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Currently DNS resolution is done automatically as part of the creation of a QIOChannelSocket object instance. This works ok for network clients where you just end up a single network socket, but for servers, the results of DNS resolution may require creation of multiple sockets. Introducing a DNS resolver API allows DNS resolution to be separated from the socket object creation. This will make it practical to create multiple QIOChannelSocket instances for servers. Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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/* | ||
* QEMU DNS resolver | ||
* | ||
* Copyright (c) 2016-2017 Red Hat, Inc. | ||
* | ||
* This library is free software; you can redistribute it and/or | ||
* modify it under the terms of the GNU Lesser General Public | ||
* License as published by the Free Software Foundation; either | ||
* version 2 of the License, or (at your option) any later version. | ||
* | ||
* This library is distributed in the hope that it will be useful, | ||
* but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
* Lesser General Public License for more details. | ||
* | ||
* You should have received a copy of the GNU Lesser General Public | ||
* License along with this library; if not, see <http://www.gnu.org/licenses/>. | ||
* | ||
*/ | ||
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#ifndef QIO_DNS_RESOLVER_H | ||
#define QIO_DNS_RESOLVER_H | ||
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#include "qemu-common.h" | ||
#include "qom/object.h" | ||
#include "io/task.h" | ||
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#define TYPE_QIO_DNS_RESOLVER "qio-dns-resolver" | ||
#define QIO_DNS_RESOLVER(obj) \ | ||
OBJECT_CHECK(QIODNSResolver, (obj), TYPE_QIO_DNS_RESOLVER) | ||
#define QIO_DNS_RESOLVER_CLASS(klass) \ | ||
OBJECT_CLASS_CHECK(QIODNSResolverClass, klass, TYPE_QIO_DNS_RESOLVER) | ||
#define QIO_DNS_RESOLVER_GET_CLASS(obj) \ | ||
OBJECT_GET_CLASS(QIODNSResolverClass, obj, TYPE_QIO_DNS_RESOLVER) | ||
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typedef struct QIODNSResolver QIODNSResolver; | ||
typedef struct QIODNSResolverClass QIODNSResolverClass; | ||
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/** | ||
* QIODNSResolver: | ||
* | ||
* The QIODNSResolver class provides a framework for doing | ||
* DNS resolution on SocketAddress objects, independently | ||
* of socket creation. | ||
* | ||
* <example> | ||
* <title>Resolving addresses synchronously</title> | ||
* <programlisting> | ||
* int mylisten(SocketAddress *addr, Error **errp) { | ||
* QIODNSResolver *resolver = qio_dns_resolver_get_instance(); | ||
* SocketAddress **rawaddrs = NULL; | ||
* size_t nrawaddrs = 0; | ||
* Error *err = NULL; | ||
* QIOChannel **socks = NULL; | ||
* size_t nsocks = 0; | ||
* | ||
* if (qio_dns_resolver_lookup_sync(dns, addr, &nrawaddrs, | ||
* &rawaddrs, errp) < 0) { | ||
* return -1; | ||
* } | ||
* | ||
* for (i = 0; i < nrawaddrs; i++) { | ||
* QIOChannel *sock = qio_channel_new(); | ||
* Error *local_err = NULL; | ||
* qio_channel_listen_sync(sock, rawaddrs[i], &local_err); | ||
* if (local_err) { | ||
* error_propagate(&err, local_err); | ||
* } else { | ||
* socks = g_renew(QIOChannelSocket *, socks, nsocks + 1); | ||
* socks[nsocks++] = sock; | ||
* } | ||
* qapi_free_SocketAddress(rawaddrs[i]); | ||
* } | ||
* g_free(rawaddrs); | ||
* | ||
* if (nsocks == 0) { | ||
* error_propagate(errp, err); | ||
* } else { | ||
* error_free(err); | ||
* } | ||
* } | ||
* </programlisting> | ||
* </example> | ||
* | ||
* <example> | ||
* <title>Resolving addresses asynchronously</title> | ||
* <programlisting> | ||
* typedef struct MyListenData { | ||
* Error *err; | ||
* QIOChannelSocket **socks; | ||
* size_t nsocks; | ||
* } MyListenData; | ||
* | ||
* void mylistenresult(QIOTask *task, void *opaque) { | ||
* MyListenData *data = opaque; | ||
* QIODNSResolver *resolver = | ||
* QIO_DNS_RESOLVER(qio_task_get_source(task); | ||
* SocketAddress **rawaddrs = NULL; | ||
* size_t nrawaddrs = 0; | ||
* Error *err = NULL; | ||
* | ||
* if (qio_task_propagate_error(task, &data->err)) { | ||
* return; | ||
* } | ||
* | ||
* qio_dns_resolver_lookup_result(resolver, task, | ||
* &nrawaddrs, &rawaddrs); | ||
* | ||
* for (i = 0; i < nrawaddrs; i++) { | ||
* QIOChannel *sock = qio_channel_new(); | ||
* Error *local_err = NULL; | ||
* qio_channel_listen_sync(sock, rawaddrs[i], &local_err); | ||
* if (local_err) { | ||
* error_propagate(&err, local_err); | ||
* } else { | ||
* socks = g_renew(QIOChannelSocket *, socks, nsocks + 1); | ||
* socks[nsocks++] = sock; | ||
* } | ||
* qapi_free_SocketAddress(rawaddrs[i]); | ||
* } | ||
* g_free(rawaddrs); | ||
* | ||
* if (nsocks == 0) { | ||
* error_propagate(&data->err, err); | ||
* } else { | ||
* error_free(err); | ||
* } | ||
* } | ||
* | ||
* void mylisten(SocketAddress *addr, MyListenData *data) { | ||
* QIODNSResolver *resolver = qio_dns_resolver_get_instance(); | ||
* qio_dns_resolver_lookup_async(dns, addr, | ||
* mylistenresult, data, NULL); | ||
* } | ||
* </programlisting> | ||
* </example> | ||
*/ | ||
struct QIODNSResolver { | ||
Object parent; | ||
}; | ||
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struct QIODNSResolverClass { | ||
ObjectClass parent; | ||
}; | ||
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/** | ||
* qio_dns_resolver_get_instance: | ||
* | ||
* Get the singleton dns resolver instance. The caller | ||
* does not own a reference on the returned object. | ||
* | ||
* Returns: the single dns resolver instance | ||
*/ | ||
QIODNSResolver *qio_dns_resolver_get_instance(void); | ||
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/** | ||
* qio_dns_resolver_lookup_sync: | ||
* @resolver: the DNS resolver instance | ||
* @addr: the address to resolve | ||
* @naddr: pointer to hold number of resolved addresses | ||
* @addrs: pointer to hold resolved addresses | ||
* @errp: pointer to NULL initialized error object | ||
* | ||
* This will attempt to resolve the address provided | ||
* in @addr. If resolution succeeds, @addrs will be filled | ||
* with all the resolved addresses. @naddrs will specify | ||
* the number of entries allocated in @addrs. The caller | ||
* is responsible for freeing each entry in @addrs, as | ||
* well as @addrs itself. @naddrs is guaranteed to be | ||
* greater than zero on success. | ||
* | ||
* DNS resolution will be done synchronously so execution | ||
* of the caller may be blocked for an arbitrary length | ||
* of time. | ||
* | ||
* Returns: 0 if resolution was successful, -1 on error | ||
*/ | ||
int qio_dns_resolver_lookup_sync(QIODNSResolver *resolver, | ||
SocketAddress *addr, | ||
size_t *naddrs, | ||
SocketAddress ***addrs, | ||
Error **errp); | ||
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/** | ||
* qio_dns_resolver_lookup_async: | ||
* @resolver: the DNS resolver instance | ||
* @addr: the address to resolve | ||
* @func: the callback to invoke on lookup completion | ||
* @opaque: data blob to pass to @func | ||
* @notify: the callback to free @opaque, or NULL | ||
* | ||
* This will attempt to resolve the address provided | ||
* in @addr. The callback @func will be invoked when | ||
* resolution has either completed or failed. On | ||
* success, the @func should call the method | ||
* qio_dns_resolver_lookup_result() to obtain the | ||
* results. | ||
* | ||
* DNS resolution will be done asynchronously so execution | ||
* of the caller will not be blocked. | ||
*/ | ||
void qio_dns_resolver_lookup_async(QIODNSResolver *resolver, | ||
SocketAddress *addr, | ||
QIOTaskFunc func, | ||
gpointer opaque, | ||
GDestroyNotify notify); | ||
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/** | ||
* qio_dns_resolver_lookup_result: | ||
* @resolver: the DNS resolver instance | ||
* @task: the task object to get results for | ||
* @naddr: pointer to hold number of resolved addresses | ||
* @addrs: pointer to hold resolved addresses | ||
* | ||
* This method should be called from the callback passed | ||
* to qio_dns_resolver_lookup_async() in order to obtain | ||
* results. @addrs will be filled with all the resolved | ||
* addresses. @naddrs will specify the number of entries | ||
* allocated in @addrs. The caller is responsible for | ||
* freeing each entry in @addrs, as well as @addrs itself. | ||
*/ | ||
void qio_dns_resolver_lookup_result(QIODNSResolver *resolver, | ||
QIOTask *task, | ||
size_t *naddrs, | ||
SocketAddress ***addrs); | ||
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#endif /* QIO_DNS_RESOLVER_H */ |
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