The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/fs/pseudofs/pseudofs_vncache.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 2001 Dag-Erling Coïdan Smørgrav
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer
   12  *    in this position and unchanged.
   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. The name of the author may not be used to endorse or promote products
   17  *    derived from this software without specific prior written permission.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   20  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   21  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   22  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   23  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   24  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   28  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   29  */
   30 
   31 #include <sys/cdefs.h>
   32 __FBSDID("$FreeBSD$");
   33 
   34 #include "opt_pseudofs.h"
   35 
   36 #include <sys/param.h>
   37 #include <sys/kernel.h>
   38 #include <sys/systm.h>
   39 #include <sys/eventhandler.h>
   40 #include <sys/lock.h>
   41 #include <sys/malloc.h>
   42 #include <sys/mutex.h>
   43 #include <sys/proc.h>
   44 #include <sys/sysctl.h>
   45 #include <sys/vnode.h>
   46 
   47 #include <fs/pseudofs/pseudofs.h>
   48 #include <fs/pseudofs/pseudofs_internal.h>
   49 
   50 static MALLOC_DEFINE(M_PFSVNCACHE, "pfs_vncache", "pseudofs vnode cache");
   51 
   52 static struct mtx pfs_vncache_mutex;
   53 static eventhandler_tag pfs_exit_tag;
   54 static void pfs_exit(void *arg, struct proc *p);
   55 static void pfs_purge_all(void);
   56 
   57 static SYSCTL_NODE(_vfs_pfs, OID_AUTO, vncache, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
   58     "pseudofs vnode cache");
   59 
   60 static int pfs_vncache_entries;
   61 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, entries, CTLFLAG_RD,
   62     &pfs_vncache_entries, 0,
   63     "number of entries in the vnode cache");
   64 
   65 static int pfs_vncache_maxentries;
   66 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, maxentries, CTLFLAG_RD,
   67     &pfs_vncache_maxentries, 0,
   68     "highest number of entries in the vnode cache");
   69 
   70 static int pfs_vncache_hits;
   71 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, hits, CTLFLAG_RD,
   72     &pfs_vncache_hits, 0,
   73     "number of cache hits since initialization");
   74 
   75 static int pfs_vncache_misses;
   76 SYSCTL_INT(_vfs_pfs_vncache, OID_AUTO, misses, CTLFLAG_RD,
   77     &pfs_vncache_misses, 0,
   78     "number of cache misses since initialization");
   79 
   80 extern struct vop_vector pfs_vnodeops;  /* XXX -> .h file */
   81 
   82 static SLIST_HEAD(pfs_vncache_head, pfs_vdata) *pfs_vncache_hashtbl;
   83 static u_long pfs_vncache_hash;
   84 #define PFS_VNCACHE_HASH(pid)   (&pfs_vncache_hashtbl[(pid) & pfs_vncache_hash])
   85 
   86 /*
   87  * Initialize vnode cache
   88  */
   89 void
   90 pfs_vncache_load(void)
   91 {
   92 
   93         mtx_init(&pfs_vncache_mutex, "pfs_vncache", NULL, MTX_DEF);
   94         pfs_vncache_hashtbl = hashinit(maxproc / 4, M_PFSVNCACHE, &pfs_vncache_hash);
   95         pfs_exit_tag = EVENTHANDLER_REGISTER(process_exit, pfs_exit, NULL,
   96             EVENTHANDLER_PRI_ANY);
   97 }
   98 
   99 /*
  100  * Tear down vnode cache
  101  */
  102 void
  103 pfs_vncache_unload(void)
  104 {
  105 
  106         EVENTHANDLER_DEREGISTER(process_exit, pfs_exit_tag);
  107         pfs_purge_all();
  108         KASSERT(pfs_vncache_entries == 0,
  109             ("%d vncache entries remaining", pfs_vncache_entries));
  110         mtx_destroy(&pfs_vncache_mutex);
  111 }
  112 
  113 /*
  114  * Allocate a vnode
  115  */
  116 int
  117 pfs_vncache_alloc(struct mount *mp, struct vnode **vpp,
  118                   struct pfs_node *pn, pid_t pid)
  119 {
  120         struct pfs_vncache_head *hash;
  121         struct pfs_vdata *pvd, *pvd2;
  122         struct vnode *vp;
  123         int error;
  124 
  125         /*
  126          * See if the vnode is in the cache.
  127          */
  128         hash = PFS_VNCACHE_HASH(pid);
  129         if (SLIST_EMPTY(hash))
  130                 goto alloc;
  131 retry:
  132         mtx_lock(&pfs_vncache_mutex);
  133         SLIST_FOREACH(pvd, hash, pvd_hash) {
  134                 if (pvd->pvd_pn == pn && pvd->pvd_pid == pid &&
  135                     pvd->pvd_vnode->v_mount == mp) {
  136                         vp = pvd->pvd_vnode;
  137                         VI_LOCK(vp);
  138                         mtx_unlock(&pfs_vncache_mutex);
  139                         if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK) == 0) {
  140                                 ++pfs_vncache_hits;
  141                                 *vpp = vp;
  142                                 /*
  143                                  * Some callers cache_enter(vp) later, so
  144                                  * we have to make sure it's not in the
  145                                  * VFS cache so it doesn't get entered
  146                                  * twice.  A better solution would be to
  147                                  * make pfs_vncache_alloc() responsible
  148                                  * for entering the vnode in the VFS
  149                                  * cache.
  150                                  */
  151                                 cache_purge(vp);
  152                                 return (0);
  153                         }
  154                         goto retry;
  155                 }
  156         }
  157         mtx_unlock(&pfs_vncache_mutex);
  158 alloc:
  159         /* nope, get a new one */
  160         pvd = malloc(sizeof *pvd, M_PFSVNCACHE, M_WAITOK);
  161         error = getnewvnode("pseudofs", mp, &pfs_vnodeops, vpp);
  162         if (error) {
  163                 free(pvd, M_PFSVNCACHE);
  164                 return (error);
  165         }
  166         pvd->pvd_pn = pn;
  167         pvd->pvd_pid = pid;
  168         (*vpp)->v_data = pvd;
  169         switch (pn->pn_type) {
  170         case pfstype_root:
  171                 (*vpp)->v_vflag = VV_ROOT;
  172 #if 0
  173                 printf("root vnode allocated\n");
  174 #endif
  175                 /* fall through */
  176         case pfstype_dir:
  177         case pfstype_this:
  178         case pfstype_parent:
  179         case pfstype_procdir:
  180                 (*vpp)->v_type = VDIR;
  181                 break;
  182         case pfstype_file:
  183                 (*vpp)->v_type = VREG;
  184                 break;
  185         case pfstype_symlink:
  186                 (*vpp)->v_type = VLNK;
  187                 break;
  188         case pfstype_none:
  189                 KASSERT(0, ("pfs_vncache_alloc called for null node\n"));
  190         default:
  191                 panic("%s has unexpected type: %d", pn->pn_name, pn->pn_type);
  192         }
  193         /*
  194          * Propagate flag through to vnode so users know it can change
  195          * if the process changes (i.e. execve)
  196          */
  197         if ((pn->pn_flags & PFS_PROCDEP) != 0)
  198                 (*vpp)->v_vflag |= VV_PROCDEP;
  199         pvd->pvd_vnode = *vpp;
  200         vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY);
  201         VN_LOCK_AREC(*vpp);
  202         error = insmntque(*vpp, mp);
  203         if (error != 0) {
  204                 free(pvd, M_PFSVNCACHE);
  205                 *vpp = NULLVP;
  206                 return (error);
  207         }
  208 retry2:
  209         mtx_lock(&pfs_vncache_mutex);
  210         /*
  211          * Other thread may race with us, creating the entry we are
  212          * going to insert into the cache. Recheck after
  213          * pfs_vncache_mutex is reacquired.
  214          */
  215         SLIST_FOREACH(pvd2, hash, pvd_hash) {
  216                 if (pvd2->pvd_pn == pn && pvd2->pvd_pid == pid &&
  217                     pvd2->pvd_vnode->v_mount == mp) {
  218                         vp = pvd2->pvd_vnode;
  219                         VI_LOCK(vp);
  220                         mtx_unlock(&pfs_vncache_mutex);
  221                         if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK) == 0) {
  222                                 ++pfs_vncache_hits;
  223                                 vgone(*vpp);
  224                                 vput(*vpp);
  225                                 *vpp = vp;
  226                                 cache_purge(vp);
  227                                 return (0);
  228                         }
  229                         goto retry2;
  230                 }
  231         }
  232         ++pfs_vncache_misses;
  233         if (++pfs_vncache_entries > pfs_vncache_maxentries)
  234                 pfs_vncache_maxentries = pfs_vncache_entries;
  235         SLIST_INSERT_HEAD(hash, pvd, pvd_hash);
  236         mtx_unlock(&pfs_vncache_mutex);
  237         return (0);
  238 }
  239 
  240 /*
  241  * Free a vnode
  242  */
  243 int
  244 pfs_vncache_free(struct vnode *vp)
  245 {
  246         struct pfs_vdata *pvd, *pvd2;
  247 
  248         mtx_lock(&pfs_vncache_mutex);
  249         pvd = (struct pfs_vdata *)vp->v_data;
  250         KASSERT(pvd != NULL, ("pfs_vncache_free(): no vnode data\n"));
  251         SLIST_FOREACH(pvd2, PFS_VNCACHE_HASH(pvd->pvd_pid), pvd_hash) {
  252                 if (pvd2 != pvd)
  253                         continue;
  254                 SLIST_REMOVE(PFS_VNCACHE_HASH(pvd->pvd_pid), pvd, pfs_vdata, pvd_hash);
  255                 --pfs_vncache_entries;
  256                 break;
  257         }
  258         mtx_unlock(&pfs_vncache_mutex);
  259 
  260         free(pvd, M_PFSVNCACHE);
  261         vp->v_data = NULL;
  262         return (0);
  263 }
  264 
  265 /*
  266  * Purge the cache of dead entries
  267  *
  268  * The code is not very efficient and this perhaps can be addressed without
  269  * a complete rewrite. Previous iteration was walking a linked list from
  270  * scratch every time. This code only walks the relevant hash chain (if pid
  271  * is provided), but still resorts to scanning the entire cache at least twice
  272  * if a specific component is to be removed which is slower. This can be
  273  * augmented with resizing the hash.
  274  *
  275  * Explanation of the previous state:
  276  *
  277  * This is extremely inefficient due to the fact that vgone() not only
  278  * indirectly modifies the vnode cache, but may also sleep.  We can
  279  * neither hold pfs_vncache_mutex across a vgone() call, nor make any
  280  * assumptions about the state of the cache after vgone() returns.  In
  281  * consequence, we must start over after every vgone() call, and keep
  282  * trying until we manage to traverse the entire cache.
  283  *
  284  * The only way to improve this situation is to change the data structure
  285  * used to implement the cache.
  286  */
  287 
  288 static void
  289 pfs_purge_one(struct vnode *vnp)
  290 {
  291 
  292         VOP_LOCK(vnp, LK_EXCLUSIVE);
  293         vgone(vnp);
  294         VOP_UNLOCK(vnp);
  295         vdrop(vnp);
  296 }
  297 
  298 void
  299 pfs_purge(struct pfs_node *pn)
  300 {
  301         struct pfs_vdata *pvd;
  302         struct vnode *vnp;
  303         u_long i, removed;
  304 
  305         mtx_lock(&pfs_vncache_mutex);
  306 restart:
  307         removed = 0;
  308         for (i = 0; i < pfs_vncache_hash; i++) {
  309 restart_chain:
  310                 SLIST_FOREACH(pvd, &pfs_vncache_hashtbl[i], pvd_hash) {
  311                         if (pn != NULL && pvd->pvd_pn != pn)
  312                                 continue;
  313                         vnp = pvd->pvd_vnode;
  314                         vhold(vnp);
  315                         mtx_unlock(&pfs_vncache_mutex);
  316                         pfs_purge_one(vnp);
  317                         removed++;
  318                         mtx_lock(&pfs_vncache_mutex);
  319                         goto restart_chain;
  320                 }
  321         }
  322         if (removed > 0)
  323                 goto restart;
  324         mtx_unlock(&pfs_vncache_mutex);
  325 }
  326 
  327 static void
  328 pfs_purge_all(void)
  329 {
  330 
  331         pfs_purge(NULL);
  332 }
  333 
  334 /*
  335  * Free all vnodes associated with a defunct process
  336  */
  337 static void
  338 pfs_exit(void *arg, struct proc *p)
  339 {
  340         struct pfs_vncache_head *hash;
  341         struct pfs_vdata *pvd;
  342         struct vnode *vnp;
  343         int pid;
  344 
  345         pid = p->p_pid;
  346         hash = PFS_VNCACHE_HASH(pid);
  347         if (SLIST_EMPTY(hash))
  348                 return;
  349 restart:
  350         mtx_lock(&pfs_vncache_mutex);
  351         SLIST_FOREACH(pvd, hash, pvd_hash) {
  352                 if (pvd->pvd_pid != pid)
  353                         continue;
  354                 vnp = pvd->pvd_vnode;
  355                 vhold(vnp);
  356                 mtx_unlock(&pfs_vncache_mutex);
  357                 pfs_purge_one(vnp);
  358                 goto restart;
  359         }
  360         mtx_unlock(&pfs_vncache_mutex);
  361 }

Cache object: fae9d0b1192550490c4789dd4767dea3


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