FreeBSD/Linux Kernel Cross Reference
sys/miscfs/nullfs/null_vnops.c

     /*      $NetBSD: null_vnops.c,v 1.32 2005/02/26 22:59:00 perry Exp $    */
     
     /*
      * Copyright (c) 1999 National Aeronautics & Space Administration
      * All rights reserved.
      *
      * This software was written by William Studenmund of the
      * Numerical Aerospace Simulation Facility, NASA Ames Research Center.
      *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the National Aeronautics & Space Administration
     *    nor the names of its contributors may be used to endorse or promote
     *    products derived from this software without specific prior written
     *    permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE NATIONAL AERONAUTICS & SPACE ADMINISTRATION
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE ADMINISTRATION OR CONTRIB-
     * UTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
     * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     * POSSIBILITY OF SUCH DAMAGE.
     */
    /*
     * Copyright (c) 1992, 1993
     *      The Regents of the University of California.  All rights reserved.
     *
     * This code is derived from software contributed to Berkeley by
     * John Heidemann of the UCLA Ficus project.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)null_vnops.c        8.6 (Berkeley) 5/27/95
     *
     * Ancestors:
     *      @(#)lofs_vnops.c        1.2 (Berkeley) 6/18/92
     *      Id: lofs_vnops.c,v 1.11 1992/05/30 10:05:43 jsp Exp jsp
     *      ...and...
     *      @(#)null_vnodeops.c 1.20 92/07/07 UCLA Ficus project
     */
    
    /*
     * Null Layer
     *
     * (See mount_null(8) for more information.)
     *
     * The null layer duplicates a portion of the file system
     * name space under a new name.  In this respect, it is
     * similar to the loopback file system.  It differs from
     * the loopback fs in two respects:  it is implemented using
     * a stackable layers technique, and its "null-nodes" stack above
     * all lower-layer vnodes, not just over directory vnodes.
     *
     * The null layer has two purposes.  First, it serves as a demonstration
     * of layering by providing a layer which does nothing (it actually
     * does everything the loopback file system does, which is slightly
     * more than nothing).  Second, the null layer can serve as a prototype
     * layer.  Since it provides all necessary layer framework,
     * new file system layers can be created very easily by starting
     * with a null layer.
     *
     * The remainder of this comment examines the null layer as a basis
     * for constructing new layers.
     *
     *
     * INSTANTIATING NEW NULL LAYERS
    *
    * New null layers are created with mount_null(8).
    * mount_null(8) takes two arguments, the pathname
    * of the lower vfs (target-pn) and the pathname where the null
    * layer will appear in the namespace (alias-pn).  After
    * the null layer is put into place, the contents
    * of target-pn subtree will be aliased under alias-pn.
    *
    *
    * OPERATION OF A NULL LAYER
    *
    * The null layer is the minimum file system layer,
    * simply bypassing all possible operations to the lower layer
    * for processing there.  The majority of its activity centers
    * on the bypass routine, through which nearly all vnode operations
    * pass.
    *
    * The bypass routine accepts arbitrary vnode operations for
    * handling by the lower layer.  It begins by examining vnode
    * operation arguments and replacing any null-nodes by their
    * lower-layer equivalents.  It then invokes the operation
    * on the lower layer.  Finally, it replaces the null-nodes
    * in the arguments and, if a vnode is returned by the operation,
    * stacks a null-node on top of the returned vnode.
    *
    * Although bypass handles most operations, vop_getattr, vop_lock,
    * vop_unlock, vop_inactive, vop_reclaim, and vop_print are not
    * bypassed. vop_getattr must change the fsid being returned.
    * vop_lock and vop_unlock must handle any locking for the
    * current vnode as well as pass the lock request down.
    * vop_inactive and vop_reclaim are not bypassed so that
    * they can handle freeing null-layer specific data. vop_print
    * is not bypassed to avoid excessive debugging information.
    * Also, certain vnode operations change the locking state within
    * the operation (create, mknod, remove, link, rename, mkdir, rmdir,
    * and symlink). Ideally these operations should not change the
    * lock state, but should be changed to let the caller of the
    * function unlock them. Otherwise all intermediate vnode layers
    * (such as union, umapfs, etc) must catch these functions to do
    * the necessary locking at their layer.
    *
    *
    * INSTANTIATING VNODE STACKS
    *
    * Mounting associates the null layer with a lower layer,
    * in effect stacking two VFSes.  Vnode stacks are instead
    * created on demand as files are accessed.
    *
    * The initial mount creates a single vnode stack for the
    * root of the new null layer.  All other vnode stacks
    * are created as a result of vnode operations on
    * this or other null vnode stacks.
    *
    * New vnode stacks come into existence as a result of
    * an operation which returns a vnode.
    * The bypass routine stacks a null-node above the new
    * vnode before returning it to the caller.
    *
    * For example, imagine mounting a null layer with
    * "mount_null /usr/include /dev/layer/null".
    * Changing directory to /dev/layer/null will assign
    * the root null-node (which was created when the null layer was mounted).
    * Now consider opening "sys".  A vop_lookup would be
    * done on the root null-node.  This operation would bypass through
    * to the lower layer which would return a vnode representing
    * the UFS "sys".  null_bypass then builds a null-node
    * aliasing the UFS "sys" and returns this to the caller.
    * Later operations on the null-node "sys" will repeat this
    * process when constructing other vnode stacks.
    *
    *
    * CREATING OTHER FILE SYSTEM LAYERS
    *
    * One of the easiest ways to construct new file system layers is to make
    * a copy of the null layer, rename all files and variables, and
    * then begin modifying the copy.  sed(1) can be used to easily rename
    * all variables.
    *
    * The umap layer is an example of a layer descended from the
    * null layer.
    *
    *
    * INVOKING OPERATIONS ON LOWER LAYERS
    *
    * There are two techniques to invoke operations on a lower layer
    * when the operation cannot be completely bypassed.  Each method
    * is appropriate in different situations.  In both cases,
    * it is the responsibility of the aliasing layer to make
    * the operation arguments "correct" for the lower layer
    * by mapping any vnode arguments to the lower layer.
    *
    * The first approach is to call the aliasing layer's bypass routine.
    * This method is most suitable when you wish to invoke the operation
    * currently being handled on the lower layer.  It has the advantage
    * that the bypass routine already must do argument mapping.
    * An example of this is null_getattrs in the null layer.
    *
    * A second approach is to directly invoke vnode operations on
    * the lower layer with the VOP_OPERATIONNAME interface.
    * The advantage of this method is that it is easy to invoke
    * arbitrary operations on the lower layer.  The disadvantage
    * is that vnode arguments must be manually mapped.
    *
    */
   
   #include <sys/cdefs.h>
   __KERNEL_RCSID(0, "$NetBSD: null_vnops.c,v 1.32 2005/02/26 22:59:00 perry Exp $");
   
   #include <sys/param.h>
   #include <sys/systm.h>
   #include <sys/proc.h>
   #include <sys/time.h>
   #include <sys/vnode.h>
   #include <sys/mount.h>
   #include <sys/namei.h>
   #include <sys/malloc.h>
   #include <sys/buf.h>
   #include <miscfs/genfs/genfs.h>
   #include <miscfs/nullfs/null.h>
   #include <miscfs/genfs/layer_extern.h>
   
   /*
    * Global vfs data structures
    */
   int (**null_vnodeop_p) __P((void *));
   const struct vnodeopv_entry_desc null_vnodeop_entries[] = {
           { &vop_default_desc,  layer_bypass },
   
           { &vop_lookup_desc,   layer_lookup },
           { &vop_setattr_desc,  layer_setattr },
           { &vop_getattr_desc,  layer_getattr },
           { &vop_access_desc,   layer_access },
           { &vop_lock_desc,     layer_lock },
           { &vop_unlock_desc,   layer_unlock },
           { &vop_islocked_desc, layer_islocked },
           { &vop_fsync_desc,    layer_fsync },
           { &vop_inactive_desc, layer_inactive },
           { &vop_reclaim_desc,  layer_reclaim },
           { &vop_print_desc,    layer_print },
           { &vop_remove_desc,   layer_remove },
           { &vop_rename_desc,   layer_rename },
           { &vop_rmdir_desc,    layer_rmdir },
   
           { &vop_open_desc,     layer_open },     /* mount option handling */
   
           { &vop_bwrite_desc,   layer_bwrite },
           { &vop_bmap_desc,     layer_bmap },
           { &vop_getpages_desc, layer_getpages },
           { &vop_putpages_desc, layer_putpages },
   
           { NULL, NULL }
   };
   const struct vnodeopv_desc null_vnodeop_opv_desc =
           { &null_vnodeop_p, null_vnodeop_entries };

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