nfs: add LOCALIO support

Add client support for bypassing NFS for localhost reads, writes, and
commits. This is only useful when the client and the server are
running on the same host.

nfs_local_probe() is stubbed out, later commits will enable client and
server handshake via a Linux-only LOCALIO auxiliary RPC protocol.

This has dynamic binding with the nfsd module (via nfs_localio module
which is part of nfs_common). LOCALIO will only work if nfsd is
already loaded.

The "localio_enabled" nfs kernel module parameter can be used to
disable and enable the ability to use LOCALIO support.

CONFIG_NFS_LOCALIO enables NFS client support for LOCALIO.

Lastly, LOCALIO uses an nfsd_file to initiate all IO. To make proper
use of nfsd_file (and nfsd's filecache) its lifetime (duration before
nfsd_file_put is called) must extend until after commit, read and
write operations. So rather than immediately drop the nfsd_file
reference in nfs_local_open_fh(), that doesn't happen until
nfs_local_pgio_release() for read/write and not until
nfs_local_release_commit_data() for commit. The same applies to the
reference held on nfsd's nn->nfsd_serv. Both objects' lifetimes and
associated references are managed through calls to
nfs_to->nfsd_file_put_local().

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Co-developed-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de> # nfs_open_local_fh
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c
index f61761ad19b1..42b479b9191f 100644
--- a/fs/nfs_common/nfslocalio.c
+++ b/fs/nfs_common/nfslocalio.c
@@ -115,6 +115,39 @@ void nfs_uuid_invalidate_one_client(nfs_uuid_t *nfs_uuid)
 }
 EXPORT_SYMBOL_GPL(nfs_uuid_invalidate_one_client);
 
+struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *uuid,
+		   struct rpc_clnt *rpc_clnt, const struct cred *cred,
+		   const struct nfs_fh *nfs_fh, const fmode_t fmode)
+{
+	struct net *net;
+	struct nfsd_file *localio;
+
+	/*
+	 * Not running in nfsd context, so must safely get reference on nfsd_serv.
+	 * But the server may already be shutting down, if so disallow new localio.
+	 * uuid->net is NOT a counted reference, but rcu_read_lock() ensures that
+	 * if uuid->net is not NULL, then calling nfsd_serv_try_get() is safe
+	 * and if it succeeds we will have an implied reference to the net.
+	 *
+	 * Otherwise NFS may not have ref on NFSD and therefore cannot safely
+	 * make 'nfs_to' calls.
+	 */
+	rcu_read_lock();
+	net = rcu_dereference(uuid->net);
+	if (!net || !nfs_to->nfsd_serv_try_get(net)) {
+		rcu_read_unlock();
+		return ERR_PTR(-ENXIO);
+	}
+	rcu_read_unlock();
+	/* We have an implied reference to net thanks to nfsd_serv_try_get */
+	localio = nfs_to->nfsd_open_local_fh(net, uuid->dom, rpc_clnt,
+					     cred, nfs_fh, fmode);
+	if (IS_ERR(localio))
+		nfs_to->nfsd_serv_put(net);
+	return localio;
+}
+EXPORT_SYMBOL_GPL(nfs_open_local_fh);
+
 /*
  * The NFS LOCALIO code needs to call into NFSD using various symbols,
  * but cannot be statically linked, because that will make the NFS