xref: /src/sys/miscfs/genfs/layer_subr.c

/*	$NetBSD: layer_subr.c,v 1.26 2009/03/14 15:36:22 dsl Exp $	*/

/*
 * Copyright (c) 1999 National Aeronautics & Space Administration
 * All rights reserved.
 *
 * This software was written by William Studenmund of the
 * Numerical Aerospace Simulation Facility, NASA Ames Research Center.
 *
 * 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. Neither the name of the National Aeronautics & Space Administration
 *    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 NATIONAL AERONAUTICS & SPACE ADMINISTRATION
 * ``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 ADMINISTRATION OR CONTRIB-
 * UTORS 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.
 */
/*
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software donated to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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. 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.
 *
 *	from: Id: lofs_subr.c,v 1.11 1992/05/30 10:05:43 jsp Exp
 *	@(#)null_subr.c	8.7 (Berkeley) 5/14/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: layer_subr.c,v 1.26 2009/03/14 15:36:22 dsl Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/time.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/kmem.h>
#include <sys/malloc.h>

#include <miscfs/specfs/specdev.h>
#include <miscfs/genfs/layer.h>
#include <miscfs/genfs/layer_extern.h>

#define	NLAYERNODECACHE 16

#ifdef LAYERFS_DIAGNOSTIC
int layerfs_debug = 1;
#endif

/*
 * layer cache:
 * Each cache entry holds a reference to the lower vnode
 * along with a pointer to the alias vnode.  When an
 * entry is added the lower vnode is VREF'd.  When the
 * alias is removed the lower vnode is vrele'd.
 */

/*
 * Initialise cache headers
 */
void
layerfs_init()
{
#ifdef LAYERFS_DIAGNOSTIC
	if (layerfs_debug)
		printf("layerfs_init\n");		/* printed during system boot */
#endif
}

/*
 * Free global resources of layerfs.
 */
void
layerfs_done()
{
#ifdef LAYERFS_DIAGNOSTIC
	if (layerfs_debug)
		printf("layerfs_done\n");		/* printed on layerfs detach */
#endif
}

/*
 * Return a locked, VREF'ed alias for lower vnode if already exists, else NULL.
 * The layermp's hashlock must be held on entry.
 * It will be held upon return iff we return NULL.
 */
struct vnode *
layer_node_find(struct mount *mp, struct vnode *lowervp)
{
	struct layer_mount *lmp = MOUNTTOLAYERMOUNT(mp);
	struct layer_node_hashhead *hd;
	struct layer_node *a;
	struct vnode *vp;
	int error;

	/*
	 * Find hash base, and then search the (two-way) linked
	 * list looking for a layer_node structure which is referencing
	 * the lower vnode.  If found, the increment the layer_node
	 * reference count (but NOT the lower vnode's VREF counter)
	 * and return the vnode locked.
	 */
	hd = LAYER_NHASH(lmp, lowervp);
loop:
	LIST_FOREACH(a, hd, layer_hash) {
		if (a->layer_lowervp == lowervp && LAYERTOV(a)->v_mount == mp) {
			vp = LAYERTOV(a);
			mutex_enter(&vp->v_interlock);
			/*
			 * If we find a node being cleaned out, then
			 * ignore it and continue.  A thread trying to
			 * clean out the extant layer vnode needs to
			 * acquire the shared lock (i.e. the lower
			 * vnode's lock), which our caller already holds.
			 * To allow the cleaning to succeed the current
			 * thread must make progress.  So, for a brief
			 * time more than one vnode in a layered file
			 * system may refer to a single vnode in the
			 * lower file system.
			 */
			if ((vp->v_iflag & VI_XLOCK) != 0) {
				mutex_exit(&vp->v_interlock);
				continue;
			}
			mutex_exit(&lmp->layerm_hashlock);
			/*
			 * We must not let vget() try to lock the layer
			 * vp, since the lower vp is already locked and
			 * locking the layer vp will involve locking
			 * the lower vp (whether or not they actually
			 * share a lock).  Instead, take the layer vp's
			 * lock separately afterward, but only if it
			 * does not share the lower vp's lock.
			 */
			error = vget(vp, LK_INTERLOCK | LK_NOWAIT);
			if (error) {
				kpause("layerfs", false, 1, NULL);
				mutex_enter(&lmp->layerm_hashlock);
				goto loop;
			}
			LAYERFS_UPPERLOCK(vp, LK_EXCLUSIVE, error);
			return (vp);
		}
	}
	return NULL;
}


/*
 * Make a new layer_node node.
 * Vp is the alias vnode, lowervp is the lower vnode.
 * Maintain a reference to lowervp.
 */
int
layer_node_alloc(struct mount *mp, struct vnode *lowervp, struct vnode **vpp)
{
	struct layer_mount *lmp = MOUNTTOLAYERMOUNT(mp);
	struct layer_node_hashhead *hd;
	struct layer_node *xp;
	struct vnode *vp, *nvp;
	int error;
	extern int (**dead_vnodeop_p)(void *);

	error = getnewvnode(lmp->layerm_tag, mp, lmp->layerm_vnodeop_p, &vp);
	if (error != 0)
		return (error);
	vp->v_type = lowervp->v_type;
	mutex_enter(&vp->v_interlock);
	vp->v_iflag |= VI_LAYER;
	mutex_exit(&vp->v_interlock);

	xp = kmem_alloc(lmp->layerm_size, KM_SLEEP);
	if (xp == NULL) {
		ungetnewvnode(vp);
		return ENOMEM;
	}
	if (vp->v_type == VBLK || vp->v_type == VCHR) {
		spec_node_init(vp, lowervp->v_rdev);
	}

	vp->v_data = xp;
	vp->v_vflag = (vp->v_vflag & ~VV_MPSAFE) |
	    (lowervp->v_vflag & VV_MPSAFE);
	xp->layer_vnode = vp;
	xp->layer_lowervp = lowervp;
	xp->layer_flags = 0;

	/*
	 * Before we insert our new node onto the hash chains,
	 * check to see if someone else has beaten us to it.
	 * (We could have slept in MALLOC.)
	 */
	mutex_enter(&lmp->layerm_hashlock);
	if ((nvp = layer_node_find(mp, lowervp)) != NULL) {
		*vpp = nvp;

		/* free the substructures we've allocated. */
		kmem_free(xp, lmp->layerm_size);
		if (vp->v_type == VBLK || vp->v_type == VCHR)
			spec_node_destroy(vp);

		vp->v_type = VBAD;		/* node is discarded */
		vp->v_op = dead_vnodeop_p;	/* so ops will still work */
		vrele(vp);			/* get rid of it. */
		return (0);
	}

	/*
	 * Now lock the new node. We rely on the fact that we were passed
	 * a locked vnode. If the lower node is exporting a struct lock
	 * (v_vnlock != NULL) then we just set the upper v_vnlock to the
	 * lower one, and both are now locked. If the lower node is exporting
	 * NULL, then we copy that up and manually lock the upper node.
	 *
	 * LAYERFS_UPPERLOCK already has the test, so we use it after copying
	 * up the v_vnlock from below.
	 */

	vp->v_vnlock = lowervp->v_vnlock;
	LAYERFS_UPPERLOCK(vp, LK_EXCLUSIVE, error);
	KASSERT(error == 0);

	/*
	 * Insert the new node into the hash.
	 * Add a reference to the lower node.
	 */

	*vpp = vp;
	VREF(lowervp);
	hd = LAYER_NHASH(lmp, lowervp);
	LIST_INSERT_HEAD(hd, xp, layer_hash);
	uvm_vnp_setsize(vp, 0);
	mutex_exit(&lmp->layerm_hashlock);
	return (0);
}


/*
 * Try to find an existing layer_node vnode refering
 * to it, otherwise make a new layer_node vnode which
 * contains a reference to the lower vnode.
 *
 * >>> we assume that the lower node is already locked upon entry, so we
 * propagate the lock state to upper node <<
 */
int
layer_node_create(struct mount *mp, struct vnode *lowervp, struct vnode **newvpp)
{
	struct vnode *aliasvp;
	struct layer_mount *lmp = MOUNTTOLAYERMOUNT(mp);

	mutex_enter(&lmp->layerm_hashlock);
	aliasvp = layer_node_find(mp, lowervp);
	if (aliasvp != NULL) {
		/*
		 * layer_node_find has taken another reference
		 * to the alias vnode and moved the lock holding to
		 * aliasvp
		 */
#ifdef LAYERFS_DIAGNOSTIC
		if (layerfs_debug)
			vprint("layer_node_create: exists", aliasvp);
#endif
	} else {
		int error;

		mutex_exit(&lmp->layerm_hashlock);

		/*
		 * Get new vnode.
		 */
#ifdef LAYERFS_DIAGNOSTIC
		if (layerfs_debug)
			printf("layer_node_create: create new alias vnode\n");
#endif

		/*
		 * Make new vnode reference the layer_node.
		 */
		if ((error = (lmp->layerm_alloc)(mp, lowervp, &aliasvp)) != 0)
			return error;

		/*
		 * aliasvp is already VREF'd by getnewvnode()
		 */
	}

	/*
	 * Now that we have VREF'd the upper vnode, release the reference
	 * to the lower node. The existence of the layer_node retains one
	 * reference to the lower node.
	 */
	vrele(lowervp);

#ifdef DIAGNOSTIC
	if (lowervp->v_usecount < 1) {
		/* Should never happen... */
		vprint("layer_node_create: alias", aliasvp);
		vprint("layer_node_create: lower", lowervp);
		panic("layer_node_create: lower has 0 usecount.");
	}
#endif

#ifdef LAYERFS_DIAGNOSTIC
	if (layerfs_debug)
		vprint("layer_node_create: alias", aliasvp);
#endif
	*newvpp = aliasvp;
	return (0);
}

#ifdef LAYERFS_DIAGNOSTIC
struct vnode *
layer_checkvp(struct vnode *vp, const char *fil, int lno)
{
	struct layer_node *a = VTOLAYER(vp);
#ifdef notyet
	/*
	 * Can't do this check because vop_reclaim runs
	 * with a funny vop vector.
	 *
	 * WRS - no it doesnt...
	 */
	if (vp->v_op != layer_vnodeop_p) {
		printf ("layer_checkvp: on non-layer-node\n");
#ifdef notyet
		while (layer_checkvp_barrier) /*WAIT*/ ;
#endif
		panic("layer_checkvp");
	};
#endif
	if (a->layer_lowervp == NULL) {
		/* Should never happen */
		int i; u_long *p;
		printf("vp = %p, ZERO ptr\n", vp);
		for (p = (u_long *) a, i = 0; i < 8; i++)
			printf(" %lx", p[i]);
		printf("\n");
		/* wait for debugger */
		panic("layer_checkvp");
	}
	if (a->layer_lowervp->v_usecount < 1) {
		int i; u_long *p;
		printf("vp = %p, unref'ed lowervp\n", vp);
		for (p = (u_long *) a, i = 0; i < 8; i++)
			printf(" %lx", p[i]);
		printf("\n");
		/* wait for debugger */
		panic ("layer with unref'ed lowervp");
	};
#ifdef notnow
	printf("layer %p/%d -> %p/%d [%s, %d]\n",
	        LAYERTOV(a), LAYERTOV(a)->v_usecount,
		a->layer_lowervp, a->layer_lowervp->v_usecount,
		fil, lno);
#endif
	return a->layer_lowervp;
}
#endif