/* $NetBSD: null_vnops.c,v 1.12 1997/10/06 09:32:33 thorpej Exp $ */ /* * 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 * ...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 #include #include #include #include #include #include #include #include #include #include int null_bug_bypass = 0; /* for debugging: enables bypass printf'ing */ int null_bypass __P((void *)); int null_getattr __P((void *)); int null_inactive __P((void *)); int null_reclaim __P((void *)); int null_print __P((void *)); int null_strategy __P((void *)); int null_bwrite __P((void *)); int null_lock __P((void *)); int null_unlock __P((void *)); int null_islocked __P((void *)); int null_lookup __P((void *)); /* * 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(v) void *v; { struct vop_generic_args /* { struct vnodeop_desc *a_desc; } */ *ap = v; 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 == NULLVP || (*this_vp_p)->v_op != null_vnodeop_p)) { old_vps[i] = NULLVP; } 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] != NULLVP) { *(vps_p[i]) = old_vps[i]; if (reles & 1) { /* they really vput them, so we must drop our locks (but mark underneath as unlocked first). Beware of vnode duplication--put it once, and rele the rest. Check this by looking at our upper flag. */ if (VTONULL(*(vps_p[i]))->null_flags & NULL_LOCKED) { VTONULL(*(vps_p[i]))->null_flags &= ~NULL_LLOCK; vput(*(vps_p[i])); } else 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); /* * This assumes that **vppp is a locked vnode (it is always * so as of this writing, NetBSD-current 1995/02/16) */ /* * (don't want to lock it if being called on behalf * of lookup--it plays weird locking games depending * on whether or not it's looking up ".", "..", etc. */ error = null_node_create(old_vps[0]->v_mount, **vppp, *vppp, descp == &vop_lookup_desc ? 0 : 1); } out: return (error); } /* * We handle getattr only to change the fsid. */ int null_getattr(v) void *v; { struct vop_getattr_args /* { struct vnode *a_vp; struct vattr *a_vap; struct ucred *a_cred; struct proc *a_p; } */ *ap = v; int error; if ((error = null_bypass(ap)) != 0) 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(v) void *v; { /* * 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(v) void *v; { struct vop_reclaim_args /* { struct vnode *a_vp; } */ *ap = v; 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; LIST_REMOVE(xp, null_hash); FREE(vp->v_data, M_TEMP); vp->v_data = NULL; vrele (lowervp); return (0); } int null_print(v) void *v; { struct vop_print_args /* { struct vnode *a_vp; } */ *ap = v; register struct vnode *vp = ap->a_vp; register struct null_node *nn = VTONULL(vp); printf ("\ttag VT_NULLFS, vp=%p, lowervp=%p\n", vp, NULLVPTOLOWERVP(vp)); #ifdef DIAGNOSTIC printf("%s%s owner pid %d retpc %p retret %p\n", (nn->null_flags & NULL_LOCKED) ? "(LOCKED) " : "", (nn->null_flags & NULL_LLOCK) ? "(LLOCK) " : "", nn->null_pid, nn->null_lockpc, nn->null_lockpc2); #else printf("%s%s\n", (nn->null_flags & NULL_LOCKED) ? "(LOCKED) " : "", (nn->null_flags & NULL_LLOCK) ? "(LLOCK) " : ""); #endif vprint("nullfs lowervp", 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(v) void *v; { struct vop_strategy_args /* { struct buf *a_bp; } */ *ap = v; 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(v) void *v; { struct vop_bwrite_args /* { struct buf *a_bp; } */ *ap = v; 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); } /* * We need a separate null lock routine, to avoid deadlocks at reclaim time. * If a process holds the lower-vnode locked when it tries to reclaim * the null upper-vnode, _and_ null_bypass is used as the locking operation, * then a process can end up locking against itself. * This has been observed when a null mount is set up to "tunnel" beneath a * union mount (that setup is useful if you still wish to be able to access * the non-union version of either the above or below union layer) */ int null_lock(v) void *v; { struct vop_lock_args *ap = v; struct vnode *vp = ap->a_vp; struct null_node *nn; #ifdef NULLFS_DIAGNOSTIC vprint("null_lock_e", ap->a_vp); printf("retpc=%p, retretpc=%p\n", RETURN_PC(0), RETURN_PC(1)); #endif start: while (vp->v_flag & VXLOCK) { vp->v_flag |= VXWANT; tsleep((caddr_t)vp, PINOD, "nulllock1", 0); } nn = VTONULL(vp); if ((nn->null_flags & NULL_LLOCK) == 0 && (vp->v_usecount != 0)) { /* * only lock underlying node if we haven't locked it yet * for null ops, and our refcount is nonzero. If usecount * is zero, we are probably being reclaimed so we need to * keep our hands off the lower node. */ VOP_LOCK(nn->null_lowervp); nn->null_flags |= NULL_LLOCK; } if (nn->null_flags & NULL_LOCKED) { #ifdef DIAGNOSTIC if (curproc && nn->null_pid == curproc->p_pid && nn->null_pid > -1 && curproc->p_pid > -1) { vprint("self-lock", vp); panic("null: locking against myself"); } #endif nn->null_flags |= NULL_WANTED; tsleep((caddr_t)nn, PINOD, "nulllock2", 0); goto start; } #ifdef DIAGNOSTIC if (curproc) nn->null_pid = curproc->p_pid; else nn->null_pid = -1; nn->null_lockpc = RETURN_PC(0); nn->null_lockpc2 = RETURN_PC(1); #endif nn->null_flags |= NULL_LOCKED; return (0); } int null_unlock(v) void *v; { struct vop_lock_args *ap = v; struct null_node *nn = VTONULL(ap->a_vp); #ifdef NULLFS_DIAGNOSTIC vprint("null_unlock_e", ap->a_vp); #endif #ifdef DIAGNOSTIC if ((nn->null_flags & NULL_LOCKED) == 0) { vprint("null_unlock", ap->a_vp); panic("null: unlocking unlocked node"); } if (curproc && nn->null_pid != curproc->p_pid && curproc->p_pid > -1 && nn->null_pid > -1) { vprint("null_unlock", ap->a_vp); panic("null: unlocking other process's null node"); } #endif nn->null_flags &= ~NULL_LOCKED; if ((nn->null_flags & NULL_LLOCK) != 0) VOP_UNLOCK(nn->null_lowervp); nn->null_flags &= ~NULL_LLOCK; if (nn->null_flags & NULL_WANTED) { nn->null_flags &= ~NULL_WANTED; wakeup((caddr_t)nn); } #ifdef DIAGNOSTIC nn->null_pid = 0; nn->null_lockpc = nn->null_lockpc2 = 0; #endif return (0); } int null_islocked(v) void *v; { struct vop_islocked_args *ap = v; return ((VTONULL(ap->a_vp)->null_flags & NULL_LOCKED) ? 1 : 0); } int null_lookup(v) void *v; { register struct vop_lookup_args /* { struct vnodeop_desc *a_desc; struct vnode *a_dvp; struct vnode **a_vpp; struct componentname *a_cnp; } */ *ap = v; register int error; register struct vnode *dvp; int flags = ap->a_cnp->cn_flags; #ifdef NULLFS_DIAGNOSTIC printf("null_lookup: dvp=%p, name='%s'\n", ap->a_dvp, ap->a_cnp->cn_nameptr); #endif /* * the starting dir (ap->a_dvp) comes in locked. */ /* set LOCKPARENT to hold on to it until done below */ ap->a_cnp->cn_flags |= LOCKPARENT; error = null_bypass(ap); if (!(flags & LOCKPARENT)) ap->a_cnp->cn_flags &= ~LOCKPARENT; if (error) /* * starting dir is still locked/has been relocked * on error return. */ return error; if (ap->a_dvp != *ap->a_vpp) { /* * Lookup returns node locked; we mark both lower and * upper nodes as locked by setting the lower lock * flag (it came back locked), and then call lock to * set upper lock flag & record pid, etc. see * null_node_create() */ VTONULL(*ap->a_vpp)->null_flags |= NULL_LLOCK; dvp = ap->a_dvp; if (flags & ISDOTDOT) { /* * If we're looking up `..' and this isn't the * last component, then the starting directory * ("parent") is _unlocked_ as a side-effect * of lookups. This is to avoid deadlocks: * lock order is always parent, child, so * looking up `..' requires dropping the lock * on the starting directory. */ /* see ufs_lookup() for hairy ugly locking protocol examples */ /* * underlying starting dir comes back locked if flags & * LOCKPARENT (which we artificially set above) and * ISLASTCN. */ if (flags & ISLASTCN) { VTONULL(dvp)->null_flags |= NULL_LLOCK; /* no-op, right? */ #ifdef NULLFS_DIAGNOSTIC if (!VOP_ISLOCKED(VTONULL(dvp)->null_lowervp)) { vprint("lowerdvp not locked after lookup\n", dvp); panic("null_lookup not locked"); } #endif } else { VTONULL(dvp)->null_flags &= ~NULL_LLOCK; #ifdef NULLFS_DIAGNOSTIC if (VOP_ISLOCKED(VTONULL(dvp)->null_lowervp)) { vprint("lowerdvp locked after lookup?\n", dvp); panic("null_lookup locked"); } #endif } /* * locking order: drop lock on lower-in-tree * element, then get lock on higher-in-tree * element, then (if needed) re-fetch lower * lock. No need for vget() since we hold a * refcount to the starting directory */ VOP_UNLOCK(dvp); VOP_LOCK(*ap->a_vpp); /* * we should return our directory locked if * (flags & LOCKPARENT) and (flags & ISLASTCN) */ if ((flags & LOCKPARENT) && (flags & ISLASTCN)) VOP_LOCK(dvp); } else { /* * Normal directory locking order: we hold the starting * directory locked; now lock our layer of the target. */ VOP_LOCK(*ap->a_vpp); /* * underlying starting dir comes back locked * if lockparent (we set it) and no error * (this leg) and ISLASTCN */ if (flags & ISLASTCN) { VTONULL(dvp)->null_flags |= NULL_LLOCK; /* no op, right? */ #ifdef NULLFS_DIAGNOSTIC if (!VOP_ISLOCKED(VTONULL(dvp)->null_lowervp)) { vprint("lowerdvp not locked after lookup\n", dvp); panic("null_lookup not locked"); } #endif } else { VTONULL(dvp)->null_flags &= ~NULL_LLOCK; #ifdef NULLFS_DIAGNOSTIC if (VOP_ISLOCKED(VTONULL(dvp)->null_lowervp)) { vprint("lowerdvp locked after lookup?\n", dvp); panic("null_lookup locked"); } #endif } /* * we should return our directory unlocked if * our caller didn't want the parent locked, * !(flags & LOCKPARENT), or we're not at the * end yet, !(flags & ISLASTCN) */ if (!(flags & LOCKPARENT) || !(flags & ISLASTCN)) VOP_UNLOCK(dvp); } } return error; } /* * Global vfs data structures */ int (**null_vnodeop_p) __P((void *)); 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_lock_desc, null_lock }, { &vop_unlock_desc, null_unlock }, { &vop_islocked_desc, null_islocked }, { &vop_lookup_desc, null_lookup }, /* special locking frob */ { &vop_strategy_desc, null_strategy }, { &vop_bwrite_desc, null_bwrite }, { (struct vnodeop_desc*)NULL, (int(*) __P((void *)))NULL } }; struct vnodeopv_desc nullfs_vnodeop_opv_desc = { &null_vnodeop_p, null_vnodeop_entries };