NFS: Share NFS superblocks per-protocol per-server per-FSID

The attached patch makes NFS share superblocks between mounts from the same
server and FSID over the same protocol.

It does this by creating each superblock with a false root and returning the
real root dentry in the vfsmount presented by get_sb(). The root dentry set
starts off as an anonymous dentry if we don't already have the dentry for its
inode, otherwise it simply returns the dentry we already have.

We may thus end up with several trees of dentries in the superblock, and if at
some later point one of anonymous tree roots is discovered by normal filesystem
activity to be located in another tree within the superblock, the anonymous
root is named and materialises attached to the second tree at the appropriate
point.

Why do it this way? Why not pass an extra argument to the mount() syscall to
indicate the subpath and then pathwalk from the server root to the desired
directory? You can't guarantee this will work for two reasons:

 (1) The root and intervening nodes may not be accessible to the client.

     With NFS2 and NFS3, for instance, mountd is called on the server to get
     the filehandle for the tip of a path. mountd won't give us handles for
     anything we don't have permission to access, and so we can't set up NFS
     inodes for such nodes, and so can't easily set up dentries (we'd have to
     have ghost inodes or something).

     With this patch we don't actually create dentries until we get handles
     from the server that we can use to set up their inodes, and we don't
     actually bind them into the tree until we know for sure where they go.

 (2) Inaccessible symbolic links.

     If we're asked to mount two exports from the server, eg:

	mount warthog:/warthog/aaa/xxx /mmm
	mount warthog:/warthog/bbb/yyy /nnn

     We may not be able to access anything nearer the root than xxx and yyy,
     but we may find out later that /mmm/www/yyy, say, is actually the same
     directory as the one mounted on /nnn. What we might then find out, for
     example, is that /warthog/bbb was actually a symbolic link to
     /warthog/aaa/xxx/www, but we can't actually determine that by talking to
     the server until /warthog is made available by NFS.

     This would lead to having constructed an errneous dentry tree which we
     can't easily fix. We can end up with a dentry marked as a directory when
     it should actually be a symlink, or we could end up with an apparently
     hardlinked directory.

     With this patch we need not make assumptions about the type of a dentry
     for which we can't retrieve information, nor need we assume we know its
     place in the grand scheme of things until we actually see that place.

This patch reduces the possibility of aliasing in the inode and page caches for
inodes that may be accessed by more than one NFS export. It also reduces the
number of superblocks required for NFS where there are many NFS exports being
used from a server (home directory server + autofs for example).

This in turn makes it simpler to do local caching of network filesystems, as it
can then be guaranteed that there won't be links from multiple inodes in
separate superblocks to the same cache file.

Obviously, cache aliasing between different levels of NFS protocol could still
be a problem, but at least that gives us another key to use when indexing the
cache.

This patch makes the following changes:

 (1) The server record construction/destruction has been abstracted out into
     its own set of functions to make things easier to get right.  These have
     been moved into fs/nfs/client.c.

     All the code in fs/nfs/client.c has to do with the management of
     connections to servers, and doesn't touch superblocks in any way; the
     remaining code in fs/nfs/super.c has to do with VFS superblock management.

 (2) The sequence of events undertaken by NFS mount is now reordered:

     (a) A volume representation (struct nfs_server) is allocated.

     (b) A server representation (struct nfs_client) is acquired.  This may be
     	 allocated or shared, and is keyed on server address, port and NFS
     	 version.

     (c) If allocated, the client representation is initialised.  The state
     	 member variable of nfs_client is used to prevent a race during
     	 initialisation from two mounts.

     (d) For NFS4 a simple pathwalk is performed, walking from FH to FH to find
     	 the root filehandle for the mount (fs/nfs/getroot.c).  For NFS2/3 we
     	 are given the root FH in advance.

     (e) The volume FSID is probed for on the root FH.

     (f) The volume representation is initialised from the FSINFO record
     	 retrieved on the root FH.

     (g) sget() is called to acquire a superblock.  This may be allocated or
     	 shared, keyed on client pointer and FSID.

     (h) If allocated, the superblock is initialised.

     (i) If the superblock is shared, then the new nfs_server record is
     	 discarded.

     (j) The root dentry for this mount is looked up from the root FH.

     (k) The root dentry for this mount is assigned to the vfsmount.

 (3) nfs_readdir_lookup() creates dentries for each of the entries readdir()
     returns; this function now attaches disconnected trees from alternate
     roots that happen to be discovered attached to a directory being read (in
     the same way nfs_lookup() is made to do for lookup ops).

     The new d_materialise_unique() function is now used to do this, thus
     permitting the whole thing to be done under one set of locks, and thus
     avoiding any race between mount and lookup operations on the same
     directory.

 (4) The client management code uses a new debug facility: NFSDBG_CLIENT which
     is set by echoing 1024 to /proc/net/sunrpc/nfs_debug.

 (5) Clone mounts are now called xdev mounts.

 (6) Use the dentry passed to the statfs() op as the handle for retrieving fs
     statistics rather than the root dentry of the superblock (which is now a
     dummy).

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 444 insertions, 763 deletions

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 5842d510d73..867b5dcd3a4 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -13,6 +13,11 @@
  *
  *  Split from inode.c by David Howells <dhowells@redhat.com>
  *
+ * - superblocks are indexed on server only - all inodes, dentries, etc. associated with a
+ *   particular server are held in the same superblock
+ * - NFS superblocks can have several effective roots to the dentry tree
+ * - directory type roots are spliced into the tree when a path from one root reaches the root
+ *   of another (see nfs_lookup())
  */
 
 #include <linux/config.h>
@@ -52,20 +57,12 @@
 
 #define NFSDBG_FACILITY		NFSDBG_VFS
 
-/* Maximum number of readahead requests
- * FIXME: this should really be a sysctl so that users may tune it to suit
- *        their needs. People that do NFS over a slow network, might for
- *        instance want to reduce it to something closer to 1 for improved
- *        interactive response.
- */
-#define NFS_MAX_READAHEAD	(RPC_DEF_SLOT_TABLE - 1)
-
 static void nfs_umount_begin(struct vfsmount *, int);
 static int  nfs_statfs(struct dentry *, struct kstatfs *);
 static int  nfs_show_options(struct seq_file *, struct vfsmount *);
 static int  nfs_show_stats(struct seq_file *, struct vfsmount *);
 static int nfs_get_sb(struct file_system_type *, int, const char *, void *, struct vfsmount *);
-static int nfs_clone_nfs_sb(struct file_system_type *fs_type,
+static int nfs_xdev_get_sb(struct file_system_type *fs_type,
 		int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
 static void nfs_kill_super(struct super_block *);
 
@@ -77,10 +74,10 @@ static struct file_system_type nfs_fs_type = {
 	.fs_flags	= FS_ODD_RENAME|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
 };
 
-struct file_system_type clone_nfs_fs_type = {
+struct file_system_type nfs_xdev_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "nfs",
-	.get_sb		= nfs_clone_nfs_sb,
+	.get_sb		= nfs_xdev_get_sb,
 	.kill_sb	= nfs_kill_super,
 	.fs_flags	= FS_ODD_RENAME|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
 };
@@ -99,10 +96,10 @@ static struct super_operations nfs_sops = {
 #ifdef CONFIG_NFS_V4
 static int nfs4_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
-static int nfs_clone_nfs4_sb(struct file_system_type *fs_type,
-		int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
-static int nfs_referral_nfs4_sb(struct file_system_type *fs_type,
-		int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
+static int nfs4_xdev_get_sb(struct file_system_type *fs_type,
+	int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
+static int nfs4_referral_get_sb(struct file_system_type *fs_type,
+	int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
 static void nfs4_kill_super(struct super_block *sb);
 
 static struct file_system_type nfs4_fs_type = {
@@ -113,18 +110,18 @@ static struct file_system_type nfs4_fs_type = {
 	.fs_flags	= FS_ODD_RENAME|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
 };
 
-struct file_system_type clone_nfs4_fs_type = {
+struct file_system_type nfs4_xdev_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "nfs4",
-	.get_sb		= nfs_clone_nfs4_sb,
+	.get_sb		= nfs4_xdev_get_sb,
 	.kill_sb	= nfs4_kill_super,
 	.fs_flags	= FS_ODD_RENAME|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
 };
 
-struct file_system_type nfs_referral_nfs4_fs_type = {
+struct file_system_type nfs4_referral_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "nfs4",
-	.get_sb		= nfs_referral_nfs4_sb,
+	.get_sb		= nfs4_referral_get_sb,
 	.kill_sb	= nfs4_kill_super,
 	.fs_flags	= FS_ODD_RENAME|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
 };
@@ -345,7 +342,7 @@ static int nfs_show_options(struct seq_file *m, struct vfsmount *mnt)
 	nfs_show_mount_options(m, nfss, 0);
 
 	seq_puts(m, ",addr=");
-	seq_escape(m, nfss->hostname, " \t\n\\");
+	seq_escape(m, nfss->nfs_client->cl_hostname, " \t\n\\");
 
 	return 0;
 }
@@ -429,714 +426,351 @@ static int nfs_show_stats(struct seq_file *m, struct vfsmount *mnt)
 
 /*
  * Begin unmount by attempting to remove all automounted mountpoints we added
- * in response to traversals
+ * in response to xdev traversals and referrals
  */
 static void nfs_umount_begin(struct vfsmount *vfsmnt, int flags)
 {
-	struct nfs_server *server;
-	struct rpc_clnt	*rpc;
-
 	shrink_submounts(vfsmnt, &nfs_automount_list);
-	if (!(flags & MNT_FORCE))
-		return;
-	/* -EIO all pending I/O */
-	server = NFS_SB(vfsmnt->mnt_sb);
-	rpc = server->client;
-	if (!IS_ERR(rpc))
-		rpc_killall_tasks(rpc);
-	rpc = server->client_acl;
-	if (!IS_ERR(rpc))
-		rpc_killall_tasks(rpc);
 }
 
 /*
- * Obtain the root inode of the file system.
+ * Validate the NFS2/NFS3 mount data
+ * - fills in the mount root filehandle
  */
-static struct inode *
-nfs_get_root(struct super_block *sb, struct nfs_fh *rootfh, struct nfs_fsinfo *fsinfo)
+static int nfs_validate_mount_data(struct nfs_mount_data *data,
+				   struct nfs_fh *mntfh)
 {
-	struct nfs_server	*server = NFS_SB(sb);
-	int			error;
-
-	error = server->nfs_client->rpc_ops->getroot(server, rootfh, fsinfo);
-	if (error < 0) {
-		dprintk("nfs_get_root: getattr error = %d\n", -error);
-		return ERR_PTR(error);
+	if (data == NULL) {
+		dprintk("%s: missing data argument\n", __FUNCTION__);
+		return -EINVAL;
 	}
 
-	server->fsid = fsinfo->fattr->fsid;
-	return nfs_fhget(sb, rootfh, fsinfo->fattr);
-}
-
-/*
- * Do NFS version-independent mount processing, and sanity checking
- */
-static int
-nfs_sb_init(struct super_block *sb, rpc_authflavor_t authflavor)
-{
-	struct nfs_server	*server;
-	struct inode		*root_inode;
-	struct nfs_fattr	fattr;
-	struct nfs_fsinfo	fsinfo = {
-					.fattr = &fattr,
-				};
-	struct nfs_pathconf pathinfo = {
-			.fattr = &fattr,
-	};
-	int no_root_error = 0;
-	unsigned long max_rpc_payload;
-
-	/* We probably want something more informative here */
-	snprintf(sb->s_id, sizeof(sb->s_id), "%x:%x", MAJOR(sb->s_dev), MINOR(sb->s_dev));
-
-	server = NFS_SB(sb);
-
-	sb->s_magic      = NFS_SUPER_MAGIC;
-
-	server->io_stats = nfs_alloc_iostats();
-	if (server->io_stats == NULL)
-		return -ENOMEM;
+	if (data->version <= 0 || data->version > NFS_MOUNT_VERSION) {
+		dprintk("%s: bad mount version\n", __FUNCTION__);
+		return -EINVAL;
+	}
 
-	root_inode = nfs_get_root(sb, &server->fh, &fsinfo);
-	/* Did getting the root inode fail? */
-	if (IS_ERR(root_inode)) {
-		no_root_error = PTR_ERR(root_inode);
-		goto out_no_root;
+	switch (data->version) {
+		case 1:
+			data->namlen = 0;
+		case 2:
+			data->bsize  = 0;
+		case 3:
+			if (data->flags & NFS_MOUNT_VER3) {
+				dprintk("%s: mount structure version %d does not support NFSv3\n",
+						__FUNCTION__,
+						data->version);
+				return -EINVAL;
+			}
+			data->root.size = NFS2_FHSIZE;
+			memcpy(data->root.data, data->old_root.data, NFS2_FHSIZE);
+		case 4:
+			if (data->flags & NFS_MOUNT_SECFLAVOUR) {
+				dprintk("%s: mount structure version %d does not support strong security\n",
+						__FUNCTION__,
+						data->version);
+				return -EINVAL;
+			}
+			/* Fill in pseudoflavor for mount version < 5 */
+			data->pseudoflavor = RPC_AUTH_UNIX;
+		case 5:
+			memset(data->context, 0, sizeof(data->context));
 	}
-	sb->s_root = d_alloc_root(root_inode);
-	if (!sb->s_root) {
-		no_root_error = -ENOMEM;
-		goto out_no_root;
+
+#ifndef CONFIG_NFS_V3
+	/* If NFSv3 is not compiled in, return -EPROTONOSUPPORT */
+	if (data->flags & NFS_MOUNT_VER3) {
+		dprintk("%s: NFSv3 not compiled into kernel\n", __FUNCTION__);
+		return -EPROTONOSUPPORT;
 	}
-	sb->s_root->d_op = server->nfs_client->rpc_ops->dentry_ops;
-
-	/* mount time stamp, in seconds */
-	server->mount_time = jiffies;
-
-	/* Get some general file system info */
-	if (server->namelen == 0 &&
-	    server->nfs_client->rpc_ops->pathconf(server, &server->fh, &pathinfo) >= 0)
-		server->namelen = pathinfo.max_namelen;
-	/* Work out a lot of parameters */
-	if (server->rsize == 0)
-		server->rsize = nfs_block_size(fsinfo.rtpref, NULL);
-	if (server->wsize == 0)
-		server->wsize = nfs_block_size(fsinfo.wtpref, NULL);
-
-	if (fsinfo.rtmax >= 512 && server->rsize > fsinfo.rtmax)
-		server->rsize = nfs_block_size(fsinfo.rtmax, NULL);
-	if (fsinfo.wtmax >= 512 && server->wsize > fsinfo.wtmax)
-		server->wsize = nfs_block_size(fsinfo.wtmax, NULL);
-
-	max_rpc_payload = nfs_block_size(rpc_max_payload(server->client), NULL);
-	if (server->rsize > max_rpc_payload)
-		server->rsize = max_rpc_payload;
-	if (server->rsize > NFS_MAX_FILE_IO_SIZE)
-		server->rsize = NFS_MAX_FILE_IO_SIZE;
-	server->rpages = (server->rsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-
-	if (server->wsize > max_rpc_payload)
-		server->wsize = max_rpc_payload;
-	if (server->wsize > NFS_MAX_FILE_IO_SIZE)
-		server->wsize = NFS_MAX_FILE_IO_SIZE;
-	server->wpages = (server->wsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+#endif /* CONFIG_NFS_V3 */
 
-	if (sb->s_blocksize == 0)
-		sb->s_blocksize = nfs_block_bits(server->wsize,
-							 &sb->s_blocksize_bits);
-	server->wtmult = nfs_block_bits(fsinfo.wtmult, NULL);
-
-	server->dtsize = nfs_block_size(fsinfo.dtpref, NULL);
-	if (server->dtsize > PAGE_CACHE_SIZE)
-		server->dtsize = PAGE_CACHE_SIZE;
-	if (server->dtsize > server->rsize)
-		server->dtsize = server->rsize;
-
-	if (server->flags & NFS_MOUNT_NOAC) {
-		server->acregmin = server->acregmax = 0;
-		server->acdirmin = server->acdirmax = 0;
-		sb->s_flags |= MS_SYNCHRONOUS;
+	/* We now require that the mount process passes the remote address */
+	if (data->addr.sin_addr.s_addr == INADDR_ANY) {
+		dprintk("%s: mount program didn't pass remote address!\n",
+			__FUNCTION__);
+		return -EINVAL;
 	}
-	server->backing_dev_info.ra_pages = server->rpages * NFS_MAX_READAHEAD;
 
-	nfs_super_set_maxbytes(sb, fsinfo.maxfilesize);
+	/* Prepare the root filehandle */
+	if (data->flags & NFS_MOUNT_VER3)
+		mntfh->size = data->root.size;
+	else
+		mntfh->size = NFS2_FHSIZE;
 
-	server->client->cl_intr = (server->flags & NFS_MOUNT_INTR) ? 1 : 0;
-	server->client->cl_softrtry = (server->flags & NFS_MOUNT_SOFT) ? 1 : 0;
+	if (mntfh->size > sizeof(mntfh->data)) {
+		dprintk("%s: invalid root filehandle\n", __FUNCTION__);
+		return -EINVAL;
+	}
+
+	memcpy(mntfh->data, data->root.data, mntfh->size);
+	if (mntfh->size < sizeof(mntfh->data))
+		memset(mntfh->data + mntfh->size, 0,
+		       sizeof(mntfh->data) - mntfh->size);
 
-	/* We're airborne Set socket buffersize */
-	rpc_setbufsize(server->client, server->wsize + 100, server->rsize + 100);
 	return 0;
-	/* Yargs. It didn't work out. */
-out_no_root:
-	dprintk("nfs_sb_init: get root inode failed: errno %d\n", -no_root_error);
-	if (!IS_ERR(root_inode))
-		iput(root_inode);
-	return no_root_error;
 }
 
 /*
- * Create an RPC client handle.
+ * Initialise the common bits of the superblock
  */
-static struct rpc_clnt *
-nfs_create_client(struct nfs_server *server, const struct nfs_mount_data *data)
+static inline void nfs_initialise_sb(struct super_block *sb)
 {
-	struct nfs_client	*clp;
-	struct rpc_clnt		*clnt;
-	int			proto = (data->flags & NFS_MOUNT_TCP) ? IPPROTO_TCP : IPPROTO_UDP;
-	int			nfsversion = 2;
-	int			err;
-
-#ifdef CONFIG_NFS_V3
-	if (server->flags & NFS_MOUNT_VER3)
-		nfsversion = 3;
-#endif
-
-	clp = nfs_get_client(server->hostname, &server->addr, nfsversion);
-	if (!clp) {
-		dprintk("%s: failed to create NFS4 client.\n", __FUNCTION__);
-		return ERR_PTR(PTR_ERR(clp));
-	}
-
-	if (clp->cl_cons_state == NFS_CS_INITING) {
-		/* Check NFS protocol revision and initialize RPC op
-		 * vector and file handle pool. */
-#ifdef CONFIG_NFS_V3
-		if (nfsversion == 3) {
-			clp->rpc_ops = &nfs_v3_clientops;
-			server->caps |= NFS_CAP_READDIRPLUS;
-		} else {
-			clp->rpc_ops = &nfs_v2_clientops;
-		}
-#else
-		clp->rpc_ops = &nfs_v2_clientops;
-#endif
-
-		/* create transport and client */
-		err = nfs_create_rpc_client(clp, proto, data->timeo,
-					    data->retrans, RPC_AUTH_UNIX);
-		if (err < 0)
-			goto client_init_error;
-
-		nfs_mark_client_ready(clp, 0);
-	}
+	struct nfs_server *server = NFS_SB(sb);
 
-	/* create an nfs_server-specific client */
-	clnt = rpc_clone_client(clp->cl_rpcclient);
-	if (IS_ERR(clnt)) {
-		dprintk("%s: couldn't create rpc_client!\n", __FUNCTION__);
-		nfs_put_client(clp);
-		return ERR_PTR(PTR_ERR(clnt));
-	}
+	sb->s_magic = NFS_SUPER_MAGIC;
 
-	if (data->pseudoflavor != clp->cl_rpcclient->cl_auth->au_flavor) {
-		struct rpc_auth *auth;
+	/* We probably want something more informative here */
+	snprintf(sb->s_id, sizeof(sb->s_id),
+		 "%x:%x", MAJOR(sb->s_dev), MINOR(sb->s_dev));
 
-		auth = rpcauth_create(data->pseudoflavor, server->client);
-		if (IS_ERR(auth)) {
-			dprintk("%s: couldn't create credcache!\n", __FUNCTION__);
-			return ERR_PTR(PTR_ERR(auth));
-		}
-	}
+	if (sb->s_blocksize == 0)
+		sb->s_blocksize = nfs_block_bits(server->wsize,
+						 &sb->s_blocksize_bits);
 
-	server->nfs_client = clp;
-	return clnt;
+	if (server->flags & NFS_MOUNT_NOAC)
+		sb->s_flags |= MS_SYNCHRONOUS;
 
-client_init_error:
-	nfs_mark_client_ready(clp, err);
-	nfs_put_client(clp);
-	return ERR_PTR(err);
+	nfs_super_set_maxbytes(sb, server->maxfilesize);
 }
 
 /*
- * Clone a server record
+ * Finish setting up an NFS2/3 superblock
  */
-static struct nfs_server *nfs_clone_server(struct super_block *sb, struct nfs_clone_mount *data)
+static void nfs_fill_super(struct super_block *sb, struct nfs_mount_data *data)
 {
 	struct nfs_server *server = NFS_SB(sb);
-	struct nfs_server *parent = NFS_SB(data->sb);
-	struct inode *root_inode;
-	struct nfs_fsinfo fsinfo;
-	void *err = ERR_PTR(-ENOMEM);
-
-	sb->s_op = data->sb->s_op;
-	sb->s_blocksize = data->sb->s_blocksize;
-	sb->s_blocksize_bits = data->sb->s_blocksize_bits;
-	sb->s_maxbytes = data->sb->s_maxbytes;
-
-	server->client_acl = ERR_PTR(-EINVAL);
-	server->io_stats = nfs_alloc_iostats();
-	if (server->io_stats == NULL)
-		goto out;
-
-	server->client = rpc_clone_client(parent->client);
-	if (IS_ERR((err = server->client)))
-		goto out;
-
-	if (!IS_ERR(parent->client_acl)) {
-		server->client_acl = rpc_clone_client(parent->client_acl);
-		if (IS_ERR((err = server->client_acl)))
-			goto out;
-	}
-	root_inode = nfs_fhget(sb, data->fh, data->fattr);
-	if (!root_inode)
-		goto out;
-	sb->s_root = d_alloc_root(root_inode);
-	if (!sb->s_root)
-		goto out_put_root;
-	fsinfo.fattr = data->fattr;
-	if (NFS_PROTO(root_inode)->fsinfo(server, data->fh, &fsinfo) == 0)
-		nfs_super_set_maxbytes(sb, fsinfo.maxfilesize);
-	sb->s_root->d_op = server->nfs_client->rpc_ops->dentry_ops;
-	sb->s_flags |= MS_ACTIVE;
-	return server;
-out_put_root:
-	iput(root_inode);
-out:
-	return err;
-}
-
-/*
- * Copy an existing superblock and attach revised data
- */
-static int nfs_clone_generic_sb(struct nfs_clone_mount *data,
-		struct super_block *(*fill_sb)(struct nfs_server *, struct nfs_clone_mount *),
-		struct nfs_server *(*fill_server)(struct super_block *, struct nfs_clone_mount *),
-		struct vfsmount *mnt)
-{
-	struct nfs_server *server;
-	struct nfs_server *parent = NFS_SB(data->sb);
-	struct super_block *sb = ERR_PTR(-EINVAL);
-	char *hostname;
-	int error = -ENOMEM;
-	int len;
-
-	server = kmalloc(sizeof(struct nfs_server), GFP_KERNEL);
-	if (server == NULL)
-		goto out_err;
-	memcpy(server, parent, sizeof(*server));
-	atomic_inc(&server->nfs_client->cl_count);
-	hostname = (data->hostname != NULL) ? data->hostname : parent->hostname;
-	len = strlen(hostname) + 1;
-	server->hostname = kmalloc(len, GFP_KERNEL);
-	if (server->hostname == NULL)
-		goto free_server;
-	memcpy(server->hostname, hostname, len);
-
-	sb = fill_sb(server, data);
-	if (IS_ERR(sb)) {
-		error = PTR_ERR(sb);
-		goto free_hostname;
-	}
 
-	if (sb->s_root)
-		goto out_share;
+	sb->s_blocksize_bits = 0;
+	sb->s_blocksize = 0;
+	if (data->bsize)
+		sb->s_blocksize = nfs_block_size(data->bsize, &sb->s_blocksize_bits);
 
-	server = fill_server(sb, data);
-	if (IS_ERR(server)) {
-		error = PTR_ERR(server);
-		goto out_deactivate;
+	if (server->flags & NFS_MOUNT_VER3) {
+		/* The VFS shouldn't apply the umask to mode bits. We will do
+		 * so ourselves when necessary.
+		 */
+		sb->s_flags |= MS_POSIXACL;
+		sb->s_time_gran = 1;
 	}
-	return simple_set_mnt(mnt, sb);
-out_deactivate:
-	up_write(&sb->s_umount);
-	deactivate_super(sb);
-	return error;
-out_share:
-	kfree(server->hostname);
-	nfs_put_client(server->nfs_client);
-	kfree(server);
-	return simple_set_mnt(mnt, sb);
-free_hostname:
-	kfree(server->hostname);
-free_server:
-	nfs_put_client(server->nfs_client);
-	kfree(server);
-out_err:
-	return error;
+
+	sb->s_op = &nfs_sops;
+ 	nfs_initialise_sb(sb);
 }
 
 /*
- * Set up an NFS2/3 superblock
- *
- * The way this works is that the mount process passes a structure
- * in the data argument which contains the server's IP address
- * and the root file handle obtained from the server's mount
- * daemon. We stash these away in the private superblock fields.
+ * Finish setting up a cloned NFS2/3 superblock
  */
-static int
-nfs_fill_super(struct super_block *sb, struct nfs_mount_data *data, int silent)
+static void nfs_clone_super(struct super_block *sb,
+			    const struct super_block *old_sb)
 {
-	struct nfs_server	*server;
-	rpc_authflavor_t	authflavor;
+	struct nfs_server *server = NFS_SB(sb);
+
+	sb->s_blocksize_bits = old_sb->s_blocksize_bits;
+	sb->s_blocksize = old_sb->s_blocksize;
+	sb->s_maxbytes = old_sb->s_maxbytes;
 
-	server           = NFS_SB(sb);
-	sb->s_blocksize_bits = 0;
-	sb->s_blocksize = 0;
-	if (data->bsize)
-		sb->s_blocksize = nfs_block_size(data->bsize, &sb->s_blocksize_bits);
-	if (data->rsize)
-		server->rsize = nfs_block_size(data->rsize, NULL);
-	if (data->wsize)
-		server->wsize = nfs_block_size(data->wsize, NULL);
-	server->flags    = data->flags & NFS_MOUNT_FLAGMASK;
-
-	server->acregmin = data->acregmin*HZ;
-	server->acregmax = data->acregmax*HZ;
-	server->acdirmin = data->acdirmin*HZ;
-	server->acdirmax = data->acdirmax*HZ;
-
-	/* Start lockd here, before we might error out */
-	if (!(server->flags & NFS_MOUNT_NONLM))
-		lockd_up();
-
-	server->namelen  = data->namlen;
-	server->hostname = kmalloc(strlen(data->hostname) + 1, GFP_KERNEL);
-	if (!server->hostname)
-		return -ENOMEM;
-	strcpy(server->hostname, data->hostname);
-
-	/* Fill in pseudoflavor for mount version < 5 */
-	if (!(data->flags & NFS_MOUNT_SECFLAVOUR))
-		data->pseudoflavor = RPC_AUTH_UNIX;
-	authflavor = data->pseudoflavor;	/* save for sb_init() */
-	/* XXX maybe we want to add a server->pseudoflavor field */
-
-	/* Create RPC client handles */
-	server->client = nfs_create_client(server, data);
-	if (IS_ERR(server->client))
-		return PTR_ERR(server->client);
-
-	/* RFC 2623, sec 2.3.2 */
 	if (server->flags & NFS_MOUNT_VER3) {
-#ifdef CONFIG_NFS_V3_ACL
-		if (!(server->flags & NFS_MOUNT_NOACL)) {
-			server->client_acl = rpc_bind_new_program(server->client, &nfsacl_program, 3);
-			/* No errors! Assume that Sun nfsacls are supported */
-			if (!IS_ERR(server->client_acl))
-				server->caps |= NFS_CAP_ACLS;
-		}
-#else
-		server->flags &= ~NFS_MOUNT_NOACL;
-#endif /* CONFIG_NFS_V3_ACL */
-		/*
-		 * The VFS shouldn't apply the umask to mode bits. We will
-		 * do so ourselves when necessary.
+		/* The VFS shouldn't apply the umask to mode bits. We will do
+		 * so ourselves when necessary.
 		 */
 		sb->s_flags |= MS_POSIXACL;
-		if (server->namelen == 0 || server->namelen > NFS3_MAXNAMLEN)
-			server->namelen = NFS3_MAXNAMLEN;
 		sb->s_time_gran = 1;
-	} else {
-		if (server->namelen == 0 || server->namelen > NFS2_MAXNAMLEN)
-			server->namelen = NFS2_MAXNAMLEN;
 	}
 
-	sb->s_op = &nfs_sops;
-	return nfs_sb_init(sb, authflavor);
+	sb->s_op = old_sb->s_op;
+ 	nfs_initialise_sb(sb);
 }
 
-static int nfs_set_super(struct super_block *s, void *data)
+static int nfs_set_super(struct super_block *s, void *_server)
 {
-	s->s_fs_info = data;
-	return set_anon_super(s, data);
+	struct nfs_server *server = _server;
+	int ret;
+
+	s->s_fs_info = server;
+	ret = set_anon_super(s, server);
+	if (ret == 0)
+		server->s_dev = s->s_dev;
+	return ret;
 }
 
 static int nfs_compare_super(struct super_block *sb, void *data)
 {
-	struct nfs_server *server = data;
-	struct nfs_server *old = NFS_SB(sb);
+	struct nfs_server *server = data, *old = NFS_SB(sb);
 
-	if (old->addr.sin_addr.s_addr != server->addr.sin_addr.s_addr)
+	if (old->nfs_client != server->nfs_client)
 		return 0;
-	if (old->addr.sin_port != server->addr.sin_port)
+	if (memcmp(&old->fsid, &server->fsid, sizeof(old->fsid)) != 0)
 		return 0;
-	return !nfs_compare_fh(&old->fh, &server->fh);
+	return 1;
 }
 
 static int nfs_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
 {
-	int error;
 	struct nfs_server *server = NULL;
 	struct super_block *s;
-	struct nfs_fh *root;
+	struct nfs_fh mntfh;
 	struct nfs_mount_data *data = raw_data;
+	struct dentry *mntroot;
+	int error;
 
-	error = -EINVAL;
-	if (data == NULL) {
-		dprintk("%s: missing data argument\n", __FUNCTION__);
-		goto out_err_noserver;
-	}
-	if (data->version <= 0 || data->version > NFS_MOUNT_VERSION) {
-		dprintk("%s: bad mount version\n", __FUNCTION__);
-		goto out_err_noserver;
-	}
-	switch (data->version) {
-		case 1:
-			data->namlen = 0;
-		case 2:
-			data->bsize  = 0;
-		case 3:
-			if (data->flags & NFS_MOUNT_VER3) {
-				dprintk("%s: mount structure version %d does not support NFSv3\n",
-						__FUNCTION__,
-						data->version);
-				goto out_err_noserver;
-			}
-			data->root.size = NFS2_FHSIZE;
-			memcpy(data->root.data, data->old_root.data, NFS2_FHSIZE);
-		case 4:
-			if (data->flags & NFS_MOUNT_SECFLAVOUR) {
-				dprintk("%s: mount structure version %d does not support strong security\n",
-						__FUNCTION__,
-						data->version);
-				goto out_err_noserver;
-			}
-		case 5:
-			memset(data->context, 0, sizeof(data->context));
-	}
-#ifndef CONFIG_NFS_V3
-	/* If NFSv3 is not compiled in, return -EPROTONOSUPPORT */
-	error = -EPROTONOSUPPORT;
-	if (data->flags & NFS_MOUNT_VER3) {
-		dprintk("%s: NFSv3 not compiled into kernel\n", __FUNCTION__);
-		goto out_err_noserver;
-	}
-#endif /* CONFIG_NFS_V3 */
+	/* Validate the mount data */
+	error = nfs_validate_mount_data(data, &mntfh);
+	if (error < 0)
+		return error;
 
-	error = -ENOMEM;
-	server = kzalloc(sizeof(struct nfs_server), GFP_KERNEL);
-	if (!server)
+	/* Get a volume representation */
+	server = nfs_create_server(data, &mntfh);
+	if (IS_ERR(server)) {
+		error = PTR_ERR(server);
 		goto out_err_noserver;
-	/* Zero out the NFS state stuff */
-	init_nfsv4_state(server);
-	server->client = server->client_acl = ERR_PTR(-EINVAL);
-
-	root = &server->fh;
-	if (data->flags & NFS_MOUNT_VER3)
-		root->size = data->root.size;
-	else
-		root->size = NFS2_FHSIZE;
-	error = -EINVAL;
-	if (root->size > sizeof(root->data)) {
-		dprintk("%s: invalid root filehandle\n", __FUNCTION__);
-		goto out_err;
-	}
-	memcpy(root->data, data->root.data, root->size);
-
-	/* We now require that the mount process passes the remote address */
-	memcpy(&server->addr, &data->addr, sizeof(server->addr));
-	if (server->addr.sin_addr.s_addr == INADDR_ANY) {
-		dprintk("%s: mount program didn't pass remote address!\n",
-				__FUNCTION__);
-		goto out_err;
 	}
 
+	/* Get a superblock - note that we may end up sharing one that already exists */
 	s = sget(fs_type, nfs_compare_super, nfs_set_super, server);
 	if (IS_ERR(s)) {
 		error = PTR_ERR(s);
-		goto out_err;
+		goto out_err_nosb;
 	}
 
-	if (s->s_root)
-		goto out_share;
+	if (s->s_fs_info != server) {
+		nfs_free_server(server);
+		server = NULL;
+	}
 
-	s->s_flags = flags;
+	if (!s->s_root) {
+		/* initial superblock/root creation */
+		s->s_flags = flags;
+		nfs_fill_super(s, data);
+	}
 
-	error = nfs_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
-	if (error) {
-		up_write(&s->s_umount);
-		deactivate_super(s);
-		return error;
+	mntroot = nfs_get_root(s, &mntfh);
+	if (IS_ERR(mntroot)) {
+		error = PTR_ERR(mntroot);
+		goto error_splat_super;
 	}
-	s->s_flags |= MS_ACTIVE;
-	return simple_set_mnt(mnt, s);
 
-out_share:
-	kfree(server);
-	return simple_set_mnt(mnt, s);
+	s->s_flags |= MS_ACTIVE;
+	mnt->mnt_sb = s;
+	mnt->mnt_root = mntroot;
+	return 0;
 
-out_err:
-	kfree(server);
+out_err_nosb:
+	nfs_free_server(server);
 out_err_noserver:
 	return error;
+
+error_splat_super:
+	up_write(&s->s_umount);
+	deactivate_super(s);
+	return error;
 }
 
+/*
+ * Destroy an NFS2/3 superblock
+ */
 static void nfs_kill_super(struct super_block *s)
 {
 	struct nfs_server *server = NFS_SB(s);
 
 	kill_anon_super(s);
-
-	if (!IS_ERR(server->client))
-		rpc_shutdown_client(server->client);
-	if (!IS_ERR(server->client_acl))
-		rpc_shutdown_client(server->client_acl);
-
-	if (!(server->flags & NFS_MOUNT_NONLM))
-		lockd_down();	/* release rpc.lockd */
-
-	nfs_free_iostats(server->io_stats);
-	kfree(server->hostname);
-	nfs_put_client(server->nfs_client);
-	kfree(server);
-	nfs_release_automount_timer();
+	nfs_free_server(server);
 }
 
-static struct super_block *nfs_clone_sb(struct nfs_server *server, struct nfs_clone_mount *data)
-{
-	struct super_block *sb;
-
-	server->fsid = data->fattr->fsid;
-	nfs_copy_fh(&server->fh, data->fh);
-	sb = sget(&nfs_fs_type, nfs_compare_super, nfs_set_super, server);
-	if (!IS_ERR(sb) && sb->s_root == NULL && !(server->flags & NFS_MOUNT_NONLM))
-		lockd_up();
-	return sb;
-}
-
-static int nfs_clone_nfs_sb(struct file_system_type *fs_type,
-		int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
+/*
+ * Clone an NFS2/3 server record on xdev traversal (FSID-change)
+ */
+static int nfs_xdev_get_sb(struct file_system_type *fs_type, int flags,
+			   const char *dev_name, void *raw_data,
+			   struct vfsmount *mnt)
 {
 	struct nfs_clone_mount *data = raw_data;
-	return nfs_clone_generic_sb(data, nfs_clone_sb, nfs_clone_server, mnt);
-}
+	struct super_block *s;
+	struct nfs_server *server;
+	struct dentry *mntroot;
+	int error;
 
-#ifdef CONFIG_NFS_V4
-static struct rpc_clnt *nfs4_create_client(struct nfs_server *server,
-	int timeo, int retrans, int proto, rpc_authflavor_t flavor)
-{
-	struct nfs_client *clp;
-	struct rpc_clnt *clnt = NULL;
-	int err = -EIO;
-
-	clp = nfs_get_client(server->hostname, &server->addr, 4);
-	if (!clp) {
-		dprintk("%s: failed to create NFS4 client.\n", __FUNCTION__);
-		return ERR_PTR(err);
-	}
+	dprintk("--> nfs_xdev_get_sb()\n");
 
-	/* Now create transport and client */
-	if (clp->cl_cons_state == NFS_CS_INITING) {
-		clp->rpc_ops = &nfs_v4_clientops;
+	/* create a new volume representation */
+	server = nfs_clone_server(NFS_SB(data->sb), data->fh, data->fattr);
+	if (IS_ERR(server)) {
+		error = PTR_ERR(server);
+		goto out_err_noserver;
+	}
 
-		err = nfs_create_rpc_client(clp, proto, timeo, retrans, flavor);
-		if (err < 0)
-			goto client_init_error;
+	/* Get a superblock - note that we may end up sharing one that already exists */
+	s = sget(&nfs_fs_type, nfs_compare_super, nfs_set_super, server);
+	if (IS_ERR(s)) {
+		error = PTR_ERR(s);
+		goto out_err_nosb;
+	}
 
-		memcpy(clp->cl_ipaddr, server->ip_addr, sizeof(clp->cl_ipaddr));
-		err = nfs_idmap_new(clp);
-		if (err < 0) {
-			dprintk("%s: failed to create idmapper.\n",
-				__FUNCTION__);
-			goto client_init_error;
-		}
-		__set_bit(NFS_CS_IDMAP, &clp->cl_res_state);
-		nfs_mark_client_ready(clp, 0);
+	if (s->s_fs_info != server) {
+		nfs_free_server(server);
+		server = NULL;
 	}
 
-	clnt = rpc_clone_client(clp->cl_rpcclient);
+	if (!s->s_root) {
+		/* initial superblock/root creation */
+		s->s_flags = flags;
+		nfs_clone_super(s, data->sb);
+	}
 
-	if (IS_ERR(clnt)) {
-		dprintk("%s: cannot create RPC client. Error = %d\n",
-				__FUNCTION__, err);
-		return clnt;
+	mntroot = nfs_get_root(s, data->fh);
+	if (IS_ERR(mntroot)) {
+		error = PTR_ERR(mntroot);
+		goto error_splat_super;
 	}
 
-	if (clnt->cl_auth->au_flavor != flavor) {
-		struct rpc_auth *auth;
+	s->s_flags |= MS_ACTIVE;
+	mnt->mnt_sb = s;
+	mnt->mnt_root = mntroot;
 
-		auth = rpcauth_create(flavor, clnt);
-		if (IS_ERR(auth)) {
-			dprintk("%s: couldn't create credcache!\n", __FUNCTION__);
-			return (struct rpc_clnt *)auth;
-		}
-	}
+	dprintk("<-- nfs_xdev_get_sb() = 0\n");
+	return 0;
 
-	server->nfs_client = clp;
-	down_write(&clp->cl_sem);
-	list_add_tail(&server->nfs4_siblings, &clp->cl_superblocks);
-	up_write(&clp->cl_sem);
-	return clnt;
+out_err_nosb:
+	nfs_free_server(server);
+out_err_noserver:
+	dprintk("<-- nfs_xdev_get_sb() = %d [error]\n", error);
+	return error;
 
-client_init_error:
-	nfs_mark_client_ready(clp, err);
-	nfs_put_client(clp);
-	return ERR_PTR(err);
+error_splat_super:
+	up_write(&s->s_umount);
+	deactivate_super(s);
+	dprintk("<-- nfs_xdev_get_sb() = %d [splat]\n", error);
+	return error;
 }
 
+#ifdef CONFIG_NFS_V4
+
 /*
- * Set up an NFS4 superblock
+ * Finish setting up a cloned NFS4 superblock
  */
-static int nfs4_fill_super(struct super_block *sb, struct nfs4_mount_data *data, int silent)
+static void nfs4_clone_super(struct super_block *sb,
+			    const struct super_block *old_sb)
 {
-	struct nfs_server *server;
-	rpc_authflavor_t authflavour;
-	int err = -EIO;
-
-	sb->s_blocksize_bits = 0;
-	sb->s_blocksize = 0;
-	server = NFS_SB(sb);
-	if (data->rsize != 0)
-		server->rsize = nfs_block_size(data->rsize, NULL);
-	if (data->wsize != 0)
-		server->wsize = nfs_block_size(data->wsize, NULL);
-	server->flags = data->flags & NFS_MOUNT_FLAGMASK;
-	server->caps = NFS_CAP_ATOMIC_OPEN;
-
-	server->acregmin = data->acregmin*HZ;
-	server->acregmax = data->acregmax*HZ;
-	server->acdirmin = data->acdirmin*HZ;
-	server->acdirmax = data->acdirmax*HZ;
-
-	/* Now create transport and client */
-	authflavour = RPC_AUTH_UNIX;
-	if (data->auth_flavourlen != 0) {
-		if (data->auth_flavourlen != 1) {
-			dprintk("%s: Invalid number of RPC auth flavours %d.\n",
-					__FUNCTION__, data->auth_flavourlen);
-			err = -EINVAL;
-			goto out_fail;
-		}
-		if (copy_from_user(&authflavour, data->auth_flavours, sizeof(authflavour))) {
-			err = -EFAULT;
-			goto out_fail;
-		}
-	}
-
-	server->client = nfs4_create_client(server, data->timeo, data->retrans,
-					    data->proto, authflavour);
-	if (IS_ERR(server->client)) {
-		err = PTR_ERR(server->client);
-			dprintk("%s: cannot create RPC client. Error = %d\n",
-					__FUNCTION__, err);
-			goto out_fail;
-	}
-
+	sb->s_blocksize_bits = old_sb->s_blocksize_bits;
+	sb->s_blocksize = old_sb->s_blocksize;
+	sb->s_maxbytes = old_sb->s_maxbytes;
 	sb->s_time_gran = 1;
-
-	sb->s_op = &nfs4_sops;
-	err = nfs_sb_init(sb, authflavour);
-
- out_fail:
-	return err;
+	sb->s_op = old_sb->s_op;
+ 	nfs_initialise_sb(sb);
 }
 
-static int nfs4_compare_super(struct super_block *sb, void *data)
+/*
+ * Set up an NFS4 superblock
+ */
+static void nfs4_fill_super(struct super_block *sb)
 {
-	struct nfs_server *server = data;
-	struct nfs_server *old = NFS_SB(sb);
-
-	if (strcmp(server->hostname, old->hostname) != 0)
-		return 0;
-	if (strcmp(server->mnt_path, old->mnt_path) != 0)
-		return 0;
-	return 1;
+	sb->s_time_gran = 1;
+	sb->s_op = &nfs4_sops;
+	nfs_initialise_sb(sb);
 }
 
-static void *
-nfs_copy_user_string(char *dst, struct nfs_string *src, int maxlen)
+static void *nfs_copy_user_string(char *dst, struct nfs_string *src, int maxlen)
 {
 	void *p = NULL;
 
@@ -1157,14 +791,22 @@ nfs_copy_user_string(char *dst, struct nfs_string *src, int maxlen)
 	return dst;
 }
 
+/*
+ * Get the superblock for an NFS4 mountpoint
+ */
 static int nfs4_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
 {
-	int error;
-	struct nfs_server *server;
-	struct super_block *s;
 	struct nfs4_mount_data *data = raw_data;
+	struct super_block *s;
+	struct nfs_server *server;
+	struct sockaddr_in addr;
+	rpc_authflavor_t authflavour;
+	struct nfs_fh mntfh;
+	struct dentry *mntroot;
+	char *mntpath = NULL, *hostname = NULL, ip_addr[16];
 	void *p;
+	int error;
 
 	if (data == NULL) {
 		dprintk("%s: missing data argument\n", __FUNCTION__);
@@ -1175,75 +817,107 @@ static int nfs4_get_sb(struct file_system_type *fs_type,
 		return -EINVAL;
 	}
 
-	server = kzalloc(sizeof(struct nfs_server), GFP_KERNEL);
-	if (!server)
-		return -ENOMEM;
-	/* Zero out the NFS state stuff */
-	init_nfsv4_state(server);
-	server->client = server->client_acl = ERR_PTR(-EINVAL);
+	/* We now require that the mount process passes the remote address */
+	if (data->host_addrlen != sizeof(addr))
+		return -EINVAL;
+
+	if (copy_from_user(&addr, data->host_addr, sizeof(addr)))
+		return -EFAULT;
+
+	if (addr.sin_family != AF_INET ||
+	    addr.sin_addr.s_addr == INADDR_ANY
+	    ) {
+		dprintk("%s: mount program didn't pass remote IP address!\n",
+				__FUNCTION__);
+		return -EINVAL;
+	}
+
+	/* Grab the authentication type */
+	authflavour = RPC_AUTH_UNIX;
+	if (data->auth_flavourlen != 0) {
+		if (data->auth_flavourlen != 1) {
+			dprintk("%s: Invalid number of RPC auth flavours %d.\n",
+					__FUNCTION__, data->auth_flavourlen);
+			error = -EINVAL;
+			goto out_err_noserver;
+		}
+
+		if (copy_from_user(&authflavour, data->auth_flavours,
+				   sizeof(authflavour))) {
+			error = -EFAULT;
+			goto out_err_noserver;
+		}
+	}
 
 	p = nfs_copy_user_string(NULL, &data->hostname, 256);
 	if (IS_ERR(p))
 		goto out_err;
-	server->hostname = p;
+	hostname = p;
 
 	p = nfs_copy_user_string(NULL, &data->mnt_path, 1024);
 	if (IS_ERR(p))
 		goto out_err;
-	server->mnt_path = p;
+	mntpath = p;
 
-	p = nfs_copy_user_string(server->ip_addr, &data->client_addr,
-			sizeof(server->ip_addr) - 1);
+	dprintk("MNTPATH: %s\n", mntpath);
+
+	p = nfs_copy_user_string(ip_addr, &data->client_addr,
+				 sizeof(ip_addr) - 1);
 	if (IS_ERR(p))
 		goto out_err;
 
-	/* We now require that the mount process passes the remote address */
-	if (data->host_addrlen != sizeof(server->addr)) {
-		error = -EINVAL;
-		goto out_free;
-	}
-	if (copy_from_user(&server->addr, data->host_addr, sizeof(server->addr))) {
-		error = -EFAULT;
-		goto out_free;
-	}
-	if (server->addr.sin_family != AF_INET ||
-	    server->addr.sin_addr.s_addr == INADDR_ANY) {
-		dprintk("%s: mount program didn't pass remote IP address!\n",
-				__FUNCTION__);
-		error = -EINVAL;
-		goto out_free;
+	/* Get a volume representation */
+	server = nfs4_create_server(data, hostname, &addr, mntpath, ip_addr,
+				    authflavour, &mntfh);
+	if (IS_ERR(server)) {
+		error = PTR_ERR(server);
+		goto out_err_noserver;
 	}
 
-	s = sget(fs_type, nfs4_compare_super, nfs_set_super, server);
+	/* Get a superblock - note that we may end up sharing one that already exists */
+	s = sget(fs_type, nfs_compare_super, nfs_set_super, server);
 	if (IS_ERR(s)) {
 		error = PTR_ERR(s);
 		goto out_free;
 	}
 
-	if (s->s_root) {
-		kfree(server->mnt_path);
-		kfree(server->hostname);
-		kfree(server);
-		return simple_set_mnt(mnt, s);
-	}
+	if (!s->s_root) {
+		/* initial superblock/root creation */
+		s->s_flags = flags;
 
-	s->s_flags = flags;
+		nfs4_fill_super(s);
+	} else {
+		nfs_free_server(server);
+	}
 
-	error = nfs4_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
-	if (error) {
-		up_write(&s->s_umount);
-		deactivate_super(s);
-		return error;
+	mntroot = nfs4_get_root(s, &mntfh);
+	if (IS_ERR(mntroot)) {
+		error = PTR_ERR(mntroot);
+		goto error_splat_super;
 	}
+
 	s->s_flags |= MS_ACTIVE;
-	return simple_set_mnt(mnt, s);
+	mnt->mnt_sb = s;
+	mnt->mnt_root = mntroot;
+	kfree(mntpath);
+	kfree(hostname);
+	return 0;
+
 out_err:
 	error = PTR_ERR(p);
+	goto out_err_noserver;
+
 out_free:
-	kfree(server->mnt_path);
-	kfree(server->hostname);
-	kfree(server);
+	nfs_free_server(server);
+out_err_noserver:
+	kfree(mntpath);
+	kfree(hostname);
 	return error;
+
+error_splat_super:
+	up_write(&s->s_umount);
+	deactivate_super(s);
+	goto out_err_noserver;
 }
 
 static void nfs4_kill_super(struct super_block *sb)
@@ -1254,133 +928,140 @@ static void nfs4_kill_super(struct super_block *sb)
 	kill_anon_super(sb);
 
 	nfs4_renewd_prepare_shutdown(server);
-
-	if (server->client != NULL && !IS_ERR(server->client))
-		rpc_shutdown_client(server->client);
-
-	destroy_nfsv4_state(server);
-
-	nfs_free_iostats(server->io_stats);
-	kfree(server->hostname);
-	kfree(server);
-	nfs_release_automount_timer();
+	nfs_free_server(server);
 }
 
 /*
- * Constructs the SERVER-side path
+ * Clone an NFS4 server record on xdev traversal (FSID-change)
  */
-static inline char *nfs4_dup_path(const struct dentry *dentry)
+static int nfs4_xdev_get_sb(struct file_system_type *fs_type, int flags,
+			    const char *dev_name, void *raw_data,
+			    struct vfsmount *mnt)
 {
-	char *page = (char *) __get_free_page(GFP_USER);
-	char *path;
+	struct nfs_clone_mount *data = raw_data;
+	struct super_block *s;
+	struct nfs_server *server;
+	struct dentry *mntroot;
+	int error;
 
-	path = nfs4_path(dentry, page, PAGE_SIZE);
-	if (!IS_ERR(path)) {
-		int len = PAGE_SIZE + page - path;
-		char *tmp = path;
+	dprintk("--> nfs4_xdev_get_sb()\n");
 
-		path = kmalloc(len, GFP_KERNEL);
-		if (path)
-			memcpy(path, tmp, len);
-		else
-			path = ERR_PTR(-ENOMEM);
+	/* create a new volume representation */
+	server = nfs_clone_server(NFS_SB(data->sb), data->fh, data->fattr);
+	if (IS_ERR(server)) {
+		error = PTR_ERR(server);
+		goto out_err_noserver;
 	}
-	free_page((unsigned long)page);
-	return path;
-}
 
-static struct super_block *nfs4_clone_sb(struct nfs_server *server, struct nfs_clone_mount *data)
-{
-	const struct dentry *dentry = data->dentry;
-	struct nfs_client *clp = server->nfs_client;
-	struct super_block *sb;
-
-	server->fsid = data->fattr->fsid;
-	nfs_copy_fh(&server->fh, data->fh);
-	server->mnt_path = nfs4_dup_path(dentry);
-	if (IS_ERR(server->mnt_path)) {
-		sb = (struct super_block *)server->mnt_path;
-		goto err;
+	/* Get a superblock - note that we may end up sharing one that already exists */
+	s = sget(&nfs_fs_type, nfs_compare_super, nfs_set_super, server);
+	if (IS_ERR(s)) {
+		error = PTR_ERR(s);
+		goto out_err_nosb;
 	}
-	sb = sget(&nfs4_fs_type, nfs4_compare_super, nfs_set_super, server);
-	if (IS_ERR(sb) || sb->s_root)
-		goto free_path;
-	nfs4_server_capabilities(server, &server->fh);
-
-	down_write(&clp->cl_sem);
-	list_add_tail(&server->nfs4_siblings, &clp->cl_superblocks);
-	up_write(&clp->cl_sem);
-	return sb;
-free_path:
-	kfree(server->mnt_path);
-err:
-	server->mnt_path = NULL;
-	return sb;
-}
 
-static int nfs_clone_nfs4_sb(struct file_system_type *fs_type,
-		int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
-{
-	struct nfs_clone_mount *data = raw_data;
-	return nfs_clone_generic_sb(data, nfs4_clone_sb, nfs_clone_server, mnt);
-}
+	if (s->s_fs_info != server) {
+		nfs_free_server(server);
+		server = NULL;
+	}
 
-static struct super_block *nfs4_referral_sb(struct nfs_server *server, struct nfs_clone_mount *data)
-{
-	struct super_block *sb = ERR_PTR(-ENOMEM);
-	int len;
-
-	len = strlen(data->mnt_path) + 1;
-	server->mnt_path = kmalloc(len, GFP_KERNEL);
-	if (server->mnt_path == NULL)
-		goto err;
-	memcpy(server->mnt_path, data->mnt_path, len);
-	memcpy(&server->addr, data->addr, sizeof(struct sockaddr_in));
-
-	sb = sget(&nfs4_fs_type, nfs4_compare_super, nfs_set_super, server);
-	if (IS_ERR(sb) || sb->s_root)
-		goto free_path;
-	return sb;
-free_path:
-	kfree(server->mnt_path);
-err:
-	server->mnt_path = NULL;
-	return sb;
-}
+	if (!s->s_root) {
+		/* initial superblock/root creation */
+		s->s_flags = flags;
+		nfs4_clone_super(s, data->sb);
+	}
 
-static struct nfs_server *nfs4_referral_server(struct super_block *sb, struct nfs_clone_mount *data)
-{
-	struct nfs_server *server = NFS_SB(sb);
-	int proto, timeo, retrans;
-	void *err;
-
-	proto = IPPROTO_TCP;
-	/* Since we are following a referral and there may be alternatives,
-	   set the timeouts and retries to low values */
-	timeo = 2;
-	retrans = 1;
-
-	nfs_put_client(server->nfs_client);
-	server->nfs_client = NULL;
-	server->client = nfs4_create_client(server, timeo, retrans, proto,
-					    data->authflavor);
-	if (IS_ERR((err = server->client)))
-		goto out_err;
+	mntroot = nfs4_get_root(s, data->fh);
+	if (IS_ERR(mntroot)) {
+		error = PTR_ERR(mntroot);
+		goto error_splat_super;
+	}
 
-	sb->s_time_gran = 1;
-	sb->s_op = &nfs4_sops;
-	err = ERR_PTR(nfs_sb_init(sb, data->authflavor));
-	if (!IS_ERR(err))
-		return server;
-out_err:
-	return (struct nfs_server *)err;
+	s->s_flags |= MS_ACTIVE;
+	mnt->mnt_sb = s;
+	mnt->mnt_root = mntroot;
+
+	dprintk("<-- nfs4_xdev_get_sb() = 0\n");
+	return 0;
+
+out_err_nosb:
+	nfs_free_server(server);
+out_err_noserver:
+	dprintk("<-- nfs4_xdev_get_sb() = %d [error]\n", error);
+	return error;
+
+error_splat_super:
+	up_write(&s->s_umount);
+	deactivate_super(s);
+	dprintk("<-- nfs4_xdev_get_sb() = %d [splat]\n", error);
+	return error;
 }
 
-static int nfs_referral_nfs4_sb(struct file_system_type *fs_type,
-		int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
+/*
+ * Create an NFS4 server record on referral traversal
+ */
+static int nfs4_referral_get_sb(struct file_system_type *fs_type, int flags,
+				const char *dev_name, void *raw_data,
+				struct vfsmount *mnt)
 {
 	struct nfs_clone_mount *data = raw_data;
-	return nfs_clone_generic_sb(data, nfs4_referral_sb, nfs4_referral_server, mnt);
+	struct super_block *s;
+	struct nfs_server *server;
+	struct dentry *mntroot;
+	struct nfs_fh mntfh;
+	int error;
+
+	dprintk("--> nfs4_referral_get_sb()\n");
+
+	/* create a new volume representation */
+	server = nfs4_create_referral_server(data, &mntfh);
+	if (IS_ERR(server)) {
+		error = PTR_ERR(server);
+		goto out_err_noserver;
+	}
+
+	/* Get a superblock - note that we may end up sharing one that already exists */
+	s = sget(&nfs_fs_type, nfs_compare_super, nfs_set_super, server);
+	if (IS_ERR(s)) {
+		error = PTR_ERR(s);
+		goto out_err_nosb;
+	}
+
+	if (s->s_fs_info != server) {
+		nfs_free_server(server);
+		server = NULL;
+	}
+
+	if (!s->s_root) {
+		/* initial superblock/root creation */
+		s->s_flags = flags;
+		nfs4_fill_super(s);
+	}
+
+	mntroot = nfs4_get_root(s, data->fh);
+	if (IS_ERR(mntroot)) {
+		error = PTR_ERR(mntroot);
+		goto error_splat_super;
+	}
+
+	s->s_flags |= MS_ACTIVE;
+	mnt->mnt_sb = s;
+	mnt->mnt_root = mntroot;
+
+	dprintk("<-- nfs4_referral_get_sb() = 0\n");
+	return 0;
+
+out_err_nosb:
+	nfs_free_server(server);
+out_err_noserver:
+	dprintk("<-- nfs4_referral_get_sb() = %d [error]\n", error);
+	return error;
+
+error_splat_super:
+	up_write(&s->s_umount);
+	deactivate_super(s);
+	dprintk("<-- nfs4_referral_get_sb() = %d [splat]\n", error);
+	return error;
 }
 
-#endif
+#endif /* CONFIG_NFS_V4 */