genetlink/pmcraid: use proper genetlink multicast API

The pmcraid driver is abusing the genetlink API and is using its
family ID as the multicast group ID, which is invalid and may
belong to somebody else (and likely will.)

Make it use the correct API, but since this may already be used
as-is by userspace, reserve a family ID for this code and also
reserve that group ID to not break userspace assumptions.

My previous patch broke event delivery in the driver as I missed
that it wasn't using the right API and forgot to update it later
in my series.

While changing this, I noticed that the genetlink code could use
the static group ID instead of a strcmp(), so also do that for
the VFS_DQUOT family.

Cc: Anil Ravindranath <anil_ravindranath@pmc-sierra.com>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/scsi/pmcraid.c

@@ -1404,11 +1404,22 @@ enum {
 };
 #define PMCRAID_AEN_CMD_MAX (__PMCRAID_AEN_CMD_MAX - 1)
 
+static struct genl_multicast_group pmcraid_mcgrps[] = {
+	{ .name = "events", /* not really used - see ID discussion below */ },
+};
+
 static struct genl_family pmcraid_event_family = {
-	.id = GENL_ID_GENERATE,
+	/*
+	 * Due to prior multicast group abuse (the code having assumed that
+	 * the family ID can be used as a multicast group ID) we need to
+	 * statically allocate a family (and thus group) ID.
+	 */
+	.id = GENL_ID_PMCRAID,
 	.name = "pmcraid",
 	.version = 1,
-	.maxattr = PMCRAID_AEN_ATTR_MAX
+	.maxattr = PMCRAID_AEN_ATTR_MAX,
+	.mcgrps = pmcraid_mcgrps,
+	.n_mcgrps = ARRAY_SIZE(pmcraid_mcgrps),
 };
 
 /**
@@ -1511,9 +1522,8 @@ static int pmcraid_notify_aen(
 		return result;
 	}
 
-	result =
-		genlmsg_multicast(&pmcraid_event_family, skb, 0,
-				  pmcraid_event_family.id, GFP_ATOMIC);
+	result = genlmsg_multicast(&pmcraid_event_family, skb,
+				   0, 0, GFP_ATOMIC);
 
 	/* If there are no listeners, genlmsg_multicast may return non-zero
 	 * value.

include/uapi/linux/genetlink.h

@@ -28,6 +28,7 @@ struct genlmsghdr {
 #define GENL_ID_GENERATE	0
 #define GENL_ID_CTRL		NLMSG_MIN_TYPE
 #define GENL_ID_VFS_DQUOT	(NLMSG_MIN_TYPE + 1)
+#define GENL_ID_PMCRAID		(NLMSG_MIN_TYPE + 2)
 
 /**************************************************************************
  * Controller

net/netlink/genetlink.c

@@ -74,9 +74,12 @@ static struct list_head family_ht[GENL_FAM_TAB_SIZE];
  * 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.
+ * Bit 18 is marked as already used since the PMCRAID driver
+ * did the same thing as the VFS quota code (maybe copied?)
  */
 static unsigned long mc_group_start = 0x3 | BIT(GENL_ID_CTRL) |
-				      BIT(GENL_ID_VFS_DQUOT);
+				      BIT(GENL_ID_VFS_DQUOT) |
+				      BIT(GENL_ID_PMCRAID);
 static unsigned long *mc_groups = &mc_group_start;
 static unsigned long mc_groups_longs = 1;
 
@@ -139,6 +142,7 @@ static u16 genl_generate_id(void)
 
 	for (i = 0; i <= GENL_MAX_ID - GENL_MIN_ID; i++) {
 		if (id_gen_idx != GENL_ID_VFS_DQUOT &&
+		    id_gen_idx != GENL_ID_PMCRAID &&
 		    !genl_family_find_byid(id_gen_idx))
 			return id_gen_idx;
 		if (++id_gen_idx > GENL_MAX_ID)
@@ -236,9 +240,12 @@ static int genl_validate_assign_mc_groups(struct genl_family *family)
 	} else if (strcmp(family->name, "NET_DM") == 0) {
 		first_id = 1;
 		BUG_ON(n_groups != 1);
-	} else if (strcmp(family->name, "VFS_DQUOT") == 0) {
+	} else if (family->id == GENL_ID_VFS_DQUOT) {
 		first_id = GENL_ID_VFS_DQUOT;
 		BUG_ON(n_groups != 1);
+	} else if (family->id == GENL_ID_PMCRAID) {
+		first_id = GENL_ID_PMCRAID;
+		BUG_ON(n_groups != 1);
 	} else {
 		groups_allocated = true;
 		err = genl_allocate_reserve_groups(n_groups, &first_id);