/* * 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. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by the University of * California, Berkeley and its contributors. * 4. 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 8.1 (Berkeley) 6/10/93 * * $Id: null_vnops.c,v 1.2 1994/08/02 07:45:06 davidg Exp $ */ /* * 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 techniques, and it's "null-node"s 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 proving 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 be starting * with a null layer. * * The remainder of this man page 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, though which nearly all vnode operations * pass. * * The bypass routine accepts arbitrary vnode operations for * handling by the lower layer. It begins by examing vnode * operation arguments and replacing any null-nodes by their * lower-layer equivlants. It then invokes the operation * on the lower layer. Finally, it replaces the null-nodes * in the arguments and, if a vnode is return by the operation, * stacks a null-node on top of the returned vnode. * * Although bypass handles most operations, * vop_getattr, _inactive, _reclaim, and _print are not bypassed. * Vop_getattr must change the fsid being returned. * 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. * * * INSTANTIATING VNODE STACKS * * Mounting associates the null layer with a lower layer, * 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 existance 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 modifing the copy. Sed 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 an 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 hanldled 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 invoked 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 vnodes arguments must be manualy mapped. * */ #include #include #include #include #include #include #include #include #include #include #include int null_bug_bypass = 0; /* for debugging: enables bypass printf'ing */ /* * This is the 10-Apr-92 bypass routine. * This version has been optimized for speed, throwing away some * safety checks. It should still always work, but it's not as * robust to programmer errors. * Define SAFETY to include some error checking code. * * In general, we map all vnodes going down and unmap them on the way back. * As an exception to this, vnodes can be marked "unmapped" by setting * the Nth bit in operation's vdesc_flags. * * Also, some BSD vnode operations have the side effect of vrele'ing * their arguments. With stacking, the reference counts are held * by the upper node, not the lower one, so we must handle these * side-effects here. This is not of concern in Sun-derived systems * since there are no such side-effects. * * This makes the following assumptions: * - only one returned vpp * - no INOUT vpp's (Sun's vop_open has one of these) * - the vnode operation vector of the first vnode should be used * to determine what implementation of the op should be invoked * - all mapped vnodes are of our vnode-type (NEEDSWORK: * problems on rmdir'ing mount points and renaming?) */ int null_bypass(ap) struct vop_generic_args /* { struct vnodeop_desc *a_desc; } */ *ap; { register struct vnode **this_vp_p; int error; struct vnode *old_vps[VDESC_MAX_VPS]; struct vnode **vps_p[VDESC_MAX_VPS]; struct vnode ***vppp; struct vnodeop_desc *descp = ap->a_desc; int reles, i; if (null_bug_bypass) printf ("null_bypass: %s\n", descp->vdesc_name); #ifdef SAFETY /* * We require at least one vp. */ if (descp->vdesc_vp_offsets == NULL || descp->vdesc_vp_offsets[0] == VDESC_NO_OFFSET) panic ("null_bypass: no vp's in map.\n"); #endif /* * Map the vnodes going in. * Later, we'll invoke the operation based on * the first mapped vnode's operation vector. */ reles = descp->vdesc_flags; for (i = 0; i < VDESC_MAX_VPS; reles >>= 1, i++) { if (descp->vdesc_vp_offsets[i] == VDESC_NO_OFFSET) break; /* bail out at end of list */ vps_p[i] = this_vp_p = VOPARG_OFFSETTO(struct vnode**,descp->vdesc_vp_offsets[i],ap); /* * We're not guaranteed that any but the first vnode * are of our type. Check for and don't map any * that aren't. (We must always map first vp or vclean fails.) */ if (i && (*this_vp_p)->v_op != null_vnodeop_p) { old_vps[i] = NULL; } else { old_vps[i] = *this_vp_p; *(vps_p[i]) = NULLVPTOLOWERVP(*this_vp_p); /* * XXX - Several operations have the side effect * of vrele'ing their vp's. We must account for * that. (This should go away in the future.) */ if (reles & 1) VREF(*this_vp_p); } } /* * Call the operation on the lower layer * with the modified argument structure. */ error = VCALL(*(vps_p[0]), descp->vdesc_offset, ap); /* * Maintain the illusion of call-by-value * by restoring vnodes in the argument structure * to their original value. */ reles = descp->vdesc_flags; for (i = 0; i < VDESC_MAX_VPS; reles >>= 1, i++) { if (descp->vdesc_vp_offsets[i] == VDESC_NO_OFFSET) break; /* bail out at end of list */ if (old_vps[i]) { *(vps_p[i]) = old_vps[i]; if (reles & 1) vrele(*(vps_p[i])); } } /* * Map the possible out-going vpp * (Assumes that the lower layer always returns * a VREF'ed vpp unless it gets an error.) */ if (descp->vdesc_vpp_offset != VDESC_NO_OFFSET && !(descp->vdesc_flags & VDESC_NOMAP_VPP) && !error) { /* * XXX - even though some ops have vpp returned vp's, * several ops actually vrele this before returning. * We must avoid these ops. * (This should go away when these ops are regularized.) */ if (descp->vdesc_flags & VDESC_VPP_WILLRELE) goto out; vppp = VOPARG_OFFSETTO(struct vnode***, descp->vdesc_vpp_offset,ap); error = null_node_create(old_vps[0]->v_mount, **vppp, *vppp); } out: return (error); } /* * We handle getattr only to change the fsid. */ int null_getattr(ap) struct vop_getattr_args /* { struct vnode *a_vp; struct vattr *a_vap; struct ucred *a_cred; struct proc *a_p; } */ *ap; { int error; if (error = null_bypass(ap)) return (error); /* Requires that arguments be restored. */ ap->a_vap->va_fsid = ap->a_vp->v_mount->mnt_stat.f_fsid.val[0]; return (0); } int null_inactive(ap) struct vop_inactive_args /* { struct vnode *a_vp; } */ *ap; { /* * Do nothing (and _don't_ bypass). * Wait to vrele lowervp until reclaim, * so that until then our null_node is in the * cache and reusable. * * NEEDSWORK: Someday, consider inactive'ing * the lowervp and then trying to reactivate it * with capabilities (v_id) * like they do in the name lookup cache code. * That's too much work for now. */ return (0); } int null_reclaim(ap) struct vop_reclaim_args /* { struct vnode *a_vp; } */ *ap; { struct vnode *vp = ap->a_vp; struct null_node *xp = VTONULL(vp); struct vnode *lowervp = xp->null_lowervp; /* * Note: in vop_reclaim, vp->v_op == dead_vnodeop_p, * so we can't call VOPs on ourself. */ /* After this assignment, this node will not be re-used. */ xp->null_lowervp = NULL; remque(xp); FREE(vp->v_data, M_TEMP); vp->v_data = NULL; vrele (lowervp); return (0); } int null_print(ap) struct vop_print_args /* { struct vnode *a_vp; } */ *ap; { register struct vnode *vp = ap->a_vp; printf ("\ttag VT_NULLFS, vp=%x, lowervp=%x\n", vp, NULLVPTOLOWERVP(vp)); return (0); } /* * XXX - vop_strategy must be hand coded because it has no * vnode in its arguments. * This goes away with a merged VM/buffer cache. */ int null_strategy(ap) struct vop_strategy_args /* { struct buf *a_bp; } */ *ap; { struct buf *bp = ap->a_bp; int error; struct vnode *savedvp; savedvp = bp->b_vp; bp->b_vp = NULLVPTOLOWERVP(bp->b_vp); error = VOP_STRATEGY(bp); bp->b_vp = savedvp; return (error); } /* * XXX - like vop_strategy, vop_bwrite must be hand coded because it has no * vnode in its arguments. * This goes away with a merged VM/buffer cache. */ int null_bwrite(ap) struct vop_bwrite_args /* { struct buf *a_bp; } */ *ap; { struct buf *bp = ap->a_bp; int error; struct vnode *savedvp; savedvp = bp->b_vp; bp->b_vp = NULLVPTOLOWERVP(bp->b_vp); error = VOP_BWRITE(bp); bp->b_vp = savedvp; return (error); } /* * Global vfs data structures */ int (**null_vnodeop_p)(); struct vnodeopv_entry_desc null_vnodeop_entries[] = { { &vop_default_desc, null_bypass }, { &vop_getattr_desc, null_getattr }, { &vop_inactive_desc, null_inactive }, { &vop_reclaim_desc, null_reclaim }, { &vop_print_desc, null_print }, { &vop_strategy_desc, null_strategy }, { &vop_bwrite_desc, null_bwrite }, { (struct vnodeop_desc*)NULL, (int(*)())NULL } }; struct vnodeopv_desc null_vnodeop_opv_desc = { &null_vnodeop_p, null_vnodeop_entries };