afs: Support the AFS dynamic root

Support the AFS dynamic root which is a pseudo-volume that doesn't connect
to any server resource, but rather is just a root directory that
dynamically creates mountpoint directories where the name of such a
directory is the name of the cell.

Such a mount can be created thus:

	mount -t afs none /afs -o dyn

Dynamic root superblocks aren't shared except by bind mounts and
propagation.  Cell root volumes can then be mounted by referring to them by
name, e.g.:

	ls /afs/grand.central.org/
	ls /afs/.grand.central.org/

The kernel will upcall to consult the DNS if the address wasn't supplied
directly.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 12 insertions, 10 deletions

diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
index af781010753b..49da67034f29 100644
--- a/net/dns_resolver/dns_query.c
+++ b/net/dns_resolver/dns_query.c
@@ -52,11 +52,11 @@
  * @name: Name to look up
  * @namelen: Length of name
  * @options: Request options (or NULL if no options)
- * @_result: Where to place the returned data.
+ * @_result: Where to place the returned data (or NULL)
  * @_expiry: Where to store the result expiry time (or NULL)
  *
- * The data will be returned in the pointer at *result, and the caller is
- * responsible for freeing it.
+ * The data will be returned in the pointer at *result, if provided, and the
+ * caller is responsible for freeing it.
  *
  * The description should be of the form "[<query_type>:]<domain_name>", and
  * the options need to be appropriate for the query type requested.  If no
@@ -81,7 +81,7 @@ int dns_query(const char *type, const char *name, size_t namelen,
 	kenter("%s,%*.*s,%zu,%s",
 	       type, (int)namelen, (int)namelen, name, namelen, options);
 
-	if (!name || namelen == 0 || !_result)
+	if (!name || namelen == 0)
 		return -EINVAL;
 
 	/* construct the query key description as "[<type>:]<name>" */
@@ -146,13 +146,15 @@ int dns_query(const char *type, const char *name, size_t namelen,
 	upayload = user_key_payload_locked(rkey);
 	len = upayload->datalen;
 
-	ret = -ENOMEM;
-	*_result = kmalloc(len + 1, GFP_KERNEL);
-	if (!*_result)
-		goto put;
+	if (_result) {
+		ret = -ENOMEM;
+		*_result = kmalloc(len + 1, GFP_KERNEL);
+		if (!*_result)
+			goto put;
 
-	memcpy(*_result, upayload->data, len);
-	(*_result)[len] = '\0';
+		memcpy(*_result, upayload->data, len);
+		(*_result)[len] = '\0';
+	}
 
 	if (_expiry)
 		*_expiry = rkey->expiry;