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Diffstat (limited to 'sys/fs/nullfs/null_vnops.c')
-rw-r--r-- | sys/fs/nullfs/null_vnops.c | 462 |
1 files changed, 462 insertions, 0 deletions
diff --git a/sys/fs/nullfs/null_vnops.c b/sys/fs/nullfs/null_vnops.c new file mode 100644 index 0000000..115ff6f --- /dev/null +++ b/sys/fs/nullfs/null_vnops.c @@ -0,0 +1,462 @@ +/* + * 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 + * + * 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 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 <sys/param.h> +#include <sys/systm.h> +#include <sys/proc.h> +#include <sys/time.h> +#include <sys/types.h> +#include <sys/vnode.h> +#include <sys/mount.h> +#include <sys/namei.h> +#include <sys/malloc.h> +#include <sys/buf.h> +#include <miscfs/nullfs/null.h> + + +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; + <other random data follows, presumably> + } */ *ap; +{ + extern int (**null_vnodeop_p)(); /* not extern, really "forward" */ + 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 }; |