nfs_kq.c

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    1 /*      $NetBSD: nfs_kq.c,v 1.32 2021/10/20 03:08:18 thorpej Exp $      */
    2 
    3 /*-
    4  * Copyright (c) 2002, 2008 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * This code is derived from software contributed to The NetBSD Foundation
    8  * by Jaromir Dolecek.
    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  *
   19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   29  * POSSIBILITY OF SUCH DAMAGE.
   30  */
   31 
   32 #include <sys/cdefs.h>
   33 __KERNEL_RCSID(0, "$NetBSD: nfs_kq.c,v 1.32 2021/10/20 03:08:18 thorpej Exp $");
   34 
   35 #include <sys/param.h>
   36 #include <sys/systm.h>
   37 #include <sys/condvar.h>
   38 #include <sys/kernel.h>
   39 #include <sys/proc.h>
   40 #include <sys/kmem.h>
   41 #include <sys/mount.h>
   42 #include <sys/mutex.h>
   43 #include <sys/vnode.h>
   44 #include <sys/unistd.h>
   45 #include <sys/file.h>
   46 #include <sys/kthread.h>
   47 
   48 #include <nfs/rpcv2.h>
   49 #include <nfs/nfsproto.h>
   50 #include <nfs/nfs.h>
   51 #include <nfs/nfsnode.h>
   52 #include <nfs/nfs_var.h>
   53 
   54 struct kevq {
   55         SLIST_ENTRY(kevq)       kev_link;
   56         struct vnode            *vp;
   57         u_int                   usecount;
   58         u_int                   flags;
   59 #define KEVQ_BUSY       0x01    /* currently being processed */
   60         struct timespec         omtime; /* old modification time */
   61         struct timespec         octime; /* old change time */
   62         nlink_t                 onlink; /* old number of references to file */
   63         kcondvar_t              cv;
   64 };
   65 SLIST_HEAD(kevqlist, kevq);
   66 
   67 static kmutex_t nfskq_lock;
   68 static struct lwp *nfskq_thread;
   69 static kcondvar_t nfskq_cv;
   70 static struct kevqlist kevlist = SLIST_HEAD_INITIALIZER(kevlist);
   71 static bool nfskq_thread_exit;
   72 
   73 void
   74 nfs_kqinit(void)
   75 {
   76 
   77         mutex_init(&nfskq_lock, MUTEX_DEFAULT, IPL_NONE);
   78         cv_init(&nfskq_cv, "nfskqpw");
   79 }
   80 
   81 void
   82 nfs_kqfini(void)
   83 {
   84 
   85         if (nfskq_thread != NULL) {
   86                 mutex_enter(&nfskq_lock);
   87                 nfskq_thread_exit = true;
   88                 cv_broadcast(&nfskq_cv);
   89                 do {
   90                         cv_wait(&nfskq_cv, &nfskq_lock);
   91                 } while (nfskq_thread != NULL);
   92                 mutex_exit(&nfskq_lock);
   93         }
   94         mutex_destroy(&nfskq_lock);
   95         cv_destroy(&nfskq_cv);
   96 }
   97 
   98 /*
   99  * This quite simplistic routine periodically checks for server changes
  100  * of any of the watched files every NFS_MINATTRTIMO/2 seconds.
  101  * Only changes in size, modification time, change time and nlinks
  102  * are being checked, everything else is ignored.
  103  * The routine only calls VOP_GETATTR() when it's likely it would get
  104  * some new data, i.e. when the vnode expires from attrcache. This
  105  * should give same result as periodically running stat(2) from userland,
  106  * while keeping CPU/network usage low, and still provide proper kevent
  107  * semantics.
  108  * The poller thread is created when first vnode is added to watch list,
  109  * and exits when the watch list is empty. The overhead of thread creation
  110  * isn't really important, neither speed of attach and detach of knote.
  111  */
  112 /* ARGSUSED */
  113 static void
  114 nfs_kqpoll(void *arg)
  115 {
  116         struct kevq *ke;
  117         struct vattr attr;
  118         struct lwp *l = curlwp;
  119         u_quad_t osize;
  120 
  121         mutex_enter(&nfskq_lock);
  122         while (!nfskq_thread_exit) {
  123                 SLIST_FOREACH(ke, &kevlist, kev_link) {
  124                         /* skip if still in attrcache */
  125                         if (nfs_getattrcache(ke->vp, &attr) != ENOENT)
  126                                 continue;
  127 
  128                         /*
  129                          * Mark entry busy, release lock and check
  130                          * for changes.
  131                          */
  132                         ke->flags |= KEVQ_BUSY;
  133                         mutex_exit(&nfskq_lock);
  134 
  135                         /* save v_size, nfs_getattr() updates it */
  136                         osize = ke->vp->v_size;
  137 
  138                         memset(&attr, 0, sizeof(attr));
  139                         vn_lock(ke->vp, LK_SHARED | LK_RETRY);
  140                         (void) VOP_GETATTR(ke->vp, &attr, l->l_cred);
  141                         VOP_UNLOCK(ke->vp);
  142 
  143                         /* following is a bit fragile, but about best
  144                          * we can get */
  145                         if (attr.va_size != osize) {
  146                                 int extended = (attr.va_size > osize);
  147                                 VN_KNOTE(ke->vp, NOTE_WRITE
  148                                         | (extended ? NOTE_EXTEND : 0));
  149                                 ke->omtime = attr.va_mtime;
  150                         } else if (attr.va_mtime.tv_sec != ke->omtime.tv_sec
  151                             || attr.va_mtime.tv_nsec != ke->omtime.tv_nsec) {
  152                                 VN_KNOTE(ke->vp, NOTE_WRITE);
  153                                 ke->omtime = attr.va_mtime;
  154                         }
  155 
  156                         if (attr.va_ctime.tv_sec != ke->octime.tv_sec
  157                             || attr.va_ctime.tv_nsec != ke->octime.tv_nsec) {
  158                                 VN_KNOTE(ke->vp, NOTE_ATTRIB);
  159                                 ke->octime = attr.va_ctime;
  160                         }
  161 
  162                         if (attr.va_nlink != ke->onlink) {
  163                                 VN_KNOTE(ke->vp, NOTE_LINK);
  164                                 ke->onlink = attr.va_nlink;
  165                         }
  166 
  167                         mutex_enter(&nfskq_lock);
  168                         ke->flags &= ~KEVQ_BUSY;
  169                         cv_signal(&ke->cv);
  170                 }
  171 
  172                 if (SLIST_EMPTY(&kevlist)) {
  173                         /* Nothing more to watch, exit */
  174                         nfskq_thread = NULL;
  175                         mutex_exit(&nfskq_lock);
  176                         kthread_exit(0);
  177                 }
  178 
  179                 /* wait a while before checking for changes again */
  180                 cv_timedwait(&nfskq_cv, &nfskq_lock,
  181                     NFS_MINATTRTIMO * hz / 2);
  182         }
  183         nfskq_thread = NULL;
  184         cv_broadcast(&nfskq_cv);
  185         mutex_exit(&nfskq_lock);
  186 }
  187 
  188 static void
  189 filt_nfsdetach(struct knote *kn)
  190 {
  191         struct vnode *vp = (struct vnode *)kn->kn_hook;
  192         struct kevq *ke;
  193 
  194         vn_knote_detach(vp, kn);
  195 
  196         /* Remove the vnode from watch list */
  197         mutex_enter(&nfskq_lock);
  198         SLIST_FOREACH(ke, &kevlist, kev_link) {
  199                 if (ke->vp == vp) {
  200                         while (ke->flags & KEVQ_BUSY) {
  201                                 cv_wait(&ke->cv, &nfskq_lock);
  202                         }
  203 
  204                         if (ke->usecount > 1) {
  205                                 /* keep, other kevents need this */
  206                                 ke->usecount--;
  207                         } else {
  208                                 /* last user, g/c */
  209                                 cv_destroy(&ke->cv);
  210                                 SLIST_REMOVE(&kevlist, ke, kevq, kev_link);
  211                                 kmem_free(ke, sizeof(*ke));
  212                         }
  213                         break;
  214                 }
  215         }
  216         mutex_exit(&nfskq_lock);
  217 }
  218 
  219 static int
  220 filt_nfsread(struct knote *kn, long hint)
  221 {
  222         struct vnode *vp = (struct vnode *)kn->kn_hook;
  223         int rv;
  224 
  225         /*
  226          * filesystem is gone, so set the EOF flag and schedule
  227          * the knote for deletion.
  228          */
  229         switch (hint) {
  230         case NOTE_REVOKE:
  231                 KASSERT(mutex_owned(vp->v_interlock));
  232                 knote_set_eof(kn, EV_ONESHOT);
  233                 return (1);
  234         case 0:
  235                 mutex_enter(vp->v_interlock);
  236                 kn->kn_data = vp->v_size - ((file_t *)kn->kn_obj)->f_offset;
  237                 rv = (kn->kn_data != 0);
  238                 mutex_exit(vp->v_interlock);
  239                 return rv;
  240         default:
  241                 KASSERT(mutex_owned(vp->v_interlock));
  242                 kn->kn_data = vp->v_size - ((file_t *)kn->kn_obj)->f_offset;
  243                 return (kn->kn_data != 0);
  244         }
  245 }
  246 
  247 static int
  248 filt_nfsvnode(struct knote *kn, long hint)
  249 {
  250         struct vnode *vp = (struct vnode *)kn->kn_hook;
  251         int fflags;
  252 
  253         switch (hint) {
  254         case NOTE_REVOKE:
  255                 KASSERT(mutex_owned(vp->v_interlock));
  256                 knote_set_eof(kn, 0);
  257                 if ((kn->kn_sfflags & hint) != 0)
  258                         kn->kn_fflags |= hint;
  259                 return (1);
  260         case 0:
  261                 mutex_enter(vp->v_interlock);
  262                 fflags = kn->kn_fflags;
  263                 mutex_exit(vp->v_interlock);
  264                 break;
  265         default:
  266                 KASSERT(mutex_owned(vp->v_interlock));
  267                 if ((kn->kn_sfflags & hint) != 0)
  268                         kn->kn_fflags |= hint;
  269                 fflags = kn->kn_fflags;
  270                 break;
  271         }
  272 
  273         return (fflags != 0);
  274 }
  275 
  276 
  277 static const struct filterops nfsread_filtops = {
  278         .f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
  279         .f_attach = NULL,
  280         .f_detach = filt_nfsdetach,
  281         .f_event = filt_nfsread,
  282 };
  283 
  284 static const struct filterops nfsvnode_filtops = {
  285         .f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
  286         .f_attach = NULL,
  287         .f_detach = filt_nfsdetach,
  288         .f_event = filt_nfsvnode,
  289 };
  290 
  291 int
  292 nfs_kqfilter(void *v)
  293 {
  294         struct vop_kqfilter_args /* {
  295                 struct vnode    *a_vp;
  296                 struct knote    *a_kn;
  297         } */ *ap = v;
  298         struct vnode *vp;
  299         struct knote *kn;
  300         struct kevq *ke;
  301         int error = 0;
  302         struct vattr attr;
  303         struct lwp *l = curlwp;
  304 
  305         vp = ap->a_vp;
  306         kn = ap->a_kn;
  307         switch (kn->kn_filter) {
  308         case EVFILT_READ:
  309                 kn->kn_fop = &nfsread_filtops;
  310                 break;
  311         case EVFILT_VNODE:
  312                 kn->kn_fop = &nfsvnode_filtops;
  313                 break;
  314         default:
  315                 return (EINVAL);
  316         }
  317 
  318         /*
  319          * Put the vnode to watched list.
  320          */
  321 
  322         /*
  323          * Fetch current attributes. It's only needed when the vnode
  324          * is not watched yet, but we need to do this without lock
  325          * held. This is likely cheap due to attrcache, so do it now.
  326          */
  327         memset(&attr, 0, sizeof(attr));
  328         vn_lock(vp, LK_SHARED | LK_RETRY);
  329         (void) VOP_GETATTR(vp, &attr, l->l_cred);
  330         VOP_UNLOCK(vp);
  331 
  332         mutex_enter(&nfskq_lock);
  333 
  334         /* ensure the poller is running */
  335         if (!nfskq_thread) {
  336                 error = kthread_create(PRI_NONE, 0, NULL, nfs_kqpoll,
  337                     NULL, &nfskq_thread, "nfskqpoll");
  338                 if (error) {
  339                         mutex_exit(&nfskq_lock);
  340                         return error;
  341                 }
  342         }
  343 
  344         SLIST_FOREACH(ke, &kevlist, kev_link) {
  345                 if (ke->vp == vp)
  346                         break;
  347         }
  348 
  349         if (ke) {
  350                 /* already watched, so just bump usecount */
  351                 ke->usecount++;
  352         } else {
  353                 /* need a new one */
  354                 ke = kmem_alloc(sizeof(*ke), KM_SLEEP);
  355                 ke->vp = vp;
  356                 ke->usecount = 1;
  357                 ke->flags = 0;
  358                 ke->omtime = attr.va_mtime;
  359                 ke->octime = attr.va_ctime;
  360                 ke->onlink = attr.va_nlink;
  361                 cv_init(&ke->cv, "nfskqdet");
  362                 SLIST_INSERT_HEAD(&kevlist, ke, kev_link);
  363         }
  364 
  365         kn->kn_hook = vp;
  366 
  367         vn_knote_attach(vp, kn);
  368 
  369         /* kick the poller */
  370         cv_signal(&nfskq_cv);
  371         mutex_exit(&nfskq_lock);
  372 
  373         return (error);
  374 }
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FreeBSD/Linux Kernel Cross Reference sys/nfs/nfs_kq.c

FreeBSD/Linux Kernel Cross Reference
sys/nfs/nfs_kq.c
