freebsd-dev/sys/miscfs/nullfs/null_vnops.c
1995-05-30 08:16:23 +00:00

462 lines
14 KiB
C

/*
* 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 1.7 1995/03/19 14:28:54 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 <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.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;
{
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.");
#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;
error = null_bypass(ap);
if (error)
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=%p, lowervp=%p\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 };
VNODEOP_SET(null_vnodeop_opv_desc);