[PATCH v14 14/25] nfs_common: add NFS LOCALIO auxiliary protocol enablement

[Mike Snitzer <snitzer@kernel.org>]

fs/nfs_common/nfslocalio.c provides interfaces that enable an NFS
client to generate a nonce (single-use UUID) and associated
short-lived nfs_uuid_t struct, register it with nfs_common for
subsequent lookup and verification by the NFS server and if matched
the NFS server populates members in the nfs_uuid_t struct.

nfs_common's nfs_uuids list is the basis for localio enablement, as
such it has members that point to nfsd memory for direct use by the
client (e.g. 'net' is the server's network namespace, through it the
client can access nn->nfsd_serv with proper rcu read access).

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
 fs/nfs_common/Makefile     |  3 ++
 fs/nfs_common/nfslocalio.c | 74 ++++++++++++++++++++++++++++++++++++++
 include/linux/nfslocalio.h | 31 ++++++++++++++++
 3 files changed, 108 insertions(+)
 create mode 100644 fs/nfs_common/nfslocalio.c
 create mode 100644 include/linux/nfslocalio.h

diff --git a/fs/nfs_common/Makefile b/fs/nfs_common/Makefile
index e58b01bb8dda..a5e54809701e 100644
--- a/fs/nfs_common/Makefile
+++ b/fs/nfs_common/Makefile
@@ -6,6 +6,9 @@
 obj-$(CONFIG_NFS_ACL_SUPPORT) += nfs_acl.o
 nfs_acl-objs := nfsacl.o
 
+obj-$(CONFIG_NFS_COMMON_LOCALIO_SUPPORT) += nfs_localio.o
+nfs_localio-objs := nfslocalio.o
+
 obj-$(CONFIG_GRACE_PERIOD) += grace.o
 obj-$(CONFIG_NFS_V4_2_SSC_HELPER) += nfs_ssc.o
 
diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c
new file mode 100644
index 000000000000..1a35a4a6dbe0
--- /dev/null
+++ b/fs/nfs_common/nfslocalio.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 Mike Snitzer <snitzer@hammerspace.com>
+ */
+
+#include <linux/module.h>
+#include <linux/rculist.h>
+#include <linux/nfslocalio.h>
+#include <net/netns/generic.h>
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("NFS localio protocol bypass support");
+
+DEFINE_MUTEX(nfs_uuid_mutex);
+
+/*
+ * Global list of nfs_uuid_t instances, add/remove
+ * is protected by nfs_uuid_mutex.
+ * Reads are protected by RCU read lock (see below).
+ */
+LIST_HEAD(nfs_uuids);
+
+void nfs_uuid_begin(nfs_uuid_t *nfs_uuid)
+{
+	nfs_uuid->net = NULL;
+	nfs_uuid->dom = NULL;
+	uuid_gen(&nfs_uuid->uuid);
+
+	mutex_lock(&nfs_uuid_mutex);
+	list_add_tail_rcu(&nfs_uuid->list, &nfs_uuids);
+	mutex_unlock(&nfs_uuid_mutex);
+}
+EXPORT_SYMBOL_GPL(nfs_uuid_begin);
+
+void nfs_uuid_end(nfs_uuid_t *nfs_uuid)
+{
+	mutex_lock(&nfs_uuid_mutex);
+	list_del_rcu(&nfs_uuid->list);
+	mutex_unlock(&nfs_uuid_mutex);
+}
+EXPORT_SYMBOL_GPL(nfs_uuid_end);
+
+/* Must be called with RCU read lock held. */
+static nfs_uuid_t * nfs_uuid_lookup(const uuid_t *uuid)
+{
+	nfs_uuid_t *nfs_uuid;
+
+	list_for_each_entry_rcu(nfs_uuid, &nfs_uuids, list)
+		if (uuid_equal(&nfs_uuid->uuid, uuid))
+			return nfs_uuid;
+
+	return NULL;
+}
+
+bool nfs_uuid_is_local(const uuid_t *uuid, struct net *net, struct auth_domain *dom)
+{
+	bool is_local = false;
+	nfs_uuid_t *nfs_uuid;
+
+	rcu_read_lock();
+	nfs_uuid = nfs_uuid_lookup(uuid);
+	if (nfs_uuid) {
+		nfs_uuid->net = maybe_get_net(net);
+		if (nfs_uuid->net) {
+			is_local = true;
+			kref_get(&dom->ref);
+			nfs_uuid->dom = dom;
+		}
+	}
+	rcu_read_unlock();
+
+	return is_local;
+}
+EXPORT_SYMBOL_GPL(nfs_uuid_is_local);
diff --git a/include/linux/nfslocalio.h b/include/linux/nfslocalio.h
new file mode 100644
index 000000000000..9735ae8d3e5e
--- /dev/null
+++ b/include/linux/nfslocalio.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2024 Mike Snitzer <snitzer@hammerspace.com>
+ */
+#ifndef __LINUX_NFSLOCALIO_H
+#define __LINUX_NFSLOCALIO_H
+
+#include <linux/list.h>
+#include <linux/uuid.h>
+#include <linux/sunrpc/svcauth.h>
+#include <linux/nfs.h>
+#include <net/net_namespace.h>
+
+/*
+ * Useful to allow a client to negotiate if localio
+ * possible with its server.
+ *
+ * See Documentation/filesystems/nfs/localio.rst for more detail.
+ */
+typedef struct {
+	uuid_t uuid;
+	struct list_head list;
+	struct net *net; /* nfsd's network namespace */
+	struct auth_domain *dom; /* auth_domain for localio */
+} nfs_uuid_t;
+
+void nfs_uuid_begin(nfs_uuid_t *);
+void nfs_uuid_end(nfs_uuid_t *);
+bool nfs_uuid_is_local(const uuid_t *, struct net *, struct auth_domain *);
+
+#endif  /* __LINUX_NFSLOCALIO_H */
-- 
2.44.0