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 <nullfs/null.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 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.
 */

/*
 * 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 lower vnode
 */
static struct null_node_cache *
null_node_hash(lowervp)
struct vnode *lowervp;
{

        return (&null_node_cache[NULL_NHASH(lowervp)]);
}


/*
 * XXX - this should go elsewhere.
 * Just like vget, but with no lock at the end.
 */
int
vget_nolock(vp)
        register struct vnode *vp;
{
        extern struct vnode *vfreeh, **vfreet;
        register struct vnode *vq;

        if (vp->v_flag & VXLOCK) {
                vp->v_flag |= VXWANT;
                sleep((caddr_t)vp, PINOD);
                return (1);
        }
        if (vp->v_usecount == 0) {
                if (vq = vp->v_freef)
                        vq->v_freeb = vp->v_freeb;
                else
                        vfreet = vp->v_freeb;
                *vp->v_freeb = vq;
                vp->v_freef = NULL;
                vp->v_freeb = NULL;
        }
        VREF(vp);
        /* VOP_LOCK(vp); */
        return (0);
}


/*
 * Return a VREF'ed alias for lower vnode if already exists, else 0.
 */
static struct vnode *
null_node_find(mp, lowervp)
        struct mount *mp;
        struct vnode *lowervp;
{
        struct null_node_cache *hd;
        struct null_node *a;
        struct vnode *vp;

        /*
         * Find hash base, and then search the (two-way) linked
         * list looking for a null_node structure which is referencing
         * the lower vnode.  If found, the increment the null_node
         * reference count (but NOT the lower vnode's VREF counter).
         */
        hd = null_node_hash(lowervp);
loop:
        for (a = hd->ac_forw; a != (struct null_node *) hd; a = a->null_forw) {
                if (a->null_lowervp == lowervp && NULLTOV(a)->v_mount == mp) {
                        vp = NULLTOV(a);
                        /*
                         * We need vget for the VXLOCK
                         * stuff, but we don't want to lock
                         * the lower node.
                         */
                        if (vget_nolock(vp)) {
                                printf ("null_node_find: vget failed.\n");
                                goto loop;
                        };
                        return (vp);
                }
        }

        return NULL;
}


/*
 * Make a new null_node node.
 * Vp is the alias vnode, lofsvp is the lower vnode.
 * Maintain a reference to (lowervp).
 */
static int
null_node_alloc(mp, lowervp, vpp)
        struct mount *mp;
        struct vnode *lowervp;
        struct vnode **vpp;
{
        struct null_node_cache *hd;
        struct null_node *xp;
        struct vnode *othervp, *vp;
        int error;

        if (error = getnewvnode(VT_UFS, mp, null_vnodeop_p, vpp))
                return (error); /* XXX: VT_NULL above */
        vp = *vpp;

        MALLOC(xp, struct null_node *, sizeof(struct null_node), M_TEMP, M_WAITOK);
        vp->v_type = lowervp->v_type;
        xp->null_vnode = vp;
        vp->v_data = xp;
        xp->null_lowervp = lowervp;
        /*
         * 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.)
         */
        if (othervp = null_node_find(lowervp)) {
                FREE(xp, M_TEMP);
                vp->v_type = VBAD;      /* node is discarded */
                vp->v_usecount = 0;     /* XXX */
                *vpp = othervp;
                return 0;
        };
        VREF(lowervp);   /* Extra VREF will be vrele'd in null_node_create */
        hd = null_node_hash(lowervp);
        insque(xp, hd);
        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 lower vnode.
 */
int
null_node_create(mp, lowervp, newvpp)
        struct mount *mp;
        struct vnode *lowervp;
        struct vnode **newvpp;
{
        struct vnode *aliasvp;

        if (aliasvp = null_node_find(mp, lowervp)) {
                /*
                 * null_node_find has taken another reference
                 * to the alias vnode.
                 */
#ifdef NULLFS_DIAGNOSTIC
                vprint("null_node_create: exists", NULLTOV(ap));
#endif
                /* VREF(aliasvp); --- done in null_node_find */
        } else {
                int error;

                /*
                 * Get new vnode.
                 */
#ifdef NULLFS_DIAGNOSTIC
                printf("null_node_create: create new alias vnode\n");
#endif

                /*
                 * Make new vnode reference the null_node.
                 */
                if (error = null_node_alloc(mp, lowervp, &aliasvp))
                        return error;

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

        vrele(lowervp);

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

#ifdef NULLFS_DIAGNOSTIC
        vprint("null_node_create: alias", aliasvp);
        vprint("null_node_create: lower", lowervp);
#endif

        *newvpp = aliasvp;
        return (0);
}
#ifdef NULLFS_DIAGNOSTIC
struct vnode *
null_checkvp(vp, fil, lno)
        struct vnode *vp;
        char *fil;
        int lno;
{
        struct null_node *a = VTONULL(vp);
#if 0
        /*
         * Can't do this check because vop_reclaim runs
         * with a funny vop vector.
         */
        if (vp->v_op != null_vnodeop_p) {
                printf ("null_checkvp: on non-null-node\n");
                while (null_checkvp_barrier) /*WAIT*/ ;
                panic("null_checkvp");
        };
#endif
        if (a->null_lowervp == NULL) {
                /* Should never happen */
                int i; u_long *p;
                printf("vp = %x, ZERO ptr\n", vp);
                for (p = (u_long *) a, i = 0; i < 8; i++)
                        printf(" %x", p[i]);
                printf("\n");
                /* wait for debugger */
                while (null_checkvp_barrier) /*WAIT*/ ;
                panic("null_checkvp");
        }
        if (a->null_lowervp->v_usecount < 1) {
                int i; u_long *p;
                printf("vp = %x, unref'ed lowervp\n", vp);
                for (p = (u_long *) a, i = 0; i < 8; i++)
                        printf(" %x", p[i]);
                printf("\n");
                /* wait for debugger */
                while (null_checkvp_barrier) /*WAIT*/ ;
                panic ("null with unref'ed lowervp");
        };
#if 0
        printf("null %x/%d -> %x/%d [%s, %d]\n",
                NULLTOV(a), NULLTOV(a)->v_usecount,
                a->null_lowervp, a->null_lowervp->v_usecount,
                fil, lno);
#endif
        return a->null_lowervp;
}
#endif