null_subr.c

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    1 /*
    2  * Copyright (c) 1992, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * This code is derived from software donated to Berkeley by
    6  * Jan-Simon Pendry.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. All advertising materials mentioning features or use of this software
   17  *    must display the following acknowledgement:
   18  *      This product includes software developed by the University of
   19  *      California, Berkeley and its contributors.
   20  * 4. Neither the name of the University nor the names of its contributors
   21  *    may be used to endorse or promote products derived from this software
   22  *    without specific prior written permission.
   23  *
   24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   34  * SUCH DAMAGE.
   35  *
   36  *      @(#)null_subr.c 8.7 (Berkeley) 5/14/95
   37  *
   38  * $FreeBSD: releng/5.0/sys/fs/nullfs/null_subr.c 105077 2002-10-14 03:20:36Z mckusick $
   39  */
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/lock.h>
   45 #include <sys/mutex.h>
   46 #include <sys/malloc.h>
   47 #include <sys/mount.h>
   48 #include <sys/proc.h>
   49 #include <sys/vnode.h>
   50 
   51 #include <fs/nullfs/null.h>
   52 
   53 #define LOG2_SIZEVNODE 7                /* log2(sizeof struct vnode) */
   54 #define NNULLNODECACHE 16
   55 
   56 /*
   57  * Null layer cache:
   58  * Each cache entry holds a reference to the lower vnode
   59  * along with a pointer to the alias vnode.  When an
   60  * entry is added the lower vnode is VREF'd.  When the
   61  * alias is removed the lower vnode is vrele'd.
   62  */
   63 
   64 #define NULL_NHASH(vp) \
   65         (&null_node_hashtbl[(((uintptr_t)vp)>>LOG2_SIZEVNODE) & null_node_hash])
   66 
   67 static LIST_HEAD(null_node_hashhead, null_node) *null_node_hashtbl;
   68 static u_long null_node_hash;
   69 struct mtx null_hashmtx;
   70 
   71 static MALLOC_DEFINE(M_NULLFSHASH, "NULLFS hash", "NULLFS hash table");
   72 MALLOC_DEFINE(M_NULLFSNODE, "NULLFS node", "NULLFS vnode private part");
   73 
   74 static struct vnode * null_hashget(struct vnode *);
   75 static struct vnode * null_hashins(struct null_node *);
   76 
   77 /*
   78  * Initialise cache headers
   79  */
   80 int
   81 nullfs_init(vfsp)
   82         struct vfsconf *vfsp;
   83 {
   84 
   85         NULLFSDEBUG("nullfs_init\n");           /* printed during system boot */
   86         null_node_hashtbl = hashinit(NNULLNODECACHE, M_NULLFSHASH, &null_node_hash);
   87         mtx_init(&null_hashmtx, "nullhs", NULL, MTX_DEF);
   88         return (0);
   89 }
   90 
   91 int
   92 nullfs_uninit(vfsp)
   93         struct vfsconf *vfsp;
   94 {
   95 
   96         mtx_destroy(&null_hashmtx);
   97         free(null_node_hashtbl, M_NULLFSHASH);
   98         return (0);
   99 }
  100 
  101 /*
  102  * Return a VREF'ed alias for lower vnode if already exists, else 0.
  103  * Lower vnode should be locked on entry and will be left locked on exit.
  104  */
  105 static struct vnode *
  106 null_hashget(lowervp)
  107         struct vnode *lowervp;
  108 {
  109         struct thread *td = curthread;  /* XXX */
  110         struct null_node_hashhead *hd;
  111         struct null_node *a;
  112         struct vnode *vp;
  113 
  114         /*
  115          * Find hash base, and then search the (two-way) linked
  116          * list looking for a null_node structure which is referencing
  117          * the lower vnode.  If found, the increment the null_node
  118          * reference count (but NOT the lower vnode's VREF counter).
  119          */
  120         hd = NULL_NHASH(lowervp);
  121 loop:
  122         mtx_lock(&null_hashmtx);
  123         LIST_FOREACH(a, hd, null_hash) {
  124                 if (a->null_lowervp == lowervp) {
  125                         vp = NULLTOV(a);
  126                         mtx_lock(&vp->v_interlock);
  127                         mtx_unlock(&null_hashmtx);
  128                         /*
  129                          * We need vget for the VXLOCK
  130                          * stuff, but we don't want to lock
  131                          * the lower node.
  132                          */
  133                         if (vget(vp, LK_EXCLUSIVE | LK_THISLAYER | LK_INTERLOCK, td))
  134                                 goto loop;
  135 
  136                         return (vp);
  137                 }
  138         }
  139         mtx_unlock(&null_hashmtx);
  140         return (NULLVP);
  141 }
  142 
  143 /*
  144  * Act like null_hashget, but add passed null_node to hash if no existing
  145  * node found.
  146  */
  147 static struct vnode *
  148 null_hashins(xp)
  149         struct null_node *xp;
  150 {
  151         struct thread *td = curthread;  /* XXX */
  152         struct null_node_hashhead *hd;
  153         struct null_node *oxp;
  154         struct vnode *ovp;
  155 
  156         hd = NULL_NHASH(xp->null_lowervp);
  157 loop:
  158         mtx_lock(&null_hashmtx);
  159         LIST_FOREACH(oxp, hd, null_hash) {
  160                 if (oxp->null_lowervp == xp->null_lowervp) {
  161                         ovp = NULLTOV(oxp);
  162                         mtx_lock(&ovp->v_interlock);
  163                         mtx_unlock(&null_hashmtx);
  164                         if (vget(ovp, LK_EXCLUSIVE | LK_THISLAYER | LK_INTERLOCK, td))
  165                                 goto loop;
  166 
  167                         return (ovp);
  168                 }
  169         }
  170         LIST_INSERT_HEAD(hd, xp, null_hash);
  171         mtx_unlock(&null_hashmtx);
  172         return (NULLVP);
  173 }
  174 
  175 /*
  176  * Make a new or get existing nullfs node.
  177  * Vp is the alias vnode, lowervp is the lower vnode.
  178  * 
  179  * The lowervp assumed to be locked and having "spare" reference. This routine
  180  * vrele lowervp if nullfs node was taken from hash. Otherwise it "transfers"
  181  * the caller's "spare" reference to created nullfs vnode.
  182  */
  183 int
  184 null_nodeget(mp, lowervp, vpp)
  185         struct mount *mp;
  186         struct vnode *lowervp;
  187         struct vnode **vpp;
  188 {
  189         struct thread *td = curthread;  /* XXX */
  190         struct null_node *xp;
  191         struct vnode *vp;
  192         int error;
  193 
  194         /* Lookup the hash firstly */
  195         *vpp = null_hashget(lowervp);
  196         if (*vpp != NULL) {
  197                 vrele(lowervp);
  198                 return (0);
  199         }
  200 
  201         /*
  202          * We do not serialize vnode creation, instead we will check for
  203          * duplicates later, when adding new vnode to hash.
  204          *
  205          * Note that duplicate can only appear in hash if the lowervp is
  206          * locked LK_SHARED.
  207          */
  208 
  209         /*
  210          * Do the MALLOC before the getnewvnode since doing so afterward
  211          * might cause a bogus v_data pointer to get dereferenced
  212          * elsewhere if MALLOC should block.
  213          */
  214         MALLOC(xp, struct null_node *, sizeof(struct null_node),
  215             M_NULLFSNODE, M_WAITOK);
  216 
  217         error = getnewvnode("null", mp, null_vnodeop_p, &vp);
  218         if (error) {
  219                 FREE(xp, M_NULLFSNODE);
  220                 return (error);
  221         }
  222 
  223         xp->null_vnode = vp;
  224         xp->null_lowervp = lowervp;
  225 
  226         vp->v_type = lowervp->v_type;
  227         vp->v_data = xp;
  228 
  229         /*
  230          * From NetBSD:
  231          * Now lock the new node. We rely on the fact that we were passed
  232          * a locked vnode. If the lower node is exporting a struct lock
  233          * (v_vnlock != NULL) then we just set the upper v_vnlock to the
  234          * lower one, and both are now locked. If the lower node is exporting
  235          * NULL, then we copy that up and manually lock the new vnode.
  236          */
  237 
  238         vp->v_vnlock = lowervp->v_vnlock;
  239         error = VOP_LOCK(vp, LK_EXCLUSIVE | LK_THISLAYER, td);
  240         if (error)
  241                 panic("null_nodeget: can't lock new vnode\n");
  242 
  243         /*
  244          * Atomically insert our new node into the hash or vget existing 
  245          * if someone else has beaten us to it.
  246          */
  247         *vpp = null_hashins(xp);
  248         if (*vpp != NULL) {
  249                 vrele(lowervp);
  250                 VOP_UNLOCK(vp, LK_THISLAYER, td);
  251                 vp->v_vnlock = NULL;
  252                 xp->null_lowervp = NULL;
  253                 vrele(vp);
  254                 return (0);
  255         }
  256 
  257         /*
  258          * XXX We take extra vref just to workaround UFS's XXX:
  259          * UFS can vrele() vnode in VOP_CLOSE() in some cases. Luckily, this
  260          * can only happen if v_usecount == 1. To workaround, we just don't
  261          * let v_usecount be 1, it will be 2 or more.
  262          */
  263         VREF(lowervp);
  264 
  265         *vpp = vp;
  266 
  267         return (0);
  268 }
  269 
  270 /*
  271  * Remove node from hash.
  272  */
  273 void
  274 null_hashrem(xp)
  275         struct null_node *xp;
  276 {
  277 
  278         mtx_lock(&null_hashmtx);
  279         LIST_REMOVE(xp, null_hash);
  280         mtx_unlock(&null_hashmtx);
  281 }
  282 
  283 #ifdef DIAGNOSTIC
  284 #include "opt_ddb.h"
  285 
  286 #ifdef DDB
  287 #define null_checkvp_barrier    1
  288 #else
  289 #define null_checkvp_barrier    0
  290 #endif
  291 
  292 struct vnode *
  293 null_checkvp(vp, fil, lno)
  294         struct vnode *vp;
  295         char *fil;
  296         int lno;
  297 {
  298         struct null_node *a = VTONULL(vp);
  299 #ifdef notyet
  300         /*
  301          * Can't do this check because vop_reclaim runs
  302          * with a funny vop vector.
  303          */
  304         if (vp->v_op != null_vnodeop_p) {
  305                 printf ("null_checkvp: on non-null-node\n");
  306                 while (null_checkvp_barrier) /*WAIT*/ ;
  307                 panic("null_checkvp");
  308         };
  309 #endif
  310         if (a->null_lowervp == NULLVP) {
  311                 /* Should never happen */
  312                 int i; u_long *p;
  313                 printf("vp = %p, ZERO ptr\n", (void *)vp);
  314                 for (p = (u_long *) a, i = 0; i < 8; i++)
  315                         printf(" %lx", p[i]);
  316                 printf("\n");
  317                 /* wait for debugger */
  318                 while (null_checkvp_barrier) /*WAIT*/ ;
  319                 panic("null_checkvp");
  320         }
  321         if (vrefcnt(a->null_lowervp) < 1) {
  322                 int i; u_long *p;
  323                 printf("vp = %p, unref'ed lowervp\n", (void *)vp);
  324                 for (p = (u_long *) a, i = 0; i < 8; i++)
  325                         printf(" %lx", p[i]);
  326                 printf("\n");
  327                 /* wait for debugger */
  328                 while (null_checkvp_barrier) /*WAIT*/ ;
  329                 panic ("null with unref'ed lowervp");
  330         };
  331 #ifdef notyet
  332         printf("null %x/%d -> %x/%d [%s, %d]\n",
  333                 NULLTOV(a), vrefcnt(NULLTOV(a)),
  334                 a->null_lowervp, vrefcnt(a->null_lowervp),
  335                 fil, lno);
  336 #endif
  337         return a->null_lowervp;
  338 }
  339 #endif
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FreeBSD/Linux Kernel Cross Reference sys/fs/nullfs/null_subr.c

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