usr/src/sys/miscfs/nullfs/null_subr.c

/*
 * Copyright (c) 1992 The Regents of the University of California
 * Copyright (c) 1990, 1992 Jan-Simon Pendry
 * All rights reserved.
 *
 * This code is derived from software donated to Berkeley by
 * Jan-Simon Pendry.
 *
 * %sccs.include.redist.c%
 *
 *      @(#)lofs_subr.c 1.2 (Berkeley) 6/18/92
 *
 * $Id: lofs_subr.c,v 1.11 1992/05/30 10:05:43 jsp Exp jsp $
 */

#include <sys/param.h>
#include <sys/systm.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 <lofs/lofs.h>

#define LOG2_SIZEVNODE 7                /* log2(sizeof struct vnode) */
#define NNULLNODECACHE 16
#define NULL_NHASH(vp) ((((u_long)vp)>>LOG2_SIZEVNODE) & (NNULLNODECACHE-1))

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

/*
 * Cache head
 */
struct null_node_cache {
        struct null_node        *ac_forw;
        struct null_node        *ac_back;
};

static struct null_node_cache null_node_cache[NNULLNODECACHE];

/*
 * Initialise cache headers
 */
nullfs_init()
{
        struct null_node_cache *ac;
#ifdef NULLFS_DIAGNOSTIC
        printf("nullfs_init\n");                /* printed during system boot */
#endif

        for (ac = null_node_cache; ac < null_node_cache + NNULLNODECACHE; ac++)
                ac->ac_forw = ac->ac_back = (struct null_node *) ac;
}

/*
 * Compute hash list for given target vnode
 */
static struct null_node_cache *
null_node_hash(targetvp)
struct vnode *targetvp;
{
        return (&null_node_cache[NULL_NHASH(targetvp)]);
}

/*
 * Make a new null_node node.
 * Vp is the alias vnode, lofsvp is the target vnode.
 * Maintain a reference to (targetvp).
 */
static void
null_node_alloc(vp, targetvp)
        struct vnode *vp;
        struct vnode *targetvp;
{
        struct null_node_cache *hd;
        struct null_node *a;

#ifdef NULLFS_DIAGNOSTIC
        printf("null_node_alloc(%x, %x)\n", vp, targetvp);
#endif

        MALLOC(a, struct null_node *, sizeof(struct null_node), M_TEMP, M_WAITOK);
        a->null_vnode = vp;
        vp->v_data = a;
        VREF(targetvp);
        a->null_lowervp = targetvp;
        hd = null_node_hash(targetvp);
        insque(a, hd);

#ifdef NULLFS_DIAGNOSTIC
        vprint("alloc vp", vp);
        vprint("alloc targetvp", targetvp);
#endif
}

#ifdef NULLFS_DIAGNOSTIC
void
null_node_flushmp (mp)
        struct mount *mp;
{
        struct null_node_cache *ac;
        int i = 0;
        struct null_node *roota;

        printf("null_node_flushmp (%x)\n", mp);

        roota = VTONULLNODE(MOUNTTONULLMOUNT(mp)->nullm_rootvp);

        for (ac = null_node_cache; ac < null_node_cache + NNULLNODECACHE; ac++) {
                struct null_node *a = ac->ac_forw;
                while (a != (struct null_node *) ac) {
                        if (a != roota && a->null_vnode->v_mount == mp) {
                                struct vnode *vp = a->null_lowervp;
                                if (vp) {
                                        a->null_lowervp = 0;
                                        vprint("would vrele", vp);
                                        /*vrele(vp);*/
                                        i++;
                                }
                        }
                        a = a->null_forw;
                }
        }
        if (i > 0)
                printf("null_node: vrele'd %d aliases\n", i);
}
#endif

/*
 * Return alias for target vnode if already exists, else 0.
 */
static struct null_node *
null_node_find(mp, targetvp)
        struct mount *mp;
        struct vnode *targetvp;
{
        struct null_node_cache *hd;
        struct null_node *a;

#ifdef NULLFS_DIAGNOSTIC
        printf("null_node_find(mp = %x, target = %x)\n", mp, targetvp);
#endif

        /*
         * Find hash base, and then search the (two-way) linked
         * list looking for a null_node structure which is referencing
         * the target vnode.  If found, the increment the null_node
         * reference count (but NOT the target vnode's VREF counter).
         */
        hd = null_node_hash(targetvp);

        for (a = hd->ac_forw; a != (struct null_node *) hd; a = a->null_forw) {
                if (a->null_lowervp == targetvp && a->null_vnode->v_mount == mp) {
#ifdef NULLFS_DIAGNOSTIC
                        printf("null_node_find(%x): found (%x,%x)->%x\n",
                                targetvp, mp, a->null_vnode, targetvp);
#endif
                        return (a);
                }
        }

#ifdef NULLFS_DIAGNOSTIC
        printf("null_node_find(%x, %x): NOT found\n", mp, targetvp);
#endif

        return (0);
}

static int
null_node_alias(mp, targetvp, newvpp)
        struct mount *mp;
        struct vnode *targetvp;
        struct vnode **newvpp;
{
        struct null_node *ap;
        struct vnode *aliasvp;

        if (targetvp->v_type != VDIR || targetvp->v_op == null_vnodeop_p) {
                *newvpp = targetvp;
                return;
        }

        ap = null_node_find(mp, targetvp);

        if (ap) {
                /*
                 * Take another reference to the alias vnode
                 */
#ifdef NULLFS_DIAGNOSTIC
                vprint("null_node_alias: exists", ap->null_vnode);
#endif
                aliasvp = ap->null_vnode;
                VREF(aliasvp);
        } else {
                int error;

                /*
                 * Get new vnode.
                 */
#ifdef NULLFS_DIAGNOSTIC
                printf("null_node_alias: create new alias vnode\n");
#endif
                if (error = getnewvnode(VT_UFS, mp, null_vnodeop_p, &aliasvp))
                        return (error); /* XXX: VT_LOFS above */

                /*
                 * Must be a directory
                 */
                aliasvp->v_type = VDIR;

                /*
                 * Make new vnode reference the null_node.
                 */
                null_node_alloc(aliasvp, targetvp);

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

        vrele(targetvp);

#ifdef NULLFS_DIAGNOSTIC
        vprint("null_node_alias alias", aliasvp);
        vprint("null_node_alias target", targetvp);
#endif

        *newvpp = aliasvp;
        return (0);
}

/*
 * Try to find an existing null_node vnode refering
 * to it, otherwise make a new null_node vnode which
 * contains a reference to the target vnode.
 */
make_null_node(mp, vpp)
        struct mount *mp;
        struct vnode **vpp;
{
        int error;
        struct vnode *aliasvp;
        struct vnode *targetvp;

#ifdef NULLFS_DIAGNOSTIC
        printf("make_null_node(mp = %x, vp = %x\n", mp, *vpp);
#endif

        /*
         * (targetvp) is locked at this point.
         */
        targetvp = *vpp;

#ifdef NULLFS_DIAGNOSTIC
        if (targetvp == 0)
                panic("make_null_node: null vp");
#endif

        /*
         * Try to find an existing reference to the target vnodes.
         */
        return (null_node_alias(mp, targetvp, vpp));
}

#ifdef NULLFS_DIAGNOSTIC
struct vnode *
null_checkvp(vp, fil, lno)
        struct vnode *vp;
        char *fil;
        int lno;
{
        struct null_node *a = VTONULLNODE(vp);
        if (a->null_lowervp == 0) {
                int i; u_long *p;
                printf("vp = %x, ZERO ptr\n", vp);
#ifdef notdef
                for (p = (u_long *) a, i = 0; i < 8; i++)
                        printf(" %x", p[i]);
                printf("\n");
                DELAY(2000000);
                panic("null_checkvp");
#endif
        }
        printf("aliasvp %x/%d -> %x/%d [%s, %d]\n",
                a->null_vnode, a->null_vnode->v_usecount,
                a->null_lowervp, a->null_lowervp ? a->null_lowervp->v_usecount : -42,
                fil, lno);
        return a->null_lowervp;
}
#endif