nfsd: add NFSD_CMD_CACHE_FLUSH netlink command

Add a new NFSD_CMD_CACHE_FLUSH generic netlink command that allows
userspace to flush the nfsd export caches (svc_export and expkey)
without writing to /proc/net/rpc/*/flush.

An optional NFSD_A_CACHE_FLUSH_MASK u32 attribute selects which caches
to flush (bit 1 = svc_export, bit 2 = expkey). If the attribute is
omitted, all nfsd 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>

Documentation/netlink/specs/nfsd.yaml

@@ -293,6 +293,14 @@ attribute-sets:
         type: nest
         nested-attributes: expkey
         multi-attr: true
+  -
+    name: cache-flush
+    attributes:
+      -
+        name: mask
+        type: u32
+        enum: cache-type
+        enum-as-flags: true
 
 operations:
   list:
@@ -438,6 +446,15 @@ operations:
           request:
             attributes:
               - requests
+    -
+      name: cache-flush
+      doc: Flush nfsd caches (svc_export and/or expkey)
+      attribute-set: cache-flush
+      flags: [admin-perm]
+      do:
+        request:
+          attributes:
+            - mask
 
 mcast-groups:
   list:

fs/nfsd/netlink.c

@@ -108,6 +108,11 @@ static const struct nla_policy nfsd_expkey_set_reqs_nl_policy[NFSD_A_EXPKEY_REQS
 	[NFSD_A_EXPKEY_REQS_REQUESTS] = NLA_POLICY_NESTED(nfsd_expkey_nl_policy),
 };
 
+/* NFSD_CMD_CACHE_FLUSH - do */
+static const struct nla_policy nfsd_cache_flush_nl_policy[NFSD_A_CACHE_FLUSH_MASK + 1] = {
+	[NFSD_A_CACHE_FLUSH_MASK] = NLA_POLICY_MASK(NLA_U32, 0x3),
+};
+
 /* Ops table for nfsd */
 static const struct genl_split_ops nfsd_nl_ops[] = {
 	{
@@ -191,6 +196,13 @@ static const struct genl_split_ops nfsd_nl_ops[] = {
 		.maxattr	= NFSD_A_EXPKEY_REQS_REQUESTS,
 		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
 	},
+	{
+		.cmd		= NFSD_CMD_CACHE_FLUSH,
+		.doit		= nfsd_nl_cache_flush_doit,
+		.policy		= nfsd_cache_flush_nl_policy,
+		.maxattr	= NFSD_A_CACHE_FLUSH_MASK,
+		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
+	},
 };
 
 static const struct genl_multicast_group nfsd_nl_mcgrps[] = {

fs/nfsd/netlink.h

@@ -38,6 +38,7 @@ int nfsd_nl_svc_export_set_reqs_doit(struct sk_buff *skb,
 int nfsd_nl_expkey_get_reqs_dumpit(struct sk_buff *skb,
 				   struct netlink_callback *cb);
 int nfsd_nl_expkey_set_reqs_doit(struct sk_buff *skb, struct genl_info *info);
+int nfsd_nl_cache_flush_doit(struct sk_buff *skb, struct genl_info *info);
 
 enum {
 	NFSD_NLGRP_NONE,

fs/nfsd/nfsctl.c

@@ -10,6 +10,7 @@
 #include <linux/ctype.h>
 #include <linux/fs_context.h>
 
+#include <linux/sunrpc/cache.h>
 #include <linux/sunrpc/svcsock.h>
 #include <linux/lockd/bind.h>
 #include <linux/sunrpc/addr.h>
@@ -2212,6 +2213,41 @@ int nfsd_nl_pool_mode_get_doit(struct sk_buff *skb, struct genl_info *info)
 	return err;
 }
 
+/**
+ * nfsd_nl_cache_flush_doit - flush nfsd caches via netlink
+ * @skb: reply buffer
+ * @info: netlink metadata and command arguments
+ *
+ * Flush the svc_export and/or expkey caches. If NFSD_A_CACHE_FLUSH_MASK
+ * is provided, only flush the caches indicated by the bitmask (bit 0 =
+ * svc_export, bit 1 = expkey). If omitted, flush both.
+ *
+ * Return 0 on success or a negative errno.
+ */
+int nfsd_nl_cache_flush_doit(struct sk_buff *skb, struct genl_info *info)
+{
+	struct net *net = genl_info_net(info);
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	u32 mask = ~0U;
+
+	if (info->attrs[NFSD_A_CACHE_FLUSH_MASK])
+		mask = nla_get_u32(info->attrs[NFSD_A_CACHE_FLUSH_MASK]);
+
+	mutex_lock(&nfsd_mutex);
+
+	if ((mask & NFSD_CACHE_TYPE_SVC_EXPORT) &&
+	    nn->svc_export_cache)
+		cache_purge(nn->svc_export_cache);
+
+	if ((mask & NFSD_CACHE_TYPE_EXPKEY) &&
+	    nn->svc_expkey_cache)
+		cache_purge(nn->svc_expkey_cache);
+
+	mutex_unlock(&nfsd_mutex);
+
+	return 0;
+}
+
 int nfsd_cache_notify(struct cache_detail *cd, struct cache_head *h, u32 cache_type)
 {
 	struct genlmsghdr *hdr;

include/uapi/linux/nfsd_netlink.h

@@ -197,6 +197,13 @@ enum {
 	NFSD_A_EXPKEY_REQS_MAX = (__NFSD_A_EXPKEY_REQS_MAX - 1)
 };
 
+enum {
+	NFSD_A_CACHE_FLUSH_MASK = 1,
+
+	__NFSD_A_CACHE_FLUSH_MAX,
+	NFSD_A_CACHE_FLUSH_MAX = (__NFSD_A_CACHE_FLUSH_MAX - 1)
+};
+
 enum {
 	NFSD_CMD_RPC_STATUS_GET = 1,
 	NFSD_CMD_THREADS_SET,
@@ -212,6 +219,7 @@ enum {
 	NFSD_CMD_SVC_EXPORT_SET_REQS,
 	NFSD_CMD_EXPKEY_GET_REQS,
 	NFSD_CMD_EXPKEY_SET_REQS,
+	NFSD_CMD_CACHE_FLUSH,
 
 	__NFSD_CMD_MAX,
 	NFSD_CMD_MAX = (__NFSD_CMD_MAX - 1)