/*      $NetBSD: linux_inotify.c,v 1.8 2025/06/27 21:36:23 andvar Exp $ */

/*-
 * Copyright (c) 2023 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Theodore Preduta.
 *
 * 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: linux_inotify.c,v 1.8 2025/06/27 21:36:23 andvar Exp $");

#include <sys/param.h>
#include <sys/types.h>
#include <sys/bitops.h>
#include <sys/dirent.h>
#include <sys/event.h>
#include <sys/eventvar.h>
#include <sys/errno.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/fcntl.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/selinfo.h>
#include <sys/select.h>
#include <sys/signal.h>
#include <sys/vnode.h>

#include <sys/syscallargs.h>

#include <compat/linux/common/linux_machdep.h>
#include <compat/linux/common/linux_fcntl.h>
#include <compat/linux/common/linux_inotify.h>
#include <compat/linux/common/linux_ipc.h>
#include <compat/linux/common/linux_sched.h>
#include <compat/linux/common/linux_sem.h>
#include <compat/linux/common/linux_signal.h>

#include <compat/linux/linux_syscallargs.h>

/*
 * inotify(2).  This interface allows the user to get file system
 * events and (unlike kqueue(2)) their order is strictly preserved.
 * While nice, the API has sufficient gotchas that mean we don't want
 * to add native entry points for it.  They are:
 *
 * - Because data is returned via read(2), this API is prone to
 *   unaligned memory accesses.  There is a note in the Linux man page
 *   that says the name field of struct linux_inotify_event *can* be
 *   used for alignment purposes.  In practice, even Linux doesn't
 *   always do this, so for simplicity, we don't ever do this.
 */

#define LINUX_INOTIFY_MAX_QUEUED        16384
#define LINUX_INOTIFY_MAX_FROM_KEVENT   3

#if DEBUG_LINUX
#define DPRINTF(x) uprintf x
#else
#define DPRINTF(x) __nothing
#endif

struct inotify_entry {
        TAILQ_ENTRY(inotify_entry)      ie_entries;
        char                            ie_name[NAME_MAX + 1];
        struct linux_inotify_event      ie_event;
};

struct inotify_dir_entries {
        size_t  ide_count;
        struct inotify_dir_entry {
                char    name[NAME_MAX + 1];
                ino_t   fileno;
        } ide_entries[];
};
#define INOTIFY_DIR_ENTRIES_SIZE(count) (sizeof(struct inotify_dir_entries) \
    + count * sizeof(struct inotify_dir_entry))

struct inotifyfd {
        int             ifd_kqfd;       /* kqueue fd used by this inotify */
                                        /* instance */
        struct selinfo  ifd_sel;        /* for EVFILT_READ by epoll */
        kmutex_t        ifd_lock;       /* lock for ifd_sel, ifd_wds and */
                                        /* ifd_nwds */

        struct inotify_dir_entries **ifd_wds;
                                        /* keeps track of watch descriptors */
                                        /* for directories: snapshot of the */
                                        /* directory state */
                                        /* for files: an inotify_dir_entries */
                                        /* with ide_count == 0 */
        size_t          ifd_nwds;       /* max watch descriptor that can be */
                                        /* stored in ifd_wds + 1 */

        TAILQ_HEAD(, inotify_entry) ifd_qhead;  /* queue of pending events */
        size_t          ifd_qcount;     /* number of pending events */
        kcondvar_t      ifd_qcv;        /* condvar for blocking reads */
        kmutex_t        ifd_qlock;      /* lock for ifd_q* and interlock */
                                        /* for ifd_qcv */
};

struct inotify_kevent_mask_pair {
        uint32_t inotify;
        uint32_t kevent;
};

static int      inotify_kev_fetch_changes(void *, const struct kevent *,
    struct kevent *, size_t, int);
static int      do_inotify_init(struct lwp *, register_t *, int);
static int      inotify_close_wd(struct inotifyfd *, int);
static uint32_t inotify_mask_to_kevent_fflags(uint32_t, enum vtype);
static void     do_kevent_to_inotify(int32_t, uint32_t, uint32_t,
    struct inotify_entry *, size_t *, char *);
static int      kevent_to_inotify(struct inotifyfd *, int, enum vtype, uint32_t,
    uint32_t, struct inotify_entry *, size_t *);
static int      inotify_readdir(file_t *, struct dirent *, int *, bool);
static struct inotify_dir_entries *get_inotify_dir_entries(int, bool);

static int      inotify_filt_attach(struct knote *);
static void     inotify_filt_detach(struct knote *);
static int      inotify_filt_event(struct knote *, long);
static void     inotify_read_filt_detach(struct knote *);
static int      inotify_read_filt_event(struct knote *, long);

static int      inotify_read(file_t *, off_t *, struct uio *, kauth_cred_t, int);
static int      inotify_close(file_t *);
static int      inotify_poll(file_t *, int);
static int      inotify_kqfilter(file_t *, struct knote *);
static void     inotify_restart(file_t *);

static const char inotify_filtname[] = "LINUX_INOTIFY";
static int inotify_filtid;

/* "fake" EVFILT_VNODE that gets attached to ifd_deps */
static const struct filterops inotify_filtops = {
        .f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
        .f_attach = inotify_filt_attach,
        .f_detach = inotify_filt_detach,
        .f_event = inotify_filt_event,
        .f_touch = NULL,
};

/* EVFILT_READ attached to inotifyfd (to support watching via epoll) */
static const struct filterops inotify_read_filtops = {
        .f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
        .f_attach = NULL, /* attached via .fo_kqfilter */
        .f_detach = inotify_read_filt_detach,
        .f_event = inotify_read_filt_event,
        .f_touch = NULL,
};

static const struct fileops inotify_fileops = {
        .fo_name = "inotify",
        .fo_read = inotify_read,
        .fo_write = fbadop_write,
        .fo_ioctl = fbadop_ioctl,
        .fo_fcntl = fnullop_fcntl,
        .fo_poll = inotify_poll,
        .fo_stat = fbadop_stat,
        .fo_close = inotify_close,
        .fo_kqfilter = inotify_kqfilter,
        .fo_restart = inotify_restart,
        .fo_fpathconf = (void *)eopnotsupp,
};

/* basic flag translations */
static const struct inotify_kevent_mask_pair common_inotify_to_kevent[] = {
        { .inotify = LINUX_IN_ATTRIB,           .kevent = NOTE_ATTRIB, },
        { .inotify = LINUX_IN_CLOSE_NOWRITE,    .kevent = NOTE_CLOSE, },
        { .inotify = LINUX_IN_OPEN,             .kevent = NOTE_OPEN, },
        { .inotify = LINUX_IN_MOVE_SELF,        .kevent = NOTE_RENAME, },
};
static const size_t common_inotify_to_kevent_len =
    __arraycount(common_inotify_to_kevent);

static const struct inotify_kevent_mask_pair vreg_inotify_to_kevent[] = {
        { .inotify = LINUX_IN_ACCESS,           .kevent = NOTE_READ, },
        { .inotify = LINUX_IN_ATTRIB,           .kevent = NOTE_ATTRIB|NOTE_LINK, },
        { .inotify = LINUX_IN_CLOSE_WRITE,      .kevent = NOTE_CLOSE_WRITE, },
        { .inotify = LINUX_IN_MODIFY,           .kevent = NOTE_WRITE, },
};
static const size_t vreg_inotify_to_kevent_len =
    __arraycount(vreg_inotify_to_kevent);

static const struct inotify_kevent_mask_pair vdir_inotify_to_kevent[] = {
        { .inotify = LINUX_IN_ACCESS,           .kevent = NOTE_READ, },
        { .inotify = LINUX_IN_CREATE,           .kevent = NOTE_WRITE, },
        { .inotify = LINUX_IN_DELETE,           .kevent = NOTE_WRITE, },
        { .inotify = LINUX_IN_MOVED_FROM,       .kevent = NOTE_WRITE, },
        { .inotify = LINUX_IN_MOVED_TO,         .kevent = NOTE_WRITE, },
};
static const size_t vdir_inotify_to_kevent_len =
    __arraycount(vdir_inotify_to_kevent);

static const struct inotify_kevent_mask_pair common_kevent_to_inotify[] = {
        { .kevent = NOTE_ATTRIB,        .inotify = LINUX_IN_ATTRIB, },
        { .kevent = NOTE_CLOSE,         .inotify = LINUX_IN_CLOSE_NOWRITE, },
        { .kevent = NOTE_CLOSE_WRITE,   .inotify = LINUX_IN_CLOSE_WRITE, },
        { .kevent = NOTE_OPEN,          .inotify = LINUX_IN_OPEN, },
        { .kevent = NOTE_READ,          .inotify = LINUX_IN_ACCESS, },
        { .kevent = NOTE_RENAME,        .inotify = LINUX_IN_MOVE_SELF, },
        { .kevent = NOTE_REVOKE,        .inotify = LINUX_IN_UNMOUNT, },
};
static const size_t common_kevent_to_inotify_len =
    __arraycount(common_kevent_to_inotify);

static const struct inotify_kevent_mask_pair vreg_kevent_to_inotify[] = {
        { .kevent = NOTE_DELETE|NOTE_LINK, .inotify = LINUX_IN_ATTRIB, },
        { .kevent = NOTE_WRITE,         .inotify = LINUX_IN_MODIFY, },
};
static const size_t vreg_kevent_to_inotify_len =
    __arraycount(vreg_kevent_to_inotify);

/*
 * Register the custom kfilter for inotify.
 */
int
linux_inotify_init(void)
{
        return kfilter_register(inotify_filtname, &inotify_filtops,
            &inotify_filtid);
}

/*
 * Unregister the custom kfilter for inotify.
 */
int
linux_inotify_fini(void)
{
        return kfilter_unregister(inotify_filtname);
}

/*
 * Copyin callback used by kevent.  This copies already converted
 * filters from kernel memory to the kevent internal kernel memory.
 * Hence the memcpy instead of copyin.
 */
static int
inotify_kev_fetch_changes(void *ctx, const struct kevent *changelist,
    struct kevent *changes, size_t index, int n)
{
        memcpy(changes, changelist + index, n * sizeof(*changes));

        return 0;
}

/*
 * Initialize a new inotify fd.
 */
static int
do_inotify_init(struct lwp *l, register_t *retval, int flags)
{
        file_t *fp;
        int error, fd;
        struct proc *p = l->l_proc;
        struct inotifyfd *ifd;
        struct sys_kqueue1_args kqa;

        if (flags & ~(LINUX_IN_ALL_FLAGS))
                return EINVAL;

        ifd = kmem_zalloc(sizeof(*ifd), KM_SLEEP);
        mutex_init(&ifd->ifd_lock, MUTEX_DEFAULT, IPL_NONE);
        mutex_init(&ifd->ifd_qlock, MUTEX_DEFAULT, IPL_NONE);
        cv_init(&ifd->ifd_qcv, "inotify");
        selinit(&ifd->ifd_sel);
        TAILQ_INIT(&ifd->ifd_qhead);

        ifd->ifd_nwds = 1;
        ifd->ifd_wds = kmem_zalloc(ifd->ifd_nwds * sizeof(*ifd->ifd_wds),
        KM_SLEEP);

        SCARG(&kqa, flags) = 0;
        if (flags & LINUX_IN_NONBLOCK)
                SCARG(&kqa, flags) |= O_NONBLOCK;
        error = sys_kqueue1(l, &kqa, retval);
        if (error != 0)
                goto leave0;
        ifd->ifd_kqfd = *retval;

        error = fd_allocfile(&fp, &fd);
        if (error != 0)
                goto leave1;

        fp->f_flag = FREAD;
        if (flags & LINUX_IN_NONBLOCK)
                fp->f_flag |= FNONBLOCK;
        fp->f_type = DTYPE_MISC;
        fp->f_ops = &inotify_fileops;
        fp->f_data = ifd;
        fd_set_exclose(l, fd, (flags & LINUX_IN_CLOEXEC) != 0);
        fd_affix(p, fp, fd);

        *retval = fd;
        return 0;

leave1:
        KASSERT(fd_getfile(ifd->ifd_kqfd) != NULL);
        fd_close(ifd->ifd_kqfd);
leave0:
        kmem_free(ifd->ifd_wds, ifd->ifd_nwds * sizeof(*ifd->ifd_wds));
        kmem_free(ifd, sizeof(*ifd));

        mutex_destroy(&ifd->ifd_lock);
        mutex_destroy(&ifd->ifd_qlock);
        cv_destroy(&ifd->ifd_qcv);
        seldestroy(&ifd->ifd_sel);

        return error;
}

#ifndef __aarch64__
/*
 * inotify_init(2).  Initialize a new inotify fd with flags=0.
 */
int
linux_sys_inotify_init(struct lwp *l, const void *v, register_t *retval)
{
        return do_inotify_init(l, retval, 0);
}
#endif

/*
 * inotify_init(2).  Initialize a new inotify fd with the given flags.
 */
int
linux_sys_inotify_init1(struct lwp *l,
    const struct linux_sys_inotify_init1_args *uap, register_t *retval)
{
        /* {
                syscallarg(int) flags;
        } */

        return do_inotify_init(l, retval, SCARG(uap, flags));
}

/*
 * Convert inotify mask to the fflags of an equivalent kevent.
 */
static uint32_t
inotify_mask_to_kevent_fflags(uint32_t mask, enum vtype type)
{
        const struct inotify_kevent_mask_pair *type_inotify_to_kevent;
        uint32_t fflags;
        size_t i, type_inotify_to_kevent_len;

        switch (type) {
        case VREG:
        case VDIR:
        case VLNK:
                break;

        default:
                return 0;
        }

        /* flags that all watches could have */
        fflags = NOTE_DELETE|NOTE_REVOKE;
        for (i = 0; i < common_inotify_to_kevent_len; i++)
                if (mask & common_inotify_to_kevent[i].inotify)
                        fflags |= common_inotify_to_kevent[i].kevent;

        /* flags that depend on type */
        switch (type) {
        case VREG:
                type_inotify_to_kevent = vreg_inotify_to_kevent;
                type_inotify_to_kevent_len = vreg_inotify_to_kevent_len;
                break;

        case VDIR:
                type_inotify_to_kevent = vdir_inotify_to_kevent;
                type_inotify_to_kevent_len = vdir_inotify_to_kevent_len;
                break;

        default:
                type_inotify_to_kevent_len = 0;
                break;
        }
        for (i = 0; i < type_inotify_to_kevent_len; i++)
                if (mask & type_inotify_to_kevent[i].inotify)
                        fflags |= type_inotify_to_kevent[i].kevent;

        return fflags;
}

/*
 * inotify_add_watch(2).  Open a fd for pathname (if desired by mask)
 * track it and add an equivalent kqueue event for it in
 * ifd->ifd_kqfd.
 */
int
linux_sys_inotify_add_watch(struct lwp *l,
    const struct linux_sys_inotify_add_watch_args *uap, register_t *retval)
{
        /* {
                syscallarg(int) fd;
                syscallarg(const char *) pathname;
                syscallarg(uint32_t) mask;
        } */
        int wd, i, error = 0;
        file_t *fp, *wp, *cur_fp;
        struct inotifyfd *ifd;
        struct inotify_dir_entries **new_wds;
        struct knote *kn, *tmpkn;
        struct sys_open_args oa;
        struct kevent kev;
        struct vnode *wvp;
        namei_simple_flags_t sflags;
        struct kevent_ops k_ops = {
                .keo_private = NULL,
                .keo_fetch_timeout = NULL,
                .keo_fetch_changes = inotify_kev_fetch_changes,
                .keo_put_events = NULL,
        };
        const int fd = SCARG(uap, fd);
        const uint32_t mask = SCARG(uap, mask);

        if (mask & ~LINUX_IN_ADD_KNOWN)
                return EINVAL;

        fp = fd_getfile(fd);
        if (fp == NULL)
                return EBADF;

        if (fp->f_ops != &inotify_fileops) {
                /* not an inotify fd */
                error = EBADF;
                goto leave0;
        }

        ifd = fp->f_data;

        mutex_enter(&ifd->ifd_lock);

        if (mask & LINUX_IN_DONT_FOLLOW)
                sflags = NSM_NOFOLLOW_TRYEMULROOT;
        else
                sflags = NSM_FOLLOW_TRYEMULROOT;
        error = namei_simple_user(SCARG(uap, pathname), sflags, &wvp);
        if (error != 0)
                goto leave1;

        /* Check to see if we already have a descriptor to wd's file. */
        wd = -1;
        for (i = 0; i < ifd->ifd_nwds; i++) {
                if (ifd->ifd_wds[i] != NULL) {
                        cur_fp = fd_getfile(i);
                        if (cur_fp == NULL) {
                                DPRINTF(("%s: wd=%d was closed externally\n",
                                    __func__, i));
                                error = EBADF;
                                goto leave1;
                        }
                        if (cur_fp->f_type != DTYPE_VNODE) {
                                DPRINTF(("%s: wd=%d was replaced "
                                    "with a non-vnode\n", __func__, i));
                                error = EBADF;
                        }
                        if (error == 0 && cur_fp->f_vnode == wvp)
                                wd = i;
                        fd_putfile(i);
                        if (error != 0)
                                goto leave1;

                        if (wd != -1)
                                break;
                }
        }

        if (wd == -1) {
                /*
                 * If we do not have a descriptor to wd's file, we
                 * need to open the watch descriptor.
                 */
                SCARG(&oa, path) = SCARG(uap, pathname);
                SCARG(&oa, mode) = 0;
                SCARG(&oa, flags) = O_RDONLY;
                if (mask & LINUX_IN_DONT_FOLLOW)
                        SCARG(&oa, flags) |= O_NOFOLLOW;
                if (mask & LINUX_IN_ONLYDIR)
                        SCARG(&oa, flags) |= O_DIRECTORY;

                error = sys_open(l, &oa, retval);
                if (error != 0)
                        goto leave1;
                wd = *retval;
                wp = fd_getfile(wd);
                KASSERT(wp != NULL);
                KASSERT(wp->f_type == DTYPE_VNODE);

                /* translate the flags */
                memset(&kev, 0, sizeof(kev));
                EV_SET(&kev, wd, inotify_filtid, EV_ADD|EV_ENABLE,
                    NOTE_DELETE|NOTE_REVOKE, 0, ifd);
                if (mask & LINUX_IN_ONESHOT)
                        kev.flags |= EV_ONESHOT;
                kev.fflags |= inotify_mask_to_kevent_fflags(mask,
                    wp->f_vnode->v_type);

                error = kevent1(retval, ifd->ifd_kqfd, &kev, 1, NULL, 0, NULL,
                    &k_ops);
                if (error != 0) {
                        KASSERT(fd_getfile(wd) != NULL);
                        fd_close(wd);
                } else {
                        /* Success! */
                        *retval = wd;

                        /* Resize ifd_nwds to accommodate wd. */
                        if (wd+1 > ifd->ifd_nwds) {
                                new_wds = kmem_zalloc(
                                    (wd+1) * sizeof(*ifd->ifd_wds), KM_SLEEP);
                                memcpy(new_wds, ifd->ifd_wds,
                                    ifd->ifd_nwds * sizeof(*ifd->ifd_wds));

                                kmem_free(ifd->ifd_wds,
                                    ifd->ifd_nwds * sizeof(*ifd->ifd_wds));

                                ifd->ifd_wds = new_wds;
                                ifd->ifd_nwds = wd+1;
                        }

                        ifd->ifd_wds[wd] = get_inotify_dir_entries(wd, true);
                }
        } else {
                /*
                 * If we do have a descriptor to wd's file, try to edit
                 * the relevant knote.
                 */
                if (mask & LINUX_IN_MASK_CREATE) {
                        error = EEXIST;
                        goto leave1;
                }

                wp = fd_getfile(wd);
                if (wp == NULL) {
                        DPRINTF(("%s: wd=%d was closed externally "
                            "(race, probably)\n", __func__, wd));
                        error = EBADF;
                        goto leave1;
                }
                if (wp->f_type != DTYPE_VNODE) {
                        DPRINTF(("%s: wd=%d was replace with a non-vnode "
                            "(race, probably)\n", __func__, wd));
                        error = EBADF;
                        goto leave2;
                }

                kev.fflags = NOTE_DELETE | NOTE_REVOKE
                    | inotify_mask_to_kevent_fflags(mask, wp->f_vnode->v_type);

                mutex_enter(wp->f_vnode->v_interlock);

                /*
                 * XXX We are forced to find the appropriate knote
                 * manually because we cannot create a custom f_touch
                 * function for inotify_filtops.  See filter_touch()
                 * in kern_event.c for details.
                 */
                SLIST_FOREACH_SAFE(kn, &wp->f_vnode->v_klist->vk_klist,
                    kn_selnext, tmpkn) {
                        if (kn->kn_fop == &inotify_filtops
                            && ifd == kn->kn_kevent.udata) {
                                mutex_enter(&kn->kn_kq->kq_lock);
                                if (mask & LINUX_IN_MASK_ADD)
                                        kn->kn_sfflags |= kev.fflags;
                                else
                                        kn->kn_sfflags = kev.fflags;
                                wp->f_vnode->v_klist->vk_interest |=
                                    kn->kn_sfflags;
                                mutex_exit(&kn->kn_kq->kq_lock);
                        }
                }

                mutex_exit(wp->f_vnode->v_interlock);

                /* Success! */
                *retval = wd;
        }

leave2:
        fd_putfile(wd);
leave1:
        mutex_exit(&ifd->ifd_lock);
leave0:
        fd_putfile(fd);
        return error;
}

/*
 * Remove a wd from ifd and close wd.
 */
static int
inotify_close_wd(struct inotifyfd *ifd, int wd)
{
        file_t *wp;
        int error;
        register_t retval;
        struct kevent kev;
        struct kevent_ops k_ops = {
                .keo_private = NULL,
                .keo_fetch_timeout = NULL,
                .keo_fetch_changes = inotify_kev_fetch_changes,
                .keo_put_events = NULL,
        };

        mutex_enter(&ifd->ifd_lock);

        KASSERT(0 <= wd && wd < ifd->ifd_nwds && ifd->ifd_wds[wd] != NULL);

        kmem_free(ifd->ifd_wds[wd],
            INOTIFY_DIR_ENTRIES_SIZE(ifd->ifd_wds[wd]->ide_count));
        ifd->ifd_wds[wd] = NULL;

        mutex_exit(&ifd->ifd_lock);

        wp = fd_getfile(wd);
        if (wp == NULL) {
                DPRINTF(("%s: wd=%d is already closed\n", __func__, wd));
                return 0;
        }
        KASSERT(!mutex_owned(wp->f_vnode->v_interlock));

        memset(&kev, 0, sizeof(kev));
        EV_SET(&kev, wd, EVFILT_VNODE, EV_DELETE, 0, 0, 0);
        error = kevent1(&retval, ifd->ifd_kqfd, &kev, 1, NULL, 0, NULL, &k_ops);
        if (error != 0)
                DPRINTF(("%s: attempt to disable all events for wd=%d "
                    "had error=%d\n", __func__, wd, error));

        return fd_close(wd);
}

/*
 * inotify_rm_watch(2).  Close wd and remove it from ifd->ifd_wds.
 */
int
linux_sys_inotify_rm_watch(struct lwp *l,
    const struct linux_sys_inotify_rm_watch_args *uap, register_t *retval)
{
        /* {
                syscallarg(int) fd;
                syscallarg(int) wd;
        } */
        struct inotifyfd *ifd;
        file_t *fp;
        int error = 0;
        const int fd = SCARG(uap, fd);
        const int wd = SCARG(uap, wd);

        fp = fd_getfile(fd);
        if (fp == NULL)
                return EBADF;
        if (fp->f_ops != &inotify_fileops) {
                /* not an inotify fd */
                error = EINVAL;
                goto leave;
        }

        ifd = fp->f_data;
        if (wd < 0 || wd >= ifd->ifd_nwds || ifd->ifd_wds[wd] == NULL) {
                error = EINVAL;
                goto leave;
        }

        error = inotify_close_wd(ifd, wd);

leave:
        fd_putfile(fd);
        return error;
}

/*
 * Attach the inotify filter.
 */
static int
inotify_filt_attach(struct knote *kn)
{
        file_t *fp = kn->kn_obj;
        struct vnode *vp;

        KASSERT(fp->f_type == DTYPE_VNODE);
        vp = fp->f_vnode;

        /*
         * Needs to be set so that we get the same event handling as
         * EVFILT_VNODE.  Otherwise we don't get any events.
         *
         * A consequence of this is that modifications/removals of
         * this knote need to specify EVFILT_VNODE rather than
         * inotify_filtid.
         */
        kn->kn_filter = EVFILT_VNODE;

        kn->kn_fop = &inotify_filtops;
        kn->kn_hook = vp;
        vn_knote_attach(vp, kn);

        return 0;
}

/*
 * Detach the inotify filter.
 */
static void
inotify_filt_detach(struct knote *kn)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;

        vn_knote_detach(vp, kn);
}

/*
 * Create a single inotify event.
 */
static void
do_kevent_to_inotify(int32_t wd, uint32_t mask, uint32_t cookie,
    struct inotify_entry *buf, size_t *nbuf, char *name)
{
        KASSERT(*nbuf < LINUX_INOTIFY_MAX_FROM_KEVENT);

        buf += *nbuf;

        memset(buf, 0, sizeof(*buf));

        buf->ie_event.wd = wd;
        buf->ie_event.mask = mask;
        buf->ie_event.cookie = cookie;

        if (name != NULL) {
                buf->ie_event.len = strlen(name) + 1;
                KASSERT(buf->ie_event.len < sizeof(buf->ie_name));
                strcpy(buf->ie_name, name);
        }

        ++(*nbuf);
}

/*
 * Like vn_readdir(), but with vnode locking only if needs_lock is
 * true (to avoid double locking in some situations).
 */
static int
inotify_readdir(file_t *fp, struct dirent *dep, int *done, bool needs_lock)
{
        struct vnode *vp;
        struct iovec iov;
        struct uio uio;
        int error, eofflag;

        KASSERT(fp->f_type == DTYPE_VNODE);
        vp = fp->f_vnode;
        KASSERT(vp->v_type == VDIR);

        iov.iov_base = dep;
        iov.iov_len = sizeof(*dep);

        uio.uio_iov = &iov;
        uio.uio_iovcnt = 1;
        uio.uio_rw = UIO_READ;
        uio.uio_resid = sizeof(*dep);
        UIO_SETUP_SYSSPACE(&uio);

        mutex_enter(&fp->f_lock);
        uio.uio_offset = fp->f_offset;
        mutex_exit(&fp->f_lock);

        /* XXX: should pass whether to lock or not */
        if (needs_lock)
                vn_lock(vp, LK_SHARED | LK_RETRY);
        else
                /*
                 * XXX We need to temporarily drop v_interlock because
                 * it may be temporarily acquired by biowait().
                 */
                mutex_exit(vp->v_interlock);
        KASSERT(!mutex_owned(vp->v_interlock));
        error = VOP_READDIR(vp, &uio, fp->f_cred, &eofflag, NULL, NULL);
        if (needs_lock)
                VOP_UNLOCK(vp);
        else
                mutex_enter(vp->v_interlock);

        mutex_enter(&fp->f_lock);
        fp->f_offset = uio.uio_offset;
        mutex_exit(&fp->f_lock);

        *done = sizeof(*dep) - uio.uio_resid;
        return error;
}

/*
 * Create (and allocate) an appropriate inotify_dir_entries struct for wd to be
 * used on ifd_wds of inotifyfd.  If the entries on a directory fail to be read,
 * NULL is returned.  needs_lock indicates if the vnode's lock is not already
 * owned.
 */
static struct inotify_dir_entries *
get_inotify_dir_entries(int wd, bool needs_lock)
{
        struct dirent de;
        struct dirent *currdep;
        struct inotify_dir_entries *idep = NULL;
        file_t *wp;
        int done, error;
        size_t i, decount;

        wp = fd_getfile(wd);
        if (wp == NULL)
                return NULL;
        if (wp->f_type != DTYPE_VNODE)
                goto leave;

        /* for non-directories, we have 0 entries. */
        if (wp->f_vnode->v_type != VDIR) {
                idep = kmem_zalloc(INOTIFY_DIR_ENTRIES_SIZE(0), KM_SLEEP);
                goto leave;
        }

        mutex_enter(&wp->f_lock);
        wp->f_offset = 0;
        mutex_exit(&wp->f_lock);
        decount = 0;
        for (;;) {
                error = inotify_readdir(wp, &de, &done, needs_lock);
                if (error != 0)
                        goto leave;
                if (done == 0)
                        break;

                currdep = &de;
                while ((char *)currdep < ((char *)&de) + done) {
                        decount++;
                        currdep = _DIRENT_NEXT(currdep);
                }
        }

        idep = kmem_zalloc(INOTIFY_DIR_ENTRIES_SIZE(decount), KM_SLEEP);
        idep->ide_count = decount;

        mutex_enter(&wp->f_lock);
        wp->f_offset = 0;
        mutex_exit(&wp->f_lock);
        for (i = 0; i < decount;) {
                error = inotify_readdir(wp, &de, &done, needs_lock);
                if (error != 0 || done == 0) {
                        kmem_free(idep, INOTIFY_DIR_ENTRIES_SIZE(decount));
                        idep = NULL;
                        goto leave;
                }

                currdep = &de;
                while ((char *)currdep < ((char *)&de) + done) {
                        idep->ide_entries[i].fileno = currdep->d_fileno;
                        strcpy(idep->ide_entries[i].name, currdep->d_name);

                        currdep = _DIRENT_NEXT(currdep);
                        i++;
                }
        }

leave:
        fd_putfile(wd);
        return idep;
}

static size_t
find_entry(struct inotify_dir_entries *i1, struct inotify_dir_entries *i2)
{
        for (size_t i = 0; i < i2->ide_count; i++)
                if (i2->ide_entries[i].fileno != i1->ide_entries[i].fileno)
                        return i;
        KASSERTMSG(0, "Entry not found");
        return -1;
}

static void
handle_write(struct inotifyfd *ifd, int wd, struct inotify_entry *buf,
    size_t *nbuf)
{
        struct inotify_dir_entries *old_idep, *new_idep;
        size_t i;

        mutex_enter(&ifd->ifd_lock);

        old_idep = ifd->ifd_wds[wd];
        KASSERT(old_idep != NULL);
        new_idep = get_inotify_dir_entries(wd, false);
        if (new_idep == NULL) {
                DPRINTF(("%s: directory for wd=%d could not be read\n",
                    __func__, wd));
                mutex_exit(&ifd->ifd_lock);
                return;
        }


        if (old_idep->ide_count < new_idep->ide_count) {
                KASSERT(old_idep->ide_count + 1 == new_idep->ide_count);

                /* Find the new entry. */
                i = find_entry(new_idep, old_idep);
                do_kevent_to_inotify(wd, LINUX_IN_CREATE, 0,
                    buf, nbuf, new_idep->ide_entries[i].name);
                goto out;
        }

        if (old_idep->ide_count > new_idep->ide_count) {
                KASSERT(old_idep->ide_count == new_idep->ide_count + 1);

                /* Find the deleted entry. */
                i = find_entry(old_idep, new_idep);

                do_kevent_to_inotify(wd, LINUX_IN_DELETE, 0,
                    buf, nbuf, old_idep->ide_entries[i].name);
                goto out;
        }

        /*
         * XXX Because we are not watching the entire
         * file system, the only time we know for sure
         * that the event is a LINUX_IN_MOVED_FROM/
         * LINUX_IN_MOVED_TO is when the move happens
         * within a single directory...  ie. the number
         * of directory entries has not changed.
         *
         * Otherwise all we can say for sure is that
         * something was created/deleted.  So we issue a
         * LINUX_IN_CREATE/LINUX_IN_DELETE.
         */
        ino_t changed = new_idep->ide_entries[new_idep->ide_count - 1].fileno;

        /* Find the deleted entry. */
        for (i = 0; i < old_idep->ide_count; i++)
                if (old_idep->ide_entries[i].fileno == changed)
                        break;
        KASSERT(i != old_idep->ide_count);

        do_kevent_to_inotify(wd, LINUX_IN_MOVED_FROM, changed, buf, nbuf,
            old_idep->ide_entries[i].name);

        do_kevent_to_inotify(wd, LINUX_IN_MOVED_TO, changed, buf, nbuf,
            new_idep->ide_entries[new_idep->ide_count - 1].name);

out:
        ifd->ifd_wds[wd] = new_idep;
        mutex_exit(&ifd->ifd_lock);
}

/*
 * Convert a kevent flags and fflags for EVFILT_VNODE to some number
 * of inotify events.
 */
static int
kevent_to_inotify(struct inotifyfd *ifd, int wd, enum vtype wtype,
    uint32_t flags, uint32_t fflags, struct inotify_entry *buf,
    size_t *nbuf)
{
        struct stat st;
        file_t *wp;
        size_t i;
        int error = 0;

        for (i = 0; i < common_kevent_to_inotify_len; i++)
                if (fflags & common_kevent_to_inotify[i].kevent)
                        do_kevent_to_inotify(wd,
                            common_kevent_to_inotify[i].inotify, 0, buf, nbuf,
                            NULL);

        if (wtype == VREG) {
                for (i = 0; i < vreg_kevent_to_inotify_len; i++)
                        if (fflags & vreg_kevent_to_inotify[i].kevent)
                                do_kevent_to_inotify(wd,
                                    vreg_kevent_to_inotify[i].inotify, 0,
                                    buf, nbuf, NULL);
        } else if (wtype == VDIR) {
                for (i = 0; i < *nbuf; i++)
                        if (buf[i].ie_event.mask &
                            (LINUX_IN_ACCESS|LINUX_IN_ATTRIB
                            |LINUX_IN_CLOSE|LINUX_IN_OPEN))
                                buf[i].ie_event.mask |= LINUX_IN_ISDIR;

                /* Need to disambiguate the possible NOTE_WRITEs. */
                if (fflags & NOTE_WRITE)
                        handle_write(ifd, wd, buf, nbuf);
        }

        /*
         * Need to check if wd is actually has a link count of 0 to issue a
         * LINUX_IN_DELETE_SELF.
         */
        if (fflags & NOTE_DELETE) {
                wp = fd_getfile(wd);
                KASSERT(wp != NULL);
                KASSERT(wp->f_type == DTYPE_VNODE);
                vn_stat(wp->f_vnode, &st);
                fd_putfile(wd);

                if (st.st_nlink == 0)
                        do_kevent_to_inotify(wd, LINUX_IN_DELETE_SELF, 0,
                            buf, nbuf, NULL);
        }

        /* LINUX_IN_IGNORED must be the last event issued for wd. */
        if ((flags & EV_ONESHOT) || (fflags & (NOTE_REVOKE|NOTE_DELETE))) {
                do_kevent_to_inotify(wd, LINUX_IN_IGNORED, 0, buf, nbuf, NULL);
                /*
                 * XXX in theory we could call inotify_close_wd(ifd, wd) but if
                 * we get here we must already be holding v_interlock for
                 * wd... so we can't.
                 *
                 * For simplicity we do nothing, and so wd will only be closed
                 * when the inotify fd is closed.
                 */
        }

        return error;
}

/*
 * Handle an event.  Unlike EVFILT_VNODE, we translate the event to a
 * linux_inotify_event and put it in our own custom queue.
 */
static int
inotify_filt_event(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        struct inotifyfd *ifd;
        struct inotify_entry *cur_ie;
        size_t nbuf, i;
        uint32_t status;
        struct inotify_entry buf[LINUX_INOTIFY_MAX_FROM_KEVENT];

        /*
         * If KN_WILLDETACH is set then
         * 1. kn->kn_kevent.udata has already been trashed with a
         *    struct lwp *, so we don't have access to a real ifd
         *    anymore, and
         * 2. we're about to detach anyways, so we don't really care
         *    about the events.
         * (Also because of this we need to get ifd under the same
         * lock as kn->kn_status.)
         */
        mutex_enter(&kn->kn_kq->kq_lock);
        status = kn->kn_status;
        ifd = kn->kn_kevent.udata;
        mutex_exit(&kn->kn_kq->kq_lock);
        if (status & KN_WILLDETACH)
                return 0;

        /*
         * If we don't care about the NOTEs in hint, we don't generate
         * any events.
         */
        hint &= kn->kn_sfflags;
        if (hint == 0)
                return 0;

        KASSERT(mutex_owned(vp->v_interlock));
        KASSERT(!mutex_owned(&ifd->ifd_lock));

        mutex_enter(&ifd->ifd_qlock);

        /*
         * early out: there's no point even traslating the event if we
         * have nowhere to put it (and an LINUX_IN_Q_OVERFLOW has
         * already been added).
         */
        if (ifd->ifd_qcount >= LINUX_INOTIFY_MAX_QUEUED)
                goto leave;

        nbuf = 0;
        (void)kevent_to_inotify(ifd, kn->kn_id, vp->v_type, kn->kn_flags,
            hint, buf, &nbuf);
        for (i = 0; i < nbuf && ifd->ifd_qcount < LINUX_INOTIFY_MAX_QUEUED-1;
             i++) {
                cur_ie = kmem_zalloc(sizeof(*cur_ie), KM_SLEEP);
                memcpy(cur_ie, &buf[i], sizeof(*cur_ie));

                TAILQ_INSERT_TAIL(&ifd->ifd_qhead, cur_ie, ie_entries);
                ifd->ifd_qcount++;
        }
        /* handle early overflow, by adding an overflow event to the end */
        if (i != nbuf) {
                nbuf = 0;
                cur_ie = kmem_zalloc(sizeof(*cur_ie), KM_SLEEP);
                do_kevent_to_inotify(-1, LINUX_IN_Q_OVERFLOW, 0,
                    cur_ie, &nbuf, NULL);

                TAILQ_INSERT_TAIL(&ifd->ifd_qhead, cur_ie, ie_entries);
                ifd->ifd_qcount++;
        }

        if (nbuf > 0) {
                cv_signal(&ifd->ifd_qcv);

                mutex_enter(&ifd->ifd_lock);
                selnotify(&ifd->ifd_sel, 0, NOTE_LOWAT);
                mutex_exit(&ifd->ifd_lock);
        } else
                DPRINTF(("%s: hint=%lx resulted in 0 inotify events\n",
                    __func__, hint));

leave:
        mutex_exit(&ifd->ifd_qlock);
        return 0;
}

/*
 * Read inotify events from the queue.
 */
static int
inotify_read(file_t *fp, off_t *offp, struct uio *uio, kauth_cred_t cred,
    int flags)
{
        struct inotify_entry *cur_iep;
        size_t cur_size, nread;
        int error = 0;
        struct inotifyfd *ifd = fp->f_data;

        mutex_enter(&ifd->ifd_qlock);

        if (ifd->ifd_qcount == 0) {
                if (fp->f_flag & O_NONBLOCK) {
                        error = EAGAIN;
                        goto leave;
                }

                while (ifd->ifd_qcount == 0) {
                        /* wait until there is an event to read */
                        error = cv_wait_sig(&ifd->ifd_qcv, &ifd->ifd_qlock);
                        if (error != 0) {
                                error = EINTR;
                                goto leave;
                        }
                }
        }

        KASSERT(ifd->ifd_qcount > 0);
        KASSERT(mutex_owned(&ifd->ifd_qlock));

        nread = 0;
        while (ifd->ifd_qcount > 0) {
                cur_iep = TAILQ_FIRST(&ifd->ifd_qhead);
                KASSERT(cur_iep != NULL);

                cur_size = sizeof(cur_iep->ie_event) + cur_iep->ie_event.len;
                if (cur_size > uio->uio_resid) {
                        if (nread == 0)
                                error = EINVAL;
                        break;
                }

                error = uiomove(&cur_iep->ie_event, sizeof(cur_iep->ie_event),
                    uio);
                if (error != 0)
                        break;
                error = uiomove(&cur_iep->ie_name, cur_iep->ie_event.len, uio);
                if (error != 0)
                        break;

                /* cleanup */
                TAILQ_REMOVE(&ifd->ifd_qhead, cur_iep, ie_entries);
                kmem_free(cur_iep, sizeof(*cur_iep));

                nread++;
                ifd->ifd_qcount--;
        }

leave:
        /* Wake up the next reader, if the queue is not empty. */
        if (ifd->ifd_qcount > 0)
                cv_signal(&ifd->ifd_qcv);

        mutex_exit(&ifd->ifd_qlock);
        return error;
}

/*
 * Close all the file descriptors associated with fp.
 */
static int
inotify_close(file_t *fp)
{
        int error;
        size_t i;
        file_t *kqfp;
        struct inotifyfd *ifd = fp->f_data;

        for (i = 0; i < ifd->ifd_nwds; i++) {
                if (ifd->ifd_wds[i] != NULL) {
                        error = inotify_close_wd(ifd, i);
                        if (error != 0)
                                return error;
                }
        }

        /* the reference we need to hold is ifd->ifd_kqfp */
        kqfp = fd_getfile(ifd->ifd_kqfd);
        if (kqfp == NULL) {
                DPRINTF(("%s: kqfp=%d is already closed\n", __func__,
                    ifd->ifd_kqfd));
        } else {
                error = fd_close(ifd->ifd_kqfd);
                if (error != 0)
                        return error;
        }

        mutex_destroy(&ifd->ifd_lock);
        mutex_destroy(&ifd->ifd_qlock);
        cv_destroy(&ifd->ifd_qcv);
        seldestroy(&ifd->ifd_sel);

        kmem_free(ifd->ifd_wds, ifd->ifd_nwds * sizeof(*ifd->ifd_wds));
        kmem_free(ifd, sizeof(*ifd));
        fp->f_data = NULL;

        return 0;
}

/*
 * Check if there are pending read events.
 */
static int
inotify_poll(file_t *fp, int events)
{
        int revents;
        struct inotifyfd *ifd = fp->f_data;

        revents = 0;
        if (events & (POLLIN|POLLRDNORM)) {
                mutex_enter(&ifd->ifd_qlock);

                if (ifd->ifd_qcount > 0)
                        revents |= events & (POLLIN|POLLRDNORM);

                mutex_exit(&ifd->ifd_qlock);
        }

        return revents;
}

/*
 * Attach EVFILT_READ to the inotify instance in fp.
 *
 * This is so you can watch inotify with epoll.  No other kqueue
 * filter needs to be supported.
 */
static int
inotify_kqfilter(file_t *fp, struct knote *kn)
{
        struct inotifyfd *ifd = fp->f_data;

        KASSERT(fp == kn->kn_obj);

        if (kn->kn_filter != EVFILT_READ)
                return EINVAL;

        kn->kn_fop = &inotify_read_filtops;
        mutex_enter(&ifd->ifd_lock);
        selrecord_knote(&ifd->ifd_sel, kn);
        mutex_exit(&ifd->ifd_lock);

        return 0;
}

/*
 * Detach a filter from an inotify instance.
 */
static void
inotify_read_filt_detach(struct knote *kn)
{
        struct inotifyfd *ifd = ((file_t *)kn->kn_obj)->f_data;

        mutex_enter(&ifd->ifd_lock);
        selremove_knote(&ifd->ifd_sel, kn);
        mutex_exit(&ifd->ifd_lock);
}

/*
 * Handle EVFILT_READ events.  Note that nothing is put in kn_data.
 */
static int
inotify_read_filt_event(struct knote *kn, long hint)
{
        struct inotifyfd *ifd = ((file_t *)kn->kn_obj)->f_data;

        if (hint != 0) {
                KASSERT(mutex_owned(&ifd->ifd_lock));
                KASSERT(mutex_owned(&ifd->ifd_qlock));
                KASSERT(hint == NOTE_LOWAT);

                kn->kn_data = ifd->ifd_qcount;
        }

        return kn->kn_data > 0;
}

/*
 * Restart the inotify instance.
 */
static void
inotify_restart(file_t *fp)
{
        struct inotifyfd *ifd = fp->f_data;

        mutex_enter(&ifd->ifd_qlock);
        cv_broadcast(&ifd->ifd_qcv);
        mutex_exit(&ifd->ifd_qlock);
}