NFS: Use kernel DNS resolver [ver #2]

Use the kernel DNS resolver to translate hostnames to IP addresses.  Create a
new config option to choose between the legacy DNS resolver and the new
resolver.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

3 files changed, 52 insertions, 0 deletions

diff --git a/fs/nfs/Kconfig b/fs/nfs/Kconfig
index cc1bb33b59b8..c5bbdca13ac2 100644
--- a/fs/nfs/Kconfig
+++ b/fs/nfs/Kconfig
@@ -100,3 +100,19 @@ config NFS_FSCACHE
         help
           Say Y here if you want NFS data to be cached locally on disc through
           the general filesystem cache manager
+
+config NFS_USE_LEGACY_DNS
+        bool "Use the legacy NFS DNS resolver"
+        depends on NFS_V4
+        help
+          The kernel now provides a method for translating a host name into an
+          IP address.  Select Y here if you would rather use your own DNS
+          resolver script.
+
+          If unsure, say N
+
+config NFS_USE_KERNEL_DNS
+        bool
+        depends on NFS_V4 && !NFS_USE_LEGACY_DNS
+        select DNS_RESOLVER
+        default y
diff --git a/fs/nfs/dns_resolve.c b/fs/nfs/dns_resolve.c
index 76fd235d0024..dba50a5625db 100644
--- a/fs/nfs/dns_resolve.c
+++ b/fs/nfs/dns_resolve.c
@@ -6,6 +6,29 @@
  * Resolves DNS hostnames into valid ip addresses
  */
 
+#ifdef CONFIG_NFS_USE_KERNEL_DNS
+
+#include <linux/sunrpc/clnt.h>
+#include <linux/dns_resolver.h>
+
+ssize_t nfs_dns_resolve_name(char *name, size_t namelen,
+                struct sockaddr *sa, size_t salen)
+{
+        ssize_t ret;
+        char *ip_addr = NULL;
+        int ip_len;
+
+        ip_len = dns_query(NULL, name, namelen, NULL, &ip_addr, NULL);
+        if (ip_len > 0)
+                ret = rpc_pton(ip_addr, ip_len, sa, salen);
+        else
+                ret = -ESRCH;
+        kfree(ip_addr);
+        return ret;
+}
+
+#else
+
 #include <linux/hash.h>
 #include <linux/string.h>
 #include <linux/kmod.h>
@@ -346,3 +369,4 @@ void nfs_dns_resolver_destroy(void)
         nfs_cache_unregister(&nfs_dns_resolve);
 }
 
+#endif
diff --git a/fs/nfs/dns_resolve.h b/fs/nfs/dns_resolve.h
index a3f0938babf7..199bb5543a91 100644
--- a/fs/nfs/dns_resolve.h
+++ b/fs/nfs/dns_resolve.h
@@ -6,8 +6,20 @@
 
 #define NFS_DNS_HOSTNAME_MAXLEN (128)
 
+
+#ifdef CONFIG_NFS_USE_KERNEL_DNS
+static inline int nfs_dns_resolver_init(void)
+{
+        return 0;
+}
+
+static inline void nfs_dns_resolver_destroy(void)
+{}
+#else
 extern int nfs_dns_resolver_init(void);
 extern void nfs_dns_resolver_destroy(void);
+#endif
+
 extern ssize_t nfs_dns_resolve_name(char *name, size_t namelen,
                 struct sockaddr *sa, size_t salen);