/*      $NetBSD: nfs_kq.c,v 1.32 2021/10/20 03:08:18 thorpej Exp $      */

/*-
 * Copyright (c) 2002, 2008 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jaromir Dolecek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: nfs_kq.c,v 1.32 2021/10/20 03:08:18 thorpej Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/condvar.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/kmem.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/vnode.h>
#include <sys/unistd.h>
#include <sys/file.h>
#include <sys/kthread.h>

#include <nfs/rpcv2.h>
#include <nfs/nfsproto.h>
#include <nfs/nfs.h>
#include <nfs/nfsnode.h>
#include <nfs/nfs_var.h>

struct kevq {
        SLIST_ENTRY(kevq)       kev_link;
        struct vnode            *vp;
        u_int                   usecount;
        u_int                   flags;
#define KEVQ_BUSY       0x01    /* currently being processed */
        struct timespec         omtime; /* old modification time */
        struct timespec         octime; /* old change time */
        nlink_t                 onlink; /* old number of references to file */
        kcondvar_t              cv;
};
SLIST_HEAD(kevqlist, kevq);

static kmutex_t nfskq_lock;
static struct lwp *nfskq_thread;
static kcondvar_t nfskq_cv;
static struct kevqlist kevlist = SLIST_HEAD_INITIALIZER(kevlist);
static bool nfskq_thread_exit;

void
nfs_kqinit(void)
{

        mutex_init(&nfskq_lock, MUTEX_DEFAULT, IPL_NONE);
        cv_init(&nfskq_cv, "nfskqpw");
}

void
nfs_kqfini(void)
{

        if (nfskq_thread != NULL) {
                mutex_enter(&nfskq_lock);
                nfskq_thread_exit = true;
                cv_broadcast(&nfskq_cv);
                do {
                        cv_wait(&nfskq_cv, &nfskq_lock);
                } while (nfskq_thread != NULL);
                mutex_exit(&nfskq_lock);
        }
        mutex_destroy(&nfskq_lock);
        cv_destroy(&nfskq_cv);
}

/*
 * This quite simplistic routine periodically checks for server changes
 * of any of the watched files every NFS_MINATTRTIMO/2 seconds.
 * Only changes in size, modification time, change time and nlinks
 * are being checked, everything else is ignored.
 * The routine only calls VOP_GETATTR() when it's likely it would get
 * some new data, i.e. when the vnode expires from attrcache. This
 * should give same result as periodically running stat(2) from userland,
 * while keeping CPU/network usage low, and still provide proper kevent
 * semantics.
 * The poller thread is created when first vnode is added to watch list,
 * and exits when the watch list is empty. The overhead of thread creation
 * isn't really important, neither speed of attach and detach of knote.
 */
/* ARGSUSED */
static void
nfs_kqpoll(void *arg)
{
        struct kevq *ke;
        struct vattr attr;
        struct lwp *l = curlwp;
        u_quad_t osize;

        mutex_enter(&nfskq_lock);
        while (!nfskq_thread_exit) {
                SLIST_FOREACH(ke, &kevlist, kev_link) {
                        /* skip if still in attrcache */
                        if (nfs_getattrcache(ke->vp, &attr) != ENOENT)
                                continue;

                        /*
                         * Mark entry busy, release lock and check
                         * for changes.
                         */
                        ke->flags |= KEVQ_BUSY;
                        mutex_exit(&nfskq_lock);

                        /* save v_size, nfs_getattr() updates it */
                        osize = ke->vp->v_size;

                        memset(&attr, 0, sizeof(attr));
                        vn_lock(ke->vp, LK_SHARED | LK_RETRY);
                        (void) VOP_GETATTR(ke->vp, &attr, l->l_cred);
                        VOP_UNLOCK(ke->vp);

                        /* following is a bit fragile, but about best
                         * we can get */
                        if (attr.va_size != osize) {
                                int extended = (attr.va_size > osize);
                                VN_KNOTE(ke->vp, NOTE_WRITE
                                        | (extended ? NOTE_EXTEND : 0));
                                ke->omtime = attr.va_mtime;
                        } else if (attr.va_mtime.tv_sec != ke->omtime.tv_sec
                            || attr.va_mtime.tv_nsec != ke->omtime.tv_nsec) {
                                VN_KNOTE(ke->vp, NOTE_WRITE);
                                ke->omtime = attr.va_mtime;
                        }

                        if (attr.va_ctime.tv_sec != ke->octime.tv_sec
                            || attr.va_ctime.tv_nsec != ke->octime.tv_nsec) {
                                VN_KNOTE(ke->vp, NOTE_ATTRIB);
                                ke->octime = attr.va_ctime;
                        }

                        if (attr.va_nlink != ke->onlink) {
                                VN_KNOTE(ke->vp, NOTE_LINK);
                                ke->onlink = attr.va_nlink;
                        }

                        mutex_enter(&nfskq_lock);
                        ke->flags &= ~KEVQ_BUSY;
                        cv_signal(&ke->cv);
                }

                if (SLIST_EMPTY(&kevlist)) {
                        /* Nothing more to watch, exit */
                        nfskq_thread = NULL;
                        mutex_exit(&nfskq_lock);
                        kthread_exit(0);
                }

                /* wait a while before checking for changes again */
                cv_timedwait(&nfskq_cv, &nfskq_lock,
                    NFS_MINATTRTIMO * hz / 2);
        }
        nfskq_thread = NULL;
        cv_broadcast(&nfskq_cv);
        mutex_exit(&nfskq_lock);
}

static void
filt_nfsdetach(struct knote *kn)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        struct kevq *ke;

        vn_knote_detach(vp, kn);

        /* Remove the vnode from watch list */
        mutex_enter(&nfskq_lock);
        SLIST_FOREACH(ke, &kevlist, kev_link) {
                if (ke->vp == vp) {
                        while (ke->flags & KEVQ_BUSY) {
                                cv_wait(&ke->cv, &nfskq_lock);
                        }

                        if (ke->usecount > 1) {
                                /* keep, other kevents need this */
                                ke->usecount--;
                        } else {
                                /* last user, g/c */
                                cv_destroy(&ke->cv);
                                SLIST_REMOVE(&kevlist, ke, kevq, kev_link);
                                kmem_free(ke, sizeof(*ke));
                        }
                        break;
                }
        }
        mutex_exit(&nfskq_lock);
}

static int
filt_nfsread(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        int rv;

        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        switch (hint) {
        case NOTE_REVOKE:
                KASSERT(mutex_owned(vp->v_interlock));
                knote_set_eof(kn, EV_ONESHOT);
                return (1);
        case 0:
                mutex_enter(vp->v_interlock);
                kn->kn_data = vp->v_size - ((file_t *)kn->kn_obj)->f_offset;
                rv = (kn->kn_data != 0);
                mutex_exit(vp->v_interlock);
                return rv;
        default:
                KASSERT(mutex_owned(vp->v_interlock));
                kn->kn_data = vp->v_size - ((file_t *)kn->kn_obj)->f_offset;
                return (kn->kn_data != 0);
        }
}

static int
filt_nfsvnode(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        int fflags;

        switch (hint) {
        case NOTE_REVOKE:
                KASSERT(mutex_owned(vp->v_interlock));
                knote_set_eof(kn, 0);
                if ((kn->kn_sfflags & hint) != 0)
                        kn->kn_fflags |= hint;
                return (1);
        case 0:
                mutex_enter(vp->v_interlock);
                fflags = kn->kn_fflags;
                mutex_exit(vp->v_interlock);
                break;
        default:
                KASSERT(mutex_owned(vp->v_interlock));
                if ((kn->kn_sfflags & hint) != 0)
                        kn->kn_fflags |= hint;
                fflags = kn->kn_fflags;
                break;
        }

        return (fflags != 0);
}


static const struct filterops nfsread_filtops = {
        .f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
        .f_attach = NULL,
        .f_detach = filt_nfsdetach,
        .f_event = filt_nfsread,
};

static const struct filterops nfsvnode_filtops = {
        .f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
        .f_attach = NULL,
        .f_detach = filt_nfsdetach,
        .f_event = filt_nfsvnode,
};

int
nfs_kqfilter(void *v)
{
        struct vop_kqfilter_args /* {
                struct vnode    *a_vp;
                struct knote    *a_kn;
        } */ *ap = v;
        struct vnode *vp;
        struct knote *kn;
        struct kevq *ke;
        int error = 0;
        struct vattr attr;
        struct lwp *l = curlwp;

        vp = ap->a_vp;
        kn = ap->a_kn;
        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &nfsread_filtops;
                break;
        case EVFILT_VNODE:
                kn->kn_fop = &nfsvnode_filtops;
                break;
        default:
                return (EINVAL);
        }

        /*
         * Put the vnode to watched list.
         */

        /*
         * Fetch current attributes. It's only needed when the vnode
         * is not watched yet, but we need to do this without lock
         * held. This is likely cheap due to attrcache, so do it now.
         */
        memset(&attr, 0, sizeof(attr));
        vn_lock(vp, LK_SHARED | LK_RETRY);
        (void) VOP_GETATTR(vp, &attr, l->l_cred);
        VOP_UNLOCK(vp);

        mutex_enter(&nfskq_lock);

        /* ensure the poller is running */
        if (!nfskq_thread) {
                error = kthread_create(PRI_NONE, 0, NULL, nfs_kqpoll,
                    NULL, &nfskq_thread, "nfskqpoll");
                if (error) {
                        mutex_exit(&nfskq_lock);
                        return error;
                }
        }

        SLIST_FOREACH(ke, &kevlist, kev_link) {
                if (ke->vp == vp)
                        break;
        }

        if (ke) {
                /* already watched, so just bump usecount */
                ke->usecount++;
        } else {
                /* need a new one */
                ke = kmem_alloc(sizeof(*ke), KM_SLEEP);
                ke->vp = vp;
                ke->usecount = 1;
                ke->flags = 0;
                ke->omtime = attr.va_mtime;
                ke->octime = attr.va_ctime;
                ke->onlink = attr.va_nlink;
                cv_init(&ke->cv, "nfskqdet");
                SLIST_INSERT_HEAD(&kevlist, ke, kev_link);
        }

        kn->kn_hook = vp;

        vn_knote_attach(vp, kn);

        /* kick the poller */
        cv_signal(&nfskq_cv);
        mutex_exit(&nfskq_lock);

        return (error);
}