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

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2024-08-28 at 21:04 -0400, Mike Snitzer wrote:
> 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);

Why a mutex here? AFAICT, you're just using this to protect the list. A
spinlock would probably be more efficient.

> +
> +/*
> + * 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 */

-- 
Jeff Layton <jlayton@kernel.org>