sunrpc: add SUNRPC_CMD_CACHE_FLUSH netlink command

Add a new SUNRPC_CMD_CACHE_FLUSH generic netlink command that allows
userspace to flush the sunrpc auth caches (ip_map and unix_gid) without
writing to /proc/net/rpc/*/flush.

An optional SUNRPC_A_CACHE_FLUSH_MASK u32 attribute selects which caches
to flush (bit 1 = ip_map, bit 2 = unix_gid). If the attribute is
omitted, all sunrpc caches are flushed.

This is used by exportfs to replace its /proc-based cache_flush() with a
netlink equivalent, with /proc fallback for older kernels.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: jtlayton

Documentation/netlink/specs/sunrpc_cache.yaml

@@ -76,6 +76,14 @@ attribute-sets:
         type: nest
         nested-attributes: unix-gid
         multi-attr: true
+  -
+    name: cache-flush
+    attributes:
+      -
+        name: mask
+        type: u32
+        enum: cache-type
+        enum-as-flags: true
 
 operations:
   list:
@@ -123,6 +131,15 @@ operations:
           request:
             attributes:
               - requests
+    -
+      name: cache-flush
+      doc: Flush sunrpc caches (ip_map and/or unix_gid)
+      attribute-set: cache-flush
+      flags: [admin-perm]
+      do:
+        request:
+          attributes:
+            - mask
 
 mcast-groups:
   list:

include/uapi/linux/sunrpc_netlink.h

@@ -59,12 +59,20 @@ enum {
 	SUNRPC_A_UNIX_GID_REQS_MAX = (__SUNRPC_A_UNIX_GID_REQS_MAX - 1)
 };
 
+enum {
+	SUNRPC_A_CACHE_FLUSH_MASK = 1,
+
+	__SUNRPC_A_CACHE_FLUSH_MAX,
+	SUNRPC_A_CACHE_FLUSH_MAX = (__SUNRPC_A_CACHE_FLUSH_MAX - 1)
+};
+
 enum {
 	SUNRPC_CMD_CACHE_NOTIFY = 1,
 	SUNRPC_CMD_IP_MAP_GET_REQS,
 	SUNRPC_CMD_IP_MAP_SET_REQS,
 	SUNRPC_CMD_UNIX_GID_GET_REQS,
 	SUNRPC_CMD_UNIX_GID_SET_REQS,
+	SUNRPC_CMD_CACHE_FLUSH,
 
 	__SUNRPC_CMD_MAX,
 	SUNRPC_CMD_MAX = (__SUNRPC_CMD_MAX - 1)

net/sunrpc/netlink.c

@@ -49,6 +49,11 @@ static const struct nla_policy sunrpc_unix_gid_set_reqs_nl_policy[SUNRPC_A_UNIX_
 	[SUNRPC_A_UNIX_GID_REQS_REQUESTS] = NLA_POLICY_NESTED(sunrpc_unix_gid_nl_policy),
 };
 
+/* SUNRPC_CMD_CACHE_FLUSH - do */
+static const struct nla_policy sunrpc_cache_flush_nl_policy[SUNRPC_A_CACHE_FLUSH_MASK + 1] = {
+	[SUNRPC_A_CACHE_FLUSH_MASK] = NLA_POLICY_MASK(NLA_U32, 0x3),
+};
+
 /* Ops table for sunrpc */
 static const struct genl_split_ops sunrpc_nl_ops[] = {
 	{
@@ -79,6 +84,13 @@ static const struct genl_split_ops sunrpc_nl_ops[] = {
 		.maxattr	= SUNRPC_A_UNIX_GID_REQS_REQUESTS,
 		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
 	},
+	{
+		.cmd		= SUNRPC_CMD_CACHE_FLUSH,
+		.doit		= sunrpc_nl_cache_flush_doit,
+		.policy		= sunrpc_cache_flush_nl_policy,
+		.maxattr	= SUNRPC_A_CACHE_FLUSH_MASK,
+		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
+	},
 };
 
 static const struct genl_multicast_group sunrpc_nl_mcgrps[] = {

net/sunrpc/netlink.h

@@ -23,6 +23,7 @@ int sunrpc_nl_unix_gid_get_reqs_dumpit(struct sk_buff *skb,
 				       struct netlink_callback *cb);
 int sunrpc_nl_unix_gid_set_reqs_doit(struct sk_buff *skb,
 				     struct genl_info *info);
+int sunrpc_nl_cache_flush_doit(struct sk_buff *skb, struct genl_info *info);
 
 enum {
 	SUNRPC_NLGRP_NONE,

net/sunrpc/svcauth_unix.c

@@ -818,6 +818,38 @@ int sunrpc_nl_unix_gid_set_reqs_doit(struct sk_buff *skb,
 	return ret;
 }
 
+/**
+ * sunrpc_nl_cache_flush_doit - flush sunrpc caches via netlink
+ * @skb: reply buffer
+ * @info: netlink metadata and command arguments
+ *
+ * Flush the ip_map and/or unix_gid caches. If SUNRPC_A_CACHE_FLUSH_MASK
+ * is provided, only flush the caches indicated by the bitmask (bit 1 =
+ * ip_map, bit 2 = unix_gid). If omitted, flush both.
+ *
+ * Return 0 on success or a negative errno.
+ */
+int sunrpc_nl_cache_flush_doit(struct sk_buff *skb, struct genl_info *info)
+{
+	struct sunrpc_net *sn;
+	u32 mask = ~0U;
+
+	sn = net_generic(genl_info_net(info), sunrpc_net_id);
+
+	if (info->attrs[SUNRPC_A_CACHE_FLUSH_MASK])
+		mask = nla_get_u32(info->attrs[SUNRPC_A_CACHE_FLUSH_MASK]);
+
+	if ((mask & SUNRPC_CACHE_TYPE_IP_MAP) &&
+	    sn->ip_map_cache)
+		cache_purge(sn->ip_map_cache);
+
+	if ((mask & SUNRPC_CACHE_TYPE_UNIX_GID) &&
+	    sn->unix_gid_cache)
+		cache_purge(sn->unix_gid_cache);
+
+	return 0;
+}
+
 static const struct cache_detail unix_gid_cache_template = {
 	.owner		= THIS_MODULE,
 	.hash_size	= GID_HASHMAX,