1 /* $NetBSD: null_vnops.c,v 1.34 2005/12/11 12:24:51 christos 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 Simulation 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. Neither the name of the University nor the names of its contributors 51 * may be used to endorse or promote products derived from this software 52 * without specific prior written permission. 53 * 54 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 55 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 56 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 57 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 58 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 59 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 60 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 61 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 62 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 63 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 64 * SUCH DAMAGE. 65 * 66 * @(#)null_vnops.c 8.6 (Berkeley) 5/27/95 67 * 68 * Ancestors: 69 * @(#)lofs_vnops.c 1.2 (Berkeley) 6/18/92 70 * Id: lofs_vnops.c,v 1.11 1992/05/30 10:05:43 jsp Exp jsp 71 * ...and... 72 * @(#)null_vnodeops.c 1.20 92/07/07 UCLA Ficus project 73 */ 74 75 /* 76 * Null Layer 77 * 78 * (See mount_null(8) for more information.) 79 * 80 * The null layer duplicates a portion of the file system 81 * name space under a new name. In this respect, it is 82 * similar to the loopback file system. It differs from 83 * the loopback fs in two respects: it is implemented using 84 * a stackable layers technique, and its "null-nodes" stack above 85 * all lower-layer vnodes, not just over directory vnodes. 86 * 87 * The null layer has two purposes. First, it serves as a demonstration 88 * of layering by providing a layer which does nothing (it actually 89 * does everything the loopback file system does, which is slightly 90 * more than nothing). Second, the null layer can serve as a prototype 91 * layer. Since it provides all necessary layer framework, 92 * new file system layers can be created very easily by starting 93 * with a null layer. 94 * 95 * The remainder of this comment examines the null layer as a basis 96 * for constructing new layers. 97 * 98 * 99 * INSTANTIATING NEW NULL LAYERS 100 * 101 * New null layers are created with mount_null(8). 102 * mount_null(8) takes two arguments, the pathname 103 * of the lower vfs (target-pn) and the pathname where the null 104 * layer will appear in the namespace (alias-pn). After 105 * the null layer is put into place, the contents 106 * of target-pn subtree will be aliased under alias-pn. 107 * 108 * 109 * OPERATION OF A NULL LAYER 110 * 111 * The null layer is the minimum file system layer, 112 * simply bypassing all possible operations to the lower layer 113 * for processing there. The majority of its activity centers 114 * on the bypass routine, through which nearly all vnode operations 115 * pass. 116 * 117 * The bypass routine accepts arbitrary vnode operations for 118 * handling by the lower layer. It begins by examining vnode 119 * operation arguments and replacing any null-nodes by their 120 * lower-layer equivalents. It then invokes the operation 121 * on the lower layer. Finally, it replaces the null-nodes 122 * in the arguments and, if a vnode is returned by the operation, 123 * stacks a null-node on top of the returned vnode. 124 * 125 * Although bypass handles most operations, vop_getattr, vop_lock, 126 * vop_unlock, vop_inactive, vop_reclaim, and vop_print are not 127 * bypassed. vop_getattr must change the fsid being returned. 128 * vop_lock and vop_unlock must handle any locking for the 129 * current vnode as well as pass the lock request down. 130 * vop_inactive and vop_reclaim are not bypassed so that 131 * they can handle freeing null-layer specific data. vop_print 132 * is not bypassed to avoid excessive debugging information. 133 * Also, certain vnode operations change the locking state within 134 * the operation (create, mknod, remove, link, rename, mkdir, rmdir, 135 * and symlink). Ideally these operations should not change the 136 * lock state, but should be changed to let the caller of the 137 * function unlock them. Otherwise all intermediate vnode layers 138 * (such as union, umapfs, etc) must catch these functions to do 139 * the necessary locking at their layer. 140 * 141 * 142 * INSTANTIATING VNODE STACKS 143 * 144 * Mounting associates the null layer with a lower layer, 145 * in effect stacking two VFSes. Vnode stacks are instead 146 * created on demand as files are accessed. 147 * 148 * The initial mount creates a single vnode stack for the 149 * root of the new null layer. All other vnode stacks 150 * are created as a result of vnode operations on 151 * this or other null vnode stacks. 152 * 153 * New vnode stacks come into existence as a result of 154 * an operation which returns a vnode. 155 * The bypass routine stacks a null-node above the new 156 * vnode before returning it to the caller. 157 * 158 * For example, imagine mounting a null layer with 159 * "mount_null /usr/include /dev/layer/null". 160 * Changing directory to /dev/layer/null will assign 161 * the root null-node (which was created when the null layer was mounted). 162 * Now consider opening "sys". A vop_lookup would be 163 * done on the root null-node. This operation would bypass through 164 * to the lower layer which would return a vnode representing 165 * the UFS "sys". null_bypass then builds a null-node 166 * aliasing the UFS "sys" and returns this to the caller. 167 * Later operations on the null-node "sys" will repeat this 168 * process when constructing other vnode stacks. 169 * 170 * 171 * CREATING OTHER FILE SYSTEM LAYERS 172 * 173 * One of the easiest ways to construct new file system layers is to make 174 * a copy of the null layer, rename all files and variables, and 175 * then begin modifying the copy. sed(1) can be used to easily rename 176 * all variables. 177 * 178 * The umap layer is an example of a layer descended from the 179 * null layer. 180 * 181 * 182 * INVOKING OPERATIONS ON LOWER LAYERS 183 * 184 * There are two techniques to invoke operations on a lower layer 185 * when the operation cannot be completely bypassed. Each method 186 * is appropriate in different situations. In both cases, 187 * it is the responsibility of the aliasing layer to make 188 * the operation arguments "correct" for the lower layer 189 * by mapping any vnode arguments to the lower layer. 190 * 191 * The first approach is to call the aliasing layer's bypass routine. 192 * This method is most suitable when you wish to invoke the operation 193 * currently being handled on the lower layer. It has the advantage 194 * that the bypass routine already must do argument mapping. 195 * An example of this is null_getattrs in the null layer. 196 * 197 * A second approach is to directly invoke vnode operations on 198 * the lower layer with the VOP_OPERATIONNAME interface. 199 * The advantage of this method is that it is easy to invoke 200 * arbitrary operations on the lower layer. The disadvantage 201 * is that vnode arguments must be manually mapped. 202 * 203 */ 204 205 #include <sys/cdefs.h> 206 __KERNEL_RCSID(0, "$NetBSD: null_vnops.c,v 1.34 2005/12/11 12:24:51 christos Exp $"); 207 208 #include <sys/param.h> 209 #include <sys/systm.h> 210 #include <sys/proc.h> 211 #include <sys/time.h> 212 #include <sys/vnode.h> 213 #include <sys/mount.h> 214 #include <sys/namei.h> 215 #include <sys/malloc.h> 216 #include <sys/buf.h> 217 #include <miscfs/genfs/genfs.h> 218 #include <miscfs/nullfs/null.h> 219 #include <miscfs/genfs/layer_extern.h> 220 221 /* 222 * Global vfs data structures 223 */ 224 int (**null_vnodeop_p)(void *); 225 const struct vnodeopv_entry_desc null_vnodeop_entries[] = { 226 { &vop_default_desc, layer_bypass }, 227 228 { &vop_lookup_desc, layer_lookup }, 229 { &vop_setattr_desc, layer_setattr }, 230 { &vop_getattr_desc, layer_getattr }, 231 { &vop_access_desc, layer_access }, 232 { &vop_lock_desc, layer_lock }, 233 { &vop_unlock_desc, layer_unlock }, 234 { &vop_islocked_desc, layer_islocked }, 235 { &vop_fsync_desc, layer_fsync }, 236 { &vop_inactive_desc, layer_inactive }, 237 { &vop_reclaim_desc, layer_reclaim }, 238 { &vop_print_desc, layer_print }, 239 { &vop_remove_desc, layer_remove }, 240 { &vop_rename_desc, layer_rename }, 241 { &vop_rmdir_desc, layer_rmdir }, 242 243 { &vop_open_desc, layer_open }, /* mount option handling */ 244 245 { &vop_bwrite_desc, layer_bwrite }, 246 { &vop_bmap_desc, layer_bmap }, 247 { &vop_getpages_desc, layer_getpages }, 248 { &vop_putpages_desc, layer_putpages }, 249 250 { NULL, NULL } 251 }; 252 const struct vnodeopv_desc null_vnodeop_opv_desc = 253 { &null_vnodeop_p, null_vnodeop_entries }; 254