[3/9] quota/genetlink: use proper genetlink multicast APIs

diff --git a/fs/quota/netlink.c b/fs/quota/netlink.c
index 16e8abb..aa22fe0 100644
--- a/fs/quota/netlink.c
+++ b/fs/quota/netlink.c
@@ -11,13 +11,23 @@ 
 
 /* Netlink family structure for quota */
 static struct genl_family quota_genl_family = {
-	.id = GENL_ID_GENERATE,
+	/*
+	 * Needed due to multicast group ID abuse - old code assumed
+	 * the family ID was also a valid multicast group ID (which
+	 * isn't true) and userspace might thus rely on it. Assign a
+	 * static ID for this group to make dealing with that easier.
+	 */
+	.id = GENL_ID_VFS_DQUOT,
 	.hdrsize = 0,
 	.name = "VFS_DQUOT",
 	.version = 1,
 	.maxattr = QUOTA_NL_A_MAX,
 };
 
+static struct genl_multicast_group quota_mcgrp = {
+	.name = "events",
+};
+
 /**
  * quota_send_warning - Send warning to userspace about exceeded quota
  * @type: The quota type: USRQQUOTA, GRPQUOTA,...
@@ -78,7 +88,7 @@  void quota_send_warning(struct kqid qid, dev_t dev,
 		goto attr_err_out;
 	genlmsg_end(skb, msg_head);
 
-	genlmsg_multicast(skb, 0, quota_genl_family.id, GFP_NOFS);
+	genlmsg_multicast(skb, 0, quota_mcgrp.id, GFP_NOFS);
 	return;
 attr_err_out:
 	printk(KERN_ERR "VFS: Not enough space to compose quota message!\n");
@@ -92,6 +102,9 @@  static int __init quota_init(void)
 	if (genl_register_family(&quota_genl_family) != 0)
 		printk(KERN_ERR
 		       "VFS: Failed to create quota netlink interface.\n");
+	if (genl_register_mc_group(&quota_genl_family, &quota_mcgrp))
+		printk(KERN_ERR
+		       "VFS: Failed to register quota mcast group.\n");
 	return 0;
 };
 
diff --git a/include/uapi/linux/genetlink.h b/include/uapi/linux/genetlink.h
index c880a41..1af72d82 100644
--- a/include/uapi/linux/genetlink.h
+++ b/include/uapi/linux/genetlink.h
@@ -27,6 +27,7 @@  struct genlmsghdr {
  */
 #define GENL_ID_GENERATE	0
 #define GENL_ID_CTRL		NLMSG_MIN_TYPE
+#define GENL_ID_VFS_DQUOT	(NLMSG_MIN_TYPE + 1)
 
 /**************************************************************************
  * Controller
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 353909d..bee91a7 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -69,8 +69,11 @@  static struct list_head family_ht[GENL_FAM_TAB_SIZE];
  * abuses the API and thinks it can statically use group 1.
  * That group will typically conflict with other groups that
  * any proper users use.
+ * Bit 17 is marked as already used since the VFS quota code
+ * also abused this API and relied on family == group ID, we
+ * cater to that by giving it a static family and group ID.
  */
-static unsigned long mc_group_start = 0x3;
+static unsigned long mc_group_start = 0x3 | BIT(GENL_ID_VFS_DQUOT);
 static unsigned long *mc_groups = &mc_group_start;
 static unsigned long mc_groups_longs = 1;
 
@@ -130,7 +133,8 @@  static u16 genl_generate_id(void)
 	int i;
 
 	for (i = 0; i <= GENL_MAX_ID - GENL_MIN_ID; i++) {
-		if (!genl_family_find_byid(id_gen_idx))
+		if (id_gen_idx != GENL_ID_VFS_DQUOT &&
+		    !genl_family_find_byid(id_gen_idx))
 			return id_gen_idx;
 		if (++id_gen_idx > GENL_MAX_ID)
 			id_gen_idx = GENL_MIN_ID;
@@ -169,6 +173,8 @@  int genl_register_mc_group(struct genl_family *family,
 		id = GENL_ID_CTRL;
 	else if (strcmp(family->name, "NET_DM") == 0)
 		id = 1;
+	else if (strcmp(family->name, "VFS_DQUOT") == 0)
+		id = GENL_ID_VFS_DQUOT;
 	else
 		id = find_first_zero_bit(mc_groups,
 					 mc_groups_longs * BITS_PER_LONG);