/*- * 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. * 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 8.6 (Berkeley) 5/27/95 * * Ancestors: * @(#)lofs_vnops.c 1.2 (Berkeley) 6/18/92 * ...and... * @(#)null_vnodeops.c 1.20 92/07/07 UCLA Ficus project * * $FreeBSD$ */ /* * Null Layer * * (See mount_nullfs(8) for more information.) * * The null layer duplicates a portion of the filesystem * name space under a new name. In this respect, it is * similar to the loopback filesystem. It differs from * the loopback fs in two respects: it is implemented using * a stackable layers techniques, and its "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 filesystem 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 filesystem 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_nullfs(8). * Mount_nullfs(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 filesystem 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 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, 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, * 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_nullfs /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 filesystem 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 a 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 manualy mapped. * */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include static int null_bug_bypass = 0; /* for debugging: enables bypass printf'ing */ SYSCTL_INT(_debug, OID_AUTO, nullfs_bug_bypass, CTLFLAG_RW, &null_bug_bypass, 0, ""); /* * 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. * * 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(struct vop_generic_args *ap) { 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 DIAGNOSTIC /* * 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"); #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_vnodeops)) { 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 & VDESC_VP0_WILLRELE) VREF(*this_vp_p); } } /* * Call the operation on the lower layer * with the modified argument structure. */ if (vps_p[0] && *vps_p[0]) error = VCALL(ap); else { printf("null_bypass: no map for %s\n", descp->vdesc_name); error = EINVAL; } /* * 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 0 if (reles & VDESC_VP0_WILLUNLOCK) VOP_UNLOCK(*(vps_p[i]), 0, curthread); #endif if (reles & VDESC_VP0_WILLRELE) 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); if (*vppp) error = null_nodeget(old_vps[0]->v_mount, **vppp, *vppp); } out: return (error); } /* * We have to carry on the locking protocol on the null layer vnodes * as we progress through the tree. We also have to enforce read-only * if this layer is mounted read-only. */ static int null_lookup(struct vop_lookup_args *ap) { struct componentname *cnp = ap->a_cnp; struct vnode *dvp = ap->a_dvp; int flags = cnp->cn_flags; struct vnode *vp, *ldvp, *lvp; int error; if ((flags & ISLASTCN) && (dvp->v_mount->mnt_flag & MNT_RDONLY) && (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) return (EROFS); /* * Although it is possible to call null_bypass(), we'll do * a direct call to reduce overhead */ ldvp = NULLVPTOLOWERVP(dvp); vp = lvp = NULL; error = VOP_LOOKUP(ldvp, &lvp, cnp); if (error == EJUSTRETURN && (flags & ISLASTCN) && (dvp->v_mount->mnt_flag & MNT_RDONLY) && (cnp->cn_nameiop == CREATE || cnp->cn_nameiop == RENAME)) error = EROFS; if ((error == 0 || error == EJUSTRETURN) && lvp != NULL) { if (ldvp == lvp) { *ap->a_vpp = dvp; VREF(dvp); vrele(lvp); } else { error = null_nodeget(dvp->v_mount, lvp, &vp); if (error) { /* XXX Cleanup needed... */ panic("null_nodeget failed"); } *ap->a_vpp = vp; } } return (error); } static int null_open(struct vop_open_args *ap) { int retval; struct vnode *vp, *ldvp; vp = ap->a_vp; ldvp = NULLVPTOLOWERVP(vp); retval = null_bypass(&ap->a_gen); if (retval == 0) vp->v_object = ldvp->v_object; return (retval); } /* * Setattr call. Disallow write attempts if the layer is mounted read-only. */ static int null_setattr(struct vop_setattr_args *ap) { struct vnode *vp = ap->a_vp; struct vattr *vap = ap->a_vap; if ((vap->va_flags != VNOVAL || vap->va_uid != (uid_t)VNOVAL || vap->va_gid != (gid_t)VNOVAL || vap->va_atime.tv_sec != VNOVAL || vap->va_mtime.tv_sec != VNOVAL || vap->va_mode != (mode_t)VNOVAL) && (vp->v_mount->mnt_flag & MNT_RDONLY)) return (EROFS); if (vap->va_size != VNOVAL) { switch (vp->v_type) { case VDIR: return (EISDIR); case VCHR: case VBLK: case VSOCK: case VFIFO: if (vap->va_flags != VNOVAL) return (EOPNOTSUPP); return (0); case VREG: case VLNK: default: /* * Disallow write attempts if the filesystem is * mounted read-only. */ if (vp->v_mount->mnt_flag & MNT_RDONLY) return (EROFS); } } return (null_bypass((struct vop_generic_args *)ap)); } /* * We handle getattr only to change the fsid. */ static int null_getattr(struct vop_getattr_args *ap) { int error; if ((error = null_bypass((struct vop_generic_args *)ap)) != 0) return (error); ap->a_vap->va_fsid = ap->a_vp->v_mount->mnt_stat.f_fsid.val[0]; return (0); } /* * Handle to disallow write access if mounted read-only. */ static int null_access(struct vop_access_args *ap) { struct vnode *vp = ap->a_vp; mode_t mode = ap->a_mode; /* * Disallow write attempts on read-only layers; * unless the file is a socket, fifo, or a block or * character device resident on the filesystem. */ if (mode & VWRITE) { switch (vp->v_type) { case VDIR: case VLNK: case VREG: if (vp->v_mount->mnt_flag & MNT_RDONLY) return (EROFS); break; default: break; } } return (null_bypass((struct vop_generic_args *)ap)); } /* * We handle this to eliminate null FS to lower FS * file moving. Don't know why we don't allow this, * possibly we should. */ static int null_rename(struct vop_rename_args *ap) { struct vnode *tdvp = ap->a_tdvp; struct vnode *fvp = ap->a_fvp; struct vnode *fdvp = ap->a_fdvp; struct vnode *tvp = ap->a_tvp; /* Check for cross-device rename. */ if ((fvp->v_mount != tdvp->v_mount) || (tvp && (fvp->v_mount != tvp->v_mount))) { if (tdvp == tvp) vrele(tdvp); else vput(tdvp); if (tvp) vput(tvp); vrele(fdvp); vrele(fvp); return (EXDEV); } return (null_bypass((struct vop_generic_args *)ap)); } /* * We need to process our own vnode lock and then clear the * interlock flag as it applies only to our vnode, not the * vnodes below us on the stack. */ static int null_lock(struct vop_lock_args *ap) { struct vnode *vp = ap->a_vp; int flags = ap->a_flags; struct thread *td = ap->a_td; struct null_node *nn; struct vnode *lvp; int error; if ((flags & LK_INTERLOCK) == 0) { VI_LOCK(vp); ap->a_flags = flags |= LK_INTERLOCK; } nn = VTONULL(vp); /* * If we're still active we must ask the lower layer to * lock as ffs has special lock considerations in it's * vop lock. */ if (nn != NULL && (lvp = NULLVPTOLOWERVP(vp)) != NULL) { VI_LOCK_FLAGS(lvp, MTX_DUPOK); VI_UNLOCK(vp); /* * We have to hold the vnode here to solve a potential * reclaim race. If we're forcibly vgone'd while we * still have refs, a thread could be sleeping inside * the lowervp's vop_lock routine. When we vgone we will * drop our last ref to the lowervp, which would allow it * to be reclaimed. The lowervp could then be recycled, * in which case it is not legal to be sleeping in it's VOP. * We prevent it from being recycled by holding the vnode * here. */ vholdl(lvp); error = VOP_LOCK(lvp, flags, td); vdrop(lvp); } else error = vop_stdlock(ap); return (error); } /* * We need to process our own vnode unlock and then clear the * interlock flag as it applies only to our vnode, not the * vnodes below us on the stack. */ static int null_unlock(struct vop_unlock_args *ap) { struct vnode *vp = ap->a_vp; int flags = ap->a_flags; struct thread *td = ap->a_td; struct null_node *nn; struct vnode *lvp; int error; if ((flags & LK_INTERLOCK) != 0) { VI_UNLOCK(vp); ap->a_flags = flags &= ~LK_INTERLOCK; } nn = VTONULL(vp); if (nn != NULL && (lvp = NULLVPTOLOWERVP(vp)) != NULL) error = VOP_UNLOCK(lvp, flags, td); else error = vop_stdunlock(ap); return (error); } static int null_islocked(struct vop_islocked_args *ap) { struct vnode *vp = ap->a_vp; struct thread *td = ap->a_td; return (lockstatus(vp->v_vnlock, td)); } /* * There is no way to tell that someone issued remove/rmdir operation * on the underlying filesystem. For now we just have to release lowevrp * as soon as possible. * * Note, we can't release any resources nor remove vnode from hash before * appropriate VXLOCK stuff is is done because other process can find this * vnode in hash during inactivation and may be sitting in vget() and waiting * for null_inactive to unlock vnode. Thus we will do all those in VOP_RECLAIM. */ static int null_inactive(struct vop_inactive_args *ap) { struct vnode *vp = ap->a_vp; struct thread *td = ap->a_td; vp->v_object = NULL; /* * If this is the last reference, then free up the vnode * so as not to tie up the lower vnodes. */ vrecycle(vp, td); return (0); } /* * Now, the VXLOCK is in force and we're free to destroy the null vnode. */ static int null_reclaim(struct vop_reclaim_args *ap) { struct vnode *vp = ap->a_vp; struct null_node *xp = VTONULL(vp); struct vnode *lowervp = xp->null_lowervp; struct lock *vnlock; /* * Use the interlock to protect the clearing of v_data to * prevent faults in null_lock(). */ VI_LOCK(vp); vp->v_data = NULL; VI_UNLOCK(vp); if (lowervp) { null_hashrem(xp); vrele(lowervp); } vp->v_object = NULL; vnlock = vp->v_vnlock; vp->v_vnlock = &vp->v_lock; lockmgr(vp->v_vnlock, LK_EXCLUSIVE, NULL, curthread); lockmgr(vnlock, LK_RELEASE, NULL, curthread); FREE(xp, M_NULLFSNODE); return (0); } static int null_print(struct vop_print_args *ap) { struct vnode *vp = ap->a_vp; printf("\tvp=%p, lowervp=%p\n", vp, NULLVPTOLOWERVP(vp)); return (0); } /* * Global vfs data structures */ struct vop_vector null_vnodeops = { .vop_bypass = null_bypass, .vop_access = null_access, .vop_bmap = VOP_EOPNOTSUPP, .vop_getattr = null_getattr, .vop_getwritemount = vop_stdgetwritemount, .vop_inactive = null_inactive, .vop_islocked = null_islocked, .vop_lock = null_lock, .vop_lookup = null_lookup, .vop_open = null_open, .vop_print = null_print, .vop_reclaim = null_reclaim, .vop_rename = null_rename, .vop_setattr = null_setattr, .vop_strategy = VOP_EOPNOTSUPP, .vop_unlock = null_unlock, };