DNS: Separate out CIFS DNS Resolver code

Separate out the DNS resolver key type from the CIFS filesystem into its own
module so that it can be made available for general use, including the AFS
filesystem module.

This facility makes it possible for the kernel to upcall to userspace to have
it issue DNS requests, package up the replies and present them to the kernel
in a useful form.  The kernel is then able to cache the DNS replies as keys
can be retained in keyrings.

Resolver keys are of type "dns_resolver" and have a case-insensitive
description that is of the form "[<type>:]<domain_name>".  The optional <type>
indicates the particular DNS lookup and packaging that's required.  The
<domain_name> is the query to be made.

If <type> isn't given, a basic hostname to IP address lookup is made, and the
result is stored in the key in the form of a printable string consisting of a
comma-separated list of IPv4 and IPv6 addresses.

This key type is supported by userspace helpers driven from /sbin/request-key
and configured through /etc/request-key.conf.  The cifs.upcall utility is
invoked for UNC path server name to IP address resolution.

The CIFS functionality is encapsulated by the dns_resolve_unc_to_ip() function,
which is used to resolve a UNC path to an IP address for CIFS filesystem.  This
part remains in the CIFS module for now.

See the added Documentation/networking/dns_resolver.txt for more information.

Signed-off-by: Wang Lei <wang840925@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 1 insertions, 12 deletions

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 8a2cf129e535..2a0c892959f4 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -45,7 +45,6 @@
 #include "cifs_fs_sb.h"
 #include <linux/mm.h>
 #include <linux/key-type.h>
-#include "dns_resolve.h"
 #include "cifs_spnego.h"
 #include "fscache.h"
 #define CIFS_MAGIC_NUMBER 0xFF534D42    /* the first four bytes of SMB PDUs */
@@ -934,22 +933,13 @@ init_cifs(void)
         if (rc)
                 goto out_unregister_filesystem;
 #endif
-#ifdef CONFIG_CIFS_DFS_UPCALL
-        rc = cifs_init_dns_resolver();
-        if (rc)
-                goto out_unregister_key_type;
-#endif
         rc = slow_work_register_user(THIS_MODULE);
         if (rc)
-                goto out_unregister_resolver_key;
+                goto out_unregister_key_type;
 
         return 0;
 
- out_unregister_resolver_key:
-#ifdef CONFIG_CIFS_DFS_UPCALL
-        cifs_exit_dns_resolver();
  out_unregister_key_type:
-#endif
 #ifdef CONFIG_CIFS_UPCALL
         unregister_key_type(&cifs_spnego_key_type);
  out_unregister_filesystem:
@@ -976,7 +966,6 @@ exit_cifs(void)
         cifs_fscache_unregister();
 #ifdef CONFIG_CIFS_DFS_UPCALL
         cifs_dfs_release_automount_timer();
-        cifs_exit_dns_resolver();
 #endif
 #ifdef CONFIG_CIFS_UPCALL
         unregister_key_type(&cifs_spnego_key_type);