252 lines
11 KiB
C
252 lines
11 KiB
C
/* $NetBSD: null_vnops.c,v 1.20 2001/06/09 11:02:08 wiz Exp $ */
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/*
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* Copyright (c) 1999 National Aeronautics & Space Administration
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* All rights reserved.
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*
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* This software was written by William Studenmund of the
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* Numerical Aerospace Simulation Facility, NASA Ames Research Center.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the National Aeronautics & Space Administration
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* nor the names of its contributors may be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NATIONAL AERONAUTICS & SPACE ADMINISTRATION
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE ADMINISTRATION OR CONTRIB-
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* UTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
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* OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* Copyright (c) 1992, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* John Heidemann of the UCLA Ficus project.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)null_vnops.c 8.6 (Berkeley) 5/27/95
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*
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* Ancestors:
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* @(#)lofs_vnops.c 1.2 (Berkeley) 6/18/92
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* $Id: null_vnops.c,v 1.20 2001/06/09 11:02:08 wiz Exp $
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* ...and...
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* @(#)null_vnodeops.c 1.20 92/07/07 UCLA Ficus project
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*/
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/*
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* Null Layer
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*
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* (See mount_null(8) for more information.)
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*
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* The null layer duplicates a portion of the file system
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* name space under a new name. In this respect, it is
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* similar to the loopback file system. It differs from
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* the loopback fs in two respects: it is implemented using
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* a stackable layers technique, and its "null-nodes" stack above
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* all lower-layer vnodes, not just over directory vnodes.
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*
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* The null layer has two purposes. First, it serves as a demonstration
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* of layering by providing a layer which does nothing (it actually
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* does everything the loopback file system does, which is slightly
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* more than nothing). Second, the null layer can serve as a prototype
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* layer. Since it provides all necessary layer framework,
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* new file system layers can be created very easily by starting
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* with a null layer.
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*
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* The remainder of this comment examines the null layer as a basis
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* for constructing new layers.
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*
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*
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* INSTANTIATING NEW NULL LAYERS
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*
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* New null layers are created with mount_null(8).
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* mount_null(8) takes two arguments, the pathname
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* of the lower vfs (target-pn) and the pathname where the null
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* layer will appear in the namespace (alias-pn). After
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* the null layer is put into place, the contents
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* of target-pn subtree will be aliased under alias-pn.
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*
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*
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* OPERATION OF A NULL LAYER
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*
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* The null layer is the minimum file system layer,
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* simply bypassing all possible operations to the lower layer
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* for processing there. The majority of its activity centers
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* on the bypass routine, through which nearly all vnode operations
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* pass.
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*
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* The bypass routine accepts arbitrary vnode operations for
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* handling by the lower layer. It begins by examining vnode
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* operation arguments and replacing any null-nodes by their
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* lower-layer equivalents. It then invokes the operation
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* on the lower layer. Finally, it replaces the null-nodes
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* in the arguments and, if a vnode is returned by the operation,
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* stacks a null-node on top of the returned vnode.
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*
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* Although bypass handles most operations, vop_getattr, vop_lock,
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* vop_unlock, vop_inactive, vop_reclaim, and vop_print are not
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* bypassed. vop_getattr must change the fsid being returned.
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* vop_lock and vop_unlock must handle any locking for the
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* current vnode as well as pass the lock request down.
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* vop_inactive and vop_reclaim are not bypassed so that
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* they can handle freeing null-layer specific data. vop_print
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* is not bypassed to avoid excessive debugging information.
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* Also, certain vnode operations change the locking state within
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* the operation (create, mknod, remove, link, rename, mkdir, rmdir,
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* and symlink). Ideally these operations should not change the
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* lock state, but should be changed to let the caller of the
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* function unlock them. Otherwise all intermediate vnode layers
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* (such as union, umapfs, etc) must catch these functions to do
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* the necessary locking at their layer.
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*
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*
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* INSTANTIATING VNODE STACKS
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*
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* Mounting associates the null layer with a lower layer,
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* in effect stacking two VFSes. Vnode stacks are instead
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* created on demand as files are accessed.
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*
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* The initial mount creates a single vnode stack for the
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* root of the new null layer. All other vnode stacks
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* are created as a result of vnode operations on
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* this or other null vnode stacks.
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*
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* New vnode stacks come into existence as a result of
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* an operation which returns a vnode.
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* The bypass routine stacks a null-node above the new
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* vnode before returning it to the caller.
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*
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* For example, imagine mounting a null layer with
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* "mount_null /usr/include /dev/layer/null".
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* Changing directory to /dev/layer/null will assign
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* the root null-node (which was created when the null layer was mounted).
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* Now consider opening "sys". A vop_lookup would be
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* done on the root null-node. This operation would bypass through
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* to the lower layer which would return a vnode representing
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* the UFS "sys". null_bypass then builds a null-node
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* aliasing the UFS "sys" and returns this to the caller.
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* Later operations on the null-node "sys" will repeat this
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* process when constructing other vnode stacks.
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*
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*
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* CREATING OTHER FILE SYSTEM LAYERS
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*
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* One of the easiest ways to construct new file system layers is to make
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* a copy of the null layer, rename all files and variables, and
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* then begin modifying the copy. sed(1) can be used to easily rename
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* all variables.
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*
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* The umap layer is an example of a layer descended from the
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* null layer.
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*
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*
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* INVOKING OPERATIONS ON LOWER LAYERS
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*
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* There are two techniques to invoke operations on a lower layer
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* when the operation cannot be completely bypassed. Each method
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* is appropriate in different situations. In both cases,
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* it is the responsibility of the aliasing layer to make
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* the operation arguments "correct" for the lower layer
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* by mapping any vnode arguments to the lower layer.
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*
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* The first approach is to call the aliasing layer's bypass routine.
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* This method is most suitable when you wish to invoke the operation
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* currently being hanldled on the lower layer. It has the advantage
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* that the bypass routine already must do argument mapping.
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* An example of this is null_getattrs in the null layer.
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*
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* A second approach is to directly invoke vnode operations on
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* the lower layer with the VOP_OPERATIONNAME interface.
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* The advantage of this method is that it is easy to invoke
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* arbitrary operations on the lower layer. The disadvantage
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* is that vnode arguments must be manually mapped.
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*
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*/
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/proc.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#include <sys/vnode.h>
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#include <sys/mount.h>
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#include <sys/namei.h>
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#include <sys/malloc.h>
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#include <sys/buf.h>
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#include <miscfs/genfs/genfs.h>
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#include <miscfs/nullfs/null.h>
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#include <miscfs/genfs/layer_extern.h>
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/*
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* Global vfs data structures
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*/
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int (**null_vnodeop_p) __P((void *));
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const struct vnodeopv_entry_desc null_vnodeop_entries[] = {
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{ &vop_default_desc, layer_bypass },
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{ &vop_lookup_desc, layer_lookup },
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{ &vop_setattr_desc, layer_setattr },
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{ &vop_getattr_desc, layer_getattr },
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{ &vop_access_desc, layer_access },
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{ &vop_lock_desc, layer_lock },
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{ &vop_unlock_desc, layer_unlock },
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{ &vop_islocked_desc, layer_islocked },
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{ &vop_fsync_desc, layer_fsync },
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{ &vop_inactive_desc, layer_inactive },
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{ &vop_reclaim_desc, layer_reclaim },
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{ &vop_print_desc, layer_print },
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{ &vop_open_desc, layer_open }, /* mount option handling */
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{ &vop_strategy_desc, layer_strategy },
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{ &vop_bwrite_desc, layer_bwrite },
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{ &vop_bmap_desc, layer_bmap },
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{ (struct vnodeop_desc*)NULL, (int(*)__P((void *)))NULL }
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};
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const struct vnodeopv_desc null_vnodeop_opv_desc =
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{ &null_vnodeop_p, null_vnodeop_entries };
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