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>

2 files changed, 116 insertions, 12 deletions

diff --git a/net/ceph/Kconfig b/net/ceph/Kconfig
index be683f2d401..cc04dd667a1 100644
--- a/net/ceph/Kconfig
+++ b/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.
+
diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index f56aca30261..f466930e26f 100644
--- a/net/ceph/messenger.c
+++ b/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>
@@ -1078,6 +1079,101 @@ 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);