BSD 4.4 Lite Kernel Sources

1 files changed, 462 insertions, 0 deletions

diff --git a/sys/fs/nullfs/null_vnops.c b/sys/fs/nullfs/null_vnops.c
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+++ b/sys/fs/nullfs/null_vnops.c
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+/*
+ * 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 };