null_subr.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1992, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * This code is derived from software donated to Berkeley by
    8  * Jan-Simon Pendry.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 3. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)null_subr.c 8.7 (Berkeley) 5/14/95
   35  *
   36  * $FreeBSD$
   37  */
   38 
   39 #include <sys/param.h>
   40 #include <sys/systm.h>
   41 #include <sys/kernel.h>
   42 #include <sys/lock.h>
   43 #include <sys/rwlock.h>
   44 #include <sys/malloc.h>
   45 #include <sys/mount.h>
   46 #include <sys/proc.h>
   47 #include <sys/vnode.h>
   48 
   49 #include <fs/nullfs/null.h>
   50 
   51 /*
   52  * Null layer cache:
   53  * Each cache entry holds a reference to the lower vnode
   54  * along with a pointer to the alias vnode.  When an
   55  * entry is added the lower vnode is VREF'd.  When the
   56  * alias is removed the lower vnode is vrele'd.
   57  */
   58 
   59 #define NULL_NHASH(vp) (&null_node_hashtbl[vfs_hash_index(vp) & null_hash_mask])
   60 
   61 static LIST_HEAD(null_node_hashhead, null_node) *null_node_hashtbl;
   62 static struct rwlock null_hash_lock;
   63 static u_long null_hash_mask;
   64 
   65 static MALLOC_DEFINE(M_NULLFSHASH, "nullfs_hash", "NULLFS hash table");
   66 MALLOC_DEFINE(M_NULLFSNODE, "nullfs_node", "NULLFS vnode private part");
   67 
   68 static struct vnode * null_hashins(struct mount *, struct null_node *);
   69 
   70 /*
   71  * Initialise cache headers
   72  */
   73 int
   74 nullfs_init(vfsp)
   75         struct vfsconf *vfsp;
   76 {
   77 
   78         null_node_hashtbl = hashinit(desiredvnodes, M_NULLFSHASH,
   79             &null_hash_mask);
   80         rw_init(&null_hash_lock, "nullhs");
   81         return (0);
   82 }
   83 
   84 int
   85 nullfs_uninit(vfsp)
   86         struct vfsconf *vfsp;
   87 {
   88 
   89         rw_destroy(&null_hash_lock);
   90         hashdestroy(null_node_hashtbl, M_NULLFSHASH, null_hash_mask);
   91         return (0);
   92 }
   93 
   94 /*
   95  * Return a VREF'ed alias for lower vnode if already exists, else 0.
   96  * Lower vnode should be locked on entry and will be left locked on exit.
   97  */
   98 struct vnode *
   99 null_hashget(mp, lowervp)
  100         struct mount *mp;
  101         struct vnode *lowervp;
  102 {
  103         struct null_node_hashhead *hd;
  104         struct null_node *a;
  105         struct vnode *vp;
  106 
  107         ASSERT_VOP_LOCKED(lowervp, "null_hashget");
  108 
  109         /*
  110          * Find hash base, and then search the (two-way) linked
  111          * list looking for a null_node structure which is referencing
  112          * the lower vnode.  If found, the increment the null_node
  113          * reference count (but NOT the lower vnode's VREF counter).
  114          */
  115         hd = NULL_NHASH(lowervp);
  116         if (LIST_EMPTY(hd))
  117                 return (NULLVP);
  118         rw_rlock(&null_hash_lock);
  119         LIST_FOREACH(a, hd, null_hash) {
  120                 if (a->null_lowervp == lowervp && NULLTOV(a)->v_mount == mp) {
  121                         /*
  122                          * Since we have the lower node locked the nullfs
  123                          * node can not be in the process of recycling.  If
  124                          * it had been recycled before we grabed the lower
  125                          * lock it would not have been found on the hash.
  126                          */
  127                         vp = NULLTOV(a);
  128                         vref(vp);
  129                         rw_runlock(&null_hash_lock);
  130                         return (vp);
  131                 }
  132         }
  133         rw_runlock(&null_hash_lock);
  134         return (NULLVP);
  135 }
  136 
  137 /*
  138  * Act like null_hashget, but add passed null_node to hash if no existing
  139  * node found.
  140  */
  141 static struct vnode *
  142 null_hashins(mp, xp)
  143         struct mount *mp;
  144         struct null_node *xp;
  145 {
  146         struct null_node_hashhead *hd;
  147         struct null_node *oxp;
  148         struct vnode *ovp;
  149 
  150         hd = NULL_NHASH(xp->null_lowervp);
  151         rw_wlock(&null_hash_lock);
  152         LIST_FOREACH(oxp, hd, null_hash) {
  153                 if (oxp->null_lowervp == xp->null_lowervp &&
  154                     NULLTOV(oxp)->v_mount == mp) {
  155                         /*
  156                          * See null_hashget for a description of this
  157                          * operation.
  158                          */
  159                         ovp = NULLTOV(oxp);
  160                         vref(ovp);
  161                         rw_wunlock(&null_hash_lock);
  162                         return (ovp);
  163                 }
  164         }
  165         LIST_INSERT_HEAD(hd, xp, null_hash);
  166         rw_wunlock(&null_hash_lock);
  167         return (NULLVP);
  168 }
  169 
  170 static void
  171 null_destroy_proto(struct vnode *vp, void *xp)
  172 {
  173 
  174         lockmgr(&vp->v_lock, LK_EXCLUSIVE, NULL);
  175         VI_LOCK(vp);
  176         vp->v_data = NULL;
  177         vp->v_vnlock = &vp->v_lock;
  178         vp->v_op = &dead_vnodeops;
  179         VI_UNLOCK(vp);
  180         vgone(vp);
  181         vput(vp);
  182         free(xp, M_NULLFSNODE);
  183 }
  184 
  185 static void
  186 null_insmntque_dtr(struct vnode *vp, void *xp)
  187 {
  188 
  189         vput(((struct null_node *)xp)->null_lowervp);
  190         null_destroy_proto(vp, xp);
  191 }
  192 
  193 /*
  194  * Make a new or get existing nullfs node.
  195  * Vp is the alias vnode, lowervp is the lower vnode.
  196  * 
  197  * The lowervp assumed to be locked and having "spare" reference. This routine
  198  * vrele lowervp if nullfs node was taken from hash. Otherwise it "transfers"
  199  * the caller's "spare" reference to created nullfs vnode.
  200  */
  201 int
  202 null_nodeget(mp, lowervp, vpp)
  203         struct mount *mp;
  204         struct vnode *lowervp;
  205         struct vnode **vpp;
  206 {
  207         struct null_node *xp;
  208         struct vnode *vp;
  209         int error;
  210 
  211         ASSERT_VOP_LOCKED(lowervp, "lowervp");
  212         VNPASS(lowervp->v_usecount > 0, lowervp);
  213 
  214         /* Lookup the hash firstly. */
  215         *vpp = null_hashget(mp, lowervp);
  216         if (*vpp != NULL) {
  217                 vrele(lowervp);
  218                 return (0);
  219         }
  220 
  221         /*
  222          * The insmntque1() call below requires the exclusive lock on
  223          * the nullfs vnode.  Upgrade the lock now if hash failed to
  224          * provide ready to use vnode.
  225          */
  226         if (VOP_ISLOCKED(lowervp) != LK_EXCLUSIVE) {
  227                 vn_lock(lowervp, LK_UPGRADE | LK_RETRY);
  228                 if (VN_IS_DOOMED(lowervp)) {
  229                         vput(lowervp);
  230                         return (ENOENT);
  231                 }
  232         }
  233 
  234         /*
  235          * We do not serialize vnode creation, instead we will check for
  236          * duplicates later, when adding new vnode to hash.
  237          * Note that duplicate can only appear in hash if the lowervp is
  238          * locked LK_SHARED.
  239          */
  240         xp = malloc(sizeof(struct null_node), M_NULLFSNODE, M_WAITOK);
  241 
  242         error = getnewvnode("nullfs", mp, &null_vnodeops, &vp);
  243         if (error) {
  244                 vput(lowervp);
  245                 free(xp, M_NULLFSNODE);
  246                 return (error);
  247         }
  248 
  249         xp->null_vnode = vp;
  250         xp->null_lowervp = lowervp;
  251         xp->null_flags = 0;
  252         vp->v_type = lowervp->v_type;
  253         vp->v_data = xp;
  254         vp->v_vnlock = lowervp->v_vnlock;
  255         error = insmntque1(vp, mp, null_insmntque_dtr, xp);
  256         if (error != 0)
  257                 return (error);
  258         if (lowervp == MOUNTTONULLMOUNT(mp)->nullm_lowerrootvp)
  259                 vp->v_vflag |= VV_ROOT;
  260 
  261         /*
  262          * We might miss the case where lower vnode sets VIRF_PGREAD
  263          * some time after construction, which is typical case.
  264          * null_open rechecks.
  265          */
  266         if ((vn_irflag_read(lowervp) & VIRF_PGREAD) != 0) {
  267                 MPASS(lowervp->v_object != NULL);
  268                 if ((vn_irflag_read(vp) & VIRF_PGREAD) == 0) {
  269                         if (vp->v_object == NULL)
  270                                 vp->v_object = lowervp->v_object;
  271                         else
  272                                 MPASS(vp->v_object == lowervp->v_object);
  273                         vn_irflag_set_cond(vp, VIRF_PGREAD);
  274                 } else {
  275                         MPASS(vp->v_object != NULL);
  276                 }
  277         }
  278 
  279         /*
  280          * Atomically insert our new node into the hash or vget existing 
  281          * if someone else has beaten us to it.
  282          */
  283         *vpp = null_hashins(mp, xp);
  284         if (*vpp != NULL) {
  285                 vrele(lowervp);
  286                 vp->v_object = NULL;    /* in case VIRF_PGREAD set it */
  287                 null_destroy_proto(vp, xp);
  288                 return (0);
  289         }
  290         *vpp = vp;
  291 
  292         return (0);
  293 }
  294 
  295 /*
  296  * Remove node from hash.
  297  */
  298 void
  299 null_hashrem(xp)
  300         struct null_node *xp;
  301 {
  302 
  303         rw_wlock(&null_hash_lock);
  304         LIST_REMOVE(xp, null_hash);
  305         rw_wunlock(&null_hash_lock);
  306 }
  307 
  308 #ifdef DIAGNOSTIC
  309 
  310 struct vnode *
  311 null_checkvp(vp, fil, lno)
  312         struct vnode *vp;
  313         char *fil;
  314         int lno;
  315 {
  316         struct null_node *a = VTONULL(vp);
  317 
  318 #ifdef notyet
  319         /*
  320          * Can't do this check because vop_reclaim runs
  321          * with a funny vop vector.
  322          */
  323         if (vp->v_op != null_vnodeop_p) {
  324                 printf ("null_checkvp: on non-null-node\n");
  325                 panic("null_checkvp");
  326         }
  327 #endif
  328         if (a->null_lowervp == NULLVP) {
  329                 /* Should never happen */
  330                 panic("null_checkvp %p", vp);
  331         }
  332         VI_LOCK_FLAGS(a->null_lowervp, MTX_DUPOK);
  333         if (a->null_lowervp->v_usecount < 1)
  334                 panic ("null with unref'ed lowervp, vp %p lvp %p",
  335                     vp, a->null_lowervp);
  336         VI_UNLOCK(a->null_lowervp);
  337 #ifdef notyet
  338         printf("null %x/%d -> %x/%d [%s, %d]\n",
  339                 NULLTOV(a), vrefcnt(NULLTOV(a)),
  340                 a->null_lowervp, vrefcnt(a->null_lowervp),
  341                 fil, lno);
  342 #endif
  343         return (a->null_lowervp);
  344 }
  345 #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
