pseudofs_vncache.c

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    1 /*-
    2  * Copyright (c) 2001 Dag-Erling Coïdan Smørgrav
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer
   10  *    in this position and unchanged.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  * 3. The name of the author may not be used to endorse or promote products
   15  *    derived from this software without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   18  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   19  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   20  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   21  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   22  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   27  */
   28 
   29 #include <sys/cdefs.h>
   30 __FBSDID("$FreeBSD: releng/11.0/sys/fs/pseudofs/pseudofs_vncache.c 303906 2016-08-10 12:34:49Z kib $");
   31 
   32 #include "opt_pseudofs.h"
   33 
   34 #include <sys/param.h>
   35 #include <sys/kernel.h>
   36 #include <sys/systm.h>
   37 #include <sys/eventhandler.h>
   38 #include <sys/lock.h>
   39 #include <sys/malloc.h>
   40 #include <sys/mutex.h>
   41 #include <sys/proc.h>
   42 #include <sys/sysctl.h>
   43 #include <sys/vnode.h>
   44 
   45 #include <fs/pseudofs/pseudofs.h>
   46 #include <fs/pseudofs/pseudofs_internal.h>
   47 
   48 static MALLOC_DEFINE(M_PFSVNCACHE, "pfs_vncache", "pseudofs vnode cache");
   49 
   50 static struct mtx pfs_vncache_mutex;
   51 static struct pfs_vdata *pfs_vncache;
   52 static eventhandler_tag pfs_exit_tag;
   53 static void pfs_exit(void *arg, struct proc *p);
   54 
   55 static SYSCTL_NODE(_vfs_pfs, OID_AUTO, vncache, CTLFLAG_RW, 0,
   56     "pseudofs vnode cache");
   57 
   58 static int pfs_vncache_entries;
   59 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, entries, CTLFLAG_RD,
   60     &pfs_vncache_entries, 0,
   61     "number of entries in the vnode cache");
   62 
   63 static int pfs_vncache_maxentries;
   64 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, maxentries, CTLFLAG_RD,
   65     &pfs_vncache_maxentries, 0,
   66     "highest number of entries in the vnode cache");
   67 
   68 static int pfs_vncache_hits;
   69 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, hits, CTLFLAG_RD,
   70     &pfs_vncache_hits, 0,
   71     "number of cache hits since initialization");
   72 
   73 static int pfs_vncache_misses;
   74 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, misses, CTLFLAG_RD,
   75     &pfs_vncache_misses, 0,
   76     "number of cache misses since initialization");
   77 
   78 extern struct vop_vector pfs_vnodeops;  /* XXX -> .h file */
   79 
   80 /*
   81  * Initialize vnode cache
   82  */
   83 void
   84 pfs_vncache_load(void)
   85 {
   86 
   87         mtx_init(&pfs_vncache_mutex, "pfs_vncache", NULL, MTX_DEF);
   88         pfs_exit_tag = EVENTHANDLER_REGISTER(process_exit, pfs_exit, NULL,
   89             EVENTHANDLER_PRI_ANY);
   90 }
   91 
   92 /*
   93  * Tear down vnode cache
   94  */
   95 void
   96 pfs_vncache_unload(void)
   97 {
   98 
   99         EVENTHANDLER_DEREGISTER(process_exit, pfs_exit_tag);
  100         KASSERT(pfs_vncache_entries == 0,
  101             ("%d vncache entries remaining", pfs_vncache_entries));
  102         mtx_destroy(&pfs_vncache_mutex);
  103 }
  104 
  105 /*
  106  * Allocate a vnode
  107  */
  108 int
  109 pfs_vncache_alloc(struct mount *mp, struct vnode **vpp,
  110                   struct pfs_node *pn, pid_t pid)
  111 {
  112         struct pfs_vdata *pvd, *pvd2;
  113         struct vnode *vp;
  114         int error;
  115 
  116         /*
  117          * See if the vnode is in the cache.
  118          * XXX linear search is not very efficient.
  119          */
  120 retry:
  121         mtx_lock(&pfs_vncache_mutex);
  122         for (pvd = pfs_vncache; pvd; pvd = pvd->pvd_next) {
  123                 if (pvd->pvd_pn == pn && pvd->pvd_pid == pid &&
  124                     pvd->pvd_vnode->v_mount == mp) {
  125                         vp = pvd->pvd_vnode;
  126                         VI_LOCK(vp);
  127                         mtx_unlock(&pfs_vncache_mutex);
  128                         if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK, curthread) == 0) {
  129                                 ++pfs_vncache_hits;
  130                                 *vpp = vp;
  131                                 /*
  132                                  * Some callers cache_enter(vp) later, so
  133                                  * we have to make sure it's not in the
  134                                  * VFS cache so it doesn't get entered
  135                                  * twice.  A better solution would be to
  136                                  * make pfs_vncache_alloc() responsible
  137                                  * for entering the vnode in the VFS
  138                                  * cache.
  139                                  */
  140                                 cache_purge(vp);
  141                                 return (0);
  142                         }
  143                         goto retry;
  144                 }
  145         }
  146         mtx_unlock(&pfs_vncache_mutex);
  147 
  148         /* nope, get a new one */
  149         pvd = malloc(sizeof *pvd, M_PFSVNCACHE, M_WAITOK);
  150         pvd->pvd_next = pvd->pvd_prev = NULL;
  151         error = getnewvnode("pseudofs", mp, &pfs_vnodeops, vpp);
  152         if (error) {
  153                 free(pvd, M_PFSVNCACHE);
  154                 return (error);
  155         }
  156         pvd->pvd_pn = pn;
  157         pvd->pvd_pid = pid;
  158         (*vpp)->v_data = pvd;
  159         switch (pn->pn_type) {
  160         case pfstype_root:
  161                 (*vpp)->v_vflag = VV_ROOT;
  162 #if 0
  163                 printf("root vnode allocated\n");
  164 #endif
  165                 /* fall through */
  166         case pfstype_dir:
  167         case pfstype_this:
  168         case pfstype_parent:
  169         case pfstype_procdir:
  170                 (*vpp)->v_type = VDIR;
  171                 break;
  172         case pfstype_file:
  173                 (*vpp)->v_type = VREG;
  174                 break;
  175         case pfstype_symlink:
  176                 (*vpp)->v_type = VLNK;
  177                 break;
  178         case pfstype_none:
  179                 KASSERT(0, ("pfs_vncache_alloc called for null node\n"));
  180         default:
  181                 panic("%s has unexpected type: %d", pn->pn_name, pn->pn_type);
  182         }
  183         /*
  184          * Propagate flag through to vnode so users know it can change
  185          * if the process changes (i.e. execve)
  186          */
  187         if ((pn->pn_flags & PFS_PROCDEP) != 0)
  188                 (*vpp)->v_vflag |= VV_PROCDEP;
  189         pvd->pvd_vnode = *vpp;
  190         vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY);
  191         VN_LOCK_AREC(*vpp);
  192         error = insmntque(*vpp, mp);
  193         if (error != 0) {
  194                 free(pvd, M_PFSVNCACHE);
  195                 *vpp = NULLVP;
  196                 return (error);
  197         }
  198 retry2:
  199         mtx_lock(&pfs_vncache_mutex);
  200         /*
  201          * Other thread may race with us, creating the entry we are
  202          * going to insert into the cache. Recheck after
  203          * pfs_vncache_mutex is reacquired.
  204          */
  205         for (pvd2 = pfs_vncache; pvd2; pvd2 = pvd2->pvd_next) {
  206                 if (pvd2->pvd_pn == pn && pvd2->pvd_pid == pid &&
  207                     pvd2->pvd_vnode->v_mount == mp) {
  208                         vp = pvd2->pvd_vnode;
  209                         VI_LOCK(vp);
  210                         mtx_unlock(&pfs_vncache_mutex);
  211                         if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK, curthread) == 0) {
  212                                 ++pfs_vncache_hits;
  213                                 vgone(*vpp);
  214                                 vput(*vpp);
  215                                 *vpp = vp;
  216                                 cache_purge(vp);
  217                                 return (0);
  218                         }
  219                         goto retry2;
  220                 }
  221         }
  222         ++pfs_vncache_misses;
  223         if (++pfs_vncache_entries > pfs_vncache_maxentries)
  224                 pfs_vncache_maxentries = pfs_vncache_entries;
  225         pvd->pvd_prev = NULL;
  226         pvd->pvd_next = pfs_vncache;
  227         if (pvd->pvd_next)
  228                 pvd->pvd_next->pvd_prev = pvd;
  229         pfs_vncache = pvd;
  230         mtx_unlock(&pfs_vncache_mutex);
  231         return (0);
  232 }
  233 
  234 /*
  235  * Free a vnode
  236  */
  237 int
  238 pfs_vncache_free(struct vnode *vp)
  239 {
  240         struct pfs_vdata *pvd;
  241 
  242         mtx_lock(&pfs_vncache_mutex);
  243         pvd = (struct pfs_vdata *)vp->v_data;
  244         KASSERT(pvd != NULL, ("pfs_vncache_free(): no vnode data\n"));
  245         if (pvd->pvd_next)
  246                 pvd->pvd_next->pvd_prev = pvd->pvd_prev;
  247         if (pvd->pvd_prev) {
  248                 pvd->pvd_prev->pvd_next = pvd->pvd_next;
  249                 --pfs_vncache_entries;
  250         } else if (pfs_vncache == pvd) {
  251                 pfs_vncache = pvd->pvd_next;
  252                 --pfs_vncache_entries;
  253         }
  254         mtx_unlock(&pfs_vncache_mutex);
  255 
  256         free(pvd, M_PFSVNCACHE);
  257         vp->v_data = NULL;
  258         return (0);
  259 }
  260 
  261 /*
  262  * Purge the cache of dead entries
  263  *
  264  * This is extremely inefficient due to the fact that vgone() not only
  265  * indirectly modifies the vnode cache, but may also sleep.  We can
  266  * neither hold pfs_vncache_mutex across a vgone() call, nor make any
  267  * assumptions about the state of the cache after vgone() returns.  In
  268  * consequence, we must start over after every vgone() call, and keep
  269  * trying until we manage to traverse the entire cache.
  270  *
  271  * The only way to improve this situation is to change the data structure
  272  * used to implement the cache.
  273  */
  274 static void
  275 pfs_purge_locked(struct pfs_node *pn)
  276 {
  277         struct pfs_vdata *pvd;
  278         struct vnode *vnp;
  279 
  280         mtx_assert(&pfs_vncache_mutex, MA_OWNED);
  281         pvd = pfs_vncache;
  282         while (pvd != NULL) {
  283                 if (pvd->pvd_dead || (pn != NULL && pvd->pvd_pn == pn)) {
  284                         vnp = pvd->pvd_vnode;
  285                         vhold(vnp);
  286                         mtx_unlock(&pfs_vncache_mutex);
  287                         VOP_LOCK(vnp, LK_EXCLUSIVE);
  288                         vgone(vnp);
  289                         VOP_UNLOCK(vnp, 0);
  290                         mtx_lock(&pfs_vncache_mutex);
  291                         vdrop(vnp);
  292                         pvd = pfs_vncache;
  293                 } else {
  294                         pvd = pvd->pvd_next;
  295                 }
  296         }
  297 }
  298 
  299 void
  300 pfs_purge(struct pfs_node *pn)
  301 {
  302 
  303         mtx_lock(&pfs_vncache_mutex);
  304         pfs_purge_locked(pn);
  305         mtx_unlock(&pfs_vncache_mutex);
  306 }
  307 
  308 /*
  309  * Free all vnodes associated with a defunct process
  310  */
  311 static void
  312 pfs_exit(void *arg, struct proc *p)
  313 {
  314         struct pfs_vdata *pvd;
  315         int dead;
  316 
  317         if (pfs_vncache == NULL)
  318                 return;
  319         mtx_lock(&pfs_vncache_mutex);
  320         for (pvd = pfs_vncache, dead = 0; pvd != NULL; pvd = pvd->pvd_next)
  321                 if (pvd->pvd_pid == p->p_pid)
  322                         dead = pvd->pvd_dead = 1;
  323         if (dead)
  324                 pfs_purge_locked(NULL);
  325         mtx_unlock(&pfs_vncache_mutex);
  326 }
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FreeBSD/Linux Kernel Cross Reference sys/fs/pseudofs/pseudofs_vncache.c

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sys/fs/pseudofs/pseudofs_vncache.c
