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         hashdestroy(pfs_vncache_hashtbl, M_PFSVNCACHE, pfs_vncache_hash);
  112 }
  113 
  114 /*
  115  * Allocate a vnode
  116  */
  117 int
  118 pfs_vncache_alloc(struct mount *mp, struct vnode **vpp,
  119                   struct pfs_node *pn, pid_t pid)
  120 {
  121         struct pfs_vncache_head *hash;
  122         struct pfs_vdata *pvd, *pvd2;
  123         struct vnode *vp;
  124         enum vgetstate vs;
  125         int error;
  126 
  127         /*
  128          * See if the vnode is in the cache.
  129          */
  130         hash = PFS_VNCACHE_HASH(pid);
  131         if (SLIST_EMPTY(hash))
  132                 goto alloc;
  133 retry:
  134         mtx_lock(&pfs_vncache_mutex);
  135         SLIST_FOREACH(pvd, hash, pvd_hash) {
  136                 if (pvd->pvd_pn == pn && pvd->pvd_pid == pid &&
  137                     pvd->pvd_vnode->v_mount == mp) {
  138                         vp = pvd->pvd_vnode;
  139                         vs = vget_prep(vp);
  140                         mtx_unlock(&pfs_vncache_mutex);
  141                         if (vget_finish(vp, LK_EXCLUSIVE, vs) == 0) {
  142                                 ++pfs_vncache_hits;
  143                                 *vpp = vp;
  144                                 /*
  145                                  * Some callers cache_enter(vp) later, so
  146                                  * we have to make sure it's not in the
  147                                  * VFS cache so it doesn't get entered
  148                                  * twice.  A better solution would be to
  149                                  * make pfs_vncache_alloc() responsible
  150                                  * for entering the vnode in the VFS
  151                                  * cache.
  152                                  */
  153                                 cache_purge(vp);
  154                                 return (0);
  155                         }
  156                         goto retry;
  157                 }
  158         }
  159         mtx_unlock(&pfs_vncache_mutex);
  160 alloc:
  161         /* nope, get a new one */
  162         pvd = malloc(sizeof *pvd, M_PFSVNCACHE, M_WAITOK);
  163         error = getnewvnode("pseudofs", mp, &pfs_vnodeops, vpp);
  164         if (error) {
  165                 free(pvd, M_PFSVNCACHE);
  166                 return (error);
  167         }
  168         pvd->pvd_pn = pn;
  169         pvd->pvd_pid = pid;
  170         (*vpp)->v_data = pvd;
  171         switch (pn->pn_type) {
  172         case pfstype_root:
  173                 (*vpp)->v_vflag = VV_ROOT;
  174 #if 0
  175                 printf("root vnode allocated\n");
  176 #endif
  177                 /* fall through */
  178         case pfstype_dir:
  179         case pfstype_this:
  180         case pfstype_parent:
  181         case pfstype_procdir:
  182                 (*vpp)->v_type = VDIR;
  183                 break;
  184         case pfstype_file:
  185                 (*vpp)->v_type = VREG;
  186                 break;
  187         case pfstype_symlink:
  188                 (*vpp)->v_type = VLNK;
  189                 break;
  190         case pfstype_none:
  191                 KASSERT(0, ("pfs_vncache_alloc called for null node\n"));
  192         default:
  193                 panic("%s has unexpected type: %d", pn->pn_name, pn->pn_type);
  194         }
  195         /*
  196          * Propagate flag through to vnode so users know it can change
  197          * if the process changes (i.e. execve)
  198          */
  199         if ((pn->pn_flags & PFS_PROCDEP) != 0)
  200                 (*vpp)->v_vflag |= VV_PROCDEP;
  201         pvd->pvd_vnode = *vpp;
  202         vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY);
  203         VN_LOCK_AREC(*vpp);
  204         error = insmntque(*vpp, mp);
  205         if (error != 0) {
  206                 free(pvd, M_PFSVNCACHE);
  207                 *vpp = NULLVP;
  208                 return (error);
  209         }
  210 retry2:
  211         mtx_lock(&pfs_vncache_mutex);
  212         /*
  213          * Other thread may race with us, creating the entry we are
  214          * going to insert into the cache. Recheck after
  215          * pfs_vncache_mutex is reacquired.
  216          */
  217         SLIST_FOREACH(pvd2, hash, pvd_hash) {
  218                 if (pvd2->pvd_pn == pn && pvd2->pvd_pid == pid &&
  219                     pvd2->pvd_vnode->v_mount == mp) {
  220                         vp = pvd2->pvd_vnode;
  221                         VI_LOCK(vp);
  222                         mtx_unlock(&pfs_vncache_mutex);
  223                         if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK) == 0) {
  224                                 ++pfs_vncache_hits;
  225                                 vgone(*vpp);
  226                                 vput(*vpp);
  227                                 *vpp = vp;
  228                                 cache_purge(vp);
  229                                 return (0);
  230                         }
  231                         goto retry2;
  232                 }
  233         }
  234         ++pfs_vncache_misses;
  235         if (++pfs_vncache_entries > pfs_vncache_maxentries)
  236                 pfs_vncache_maxentries = pfs_vncache_entries;
  237         SLIST_INSERT_HEAD(hash, pvd, pvd_hash);
  238         mtx_unlock(&pfs_vncache_mutex);
  239         return (0);
  240 }
  241 
  242 /*
  243  * Free a vnode
  244  */
  245 int
  246 pfs_vncache_free(struct vnode *vp)
  247 {
  248         struct pfs_vdata *pvd, *pvd2;
  249 
  250         mtx_lock(&pfs_vncache_mutex);
  251         pvd = (struct pfs_vdata *)vp->v_data;
  252         KASSERT(pvd != NULL, ("pfs_vncache_free(): no vnode data\n"));
  253         SLIST_FOREACH(pvd2, PFS_VNCACHE_HASH(pvd->pvd_pid), pvd_hash) {
  254                 if (pvd2 != pvd)
  255                         continue;
  256                 SLIST_REMOVE(PFS_VNCACHE_HASH(pvd->pvd_pid), pvd, pfs_vdata, pvd_hash);
  257                 --pfs_vncache_entries;
  258                 break;
  259         }
  260         mtx_unlock(&pfs_vncache_mutex);
  261 
  262         free(pvd, M_PFSVNCACHE);
  263         vp->v_data = NULL;
  264         return (0);
  265 }
  266 
  267 /*
  268  * Purge the cache of dead entries
  269  *
  270  * The code is not very efficient and this perhaps can be addressed without
  271  * a complete rewrite. Previous iteration was walking a linked list from
  272  * scratch every time. This code only walks the relevant hash chain (if pid
  273  * is provided), but still resorts to scanning the entire cache at least twice
  274  * if a specific component is to be removed which is slower. This can be
  275  * augmented with resizing the hash.
  276  *
  277  * Explanation of the previous state:
  278  *
  279  * This is extremely inefficient due to the fact that vgone() not only
  280  * indirectly modifies the vnode cache, but may also sleep.  We can
  281  * neither hold pfs_vncache_mutex across a vgone() call, nor make any
  282  * assumptions about the state of the cache after vgone() returns.  In
  283  * consequence, we must start over after every vgone() call, and keep
  284  * trying until we manage to traverse the entire cache.
  285  *
  286  * The only way to improve this situation is to change the data structure
  287  * used to implement the cache.
  288  */
  289 
  290 static void
  291 pfs_purge_one(struct vnode *vnp)
  292 {
  293 
  294         VOP_LOCK(vnp, LK_EXCLUSIVE);
  295         vgone(vnp);
  296         VOP_UNLOCK(vnp);
  297         vdrop(vnp);
  298 }
  299 
  300 void
  301 pfs_purge(struct pfs_node *pn)
  302 {
  303         struct pfs_vdata *pvd;
  304         struct vnode *vnp;
  305         u_long i, removed;
  306 
  307         mtx_lock(&pfs_vncache_mutex);
  308 restart:
  309         removed = 0;
  310         for (i = 0; i < pfs_vncache_hash; i++) {
  311 restart_chain:
  312                 SLIST_FOREACH(pvd, &pfs_vncache_hashtbl[i], pvd_hash) {
  313                         if (pn != NULL && pvd->pvd_pn != pn)
  314                                 continue;
  315                         vnp = pvd->pvd_vnode;
  316                         vhold(vnp);
  317                         mtx_unlock(&pfs_vncache_mutex);
  318                         pfs_purge_one(vnp);
  319                         removed++;
  320                         mtx_lock(&pfs_vncache_mutex);
  321                         goto restart_chain;
  322                 }
  323         }
  324         if (removed > 0)
  325                 goto restart;
  326         mtx_unlock(&pfs_vncache_mutex);
  327 }
  328 
  329 static void
  330 pfs_purge_all(void)
  331 {
  332 
  333         pfs_purge(NULL);
  334 }
  335 
  336 /*
  337  * Free all vnodes associated with a defunct process
  338  */
  339 static void
  340 pfs_exit(void *arg, struct proc *p)
  341 {
  342         struct pfs_vncache_head *hash;
  343         struct pfs_vdata *pvd;
  344         struct vnode *vnp;
  345         int pid;
  346 
  347         pid = p->p_pid;
  348         hash = PFS_VNCACHE_HASH(pid);
  349         if (SLIST_EMPTY(hash))
  350                 return;
  351 restart:
  352         mtx_lock(&pfs_vncache_mutex);
  353         SLIST_FOREACH(pvd, hash, pvd_hash) {
  354                 if (pvd->pvd_pid != pid)
  355                         continue;
  356                 vnp = pvd->pvd_vnode;
  357                 vhold(vnp);
  358                 mtx_unlock(&pfs_vncache_mutex);
  359                 pfs_purge_one(vnp);
  360                 goto restart;
  361         }
  362         mtx_unlock(&pfs_vncache_mutex);
  363 }
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FreeBSD/Linux Kernel Cross Reference sys/fs/pseudofs/pseudofs_vncache.c

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