -1;
}
static void
@ -652,6 +669,7 @@ res_setoptions (struct resolv_conf_parser *parser, const char *options)
{ STRnLEN ("single-request"), 0, RES_SNGLKUP },
{ STRnLEN ("no_tld_query"), 0, RES_NOTLDQUERY },
{ STRnLEN ("no-tld-query"), 0, RES_NOTLDQUERY },
{ STRnLEN ("no-reload"), 0, RES_NORELOAD },
{ STRnLEN ("use-vc"), 0, RES_USEVC }
};
#define noptions (sizeof (options) / sizeof (options[0]))