sys/miscfs/nullfs/null_vnops.c

   1 /*      $NetBSD: null_vnops.c,v 1.26.6.5 2005/11/10 14:10:31 skrll 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 1.26.6.5 2005/11/10 14:10:31 skrll 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 };