rxrpc: abstract away knowledge of IDR internals

Add idr_get_cursor() / idr_set_cursor() APIs, and remove the reference
to IDR_SIZE.

Link: http://lkml.kernel.org/r/1480369871-5271-65-git-send-email-mawilcox@linuxonhyperv.com
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: David Howells <dhowells@redhat.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 2d59c9b..5f63f6d 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -762,16 +762,17 @@ static const struct net_proto_family rxrpc_family_ops = {
 static int __init af_rxrpc_init(void)
 {
 	int ret = -1;
+	unsigned int tmp;
 
 	BUILD_BUG_ON(sizeof(struct rxrpc_skb_priv) > FIELD_SIZEOF(struct sk_buff, cb));
 
 	get_random_bytes(&rxrpc_epoch, sizeof(rxrpc_epoch));
 	rxrpc_epoch |= RXRPC_RANDOM_EPOCH;
-	get_random_bytes(&rxrpc_client_conn_ids.cur,
-			 sizeof(rxrpc_client_conn_ids.cur));
-	rxrpc_client_conn_ids.cur &= 0x3fffffff;
-	if (rxrpc_client_conn_ids.cur == 0)
-		rxrpc_client_conn_ids.cur = 1;
+	get_random_bytes(&tmp, sizeof(tmp));
+	tmp &= 0x3fffffff;
+	if (tmp == 0)
+		tmp = 1;
+	idr_set_cursor(&rxrpc_client_conn_ids, tmp);
 
 	ret = -ENOMEM;
 	rxrpc_call_jar = kmem_cache_create(