ceph: use kernel DNS resolver

Change ceph_parse_ips to take either names given as
IP addresses or standard hostnames (e.g. localhost).
The DNS lookup is done using the dns_resolver facility
similar to its use in AFS, NFS, and CIFS.

This patch defines CONFIG_CEPH_LIB_USE_DNS_RESOLVER
that controls if this feature is on or off.
Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>

net/ceph/Kconfig

@@ -27,3 +27,17 @@ config CEPH_LIB_PRETTYDEBUG
 
 	  If unsure, say N.
 
+config CEPH_LIB_USE_DNS_RESOLVER
+	bool "Use in-kernel support for DNS lookup"
+	depends on CEPH_LIB
+	select DNS_RESOLVER
+	default n
+	help
+	  If you say Y here, hostnames (e.g. monitor addresses) will
+	  be resolved using the CONFIG_DNS_RESOLVER facility.
+
+	  For information on how to use CONFIG_DNS_RESOLVER consult
+	  Documentation/networking/dns_resolver.txt
+
+	  If unsure, say N.
+

net/ceph/messenger.c

@@ -11,6 +11,7 @@
 #include <linux/string.h>
 #include <linux/bio.h>
 #include <linux/blkdev.h>
+#include <linux/dns_resolver.h>
 #include <net/tcp.h>
 
 #include <linux/ceph/libceph.h>
@@ -1077,6 +1078,101 @@ static void addr_set_port(struct sockaddr_storage *ss, int p)
 	}
 }
 
+/*
+ * Unlike other *_pton function semantics, zero indicates success.
+ */
+static int ceph_pton(const char *str, size_t len, struct sockaddr_storage *ss,
+		char delim, const char **ipend)
+{
+	struct sockaddr_in *in4 = (void *)ss;
+	struct sockaddr_in6 *in6 = (void *)ss;
+
+	memset(ss, 0, sizeof(*ss));
+
+	if (in4_pton(str, len, (u8 *)&in4->sin_addr.s_addr, delim, ipend)) {
+		ss->ss_family = AF_INET;
+		return 0;
+	}
+
+	if (in6_pton(str, len, (u8 *)&in6->sin6_addr.s6_addr, delim, ipend)) {
+		ss->ss_family = AF_INET6;
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
+/*
+ * Extract hostname string and resolve using kernel DNS facility.
+ */
+#ifdef CONFIG_CEPH_LIB_USE_DNS_RESOLVER
+static int ceph_dns_resolve_name(const char *name, size_t namelen,
+		struct sockaddr_storage *ss, char delim, const char **ipend)
+{
+	const char *end, *delim_p;
+	char *colon_p, *ip_addr = NULL;
+	int ip_len, ret;
+
+	/*
+	 * The end of the hostname occurs immediately preceding the delimiter or
+	 * the port marker (':') where the delimiter takes precedence.
+	 */
+	delim_p = memchr(name, delim, namelen);
+	colon_p = memchr(name, ':', namelen);
+
+	if (delim_p && colon_p)
+		end = delim_p < colon_p ? delim_p : colon_p;
+	else if (!delim_p && colon_p)
+		end = colon_p;
+	else {
+		end = delim_p;
+		if (!end) /* case: hostname:/ */
+			end = name + namelen;
+	}
+
+	if (end <= name)
+		return -EINVAL;
+
+	/* do dns_resolve upcall */
+	ip_len = dns_query(NULL, name, end - name, NULL, &ip_addr, NULL);
+	if (ip_len > 0)
+		ret = ceph_pton(ip_addr, ip_len, ss, -1, NULL);
+	else
+		ret = -ESRCH;
+
+	kfree(ip_addr);
+
+	*ipend = end;
+
+	pr_info("resolve '%.*s' (ret=%d): %s\n", (int)(end - name), name,
+			ret, ret ? "failed" : ceph_pr_addr(ss));
+
+	return ret;
+}
+#else
+static inline int ceph_dns_resolve_name(const char *name, size_t namelen,
+		struct sockaddr_storage *ss, char delim, const char **ipend)
+{
+	return -EINVAL;
+}
+#endif
+
+/*
+ * Parse a server name (IP or hostname). If a valid IP address is not found
+ * then try to extract a hostname to resolve using userspace DNS upcall.
+ */
+static int ceph_parse_server_name(const char *name, size_t namelen,
+			struct sockaddr_storage *ss, char delim, const char **ipend)
+{
+	int ret;
+
+	ret = ceph_pton(name, namelen, ss, delim, ipend);
+	if (ret)
+		ret = ceph_dns_resolve_name(name, namelen, ss, delim, ipend);
+
+	return ret;
+}
+
 /*
  * Parse an ip[:port] list into an addr array.  Use the default
  * monitor port if a port isn't specified.
@@ -1085,15 +1181,13 @@ int ceph_parse_ips(const char *c, const char *end,
 		   struct ceph_entity_addr *addr,
 		   int max_count, int *count)
 {
-	int i;
+	int i, ret = -EINVAL;
 	const char *p = c;
 
 	dout("parse_ips on '%.*s'\n", (int)(end-c), c);
 	for (i = 0; i < max_count; i++) {
 		const char *ipend;
 		struct sockaddr_storage *ss = &addr[i].in_addr;
-		struct sockaddr_in *in4 = (void *)ss;
-		struct sockaddr_in6 *in6 = (void *)ss;
 		int port;
 		char delim = ',';
 
@@ -1102,15 +1196,11 @@ int ceph_parse_ips(const char *c, const char *end,
 			p++;
 		}
 
-		memset(ss, 0, sizeof(*ss));
-		if (in4_pton(p, end - p, (u8 *)&in4->sin_addr.s_addr,
-			     delim, &ipend))
-			ss->ss_family = AF_INET;
-		else if (in6_pton(p, end - p, (u8 *)&in6->sin6_addr.s6_addr,
-				  delim, &ipend))
-			ss->ss_family = AF_INET6;
-		else
+		ret = ceph_parse_server_name(p, end - p, ss, delim, &ipend);
+		if (ret)
 			goto bad;
+		ret = -EINVAL;
+
 		p = ipend;
 
 		if (delim == ']') {
@@ -1155,7 +1245,7 @@ int ceph_parse_ips(const char *c, const char *end,
 
 bad:
 	pr_err("parse_ips bad ip '%.*s'\n", (int)(end - c), c);
-	return -EINVAL;
+	return ret;
 }
 EXPORT_SYMBOL(ceph_parse_ips);