1 /* $NetBSD: null_vnops.c,v 1.17 2000/03/13 23:52:41 soren Exp $ */ 2 3 /* 4 * Copyright (c) 1999 National Aeronautics & Space Administration 5 * All rights reserved. 6 * 7 * This software was written by William Studenmund of the 8 * Numerical Aerospace Similation Facility, NASA Ames Research Center. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. Neither the name of the National Aeronautics & Space Administration 19 * nor the names of its contributors may be used to endorse or promote 20 * products derived from this software without specific prior written 21 * permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE NATIONAL AERONAUTICS & SPACE ADMINISTRATION 24 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 25 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 26 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE ADMINISTRATION OR CONTRIB- 27 * UTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, 28 * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 29 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 30 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 31 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 32 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 33 * POSSIBILITY OF SUCH DAMAGE. 34 */ 35 /* 36 * Copyright (c) 1992, 1993 37 * The Regents of the University of California. All rights reserved. 38 * 39 * This code is derived from software contributed to Berkeley by 40 * John Heidemann of the UCLA Ficus project. 41 * 42 * Redistribution and use in source and binary forms, with or without 43 * modification, are permitted provided that the following conditions 44 * are met: 45 * 1. Redistributions of source code must retain the above copyright 46 * notice, this list of conditions and the following disclaimer. 47 * 2. Redistributions in binary form must reproduce the above copyright 48 * notice, this list of conditions and the following disclaimer in the 49 * documentation and/or other materials provided with the distribution. 50 * 3. All advertising materials mentioning features or use of this software 51 * must display the following acknowledgement: 52 * This product includes software developed by the University of 53 * California, Berkeley and its contributors. 54 * 4. Neither the name of the University nor the names of its contributors 55 * may be used to endorse or promote products derived from this software 56 * without specific prior written permission. 57 * 58 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 59 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 60 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 61 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 62 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 63 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 64 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 65 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 66 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 67 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 68 * SUCH DAMAGE. 69 * 70 * @(#)null_vnops.c 8.6 (Berkeley) 5/27/95 71 * 72 * Ancestors: 73 * @(#)lofs_vnops.c 1.2 (Berkeley) 6/18/92 74 * $Id: null_vnops.c,v 1.17 2000/03/13 23:52:41 soren Exp $ 75 * ...and... 76 * @(#)null_vnodeops.c 1.20 92/07/07 UCLA Ficus project 77 */ 78 79 /* 80 * Null Layer 81 * 82 * (See mount_null(8) for more information.) 83 * 84 * The null layer duplicates a portion of the file system 85 * name space under a new name. In this respect, it is 86 * similar to the loopback file system. It differs from 87 * the loopback fs in two respects: it is implemented using 88 * a stackable layers techniques, and it's "null-node"s stack above 89 * all lower-layer vnodes, not just over directory vnodes. 90 * 91 * The null layer has two purposes. First, it serves as a demonstration 92 * of layering by proving a layer which does nothing. (It actually 93 * does everything the loopback file system does, which is slightly 94 * more than nothing.) Second, the null layer can serve as a prototype 95 * layer. Since it provides all necessary layer framework, 96 * new file system layers can be created very easily be starting 97 * with a null layer. 98 * 99 * The remainder of this man page examines the null layer as a basis 100 * for constructing new layers. 101 * 102 * 103 * INSTANTIATING NEW NULL LAYERS 104 * 105 * New null layers are created with mount_null(8). 106 * Mount_null(8) takes two arguments, the pathname 107 * of the lower vfs (target-pn) and the pathname where the null 108 * layer will appear in the namespace (alias-pn). After 109 * the null layer is put into place, the contents 110 * of target-pn subtree will be aliased under alias-pn. 111 * 112 * 113 * OPERATION OF A NULL LAYER 114 * 115 * The null layer is the minimum file system layer, 116 * simply bypassing all possible operations to the lower layer 117 * for processing there. The majority of its activity centers 118 * on the bypass routine, though which nearly all vnode operations 119 * pass. 120 * 121 * The bypass routine accepts arbitrary vnode operations for 122 * handling by the lower layer. It begins by examing vnode 123 * operation arguments and replacing any null-nodes by their 124 * lower-layer equivlants. It then invokes the operation 125 * on the lower layer. Finally, it replaces the null-nodes 126 * in the arguments and, if a vnode is return by the operation, 127 * stacks a null-node on top of the returned vnode. 128 * 129 * Although bypass handles most operations, vop_getattr, vop_lock, 130 * vop_unlock, vop_inactive, vop_reclaim, and vop_print are not 131 * bypassed. Vop_getattr must change the fsid being returned. 132 * Vop_lock and vop_unlock must handle any locking for the 133 * current vnode as well as pass the lock request down. 134 * Vop_inactive and vop_reclaim are not bypassed so that 135 * they can handle freeing null-layer specific data. Vop_print 136 * is not bypassed to avoid excessive debugging information. 137 * Also, certain vnode operations change the locking state within 138 * the operation (create, mknod, remove, link, rename, mkdir, rmdir, 139 * and symlink). Ideally these operations should not change the 140 * lock state, but should be changed to let the caller of the 141 * function unlock them. Otherwise all intermediate vnode layers 142 * (such as union, umapfs, etc) must catch these functions to do 143 * the necessary locking at their layer. 144 * 145 * 146 * INSTANTIATING VNODE STACKS 147 * 148 * Mounting associates the null layer with a lower layer, 149 * effect stacking two VFSes. Vnode stacks are instead 150 * created on demand as files are accessed. 151 * 152 * The initial mount creates a single vnode stack for the 153 * root of the new null layer. All other vnode stacks 154 * are created as a result of vnode operations on 155 * this or other null vnode stacks. 156 * 157 * New vnode stacks come into existance as a result of 158 * an operation which returns a vnode. 159 * The bypass routine stacks a null-node above the new 160 * vnode before returning it to the caller. 161 * 162 * For example, imagine mounting a null layer with 163 * "mount_null /usr/include /dev/layer/null". 164 * Changing directory to /dev/layer/null will assign 165 * the root null-node (which was created when the null layer was mounted). 166 * Now consider opening "sys". A vop_lookup would be 167 * done on the root null-node. This operation would bypass through 168 * to the lower layer which would return a vnode representing 169 * the UFS "sys". Null_bypass then builds a null-node 170 * aliasing the UFS "sys" and returns this to the caller. 171 * Later operations on the null-node "sys" will repeat this 172 * process when constructing other vnode stacks. 173 * 174 * 175 * CREATING OTHER FILE SYSTEM LAYERS 176 * 177 * One of the easiest ways to construct new file system layers is to make 178 * a copy of the null layer, rename all files and variables, and 179 * then begin modifing the copy. Sed can be used to easily rename 180 * all variables. 181 * 182 * The umap layer is an example of a layer descended from the 183 * null layer. 184 * 185 * 186 * INVOKING OPERATIONS ON LOWER LAYERS 187 * 188 * There are two techniques to invoke operations on a lower layer 189 * when the operation cannot be completely bypassed. Each method 190 * is appropriate in different situations. In both cases, 191 * it is the responsibility of the aliasing layer to make 192 * the operation arguments "correct" for the lower layer 193 * by mapping an vnode arguments to the lower layer. 194 * 195 * The first approach is to call the aliasing layer's bypass routine. 196 * This method is most suitable when you wish to invoke the operation 197 * currently being hanldled on the lower layer. It has the advantage 198 * that the bypass routine already must do argument mapping. 199 * An example of this is null_getattrs in the null layer. 200 * 201 * A second approach is to directly invoked vnode operations on 202 * the lower layer with the VOP_OPERATIONNAME interface. 203 * The advantage of this method is that it is easy to invoke 204 * arbitrary operations on the lower layer. The disadvantage 205 * is that vnodes arguments must be manualy mapped. 206 * 207 */ 208 209 #include <sys/param.h> 210 #include <sys/systm.h> 211 #include <sys/proc.h> 212 #include <sys/time.h> 213 #include <sys/types.h> 214 #include <sys/vnode.h> 215 #include <sys/mount.h> 216 #include <sys/namei.h> 217 #include <sys/malloc.h> 218 #include <sys/buf.h> 219 #include <miscfs/genfs/genfs.h> 220 #include <miscfs/nullfs/null.h> 221 #include <miscfs/genfs/layer_extern.h> 222 223 /* 224 * Global vfs data structures 225 */ 226 int (**null_vnodeop_p) __P((void *)); 227 struct vnodeopv_entry_desc null_vnodeop_entries[] = { 228 { &vop_default_desc, layer_bypass }, 229 230 { &vop_lookup_desc, layer_lookup }, 231 { &vop_setattr_desc, layer_setattr }, 232 { &vop_getattr_desc, layer_getattr }, 233 { &vop_access_desc, layer_access }, 234 { &vop_lock_desc, layer_lock }, 235 { &vop_unlock_desc, layer_unlock }, 236 { &vop_islocked_desc, layer_islocked }, 237 { &vop_fsync_desc, layer_fsync }, 238 { &vop_inactive_desc, layer_inactive }, 239 { &vop_reclaim_desc, layer_reclaim }, 240 { &vop_print_desc, layer_print }, 241 242 { &vop_open_desc, layer_open }, /* mount option handling */ 243 244 { &vop_strategy_desc, layer_strategy }, 245 { &vop_bwrite_desc, layer_bwrite }, 246 { &vop_bmap_desc, layer_bmap }, 247 248 { (struct vnodeop_desc*)NULL, (int(*)__P((void *)))NULL } 249 }; 250 struct vnodeopv_desc null_vnodeop_opv_desc = 251 { &null_vnodeop_p, null_vnodeop_entries }; 252