FreeBSD/Linux Kernel Cross Reference
sys/fs/nullfs/null_subr.c

     /*-
      * 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.
     * 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_subr.c 8.7 (Berkeley) 5/14/95
     *
     * $FreeBSD$
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/proc.h>
    #include <sys/vnode.h>
    
    #include <fs/nullfs/null.h>
    
    #define LOG2_SIZEVNODE 8                /* log2(sizeof struct vnode) */
    #define NNULLNODECACHE 16
    
    /*
     * 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.
     */
    
    #define NULL_NHASH(vp) \
            (&null_node_hashtbl[(((uintptr_t)vp)>>LOG2_SIZEVNODE) & null_node_hash])
    
    static LIST_HEAD(null_node_hashhead, null_node) *null_node_hashtbl;
    static u_long null_node_hash;
    struct mtx null_hashmtx;
    
    static MALLOC_DEFINE(M_NULLFSHASH, "NULLFS hash", "NULLFS hash table");
    MALLOC_DEFINE(M_NULLFSNODE, "NULLFS node", "NULLFS vnode private part");
    
    static struct vnode * null_hashget(struct mount *, struct vnode *);
    static struct vnode * null_hashins(struct mount *, struct null_node *);
    
    /*
     * Initialise cache headers
     */
    int
    nullfs_init(vfsp)
            struct vfsconf *vfsp;
    {
    
            NULLFSDEBUG("nullfs_init\n");           /* printed during system boot */
            null_node_hashtbl = hashinit(NNULLNODECACHE, M_NULLFSHASH, &null_node_hash);
            mtx_init(&null_hashmtx, "nullhs", NULL, MTX_DEF);
            return (0);
    }
    
    int
    nullfs_uninit(vfsp)
            struct vfsconf *vfsp;
    {
    
            mtx_destroy(&null_hashmtx);
            free(null_node_hashtbl, M_NULLFSHASH);
            return (0);
    }
    
    /*
     * Return a VREF'ed alias for lower vnode if already exists, else 0.
     * Lower vnode should be locked on entry and will be left locked on exit.
    */
   static struct vnode *
   null_hashget(mp, lowervp)
           struct mount *mp;
           struct vnode *lowervp;
   {
           struct thread *td = curthread;  /* XXX */
           struct null_node_hashhead *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_NHASH(lowervp);
   loop:
           mtx_lock(&null_hashmtx);
           LIST_FOREACH(a, hd, null_hash) {
                   if (a->null_lowervp == lowervp && NULLTOV(a)->v_mount == mp) {
                           vp = NULLTOV(a);
                           mtx_lock(&vp->v_interlock);
                           /*
                            * Don't block if nullfs vnode is being recycled.
                            * We already hold a lock on the lower vnode, thus
                            * waiting might deadlock against the thread
                            * recycling the nullfs vnode or another thread
                            * in vrele() waiting for the vnode lock.
                            */
                           if ((vp->v_iflag & VI_XLOCK) != 0) {
                                   VI_UNLOCK(vp);
                                   continue;
                           }
                           mtx_unlock(&null_hashmtx);
                           /*
                            * We need vget for the VXLOCK
                            * stuff, but we don't want to lock
                            * the lower node.
                            */
                           if (vget(vp, LK_EXCLUSIVE | LK_THISLAYER | LK_INTERLOCK, td))
                                   goto loop;
   
                           return (vp);
                   }
           }
           mtx_unlock(&null_hashmtx);
           return (NULLVP);
   }
   
   /*
    * Act like null_hashget, but add passed null_node to hash if no existing
    * node found.
    */
   static struct vnode *
   null_hashins(mp, xp)
           struct mount *mp;
           struct null_node *xp;
   {
           struct thread *td = curthread;  /* XXX */
           struct null_node_hashhead *hd;
           struct null_node *oxp;
           struct vnode *ovp;
   
           hd = NULL_NHASH(xp->null_lowervp);
   loop:
           mtx_lock(&null_hashmtx);
           LIST_FOREACH(oxp, hd, null_hash) {
                   if (oxp->null_lowervp == xp->null_lowervp &&
                       NULLTOV(oxp)->v_mount == mp) {
                           ovp = NULLTOV(oxp);
                           mtx_lock(&ovp->v_interlock);
                           /*
                            * Don't block if nullfs vnode is being recycled.
                            * We already hold a lock on the lower vnode, thus
                            * waiting might deadlock against the thread
                            * recycling the nullfs vnode or another thread
                            * in vrele() waiting for the vnode lock.
                            */
                           if ((ovp->v_iflag & VI_XLOCK) != 0) {
                                   VI_UNLOCK(ovp);
                                   continue;
                           }
                           mtx_unlock(&null_hashmtx);
                           if (vget(ovp, LK_EXCLUSIVE | LK_THISLAYER | LK_INTERLOCK, td))
                                   goto loop;
   
                           return (ovp);
                   }
           }
           LIST_INSERT_HEAD(hd, xp, null_hash);
           mtx_unlock(&null_hashmtx);
           return (NULLVP);
   }
   
   /*
    * Make a new or get existing nullfs node.
    * Vp is the alias vnode, lowervp is the lower vnode.
    * 
    * The lowervp assumed to be locked and having "spare" reference. This routine
    * vrele lowervp if nullfs node was taken from hash. Otherwise it "transfers"
    * the caller's "spare" reference to created nullfs vnode.
    */
   int
   null_nodeget(mp, lowervp, vpp)
           struct mount *mp;
           struct vnode *lowervp;
           struct vnode **vpp;
   {
           struct thread *td = curthread;  /* XXX */
           struct null_node *xp;
           struct vnode *vp;
           int error;
   
           /* Lookup the hash firstly */
           *vpp = null_hashget(mp, lowervp);
           if (*vpp != NULL) {
                   vrele(lowervp);
                   return (0);
           }
   
           /*
            * We do not serialize vnode creation, instead we will check for
            * duplicates later, when adding new vnode to hash.
            *
            * Note that duplicate can only appear in hash if the lowervp is
            * locked LK_SHARED.
            */
   
           /*
            * Do the MALLOC before the getnewvnode since doing so afterward
            * might cause a bogus v_data pointer to get dereferenced
            * elsewhere if MALLOC should block.
            */
           MALLOC(xp, struct null_node *, sizeof(struct null_node),
               M_NULLFSNODE, M_WAITOK);
   
           error = getnewvnode("null", mp, null_vnodeop_p, &vp);
           if (error) {
                   FREE(xp, M_NULLFSNODE);
                   return (error);
           }
   
           xp->null_vnode = vp;
           xp->null_lowervp = lowervp;
           xp->null_pending_locks = 0;
           xp->null_drain_wakeup = 0;
   
           vp->v_type = lowervp->v_type;
           vp->v_data = xp;
   
           /*
            * From NetBSD:
            * 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 new vnode.
            */
   
           vp->v_vnlock = lowervp->v_vnlock;
           error = VOP_LOCK(vp, LK_EXCLUSIVE | LK_THISLAYER, td);
           if (error)
                   panic("null_nodeget: can't lock new vnode\n");
   
           /*
            * Atomically insert our new node into the hash or vget existing 
            * if someone else has beaten us to it.
            */
           *vpp = null_hashins(mp, xp);
           if (*vpp != NULL) {
                   vrele(lowervp);
                   VOP_UNLOCK(vp, LK_THISLAYER, td);
                   vp->v_vnlock = NULL;
                   xp->null_lowervp = NULL;
                   vrele(vp);
                   return (0);
           }
   
           /*
            * XXX We take extra vref just to workaround UFS's XXX:
            * UFS can vrele() vnode in VOP_CLOSE() in some cases. Luckily, this
            * can only happen if v_usecount == 1. To workaround, we just don't
            * let v_usecount be 1, it will be 2 or more.
            */
           VREF(lowervp);
   
           *vpp = vp;
   
           return (0);
   }
   
   /*
    * Remove node from hash.
    */
   void
   null_hashrem(xp)
           struct null_node *xp;
   {
   
           mtx_lock(&null_hashmtx);
           LIST_REMOVE(xp, null_hash);
           mtx_unlock(&null_hashmtx);
   }
   
   #ifdef DIAGNOSTIC
   
   #ifdef KDB
   #define null_checkvp_barrier    1
   #else
   #define null_checkvp_barrier    0
   #endif
   
   struct vnode *
   null_checkvp(vp, fil, lno)
           struct vnode *vp;
           char *fil;
           int lno;
   {
           struct null_node *a = VTONULL(vp);
   #ifdef notyet
           /*
            * 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 == NULLVP) {
                   /* Should never happen */
                   int i; u_long *p;
                   printf("vp = %p, ZERO ptr\n", (void *)vp);
                   for (p = (u_long *) a, i = 0; i < 8; i++)
                           printf(" %lx", p[i]);
                   printf("\n");
                   /* wait for debugger */
                   while (null_checkvp_barrier) /*WAIT*/ ;
                   panic("null_checkvp");
           }
           if (vrefcnt(a->null_lowervp) < 1) {
                   int i; u_long *p;
                   printf("vp = %p, unref'ed lowervp\n", (void *)vp);
                   for (p = (u_long *) a, i = 0; i < 8; i++)
                           printf(" %lx", p[i]);
                   printf("\n");
                   /* wait for debugger */
                   while (null_checkvp_barrier) /*WAIT*/ ;
                   panic ("null with unref'ed lowervp");
           };
   #ifdef notyet
           printf("null %x/%d -> %x/%d [%s, %d]\n",
                   NULLTOV(a), vrefcnt(NULLTOV(a)),
                   a->null_lowervp, vrefcnt(a->null_lowervp),
                   fil, lno);
   #endif
           return a->null_lowervp;
   }
   #endif

Cache object: 4fe597182788bc841cc292842600a6fa