2 * Copyright (c) 1992, 1993
3 * The Regents of the University of California. All rights reserved.
5 * This code is derived from software contributed to Berkeley by
6 * John Heidemann of the UCLA Ficus project.
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 * must display the following acknowledgement:
18 * This product includes software developed by the University of
19 * California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 * may be used to endorse or promote products derived from this software
22 * without specific prior written permission.
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * @(#)null_vnops.c 8.6 (Berkeley) 5/27/95
39 * @(#)lofs_vnops.c 1.2 (Berkeley) 6/18/92
40 * $FreeBSD: src/sys/miscfs/nullfs/null_vnops.c,v 1.38.2.6 2002/07/31 00:32:28 semenu Exp $
41 * $DragonFly: src/sys/vfs/nullfs/null_vnops.c,v 1.28 2006/10/27 04:56:34 dillon Exp $
43 * @(#)null_vnodeops.c 1.20 92/07/07 UCLA Ficus project
45 * $FreeBSD: src/sys/miscfs/nullfs/null_vnops.c,v 1.38.2.6 2002/07/31 00:32:28 semenu Exp $
51 * (See mount_null(8) for more information.)
53 * The null layer duplicates a portion of the file system
54 * name space under a new name. In this respect, it is
55 * similar to the loopback file system. It differs from
56 * the loopback fs in two respects: it is implemented using
57 * a stackable layers techniques, and its "null-node"s stack above
58 * all lower-layer vnodes, not just over directory vnodes.
60 * The null layer has two purposes. First, it serves as a demonstration
61 * of layering by proving a layer which does nothing. (It actually
62 * does everything the loopback file system does, which is slightly
63 * more than nothing.) Second, the null layer can serve as a prototype
64 * layer. Since it provides all necessary layer framework,
65 * new file system layers can be created very easily be starting
68 * The remainder of this man page examines the null layer as a basis
69 * for constructing new layers.
72 * INSTANTIATING NEW NULL LAYERS
74 * New null layers are created with mount_null(8).
75 * Mount_null(8) takes two arguments, the pathname
76 * of the lower vfs (target-pn) and the pathname where the null
77 * layer will appear in the namespace (alias-pn). After
78 * the null layer is put into place, the contents
79 * of target-pn subtree will be aliased under alias-pn.
82 * OPERATION OF A NULL LAYER
84 * The null layer is the minimum file system layer,
85 * simply bypassing all possible operations to the lower layer
86 * for processing there. The majority of its activity used to center
87 * on a so-called bypass routine, through which nullfs vnodes
88 * passed on operation to their underlying peer.
90 * However, with the current implementation nullfs doesn't have any private
91 * vnodes, it rather relies on DragonFly's namecache API. That gives a much
92 * more lightweight null layer, as namecache structures are pure data, with
93 * no private operations, so there is no need of subtle dispatching routines.
95 * Unlike the old code, this implementation is not a general skeleton overlay
96 * filesystem: to get more comprehensive overlaying, we will need vnode
97 * operation dispatch. Other overlay filesystems, like unionfs might be
98 * able to get on with a hybrid solution: overlay some vnodes, and rely
99 * on namecache API for the rest.
102 #include <sys/param.h>
103 #include <sys/systm.h>
104 #include <sys/kernel.h>
105 #include <sys/sysctl.h>
106 #include <sys/vnode.h>
107 #include <sys/mount.h>
108 #include <sys/proc.h>
109 #include <sys/namei.h>
110 #include <sys/malloc.h>
114 static int null_nresolve(struct vop_nresolve_args
*ap
);
115 static int null_ncreate(struct vop_ncreate_args
*ap
);
116 static int null_nmkdir(struct vop_nmkdir_args
*ap
);
117 static int null_nmknod(struct vop_nmknod_args
*ap
);
118 static int null_nlink(struct vop_nlink_args
*ap
);
119 static int null_nsymlink(struct vop_nsymlink_args
*ap
);
120 static int null_nwhiteout(struct vop_nwhiteout_args
*ap
);
121 static int null_nremove(struct vop_nremove_args
*ap
);
122 static int null_nrmdir(struct vop_nrmdir_args
*ap
);
123 static int null_nrename(struct vop_nrename_args
*ap
);
126 null_nresolve(struct vop_nresolve_args
*ap
)
128 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
130 return vop_nresolve_ap(ap
);
134 null_ncreate(struct vop_ncreate_args
*ap
)
136 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
138 return vop_ncreate_ap(ap
);
142 null_nmkdir(struct vop_nmkdir_args
*ap
)
144 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
146 return vop_nmkdir_ap(ap
);
150 null_nmknod(struct vop_nmknod_args
*ap
)
152 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
154 return vop_nmknod_ap(ap
);
158 null_nlink(struct vop_nlink_args
*ap
)
160 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
162 return vop_nlink_ap(ap
);
166 null_nsymlink(struct vop_nsymlink_args
*ap
)
168 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
170 return vop_nsymlink_ap(ap
);
174 null_nwhiteout(struct vop_nwhiteout_args
*ap
)
176 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
178 return vop_nwhiteout_ap(ap
);
182 null_nremove(struct vop_nremove_args
*ap
)
184 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
186 return vop_nremove_ap(ap
);
190 null_nrmdir(struct vop_nrmdir_args
*ap
)
192 ap
->a_head
.a_ops
= MOUNTTONULLMOUNT(ap
->a_nch
->mount
)->nullm_vfs
->mnt_vn_norm_ops
;
194 return vop_nrmdir_ap(ap
);
198 null_nrename(struct vop_nrename_args
*ap
)
202 lmp
= MOUNTTONULLMOUNT(ap
->a_fnch
->mount
)->nullm_vfs
;
203 if (lmp
!= MOUNTTONULLMOUNT(ap
->a_tnch
->mount
)->nullm_vfs
)
206 ap
->a_head
.a_ops
= lmp
->mnt_vn_norm_ops
;
208 return vop_nrename_ap(ap
);
212 * Global vfs data structures
214 struct vop_ops null_vnode_vops
= {
215 .vop_nresolve
= null_nresolve
,
216 .vop_ncreate
= null_ncreate
,
217 .vop_nmkdir
= null_nmkdir
,
218 .vop_nmknod
= null_nmknod
,
219 .vop_nlink
= null_nlink
,
220 .vop_nsymlink
= null_nsymlink
,
221 .vop_nwhiteout
= null_nwhiteout
,
222 .vop_nremove
= null_nremove
,
223 .vop_nrmdir
= null_nrmdir
,
224 .vop_nrename
= null_nrename