/*      $OpenBSD: nfs_kq.c,v 1.37 2024/05/01 13:15:59 jsg Exp $ */
/*      $NetBSD: nfs_kq.c,v 1.7 2003/10/30 01:43:10 simonb Exp $        */

/*-
 * Copyright (c) 2002 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/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/mount.h>
#include <sys/malloc.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/kthread.h>
#include <sys/rwlock.h>
#include <sys/queue.h>

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

void    nfs_kqpoll(void *);
int     nfs_kqwatch(struct vnode *);
void    nfs_kqunwatch(struct vnode *);

void    filt_nfsdetach(struct knote *);
int     filt_nfsread(struct knote *, long);
int     filt_nfswrite(struct knote *, long);
int     filt_nfsvnode(struct knote *, long);

struct kevq {
        SLIST_ENTRY(kevq)       kev_link;
        struct vnode            *vp;
        u_int                   usecount;
        u_int                   flags;
#define KEVQ_BUSY       0x01    /* currently being processed */
#define KEVQ_WANT       0x02    /* want to change this entry */
        struct timespec         omtime; /* old modification time */
        struct timespec         octime; /* old change time */
        nlink_t                 onlink; /* old number of references to file */
};
SLIST_HEAD(kevqlist, kevq);

struct rwlock nfskevq_lock = RWLOCK_INITIALIZER("nfskqlk");
struct proc *pnfskq;
struct kevqlist kevlist = SLIST_HEAD_INITIALIZER(kevlist);

/*
 * 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.
 */
void
nfs_kqpoll(void *arg)
{
        struct kevq *ke;
        struct vattr attr;
        struct proc *p = pnfskq;
        u_quad_t osize;
        int error;

        for(;;) {
                rw_enter_write(&nfskevq_lock);
                SLIST_FOREACH(ke, &kevlist, kev_link) {
                        struct nfsnode *np = VTONFS(ke->vp);

#ifdef DEBUG
                        printf("nfs_kqpoll on: ");
                        VOP_PRINT(ke->vp);
#endif
                        /* 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;
                        rw_exit_write(&nfskevq_lock);

                        /* save v_size, nfs_getattr() updates it */
                        osize = np->n_size;

                        error = VOP_GETATTR(ke->vp, &attr, p->p_ucred, p);
                        if (error == ESTALE) {
                                NFS_INVALIDATE_ATTRCACHE(np);
                                VN_KNOTE(ke->vp, NOTE_DELETE);
                                goto next;
                        }

                        /* following is a bit fragile, but about best
                         * we can get */
                        if (attr.va_size != osize) {
                                int flags = NOTE_WRITE;

                                if (attr.va_size > osize)
                                        flags |= NOTE_EXTEND;
                                else
                                        flags |= NOTE_TRUNCATE;

                                VN_KNOTE(ke->vp, flags);
                                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;
                        }

next:
                        rw_enter_write(&nfskevq_lock);
                        ke->flags &= ~KEVQ_BUSY;
                        if (ke->flags & KEVQ_WANT) {
                                ke->flags &= ~KEVQ_WANT;
                                wakeup(ke);
                        }
                }

                if (SLIST_EMPTY(&kevlist)) {
                        /* Nothing more to watch, exit */
                        pnfskq = NULL;
                        rw_exit_write(&nfskevq_lock);
                        kthread_exit(0);
                }
                rw_exit_write(&nfskevq_lock);

                /* wait a while before checking for changes again */
                tsleep_nsec(pnfskq, PSOCK, "nfskqpw",
                    SEC_TO_NSEC(NFS_MINATTRTIMO) / 2);
        }
}

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

        klist_remove_locked(&vp->v_klist, kn);

        /* Remove the vnode from watch list */
        if ((kn->kn_flags & (__EV_POLL | __EV_SELECT)) == 0)
                nfs_kqunwatch(vp);
}

void
nfs_kqunwatch(struct vnode *vp)
{
        struct kevq *ke;

        rw_enter_write(&nfskevq_lock);
        SLIST_FOREACH(ke, &kevlist, kev_link) {
                if (ke->vp == vp) {
                        while (ke->flags & KEVQ_BUSY) {
                                ke->flags |= KEVQ_WANT;
                                rw_exit_write(&nfskevq_lock);
                                tsleep_nsec(ke, PSOCK, "nfskqdet", INFSLP);
                                rw_enter_write(&nfskevq_lock);
                        }

                        if (ke->usecount > 1) {
                                /* keep, other kevents need this */
                                ke->usecount--;
                        } else {
                                /* last user, g/c */
                                SLIST_REMOVE(&kevlist, ke, kevq, kev_link);
                                free(ke, M_KEVENT, sizeof(*ke));
                        }
                        break;
                }
        }
        rw_exit_write(&nfskevq_lock);
}

int
filt_nfsread(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        struct nfsnode *np = VTONFS(vp);

        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        if (hint == NOTE_REVOKE) {
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                return (1);
        }

        kn->kn_data = np->n_size - foffset(kn->kn_fp);
#ifdef DEBUG
        printf("nfsread event. %lld\n", kn->kn_data);
#endif
        if (kn->kn_data == 0 && kn->kn_sfflags & NOTE_EOF) {
                kn->kn_fflags |= NOTE_EOF;
                return (1);
        }

        if (kn->kn_flags & (__EV_POLL | __EV_SELECT))
                return (1);

        return (kn->kn_data != 0);
}

int
filt_nfswrite(struct knote *kn, long hint)
{
        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        if (hint == NOTE_REVOKE) {
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                return (1);
        }

        kn->kn_data = 0;
        return (1);
}

int
filt_nfsvnode(struct knote *kn, long hint)
{
        if (kn->kn_sfflags & hint)
                kn->kn_fflags |= hint;
        if (hint == NOTE_REVOKE) {
                kn->kn_flags |= EV_EOF;
                return (1);
        }
        return (kn->kn_fflags != 0);
}

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

static const struct filterops nfswrite_filtops = {
        .f_flags        = FILTEROP_ISFD,
        .f_attach       = NULL,
        .f_detach       = filt_nfsdetach,
        .f_event        = filt_nfswrite,
};

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

int
nfs_kqfilter(void *v)
{
        struct vop_kqfilter_args *ap = v;
        struct vnode *vp;
        struct knote *kn;

        vp = ap->a_vp;
        kn = ap->a_kn;

#ifdef DEBUG
        printf("nfs_kqfilter(%d) on: ", kn->kn_filter);
        VOP_PRINT(vp);
#endif

        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &nfsread_filtops;
                break;
        case EVFILT_WRITE:
                kn->kn_fop = &nfswrite_filtops;
                break;
        case EVFILT_VNODE:
                kn->kn_fop = &nfsvnode_filtops;
                break;
        default:
                return (EINVAL);
        }

        kn->kn_hook = vp;

        /*
         * Put the vnode to watched list.
         */
        if ((kn->kn_flags & (__EV_POLL | __EV_SELECT)) == 0) {
                int error;

                error = nfs_kqwatch(vp);
                if (error)
                        return (error);
        }

        klist_insert_locked(&vp->v_klist, kn);

        return (0);
}

int
nfs_kqwatch(struct vnode *vp)
{
        struct proc *p = curproc;       /* XXX */
        struct vattr attr;
        struct kevq *ke;
        int error = 0;

        /*
         * 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));
        (void) VOP_GETATTR(vp, &attr, p->p_ucred, p);

        rw_enter_write(&nfskevq_lock);

        /* ensure the poller is running */
        if (!pnfskq) {
                error = kthread_create(nfs_kqpoll, NULL, &pnfskq,
                                "nfskqpoll");
                if (error)
                        goto out;
        }

        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 = malloc(sizeof(*ke), M_KEVENT, M_WAITOK);
                ke->vp = vp;
                ke->usecount = 1;
                ke->flags = 0;
                ke->omtime = attr.va_mtime;
                ke->octime = attr.va_ctime;
                ke->onlink = attr.va_nlink;
                SLIST_INSERT_HEAD(&kevlist, ke, kev_link);
        }

        /* kick the poller */
        wakeup(pnfskq);

out:
        rw_exit_write(&nfskevq_lock);
        return (error);
}