NFS: Create a try_mount rpc op

I'm already looking up the nfs subversion in nfs_fs_mount(), so I have
easy access to rpc_ops that used to be difficult to reach.  This allows
me to set up a different mount path for NFS v2/3 and NFS v4.
Signed-off-by: NBryan Schumaker <bjschuma@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/internal.h

@@ -328,6 +328,8 @@ extern struct file_system_type nfs_xdev_fs_type;
 extern struct file_system_type nfs4_xdev_fs_type;
 extern struct file_system_type nfs4_referral_fs_type;
 #endif
+struct dentry *nfs_try_mount(int, const char *, struct nfs_mount_info *,
+			struct nfs_subversion *);
 void nfs_initialise_sb(struct super_block *);
 int nfs_set_sb_security(struct super_block *, struct dentry *, struct nfs_mount_info *);
 int nfs_clone_sb_security(struct super_block *, struct dentry *, struct nfs_mount_info *);

fs/nfs/nfs3proc.c

@@ -925,6 +925,7 @@ const struct nfs_rpc_ops nfs_v3_clientops = {
 	.file_ops	= &nfs_file_operations,
 	.getroot	= nfs3_proc_get_root,
 	.submount	= nfs_submount,
+	.try_mount	= nfs_try_mount,
 	.getattr	= nfs3_proc_getattr,
 	.setattr	= nfs3_proc_setattr,
 	.lookup		= nfs3_proc_lookup,

fs/nfs/nfs4_fs.h

@@ -367,7 +367,7 @@ extern const nfs4_stateid zero_stateid;
 /* nfs4super.c */
 struct nfs_mount_info;
 extern struct nfs_subversion nfs_v4;
-struct dentry *nfs4_try_mount(int, const char *, struct nfs_mount_info *);
+struct dentry *nfs4_try_mount(int, const char *, struct nfs_mount_info *, struct nfs_subversion *);
 int init_nfs_v4(void);
 void exit_nfs_v4(void);
 

fs/nfs/nfs4proc.c

@@ -6870,6 +6870,7 @@ const struct nfs_rpc_ops nfs_v4_clientops = {
 	.file_ops	= &nfs4_file_operations,
 	.getroot	= nfs4_proc_get_root,
 	.submount	= nfs4_submount,
+	.try_mount	= nfs4_try_mount,
 	.getattr	= nfs4_proc_getattr,
 	.setattr	= nfs4_proc_setattr,
 	.lookup		= nfs4_proc_lookup,

fs/nfs/nfs4super.c

@@ -226,7 +226,8 @@ static struct dentry *nfs_follow_remote_path(struct vfsmount *root_mnt,
 }
 
 struct dentry *nfs4_try_mount(int flags, const char *dev_name,
-			 struct nfs_mount_info *mount_info)
+			      struct nfs_mount_info *mount_info,
+			      struct nfs_subversion *nfs_mod)
 {
 	char *export_path;
 	struct vfsmount *root_mnt;

fs/nfs/proc.c

@@ -774,6 +774,7 @@ const struct nfs_rpc_ops nfs_v2_clientops = {
 	.file_ops	= &nfs_file_operations,
 	.getroot	= nfs_proc_get_root,
 	.submount	= nfs_submount,
+	.try_mount	= nfs_try_mount,
 	.getattr	= nfs_proc_getattr,
 	.setattr	= nfs_proc_setattr,
 	.lookup		= nfs_proc_lookup,

fs/nfs/super.c

@@ -1650,9 +1650,9 @@ static int nfs_request_mount(struct nfs_parsed_mount_data *args,
 	return nfs_walk_authlist(args, &request);
 }
 
-static struct dentry *nfs_try_mount(int flags, const char *dev_name,
-				    struct nfs_mount_info *mount_info,
-				    struct nfs_subversion *nfs_mod)
+struct dentry *nfs_try_mount(int flags, const char *dev_name,
+			     struct nfs_mount_info *mount_info,
+			     struct nfs_subversion *nfs_mod)
 {
 	int status;
 	struct nfs_server *server;
@@ -2403,15 +2403,9 @@ struct dentry *nfs_fs_mount(struct file_system_type *fs_type,
 		goto out;
 	}
 
-#ifdef CONFIG_NFS_V4
-	if (mount_info.parsed->version == 4)
-		mntroot = nfs4_try_mount(flags, dev_name, &mount_info);
-	else
-#endif	/* CONFIG_NFS_V4 */
-		mntroot = nfs_try_mount(flags, dev_name, &mount_info, nfs_mod);
+	mntroot = nfs_mod->rpc_ops->try_mount(flags, dev_name, &mount_info, nfs_mod);
 
 	put_nfs_version(nfs_mod);
-
 out:
 	nfs_free_parsed_mount_data(mount_info.parsed);
 	nfs_free_fhandle(mount_info.mntfh);

include/linux/nfs_xdr.h

@@ -1353,6 +1353,8 @@ struct nfs_renamedata {
 struct nfs_access_entry;
 struct nfs_client;
 struct rpc_timeout;
+struct nfs_subversion;
+struct nfs_mount_info;
 struct nfs_client_initdata;
 struct nfs_pageio_descriptor;
 
@@ -1370,6 +1372,8 @@ struct nfs_rpc_ops {
 			    struct nfs_fsinfo *);
 	struct vfsmount *(*submount) (struct nfs_server *, struct dentry *,
 				      struct nfs_fh *, struct nfs_fattr *);
+	struct dentry *(*try_mount) (int, const char *, struct nfs_mount_info *,
+				     struct nfs_subversion *);
 	int	(*getattr) (struct nfs_server *, struct nfs_fh *,
 			    struct nfs_fattr *);
 	int	(*setattr) (struct dentry *, struct nfs_fattr *,