xnu-1504.9.17.tar.gz

[apple/xnu.git] / bsd / vfs / vfs_fsevents.c

/*
 * Copyright (c) 2004-2008 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
#include <stdarg.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/event.h>         // for kqueue related stuff
#include <sys/fsevents.h>

#if CONFIG_FSE
#include <sys/namei.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/file_internal.h>
#include <sys/stat.h>
#include <sys/vnode_internal.h>
#include <sys/mount_internal.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/uio.h>
#include <sys/malloc.h>
#include <sys/dirent.h>
#include <sys/attr.h>
#include <sys/sysctl.h>
#include <sys/ubc.h>
#include <machine/cons.h>
#include <miscfs/specfs/specdev.h>
#include <miscfs/devfs/devfs.h>
#include <sys/filio.h>
#include <kern/locks.h>
#include <libkern/OSAtomic.h>
#include <kern/zalloc.h>
#include <mach/mach_time.h>
#include <kern/thread_call.h>
#include <kern/clock.h>

#include <security/audit/audit.h>
#include <bsm/audit_kevents.h>



typedef struct kfs_event {
    LIST_ENTRY(kfs_event) kevent_list;
    int16_t        type;           // type code of this event
    u_int16_t      flags,          // per-event flags
                   len;            // the length of the path in "str"
    int32_t        refcount;       // number of clients referencing this
    pid_t          pid;            // pid of the process that did the op

    uint64_t       abstime;        // when this event happened (mach_absolute_time())
    ino64_t        ino;
    dev_t          dev;
    int32_t        mode;
    uid_t          uid;
    gid_t          gid;

    const char    *str;

    struct kfs_event *dest;    // if this is a two-file op
} kfs_event;

// flags for the flags field
#define KFSE_COMBINED_EVENTS          0x0001
#define KFSE_CONTAINS_DROPPED_EVENTS  0x0002
#define KFSE_RECYCLED_EVENT           0x0004
#define KFSE_BEING_CREATED            0x0008

LIST_HEAD(kfse_list, kfs_event) kfse_list_head = LIST_HEAD_INITIALIZER(x);
int num_events_outstanding = 0;
int num_pending_rename = 0;


struct fsevent_handle;

typedef struct fs_event_watcher {
    int8_t      *event_list;             // the events we're interested in
    int32_t      num_events;
    dev_t       *devices_not_to_watch;   // report events from devices not in this list
    uint32_t     num_devices;
    int32_t      flags;
    kfs_event  **event_queue;
    int32_t      eventq_size;            // number of event pointers in queue
    int32_t      num_readers;
    int32_t      rd;                     // read index into the event_queue
    int32_t      wr;                     // write index into the event_queue
    int32_t      blockers;
    int32_t      my_id;
    uint32_t     num_dropped;
    uint64_t     max_event_id;
    struct fsevent_handle *fseh;
} fs_event_watcher;

// fs_event_watcher flags
#define WATCHER_DROPPED_EVENTS         0x0001
#define WATCHER_CLOSING                0x0002
#define WATCHER_WANTS_COMPACT_EVENTS   0x0004
#define WATCHER_WANTS_EXTENDED_INFO    0x0008


#define MAX_WATCHERS  8
static fs_event_watcher *watcher_table[MAX_WATCHERS];


#define MAX_KFS_EVENTS   4096

// we allocate kfs_event structures out of this zone
static zone_t     event_zone;
static int        fs_event_init = 0;

//
// this array records whether anyone is interested in a
// particular type of event.  if no one is, we bail out
// early from the event delivery
//
static int16_t     fs_event_type_watchers[FSE_MAX_EVENTS];

static int  watcher_add_event(fs_event_watcher *watcher, kfs_event *kfse);
static void fsevents_wakeup(fs_event_watcher *watcher);

//
// Locks
//
static lck_grp_attr_t *  fsevent_group_attr;
static lck_attr_t *      fsevent_lock_attr;
static lck_grp_t *       fsevent_mutex_group;

static lck_grp_t *       fsevent_rw_group;

static lck_rw_t  event_handling_lock; // handles locking for event manipulation and recycling
static lck_mtx_t watch_table_lock;
static lck_mtx_t event_buf_lock;
static lck_mtx_t event_writer_lock;


/* Explicitly declare qsort so compiler doesn't complain */
__private_extern__ void qsort(
    void * array,
    size_t nmembers,
    size_t member_size,
    int (*)(const void *, const void *));


static void
fsevents_internal_init(void)
{
    int i;
    
    if (fs_event_init++ != 0) {
        return;
    }

    for(i=0; i < FSE_MAX_EVENTS; i++) {
        fs_event_type_watchers[i] = 0;
    }

    memset(watcher_table, 0, sizeof(watcher_table));

    fsevent_lock_attr    = lck_attr_alloc_init();
    fsevent_group_attr   = lck_grp_attr_alloc_init();
    fsevent_mutex_group  = lck_grp_alloc_init("fsevent-mutex", fsevent_group_attr);
    fsevent_rw_group     = lck_grp_alloc_init("fsevent-rw", fsevent_group_attr);

    lck_mtx_init(&watch_table_lock, fsevent_mutex_group, fsevent_lock_attr);
    lck_mtx_init(&event_buf_lock, fsevent_mutex_group, fsevent_lock_attr);
    lck_mtx_init(&event_writer_lock, fsevent_mutex_group, fsevent_lock_attr);

    lck_rw_init(&event_handling_lock, fsevent_rw_group, fsevent_lock_attr);

    event_zone = zinit(sizeof(kfs_event),
                       MAX_KFS_EVENTS * sizeof(kfs_event),
                       MAX_KFS_EVENTS * sizeof(kfs_event),
                       "fs-event-buf");
    if (event_zone == NULL) {
        printf("fsevents: failed to initialize the event zone.\n");
    }

    if (zfill(event_zone, MAX_KFS_EVENTS) != MAX_KFS_EVENTS) {
        printf("fsevents: failed to pre-fill the event zone.\n");       
    }
    
    // mark the zone as exhaustible so that it will not
    // ever grow beyond what we initially filled it with
    zone_change(event_zone, Z_EXHAUST, TRUE);
    zone_change(event_zone, Z_COLLECT, FALSE);
}

static void
lock_watch_table(void)
{
    lck_mtx_lock(&watch_table_lock);
}

static void
unlock_watch_table(void)
{
    lck_mtx_unlock(&watch_table_lock);
}

static void
lock_fs_event_list(void)
{
    lck_mtx_lock(&event_buf_lock);
}

static void
unlock_fs_event_list(void)
{
    lck_mtx_unlock(&event_buf_lock);
}

// forward prototype
static void release_event_ref(kfs_event *kfse);

static int
watcher_cares_about_dev(fs_event_watcher *watcher, dev_t dev)
{
    unsigned int i;
    
    // if devices_not_to_watch is NULL then we care about all
    // events from all devices
    if (watcher->devices_not_to_watch == NULL) {
        return 1;
    }

    for(i=0; i < watcher->num_devices; i++) {
        if (dev == watcher->devices_not_to_watch[i]) {
            // found a match! that means we do not 
            // want events from this device.
            return 0;
        }
    }

    // if we're here it's not in the devices_not_to_watch[] 
    // list so that means we do care about it
    return 1;
}


int
need_fsevent(int type, vnode_t vp)
{
    if (type >= 0 && type < FSE_MAX_EVENTS && fs_event_type_watchers[type] == 0)
        return (0);

    // events in /dev aren't really interesting...
    if (vp->v_tag == VT_DEVFS) {
        return (0);
    }

    return 1;
}

static int
prefix_match_len(const char *str1, const char *str2)
{
    int len=0;

    while(*str1 && *str2 && *str1 == *str2) {
        len++;
        str1++;
        str2++;
    }

    if (*str1 == '\0' && *str2 == '\0') {
        len++;
    }

    return len;
}


struct history_item {
    kfs_event *kfse;
    kfs_event *oldest_kfse;
    int        counter;
};

static int
compare_history_items(const void *_a, const void *_b)
{
    const struct history_item *a = (const struct history_item *)_a;
    const struct history_item *b = (const struct history_item *)_b;

    // we want a descending order
    return (b->counter - a->counter);
}

#define is_throw_away(x)  ((x) == FSE_STAT_CHANGED || (x) == FSE_CONTENT_MODIFIED)


// Ways that an event can be reused:
//
// "combined" events mean that there were two events for 
// the same vnode or path and we're combining both events 
// into a single event.  The primary event gets a bit that
// marks it as having been combined.  The secondary event 
// is essentially dropped and the kfse structure reused.
//
// "collapsed" means that multiple events below a given
// directory are collapsed into a single event.  in this
// case, the directory that we collapse into and all of
// its children must be re-scanned.
//
// "recycled" means that we're completely blowing away 
// the event since there are other events that have info 
// about the same vnode or path (and one of those other 
// events will be marked as combined or collapsed as
// appropriate).
//
#define KFSE_COMBINED   0x0001
#define KFSE_COLLAPSED  0x0002
#define KFSE_RECYCLED   0x0004

int num_dropped         = 0;
int num_combined_events = 0;
int num_added_to_parent = 0;
int num_parent_switch   = 0;
int num_recycled_rename = 0;

//
// NOTE: you must call lock_fs_event_list() before calling
//       this function.
//
static kfs_event *
find_an_event(const char *str, int len, kfs_event *do_not_reuse, int *reuse_type, int *longest_match_len)
{
    kfs_event *kfse, *best_kfse=NULL;

// this seems to be enough to find most duplicate events for the same vnode
#define MAX_HISTORY  12 
    struct history_item history[MAX_HISTORY];
    int           i;

    *longest_match_len = 0;
    *reuse_type = 0;
    
    memset(history, 0, sizeof(history));

    //
    // now walk the list of events and try to find the best match
    // for this event.  if we have a vnode, we look for an event
    // that already references the vnode.  if we don't find one
    // we'll also take the parent of this vnode (in which case it
    // will be marked as having dropped events within it).
    //
    // if we have a string we look for the longest match on the
    // path we have.
    //

    LIST_FOREACH(kfse, &kfse_list_head, kevent_list) {
        int match_len;

        //
        // don't look at events that are still in the process of being
        // created, have a null vnode ptr or rename/exchange events.
        //
        if (   (kfse->flags & KFSE_BEING_CREATED) || kfse->type == FSE_RENAME || kfse->type == FSE_EXCHANGE) {

            continue;
        }
        
        if (str != NULL) {
            if (kfse->len != 0 && kfse->str != NULL) {
                match_len = prefix_match_len(str, kfse->str);
                if (match_len > *longest_match_len) {
                    best_kfse = kfse;
                    *longest_match_len = match_len;
                }
            }
        }

        if (kfse == do_not_reuse) {
            continue;
        }

        for(i=0; i < MAX_HISTORY; i++) {
            if (history[i].kfse == NULL) {
                break;
            }

            //
            // do a quick check to see if we've got two simple events
            // that we can cheaply combine.  if the event we're looking
            // at and one of the events in the history table are for the
            // same path then we'll just mark the newer event as combined
            // and recyle the older event.
            //
            if (history[i].kfse->str == kfse->str) {

                OSBitOrAtomic16(KFSE_COMBINED_EVENTS, &kfse->flags);
                *reuse_type = KFSE_RECYCLED;
                history[i].kfse->flags |= KFSE_RECYCLED_EVENT;
                return history[i].kfse;
            }
        }

        if (i < MAX_HISTORY && history[i].kfse == NULL) {
            history[i].kfse = kfse;
            history[i].counter = 1;
        } else if (i >= MAX_HISTORY) {
            qsort(history, MAX_HISTORY, sizeof(struct history_item), compare_history_items);

            // pluck off the lowest guy if he's only got a count of 1
            if (history[MAX_HISTORY-1].counter == 1) {
                history[MAX_HISTORY-1].kfse = kfse;
            }
        }
    }

    
    if (str != NULL && best_kfse) {
        if (*longest_match_len <= 1) {
            // if the best match we had was "/" then basically we're toast...
            *longest_match_len = 0;
            best_kfse = NULL;
        } else if (*longest_match_len != len) {
            OSBitOrAtomic16(KFSE_CONTAINS_DROPPED_EVENTS, &best_kfse->flags);
            *reuse_type = KFSE_COLLAPSED;
        } else {
            OSBitOrAtomic16(KFSE_COMBINED_EVENTS, &best_kfse->flags);
            *reuse_type = KFSE_COMBINED;
        }
    }

    return best_kfse;
}


static struct timeval last_print;

//
// These variables are used to track coalescing multiple identical
// events for the same vnode/pathname.  If we get the same event
// type and same vnode/pathname as the previous event, we just drop
// the event since it's superfluous.  This improves some micro-
// benchmarks considerably and actually has a real-world impact on
// tests like a Finder copy where multiple stat-changed events can
// get coalesced.
//
static int     last_event_type=-1;
static void   *last_ptr=NULL;
static char    last_str[MAXPATHLEN];
static int     last_nlen=0;
static int     last_vid=-1;
static uint64_t last_coalesced_time=0;
static void   *last_event_ptr=NULL;
int            last_coalesced = 0;
static mach_timebase_info_data_t    sTimebaseInfo = { 0, 0 };


int
add_fsevent(int type, vfs_context_t ctx, ...) 
{
    struct proc      *p = vfs_context_proc(ctx);
    int               i, arg_type, skip_init=0, longest_match_len, ret;
    kfs_event        *kfse, *kfse_dest=NULL, *cur;
    fs_event_watcher *watcher;
    va_list           ap;
    int               error = 0, did_alloc=0, need_event_unlock = 0;
    dev_t             dev = 0;
    uint64_t          now, elapsed;
    int               reuse_type = 0;
    char             *pathbuff=NULL;
    int               pathbuff_len;



    va_start(ap, ctx);

    // ignore bogus event types..
    if (type < 0 || type >= FSE_MAX_EVENTS) {
        return EINVAL;
    }

    // if no one cares about this type of event, bail out
    if (fs_event_type_watchers[type] == 0) {
        va_end(ap);

        return 0;
    }

    now = mach_absolute_time();

    // find a free event and snag it for our use
    // NOTE: do not do anything that would block until
    //       the lock is dropped.
    lock_fs_event_list();
    
    //
    // check if this event is identical to the previous one...
    // (as long as it's not an event type that can never be the
    // same as a previous event)
    //
    if (type != FSE_CREATE_FILE && type != FSE_DELETE && type != FSE_RENAME && type != FSE_EXCHANGE && type != FSE_CHOWN) {
        void *ptr=NULL;
        int   vid=0, was_str=0, nlen=0;

        for(arg_type=va_arg(ap, int32_t); arg_type != FSE_ARG_DONE; arg_type=va_arg(ap, int32_t)) {
            switch(arg_type) {
                case FSE_ARG_VNODE: {
                    ptr = va_arg(ap, void *);
                    vid = vnode_vid((struct vnode *)ptr);
                    last_str[0] = '\0';
                    break;
                }
                case FSE_ARG_STRING: {
                    nlen = va_arg(ap, int32_t);
                    ptr = va_arg(ap, void *);
                    was_str = 1;
                    break;
                }
            }
            if (ptr != NULL) {
                break;
            }
        }

        if ( sTimebaseInfo.denom == 0 ) {
            (void) clock_timebase_info(&sTimebaseInfo);
        }
        
        elapsed = (now - last_coalesced_time);
        if (sTimebaseInfo.denom != sTimebaseInfo.numer) {
            if (sTimebaseInfo.denom == 1) {
                elapsed *= sTimebaseInfo.numer;
            } else {
                // this could overflow... the worst that will happen is that we'll
                // send (or not send) an extra event so I'm not going to worry about
                // doing the math right like dtrace_abs_to_nano() does.
                elapsed = (elapsed * sTimebaseInfo.numer) / (uint64_t)sTimebaseInfo.denom;
            }
        }
        
        if (type == last_event_type
            && (elapsed < 1000000000)
            && 
            ((vid && vid == last_vid && last_ptr == ptr)
              ||
             (last_str[0] && last_nlen == nlen && ptr && strcmp(last_str, ptr) == 0))
           ) {
            
            last_coalesced++;
            unlock_fs_event_list();
            va_end(ap);

            return 0;
        } else {
            last_ptr = ptr;
            if (was_str) {
                strlcpy(last_str, ptr, sizeof(last_str));
            }
            last_nlen = nlen;
            last_vid = vid;
            last_event_type = type;
            last_coalesced_time = now;
        }
    }
    va_start(ap, ctx);


    kfse = zalloc_noblock(event_zone);
    if (kfse && (type == FSE_RENAME || type == FSE_EXCHANGE)) {
        kfse_dest = zalloc_noblock(event_zone);
        if (kfse_dest == NULL) {
            did_alloc = 1;
            zfree(event_zone, kfse);
            kfse = NULL;
        }
    }


    if (kfse == NULL) {        // yikes! no free events
        int len=0;
        char *str;
        
        //
        // Figure out what kind of reference we have to the
        // file in this event.  This helps us find an event
        // to combine/collapse into to make room.
        //
        // If we have a rename or exchange event then we
        // don't want to go through the normal path, we
        // want to "steal" an event instead (which is what
        // find_an_event() will do if str is null).
        //
        arg_type = va_arg(ap, int32_t);
        if (type == FSE_RENAME || type == FSE_EXCHANGE) {
            str = NULL;
        } else if (arg_type == FSE_ARG_STRING) {
            len = va_arg(ap, int32_t);
            str = va_arg(ap, char *);
        } else if (arg_type == FSE_ARG_VNODE) {
            struct vnode *vp;

            vp  = va_arg(ap, struct vnode *);
            pathbuff = get_pathbuff();
            pathbuff_len = MAXPATHLEN;
            if (vn_getpath(vp, pathbuff, &pathbuff_len) != 0 || pathbuff[0] == '\0') {
                release_pathbuff(pathbuff);
                pathbuff = NULL;
            }
            str = pathbuff;
        } else {
            str = NULL;
        }

        //
        // This will go through all events and find one that we
        // can combine with (hopefully), or "collapse" into (i.e
        // it has the same parent) or in the worst case we have
        // to "recycle" an event which means that it will combine
        // two other events and return us the now unused event.
        // failing all that, find_an_event() could still return
        // null and if it does then we have a catastrophic dropped
        // events scenario.
        //
        kfse = find_an_event(str, len, NULL, &reuse_type, &longest_match_len);

        if (kfse == NULL) {
          bail_early:
            
            unlock_fs_event_list();
            lock_watch_table();

            for(i=0; i < MAX_WATCHERS; i++) {
                watcher = watcher_table[i];
                if (watcher == NULL) {
                    continue;
                }

                watcher->flags |= WATCHER_DROPPED_EVENTS;
                fsevents_wakeup(watcher);
            }
            unlock_watch_table();

            {       
                struct timeval current_tv;

                num_dropped++;

                // only print a message at most once every 5 seconds
                microuptime(&current_tv);
                if ((current_tv.tv_sec - last_print.tv_sec) > 10) {
                    int ii;
                    void *junkptr=zalloc_noblock(event_zone), *listhead=kfse_list_head.lh_first;
                    
                    printf("add_fsevent: event queue is full! dropping events (num dropped events: %d; num events outstanding: %d).\n", num_dropped, num_events_outstanding);
                    printf("add_fsevent: kfse_list head %p ; num_pending_rename %d\n", listhead, num_pending_rename);
                    printf("add_fsevent: zalloc sez: %p\n", junkptr);
                    printf("add_fsevent: event_zone info: %d 0x%x\n", ((int *)event_zone)[0], ((int *)event_zone)[1]);
                    for(ii=0; ii < MAX_WATCHERS; ii++) {
                        if (watcher_table[ii] == NULL) {
                            continue;
                        }
                        
                        printf("add_fsevent: watcher %p: num dropped %d rd %4d wr %4d q_size %4d flags 0x%x\n",
                            watcher_table[ii], watcher_table[ii]->num_dropped,
                            watcher_table[ii]->rd, watcher_table[ii]->wr,
                            watcher_table[ii]->eventq_size, watcher_table[ii]->flags);
                    }

                    last_print = current_tv;
                    if (junkptr) {
                        zfree(event_zone, junkptr);
                    }
                }
            }

            if (pathbuff) {
                release_pathbuff(pathbuff);
                pathbuff = NULL;
            }

            return ENOSPC;
        }

        if ((type == FSE_RENAME || type == FSE_EXCHANGE) && reuse_type != KFSE_RECYCLED) {
            panic("add_fsevent: type == %d but reuse type == %d!\n", type, reuse_type);
        } else if ((kfse->type == FSE_RENAME || kfse->type == FSE_EXCHANGE) && kfse->dest == NULL) {
            panic("add_fsevent: bogus kfse %p (type %d, but dest is NULL)\n", kfse, kfse->type);
        } else if (kfse->type == FSE_RENAME || kfse->type == FSE_EXCHANGE) {
            panic("add_fsevent: we should never re-use rename events (kfse %p reuse type %d)!\n", kfse, reuse_type);
        }

        if (reuse_type == KFSE_COLLAPSED) {
            if (str) {
                const char *tmp_ptr, *new_str;
                
                //
                // if we collapsed and have a string we have to chop off the
                // tail component of the pathname to get the parent.
                //
                // NOTE: it is VERY IMPORTANT that we leave the trailing slash
                //       on the pathname.  user-level code depends on this.
                //
                if (str[0] == '\0' || longest_match_len <= 1) {
                    printf("add_fsevent: strange state (str %s / longest_match_len %d)\n", str, longest_match_len);
                    if (longest_match_len < 0) {
                        panic("add_fsevent: longest_match_len %d\n", longest_match_len);
                    }
                }
                // chop off the tail component if it's not the
                // first character...
                if (longest_match_len > 1) {
                    str[longest_match_len] = '\0';
                } else if (longest_match_len == 0) {
                    longest_match_len = 1;
                }

                new_str = vfs_addname(str, longest_match_len, 0, 0);
                if (new_str == NULL || new_str[0] == '\0') {
                    panic("add_fsevent: longest match is strange (new_str %p).\n", new_str);
                }
                
                lck_rw_lock_exclusive(&event_handling_lock);

                kfse->len      = longest_match_len;
                tmp_ptr        = kfse->str;
                kfse->str = new_str;
                kfse->ino      = 0;
                kfse->mode     = 0;
                kfse->uid      = 0;
                kfse->gid      = 0;
                
                lck_rw_unlock_exclusive(&event_handling_lock);
                
                vfs_removename(tmp_ptr);
            } else {
                panic("add_fsevent: don't have a vnode or a string pointer (kfse %p)\n", kfse);
            }
        }

        if (reuse_type == KFSE_RECYCLED && (type == FSE_RENAME || type == FSE_EXCHANGE)) {
            
            // if we're recycling this kfse and we have a rename or
            // exchange event then we need to also get an event for
            // kfse_dest. 
            //
            if (did_alloc) {
                // only happens if we allocated one but then failed
                // for kfse_dest (and thus free'd the first one we
                // allocated)
                kfse_dest = zalloc_noblock(event_zone);
                if (kfse_dest != NULL) {
                    memset(kfse_dest, 0, sizeof(kfs_event));
                    kfse_dest->refcount = 1;
                    OSBitOrAtomic16(KFSE_BEING_CREATED, &kfse_dest->flags);
                } else {
                    did_alloc = 0;
                }
            }

            if (kfse_dest == NULL) {
                int dest_reuse_type, dest_match_len;
                
                kfse_dest = find_an_event(NULL, 0, kfse, &dest_reuse_type, &dest_match_len);
                
                if (kfse_dest == NULL) {
                    // nothing we can do... gotta bail out
                    goto bail_early;
                }

                if (dest_reuse_type != KFSE_RECYCLED) {
                    panic("add_fsevent: type == %d but dest_reuse type == %d!\n", type, dest_reuse_type);
                }
            }
        }


        //
        // Here we check for some fast-path cases so that we can
        // jump over the normal initialization and just get on
        // with delivering the event.  These cases are when we're
        // combining/collapsing an event and so basically there is
        // no more work to do (aside from a little book-keeping)
        //
        if (str && kfse->len != 0) {
            kfse->abstime = now;
            OSAddAtomic(1, &kfse->refcount);
            skip_init = 1;

            if (reuse_type == KFSE_COMBINED) {
                num_combined_events++;
            } else if (reuse_type == KFSE_COLLAPSED) {
                num_added_to_parent++;
            }
        } else if (reuse_type != KFSE_RECYCLED) {
            panic("add_fsevent: I'm so confused! (reuse_type %d str %p kfse->len %d)\n",
                  reuse_type, str, kfse->len);
        }

        va_end(ap);


        if (skip_init) {
            if (kfse->refcount < 1) {
                panic("add_fsevent: line %d: kfse recount %d but should be at least 1\n", __LINE__, kfse->refcount);
            }

            last_event_ptr = kfse;
            unlock_fs_event_list();
            goto normal_delivery;
            
        } else if (reuse_type == KFSE_RECYCLED || reuse_type == KFSE_COMBINED) {

            //
            // If we're here we have to clear out the kfs_event(s)
            // that we were given by find_an_event() and set it
            // up to be re-filled in by the normal code path.
            //
            va_start(ap, ctx);

            need_event_unlock = 1;
            lck_rw_lock_exclusive(&event_handling_lock);

            OSAddAtomic(1, &kfse->refcount);

            if (kfse->refcount < 1) {
                panic("add_fsevent: line %d: kfse recount %d but should be at least 1\n", __LINE__, kfse->refcount);
            }

            if (kfse->len == 0) {
                panic("%s:%d: no more fref.vp\n", __FILE__, __LINE__);
                // vnode_rele_ext(kfse->fref.vp, O_EVTONLY, 0);
            } else {
                vfs_removename(kfse->str);
                kfse->len = 0;
            }
            kfse->str = NULL;

            if (kfse->kevent_list.le_prev != NULL) {
                num_events_outstanding--;
                if (kfse->type == FSE_RENAME) {
                    num_pending_rename--;
                }
                LIST_REMOVE(kfse, kevent_list);
                memset(&kfse->kevent_list, 0, sizeof(kfse->kevent_list));
            }

            kfse->flags = 0 | KFSE_RECYCLED_EVENT;
            
            if (kfse_dest) {
                OSAddAtomic(1, &kfse_dest->refcount);
                kfse_dest->flags = 0 | KFSE_RECYCLED_EVENT;

                if (did_alloc == 0) {
                    if (kfse_dest->len == 0) {
                        panic("%s:%d: no more fref.vp\n", __FILE__, __LINE__);
                        // vnode_rele_ext(kfse_dest->fref.vp, O_EVTONLY, 0);
                    } else {
                        vfs_removename(kfse_dest->str);
                        kfse_dest->len = 0;
                    }
                    kfse_dest->str = NULL;

                    if (kfse_dest->kevent_list.le_prev != NULL) {
                        num_events_outstanding--;
                        LIST_REMOVE(kfse_dest, kevent_list);
                        memset(&kfse_dest->kevent_list, 0, sizeof(kfse_dest->kevent_list));
                    }

                    if (kfse_dest->dest) {
                        panic("add_fsevent: should never recycle a rename event! kfse %p\n", kfse);
                    }
                }
            }

            OSBitOrAtomic16(KFSE_BEING_CREATED, &kfse->flags);
            if (kfse_dest) {
                OSBitOrAtomic16(KFSE_BEING_CREATED, &kfse_dest->flags);
            }

            goto process_normally;
        }
    }

    if (reuse_type != 0) {
        panic("fsevents: we have a reuse_type (%d) but are about to clear out kfse %p\n", reuse_type, kfse);
    }

    //
    // we only want to do this for brand new events, not
    // events which have been recycled.
    //
    memset(kfse, 0, sizeof(kfs_event));
    kfse->refcount = 1;
    OSBitOrAtomic16(KFSE_BEING_CREATED, &kfse->flags);

  process_normally:
    last_event_ptr = kfse;
    kfse->type     = type;
    kfse->abstime  = now;
    kfse->pid      = p->p_pid;
    if (type == FSE_RENAME || type == FSE_EXCHANGE) {
        if (need_event_unlock == 0) {
            memset(kfse_dest, 0, sizeof(kfs_event));
            kfse_dest->refcount = 1;
            OSBitOrAtomic16(KFSE_BEING_CREATED, &kfse_dest->flags);
        }
        kfse_dest->type     = type;
        kfse_dest->pid      = p->p_pid;
        kfse_dest->abstime  = now;
        
        kfse->dest = kfse_dest;
    }
    
    num_events_outstanding++;
    if (kfse->type == FSE_RENAME) {
        num_pending_rename++;
    }
    LIST_INSERT_HEAD(&kfse_list_head, kfse, kevent_list);

    if (kfse->refcount < 1) {
        panic("add_fsevent: line %d: kfse recount %d but should be at least 1\n", __LINE__, kfse->refcount);
    }

    unlock_fs_event_list();  // at this point it's safe to unlock

    //
    // now process the arguments passed in and copy them into
    // the kfse
    //
    if (need_event_unlock == 0) {
        lck_rw_lock_shared(&event_handling_lock);
    }
    
    cur = kfse;
    for(arg_type=va_arg(ap, int32_t); arg_type != FSE_ARG_DONE; arg_type=va_arg(ap, int32_t))

        switch(arg_type) {
            case FSE_ARG_VNODE: {
                // this expands out into multiple arguments to the client
                struct vnode *vp;
                struct vnode_attr va;

                if (kfse->str != NULL) {
                    cur = kfse_dest;
                }

                vp = va_arg(ap, struct vnode *);
                if (vp == NULL) {
                    panic("add_fsevent: you can't pass me a NULL vnode ptr (type %d)!\n",
                          cur->type);
                }

                VATTR_INIT(&va);
                VATTR_WANTED(&va, va_fsid);
                VATTR_WANTED(&va, va_fileid);
                VATTR_WANTED(&va, va_mode);
                VATTR_WANTED(&va, va_uid);
                VATTR_WANTED(&va, va_gid);
                if ((ret = vnode_getattr(vp, &va, vfs_context_kernel())) != 0) {
                    // printf("add_fsevent: failed to getattr on vp %p (%d)\n", cur->fref.vp, ret);
                    cur->str = NULL;
                    error = EINVAL;
                    if (need_event_unlock == 0) {
                        // then we only grabbed it shared 
                        lck_rw_unlock_shared(&event_handling_lock);
                    }
                    goto clean_up;
                }

                cur->dev  = dev = (dev_t)va.va_fsid;
                cur->ino  = (ino64_t)va.va_fileid;
                cur->mode = (int32_t)vnode_vttoif(vnode_vtype(vp)) | va.va_mode;
                cur->uid  = va.va_uid;
                cur->gid  = va.va_gid;

                // if we haven't gotten the path yet, get it.
                if (pathbuff == NULL) {
                    pathbuff = get_pathbuff();
                    pathbuff_len = MAXPATHLEN;
                    
                    pathbuff[0] = '\0';
                    if ((ret = vn_getpath(vp, pathbuff, &pathbuff_len)) != 0 || pathbuff[0] == '\0') {
                        struct vnode *orig_vp = vp;
                        
                        if (ret != ENOSPC) {
                                printf("add_fsevent: unable to get path for vp %p (%s; ret %d; type %d)\n",
                                       vp, vp->v_name ? vp->v_name : "-UNKNOWN-FILE", ret, type);
                        }

                        cur->flags |= KFSE_CONTAINS_DROPPED_EVENTS;
                        
                        do {
                                if (vp->v_parent != NULL) {
                                        vp = vp->v_parent;
                                } else if (vp->v_mount) {
                                        strlcpy(pathbuff, vp->v_mount->mnt_vfsstat.f_mntonname, MAXPATHLEN);
                                        break;
                                } else {
                                        vp = NULL;
                                }

                                if (vp == NULL) {
                                        break;
                                }

                                pathbuff_len = MAXPATHLEN;
                                ret = vn_getpath(vp, pathbuff, &pathbuff_len);
                        } while (ret == ENOSPC);
                                
                        if (ret != 0 || vp == NULL) {
                                printf("add_fsevent: unabled to get a path for vp %p.  dropping the event.\n", orig_vp);
                                error = ENOENT;
                                if (need_event_unlock == 0) {
                                        // then we only grabbed it shared 
                                        lck_rw_unlock_shared(&event_handling_lock);
                                }
                                goto clean_up;
                        }
                    }
                }

                // store the path by adding it to the global string table
                cur->len = pathbuff_len;
                cur->str = vfs_addname(pathbuff, pathbuff_len, 0, 0);
                if (cur->str == NULL || cur->str[0] == '\0') {
                    panic("add_fsevent: was not able to add path %s to event %p.\n", pathbuff, cur);
                }
                
                release_pathbuff(pathbuff);
                pathbuff = NULL;

                break;
            }

            case FSE_ARG_FINFO: {
                fse_info *fse;
                
                fse = va_arg(ap, fse_info *);
                
                cur->dev  = dev = (dev_t)fse->dev;
                cur->ino  = (ino64_t)fse->ino;
                cur->mode = (int32_t)fse->mode;
                cur->uid  = (uid_t)fse->uid;
                cur->gid  = (uid_t)fse->gid;
                // if it's a hard-link and this is the last link, flag it
                if ((fse->mode & FSE_MODE_HLINK) && fse->nlink == 0) {
                    cur->mode |= FSE_MODE_LAST_HLINK;
                }
                if (cur->mode & FSE_TRUNCATED_PATH) {
                        cur->flags |= KFSE_CONTAINS_DROPPED_EVENTS;
                        cur->mode &= ~FSE_TRUNCATED_PATH;
                }
                break;
            }

            case FSE_ARG_STRING:
                if (kfse->str != NULL) {
                    cur = kfse_dest;
                }

                cur->len = (int16_t)(va_arg(ap, int32_t) & 0x7fff);
                if (cur->len >= 1) {
                    cur->str = vfs_addname(va_arg(ap, char *), cur->len, 0, 0);
                } else {
                    printf("add_fsevent: funny looking string length: %d\n", (int)cur->len);
                    cur->len = 2;
                    cur->str = vfs_addname("/", cur->len, 0, 0);
                }
                if (cur->str[0] == 0) {
                    printf("add_fsevent: bogus looking string (len %d)\n", cur->len);
                }
                break;

            default:
                printf("add_fsevent: unknown type %d\n", arg_type);
                // just skip one 32-bit word and hope we sync up...
                (void)va_arg(ap, int32_t);
        }

    va_end(ap);

    OSBitAndAtomic16(~KFSE_BEING_CREATED, &kfse->flags);
    if (kfse_dest) {
        OSBitAndAtomic16(~KFSE_BEING_CREATED, &kfse_dest->flags);
    }

    if (need_event_unlock == 0) {
        // then we only grabbed it shared 
        lck_rw_unlock_shared(&event_handling_lock);
    }
    
  normal_delivery:
    // unlock this here so we don't hold it across the
    // event delivery loop.
    if (need_event_unlock) {
        lck_rw_unlock_exclusive(&event_handling_lock);
        need_event_unlock = 0;
    }

    //
    // now we have to go and let everyone know that
    // is interested in this type of event
    //
    lock_watch_table();
    
    for(i=0; i < MAX_WATCHERS; i++) {
        watcher = watcher_table[i];
        if (watcher == NULL) {
            continue;
        }
        
        if (   watcher->event_list[type] == FSE_REPORT
            && watcher_cares_about_dev(watcher, dev)) {
            
            if (watcher_add_event(watcher, kfse) != 0) {
                watcher->num_dropped++;
            }
        }

        if (kfse->refcount < 1) {
            panic("add_fsevent: line %d: kfse recount %d but should be at least 1\n", __LINE__, kfse->refcount);
        }
    }

    unlock_watch_table();

  clean_up:
    // have to check if this needs to be unlocked (in
    // case we came here from an error handling path)
    if (need_event_unlock) {
        lck_rw_unlock_exclusive(&event_handling_lock);
        need_event_unlock = 0;
    }

    if (pathbuff) {
        release_pathbuff(pathbuff);
        pathbuff = NULL;
    }

    release_event_ref(kfse);

    return error;
}


static void
release_event_ref(kfs_event *kfse)
{
    int old_refcount;
    kfs_event copy, dest_copy;
    
    
    old_refcount = OSAddAtomic(-1, &kfse->refcount);
    if (old_refcount > 1) {
        return;
    }

    lock_fs_event_list();
    if (last_event_ptr == kfse) {
            last_event_ptr = NULL;
            last_event_type = -1;
            last_coalesced_time = 0;
    }

    if (kfse->refcount < 0) {
        panic("release_event_ref: bogus kfse refcount %d\n", kfse->refcount);
    }

    if (kfse->refcount > 0 || kfse->type == FSE_INVALID) {
        // This is very subtle.  Either of these conditions can
        // be true if an event got recycled while we were waiting
        // on the fs_event_list lock or the event got recycled,
        // delivered, _and_ free'd by someone else while we were
        // waiting on the fs event list lock.  In either case
        // we need to just unlock the list and return without
        // doing anything because if the refcount is > 0 then
        // someone else will take care of free'ing it and when
        // the kfse->type is invalid then someone else already
        // has handled free'ing the event (while we were blocked
        // on the event list lock).
        //
        unlock_fs_event_list();
        return;
    }

    //
    // make a copy of this so we can free things without
    // holding the fs_event_buf lock
    //
    copy = *kfse;
    if (kfse->dest && OSAddAtomic(-1, &kfse->dest->refcount) == 1) {
        dest_copy = *kfse->dest;
    } else {
        dest_copy.str  = NULL;
        dest_copy.len  = 0;
        dest_copy.type = FSE_INVALID;
    }

    kfse->pid = kfse->type;             // save this off for debugging...
    kfse->uid = (uid_t)(long)kfse->str;       // save this off for debugging... 
    kfse->gid = (gid_t)(long)current_thread();

    kfse->str = (char *)0xdeadbeef;             // XXXdbg - catch any cheaters...

    if (dest_copy.type != FSE_INVALID) {
        kfse->dest->str = (char *)0xbadc0de;   // XXXdbg - catch any cheaters...
        kfse->dest->type = FSE_INVALID;

        if (kfse->dest->kevent_list.le_prev != NULL) {
            num_events_outstanding--;
            LIST_REMOVE(kfse->dest, kevent_list);
            memset(&kfse->dest->kevent_list, 0xa5, sizeof(kfse->dest->kevent_list));
        }

        zfree(event_zone, kfse->dest);
    }

    // mark this fsevent as invalid
    {
        int otype;
        
        otype = kfse->type;
    kfse->type = FSE_INVALID;

    if (kfse->kevent_list.le_prev != NULL) {
        num_events_outstanding--;
        if (otype == FSE_RENAME) {
            num_pending_rename--;
        }
        LIST_REMOVE(kfse, kevent_list);
        memset(&kfse->kevent_list, 0, sizeof(kfse->kevent_list));
    }
    }
    
    zfree(event_zone, kfse);
    
    unlock_fs_event_list();
    
    // if we have a pointer in the union
    if (copy.str) {
        if (copy.len == 0) {    // and it's not a string
            panic("%s:%d: no more fref.vp!\n", __FILE__, __LINE__);
            // vnode_rele_ext(copy.fref.vp, O_EVTONLY, 0);
        } else {                // else it's a string
            vfs_removename(copy.str);
        }
    }

    if (dest_copy.type != FSE_INVALID && dest_copy.str) {
        if (dest_copy.len == 0) {
            panic("%s:%d: no more fref.vp!\n", __FILE__, __LINE__);
            // vnode_rele_ext(dest_copy.fref.vp, O_EVTONLY, 0);
        } else {
            vfs_removename(dest_copy.str);
        }
    }
}


static int
add_watcher(int8_t *event_list, int32_t num_events, int32_t eventq_size, fs_event_watcher **watcher_out)
{
    int               i;
    fs_event_watcher *watcher;

    if (eventq_size <= 0 || eventq_size > 100*MAX_KFS_EVENTS) {
        eventq_size = MAX_KFS_EVENTS;
    }

    // Note: the event_queue follows the fs_event_watcher struct
    //       in memory so we only have to do one allocation
    MALLOC(watcher,
           fs_event_watcher *,
           sizeof(fs_event_watcher) + eventq_size * sizeof(kfs_event *),
           M_TEMP, M_WAITOK);
    if (watcher == NULL) {
        return ENOMEM;
    }

    watcher->event_list   = event_list;
    watcher->num_events   = num_events;
    watcher->devices_not_to_watch = NULL;
    watcher->num_devices  = 0;
    watcher->flags        = 0;
    watcher->event_queue  = (kfs_event **)&watcher[1];
    watcher->eventq_size  = eventq_size;
    watcher->rd           = 0;
    watcher->wr           = 0;
    watcher->blockers     = 0;
    watcher->num_readers  = 0;
    watcher->max_event_id = 0;
    watcher->fseh         = NULL;

    watcher->num_dropped  = 0;      // XXXdbg - debugging

    lock_watch_table();

    // now update the global list of who's interested in
    // events of a particular type...
    for(i=0; i < num_events; i++) {
        if (event_list[i] != FSE_IGNORE && i < FSE_MAX_EVENTS) {
            fs_event_type_watchers[i]++;
        }
    }

    for(i=0; i < MAX_WATCHERS; i++) {
        if (watcher_table[i] == NULL) {
            watcher->my_id   = i;
            watcher_table[i] = watcher;
            break;
        }
    }

    if (i > MAX_WATCHERS) {
        printf("fsevents: too many watchers!\n");
        unlock_watch_table();
        return ENOSPC;
    }

    unlock_watch_table();

    *watcher_out = watcher;

    return 0;
}



static void
remove_watcher(fs_event_watcher *target)
{
    int i, j, counter=0;
    fs_event_watcher *watcher;
    kfs_event *kfse;
    
    lock_watch_table();
    
    for(j=0; j < MAX_WATCHERS; j++) {
        watcher = watcher_table[j];
        if (watcher != target) {
            continue;
        }

        watcher_table[j] = NULL;

        for(i=0; i < watcher->num_events; i++) {
            if (watcher->event_list[i] != FSE_IGNORE && i < FSE_MAX_EVENTS) {
                fs_event_type_watchers[i]--;
            }
        }

        if (watcher->flags & WATCHER_CLOSING) {
            unlock_watch_table();
            return;
        }

        // printf("fsevents: removing watcher %p (rd %d wr %d num_readers %d flags 0x%x)\n", watcher, watcher->rd, watcher->wr, watcher->num_readers, watcher->flags);
        watcher->flags |= WATCHER_CLOSING;
        OSAddAtomic(1, &watcher->num_readers);
        
        unlock_watch_table();
            
        while (watcher->num_readers > 1 && counter++ < 5000) {
            fsevents_wakeup(watcher);      // in case they're asleep
            
            tsleep(watcher, PRIBIO, "fsevents-close", 1);
        }
        if (counter++ >= 5000) {
            // printf("fsevents: close: still have readers! (%d)\n", watcher->num_readers);
            panic("fsevents: close: still have readers! (%d)\n", watcher->num_readers);
        }

        // drain the event_queue 
        while(watcher->rd != watcher->wr) {
            lck_rw_lock_shared(&event_handling_lock);

            kfse = watcher->event_queue[watcher->rd];
            if (kfse->type == FSE_INVALID || kfse->refcount < 1) {
                panic("remove_watcher: bogus kfse %p during cleanup (type %d refcount %d rd %d wr %d)\n", kfse, kfse->type, kfse->refcount, watcher->rd, watcher->wr);
            }

            lck_rw_unlock_shared(&event_handling_lock);
            
            watcher->rd = (watcher->rd+1) % watcher->eventq_size;

            if (kfse != NULL) {
                release_event_ref(kfse);
            }
        }
            
        if (watcher->event_list) {
            FREE(watcher->event_list, M_TEMP);
            watcher->event_list = NULL;
        }
        if (watcher->devices_not_to_watch) {
            FREE(watcher->devices_not_to_watch, M_TEMP);
            watcher->devices_not_to_watch = NULL;
        }
        FREE(watcher, M_TEMP);

        return;
    }

    unlock_watch_table();
}


#define EVENT_DELAY_IN_MS   10
static thread_call_t event_delivery_timer = NULL;
static int timer_set = 0;


static void
delayed_event_delivery(__unused void *param0, __unused void *param1)
{
    int i;
    
    lock_watch_table();

    for(i=0; i < MAX_WATCHERS; i++) {
        if (watcher_table[i] != NULL && watcher_table[i]->rd != watcher_table[i]->wr) {
            fsevents_wakeup(watcher_table[i]);
        }
    }

    timer_set = 0;

    unlock_watch_table();
}


//
// The watch table must be locked before calling this function.
//
static void
schedule_event_wakeup(void)
{
    uint64_t deadline;
    
    if (event_delivery_timer == NULL) {
        event_delivery_timer = thread_call_allocate((thread_call_func_t)delayed_event_delivery, NULL);
    }

    clock_interval_to_deadline(EVENT_DELAY_IN_MS, 1000 * 1000, &deadline);
    
    thread_call_enter_delayed(event_delivery_timer, deadline);
    timer_set = 1;
}



#define MAX_NUM_PENDING  16

//
// NOTE: the watch table must be locked before calling
//       this routine.
//
static int
watcher_add_event(fs_event_watcher *watcher, kfs_event *kfse)
{
    if (kfse->abstime > watcher->max_event_id) {
        watcher->max_event_id = kfse->abstime;
    }

    if (((watcher->wr + 1) % watcher->eventq_size) == watcher->rd) {
        watcher->flags |= WATCHER_DROPPED_EVENTS;
        fsevents_wakeup(watcher);
        return ENOSPC;
    }

    OSAddAtomic(1, &kfse->refcount);
    watcher->event_queue[watcher->wr] = kfse;
    OSSynchronizeIO();
    watcher->wr = (watcher->wr + 1) % watcher->eventq_size;
    
    //
    // wake up the watcher if there are more than MAX_NUM_PENDING events.
    // otherwise schedule a timer (if one isn't already set) which will 
    // send any pending events if no more are received in the next 
    // EVENT_DELAY_IN_MS milli-seconds.
    //
    if (   (watcher->rd < watcher->wr && (watcher->wr - watcher->rd) > MAX_NUM_PENDING)
        || (watcher->rd > watcher->wr && (watcher->wr + watcher->eventq_size - watcher->rd) > MAX_NUM_PENDING)) {

        fsevents_wakeup(watcher);

    } else if (timer_set == 0) {

        schedule_event_wakeup();
    }

    return 0;
}

static int
fill_buff(uint16_t type, int32_t size, const void *data,
          char *buff, int32_t *_buff_idx, int32_t buff_sz,
          struct uio *uio)
{
    int32_t amt, error = 0, buff_idx = *_buff_idx;
    uint16_t tmp;
    
    //
    // the +1 on the size is to guarantee that the main data
    // copy loop will always copy at least 1 byte
    //
    if ((buff_sz - buff_idx) <= (int)(2*sizeof(uint16_t) + 1)) {
        if (buff_idx > uio_resid(uio)) {
            error = ENOSPC;
            goto get_out;
        }

        error = uiomove(buff, buff_idx, uio);
        if (error) {
            goto get_out;
        }
        buff_idx = 0;
    }

    // copy out the header (type & size)
    memcpy(&buff[buff_idx], &type, sizeof(uint16_t));
    buff_idx += sizeof(uint16_t);
    
    tmp = size & 0xffff;
    memcpy(&buff[buff_idx], &tmp, sizeof(uint16_t));
    buff_idx += sizeof(uint16_t);
    
    // now copy the body of the data, flushing along the way 
    // if the buffer fills up.
    //
    while(size > 0) {
        amt = (size < (buff_sz - buff_idx)) ? size : (buff_sz - buff_idx);
        memcpy(&buff[buff_idx], data, amt);

        size -= amt;
        buff_idx += amt;
        data = (const char *)data + amt;
        if (size > (buff_sz - buff_idx)) {
            if (buff_idx > uio_resid(uio)) {
                error = ENOSPC;
                goto get_out;
            }
            error = uiomove(buff, buff_idx, uio);
            if (error) {
                goto get_out;
            }
            buff_idx = 0;
        }

        if (amt == 0) {   // just in case...
            break;
        }
    }

  get_out:
    *_buff_idx = buff_idx;
    
    return error;
}


static int copy_out_kfse(fs_event_watcher *watcher, kfs_event *kfse, struct uio *uio)  __attribute__((noinline));

static int
copy_out_kfse(fs_event_watcher *watcher, kfs_event *kfse, struct uio *uio)
{
    int      error;
    uint16_t tmp16;
    int32_t  type;
    kfs_event *cur;
    char     evbuff[512];
    int      evbuff_idx = 0;

    if (kfse->type == FSE_INVALID) {
        panic("fsevents: copy_out_kfse: asked to copy out an invalid event (kfse %p, refcount %d fref ptr %p)\n", kfse, kfse->refcount, kfse->str);
    }

    if (kfse->flags & KFSE_BEING_CREATED) {
        return 0;
    }

    if (kfse->type == FSE_RENAME && kfse->dest == NULL) {
        //
        // This can happen if an event gets recycled but we had a
        // pointer to it in our event queue.  The event is the
        // destination of a rename which we'll process separately
        // (that is, another kfse points to this one so it's ok
        // to skip this guy because we'll process it when we process
        // the other one)
        error = 0;
        goto get_out;
    }

    if (watcher->flags & WATCHER_WANTS_EXTENDED_INFO) {

        type = (kfse->type & 0xfff);

        if (kfse->flags & KFSE_CONTAINS_DROPPED_EVENTS) {
            type |= (FSE_CONTAINS_DROPPED_EVENTS << FSE_FLAG_SHIFT);
        } else if (kfse->flags & KFSE_COMBINED_EVENTS) {
            type |= (FSE_COMBINED_EVENTS << FSE_FLAG_SHIFT);
        }

    } else {
        type = (int32_t)kfse->type;
    }

    // copy out the type of the event
    memcpy(evbuff, &type, sizeof(int32_t));
    evbuff_idx += sizeof(int32_t);

    // copy out the pid of the person that generated the event
    memcpy(&evbuff[evbuff_idx], &kfse->pid, sizeof(pid_t));
    evbuff_idx += sizeof(pid_t);

    cur = kfse;

  copy_again:

    if (cur->str == NULL || cur->str[0] == '\0') {
        printf("copy_out_kfse:2: empty/short path (%s)\n", cur->str);
        error = fill_buff(FSE_ARG_STRING, 2, "/", evbuff, &evbuff_idx, sizeof(evbuff), uio);
    } else {
        error = fill_buff(FSE_ARG_STRING, cur->len, cur->str, evbuff, &evbuff_idx, sizeof(evbuff), uio);
    }
    if (error != 0) {
        goto get_out;
    }

    if (cur->dev == 0 && cur->ino == 0) {
        // this happens when a rename event happens and the
        // destination of the rename did not previously exist.
        // it thus has no other file info so skip copying out
        // the stuff below since it isn't initialized
        goto done;
    }

    
    if (watcher->flags & WATCHER_WANTS_COMPACT_EVENTS) {
        int32_t finfo_size;
        
        finfo_size = sizeof(dev_t) + sizeof(ino64_t) + sizeof(int32_t) + sizeof(uid_t) + sizeof(gid_t);
        error = fill_buff(FSE_ARG_FINFO, finfo_size, &cur->ino, evbuff, &evbuff_idx, sizeof(evbuff), uio);
        if (error != 0) {
            goto get_out;
        }
    } else {
        ino_t ino;
        
        error = fill_buff(FSE_ARG_DEV, sizeof(dev_t), &cur->dev, evbuff, &evbuff_idx, sizeof(evbuff), uio);
        if (error != 0) {
            goto get_out;
        }

        ino = (ino_t)cur->ino;
        error = fill_buff(FSE_ARG_INO, sizeof(ino_t), &ino, evbuff, &evbuff_idx, sizeof(evbuff), uio);
        if (error != 0) {
            goto get_out;
        }

        error = fill_buff(FSE_ARG_MODE, sizeof(int32_t), &cur->mode, evbuff, &evbuff_idx, sizeof(evbuff), uio);
        if (error != 0) {
            goto get_out;
        }

        error = fill_buff(FSE_ARG_UID, sizeof(uid_t), &cur->uid, evbuff, &evbuff_idx, sizeof(evbuff), uio);
        if (error != 0) {
            goto get_out;
        }

        error = fill_buff(FSE_ARG_GID, sizeof(gid_t), &cur->gid, evbuff, &evbuff_idx, sizeof(evbuff), uio);
        if (error != 0) {
            goto get_out;
        }
    }


    if (cur->dest) {
        cur = cur->dest;
        goto copy_again;
    }

  done:
    // very last thing: the time stamp
    error = fill_buff(FSE_ARG_INT64, sizeof(uint64_t), &cur->abstime, evbuff, &evbuff_idx, sizeof(evbuff), uio);
    if (error != 0) {
        goto get_out;
    }

    // check if the FSE_ARG_DONE will fit
    if (sizeof(uint16_t) > sizeof(evbuff) - evbuff_idx) {
        if (evbuff_idx > uio_resid(uio)) {
            error = ENOSPC;
            goto get_out;
        }
        error = uiomove(evbuff, evbuff_idx, uio);
        if (error) {
            goto get_out;
        }
        evbuff_idx = 0;
    }

    tmp16 = FSE_ARG_DONE;
    memcpy(&evbuff[evbuff_idx], &tmp16, sizeof(uint16_t));
    evbuff_idx += sizeof(uint16_t);

    // flush any remaining data in the buffer (and hopefully
    // in most cases this is the only uiomove we'll do)
    if (evbuff_idx > uio_resid(uio)) {
        error = ENOSPC;
    } else {
        error = uiomove(evbuff, evbuff_idx, uio);
    }

  get_out:

    return error;
}



static int
fmod_watch(fs_event_watcher *watcher, struct uio *uio)
{
    int               error=0; 
    user_ssize_t      last_full_event_resid;
    kfs_event        *kfse;
    uint16_t          tmp16;

    last_full_event_resid = uio_resid(uio);

    // need at least 2048 bytes of space (maxpathlen + 1 event buf)
    if  (uio_resid(uio) < 2048 || watcher == NULL) {
        return EINVAL;
    }

    if (watcher->flags & WATCHER_CLOSING) {
        return 0;
    }

    if (OSAddAtomic(1, &watcher->num_readers) != 0) {
        // don't allow multiple threads to read from the fd at the same time
        OSAddAtomic(-1, &watcher->num_readers);
        return EAGAIN;
    }

    if (watcher->rd == watcher->wr) {
        if (watcher->flags & WATCHER_CLOSING) {
            OSAddAtomic(-1, &watcher->num_readers);
            return 0;
        }
        OSAddAtomic(1, &watcher->blockers);
    
        // there's nothing to do, go to sleep
        error = tsleep((caddr_t)watcher, PUSER|PCATCH, "fsevents_empty", 0);

        OSAddAtomic(-1, &watcher->blockers);

        if (error != 0 || (watcher->flags & WATCHER_CLOSING)) {
            OSAddAtomic(-1, &watcher->num_readers);
            return error;
        }
    }

    // if we dropped events, return that as an event first
    if (watcher->flags & WATCHER_DROPPED_EVENTS) {
        int32_t val = FSE_EVENTS_DROPPED;

        error = uiomove((caddr_t)&val, sizeof(int32_t), uio);
        if (error == 0) {
            val = 0;             // a fake pid
            error = uiomove((caddr_t)&val, sizeof(int32_t), uio);
            
            tmp16 = FSE_ARG_DONE;  // makes it a consistent msg
            error = uiomove((caddr_t)&tmp16, sizeof(int16_t), uio);

            last_full_event_resid = uio_resid(uio);
        } 

        if (error) {
            OSAddAtomic(-1, &watcher->num_readers);
            return error;
        }
        
        watcher->flags &= ~WATCHER_DROPPED_EVENTS;
    }

    while (uio_resid(uio) > 0 && watcher->rd != watcher->wr) {
        if (watcher->flags & WATCHER_CLOSING) {
            break;
        }
        
        //
        // check if the event is something of interest to us
        // (since it may have been recycled/reused and changed
        // its type or which device it is for)
        //
        lck_rw_lock_shared(&event_handling_lock);

        kfse = watcher->event_queue[watcher->rd];
        if (kfse->type == FSE_INVALID || kfse->refcount < 1) {
            panic("fmod_watch: someone left me a bogus kfse %p (type %d refcount %d rd %d wr %d)\n", kfse, kfse->type, kfse->refcount, watcher->rd, watcher->wr);
        }

        if (watcher->event_list[kfse->type] == FSE_REPORT && watcher_cares_about_dev(watcher, kfse->dev)) {

            error = copy_out_kfse(watcher, kfse, uio);
            if (error != 0) {
                // if an event won't fit or encountered an error while
                // we were copying it out, then backup to the last full
                // event and just bail out.  if the error was ENOENT
                // then we can continue regular processing, otherwise
                // we should unlock things and return.
                uio_setresid(uio, last_full_event_resid);
                if (error != ENOENT) {
                    lck_rw_unlock_shared(&event_handling_lock);
                    error = 0;
                    goto get_out;
                }
            }

            last_full_event_resid = uio_resid(uio);
        }

        lck_rw_unlock_shared(&event_handling_lock);

        watcher->rd = (watcher->rd + 1) % watcher->eventq_size;
        OSSynchronizeIO();
            
        if (kfse->type == FSE_INVALID || kfse->refcount < 1) {
            panic("fmod_watch:2: my kfse became bogus! kfse %p (type %d refcount %d rd %d wr %d)\n", kfse, kfse->type, kfse->refcount, watcher->rd, watcher->wr);
        }

        release_event_ref(kfse);
    }

  get_out:
    OSAddAtomic(-1, &watcher->num_readers);

    return error;
}


// release any references we might have on vnodes which are 
// the mount point passed to us (so that it can be cleanly
// unmounted).
//
// since we don't want to lose the events we'll convert the
// vnode refs to full paths.
//
void
fsevent_unmount(__unused struct mount *mp)
{
    // we no longer maintain pointers to vnodes so
    // there is nothing to do... 
}


//
// /dev/fsevents device code
//
static int fsevents_installed = 0;

typedef struct fsevent_handle {
    UInt32            flags;
    SInt32            active;
    fs_event_watcher *watcher;
    struct klist      knotes;
    struct selinfo    si;
} fsevent_handle;

#define FSEH_CLOSING   0x0001

static int
fseventsf_read(struct fileproc *fp, struct uio *uio,
               __unused int flags, __unused vfs_context_t ctx)
{
    fsevent_handle *fseh = (struct fsevent_handle *)fp->f_fglob->fg_data;
    int error;

    error = fmod_watch(fseh->watcher, uio);

    return error;
}


static int
fseventsf_write(__unused struct fileproc *fp, __unused struct uio *uio,
                __unused int flags, __unused vfs_context_t ctx)
{
    return EIO;
}

#pragma pack(push, 4)
typedef struct ext_fsevent_dev_filter_args {
    uint32_t    num_devices;
    user_addr_t devices;
} ext_fsevent_dev_filter_args;
#pragma pack(pop)

typedef struct old_fsevent_dev_filter_args {
    uint32_t  num_devices;
    int32_t   devices;
} old_fsevent_dev_filter_args;

#define OLD_FSEVENTS_DEVICE_FILTER      _IOW('s', 100, old_fsevent_dev_filter_args)
#define NEW_FSEVENTS_DEVICE_FILTER      _IOW('s', 100, ext_fsevent_dev_filter_args)

#if __LP64__
/* need this in spite of the padding due to alignment of devices */
typedef struct fsevent_dev_filter_args32 {
    uint32_t  num_devices;
    uint32_t  devices;
    int32_t   pad1;
} fsevent_dev_filter_args32;
#endif

static int
fseventsf_ioctl(struct fileproc *fp, u_long cmd, caddr_t data, vfs_context_t ctx)
{
    fsevent_handle *fseh = (struct fsevent_handle *)fp->f_fglob->fg_data;
    int ret = 0;
    ext_fsevent_dev_filter_args *devfilt_args, _devfilt_args;

    if (proc_is64bit(vfs_context_proc(ctx))) {
        devfilt_args = (ext_fsevent_dev_filter_args *)data;
    } else if (cmd == OLD_FSEVENTS_DEVICE_FILTER) {
        old_fsevent_dev_filter_args *udev_filt_args = (old_fsevent_dev_filter_args *)data;
        
        devfilt_args = &_devfilt_args;
        memset(devfilt_args, 0, sizeof(ext_fsevent_dev_filter_args));

        devfilt_args->num_devices = udev_filt_args->num_devices;
        devfilt_args->devices     = CAST_USER_ADDR_T(udev_filt_args->devices);
    } else {
#if __LP64__
        fsevent_dev_filter_args32 *udev_filt_args = (fsevent_dev_filter_args32 *)data;
#else
        fsevent_dev_filter_args *udev_filt_args = (fsevent_dev_filter_args *)data;
#endif
        
        devfilt_args = &_devfilt_args;
        memset(devfilt_args, 0, sizeof(ext_fsevent_dev_filter_args));

        devfilt_args->num_devices = udev_filt_args->num_devices;
        devfilt_args->devices     = CAST_USER_ADDR_T(udev_filt_args->devices);
    }

    OSAddAtomic(1, &fseh->active);
    if (fseh->flags & FSEH_CLOSING) {
        OSAddAtomic(-1, &fseh->active);
        return 0;
    }

    switch (cmd) {
        case FIONBIO:
        case FIOASYNC:
            break;

        case FSEVENTS_WANT_COMPACT_EVENTS: {
            fseh->watcher->flags |= WATCHER_WANTS_COMPACT_EVENTS;
            break;
        }

        case FSEVENTS_WANT_EXTENDED_INFO: {
            fseh->watcher->flags |= WATCHER_WANTS_EXTENDED_INFO;
            break;
        }

        case FSEVENTS_GET_CURRENT_ID: {
                *(uint64_t *)data = fseh->watcher->max_event_id;
                ret = 0;
                break;
        }

        case OLD_FSEVENTS_DEVICE_FILTER:
        case NEW_FSEVENTS_DEVICE_FILTER: {
            int new_num_devices;
            dev_t *devices_not_to_watch, *tmp=NULL;
            
            if (devfilt_args->num_devices > 256) {
                ret = EINVAL;
                break;
            }
            
            new_num_devices = devfilt_args->num_devices;
            if (new_num_devices == 0) {
                tmp = fseh->watcher->devices_not_to_watch;

                lock_watch_table();
                fseh->watcher->devices_not_to_watch = NULL;
                fseh->watcher->num_devices = new_num_devices;
                unlock_watch_table();

                if (tmp) {
                    FREE(tmp, M_TEMP);
                }
                break;
            }

            MALLOC(devices_not_to_watch, dev_t *,
                   new_num_devices * sizeof(dev_t),
                   M_TEMP, M_WAITOK);
            if (devices_not_to_watch == NULL) {
                ret = ENOMEM;
                break;
            }
    
            ret = copyin(devfilt_args->devices,
                         (void *)devices_not_to_watch,
                         new_num_devices * sizeof(dev_t));
            if (ret) {
                FREE(devices_not_to_watch, M_TEMP);
                break;
            }

            lock_watch_table();
            fseh->watcher->num_devices = new_num_devices;
            tmp = fseh->watcher->devices_not_to_watch;
            fseh->watcher->devices_not_to_watch = devices_not_to_watch;
            unlock_watch_table();

            if (tmp) {
                FREE(tmp, M_TEMP);
            }
            
            break;
        }           

        default:
            ret = EINVAL;
            break;
    }

    OSAddAtomic(-1, &fseh->active);
    return (ret);
}


static int
fseventsf_select(struct fileproc *fp, int which, __unused void *wql, vfs_context_t ctx)
{
    fsevent_handle *fseh = (struct fsevent_handle *)fp->f_fglob->fg_data;
    int ready = 0;

    if ((which != FREAD) || (fseh->watcher->flags & WATCHER_CLOSING)) {
        return 0;
    }


    // if there's nothing in the queue, we're not ready
    if (fseh->watcher->rd != fseh->watcher->wr) {
        ready = 1;
    }

    if (!ready) {
        selrecord(vfs_context_proc(ctx), &fseh->si, wql);
    }

    return ready;
}


#if NOTUSED
static int
fseventsf_stat(__unused struct fileproc *fp, __unused struct stat *sb, __unused vfs_context_t ctx)
{
    return ENOTSUP;
}
#endif

static int
fseventsf_close(struct fileglob *fg, __unused vfs_context_t ctx)
{
    fsevent_handle *fseh = (struct fsevent_handle *)fg->fg_data;
    fs_event_watcher *watcher;

    OSBitOrAtomic(FSEH_CLOSING, &fseh->flags);
    while (OSAddAtomic(0, &fseh->active) > 0) {
        tsleep((caddr_t)fseh->watcher, PRIBIO, "fsevents-close", 1);
    }

    watcher = fseh->watcher;
    fg->fg_data = NULL;
    fseh->watcher = NULL;

    remove_watcher(watcher);
    FREE(fseh, M_TEMP);

    return 0;
}

static void
filt_fsevent_detach(struct knote *kn)
{
        fsevent_handle *fseh = (struct fsevent_handle *)kn->kn_hook;

        lock_watch_table();

        KNOTE_DETACH(&fseh->knotes, kn);
        
        unlock_watch_table();
}

/* 
 * Determine whether this knote should be active
 * 
 * This is kind of subtle.  
 *      --First, notice if the vnode has been revoked: in so, override hint
 *      --EVFILT_READ knotes are checked no matter what the hint is
 *      --Other knotes activate based on hint.  
 *      --If hint is revoke, set special flags and activate
 */
static int
filt_fsevent(struct knote *kn, long hint)
{
        fsevent_handle *fseh = (struct fsevent_handle *)kn->kn_hook;
        int activate = 0;
        int32_t rd, wr, amt;

        if (NOTE_REVOKE == hint) {
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                activate = 1;
        }

        rd = fseh->watcher->rd;
        wr = fseh->watcher->wr;
        if (rd <= wr) {
            amt = wr - rd;
        } else {
            amt = fseh->watcher->eventq_size - (rd - wr);
        }

        switch(kn->kn_filter) {
                case EVFILT_READ:
                        kn->kn_data = amt;
                        
                        if (kn->kn_data != 0) {
                                activate = 1;
                        }
                        break;
                case EVFILT_VNODE:
                        /* Check events this note matches against the hint */
                        if (kn->kn_sfflags & hint) {
                                kn->kn_fflags |= hint; /* Set which event occurred */
                        }
                        if (kn->kn_fflags != 0) {
                                activate = 1;
                        }
                        break;
                default: {
                        // nothing to do...
                        break;
                }
        }

        return (activate);
}


struct  filterops fsevent_filtops = { 
        .f_isfd = 1, 
        .f_attach = NULL, 
        .f_detach = filt_fsevent_detach, 
        .f_event = filt_fsevent
};

static int
fseventsf_kqfilter(__unused struct fileproc *fp, __unused struct knote *kn, __unused vfs_context_t ctx)
{
    fsevent_handle *fseh = (struct fsevent_handle *)fp->f_fglob->fg_data;

    kn->kn_hook = (void*)fseh;
    kn->kn_hookid = 1;
    kn->kn_fop = &fsevent_filtops;
    
    lock_watch_table();

    KNOTE_ATTACH(&fseh->knotes, kn);

    unlock_watch_table();
    return 0;
}


static int
fseventsf_drain(struct fileproc *fp, __unused vfs_context_t ctx)
{
    int counter = 0;
    fsevent_handle *fseh = (struct fsevent_handle *)fp->f_fglob->fg_data;

    fseh->watcher->flags |= WATCHER_CLOSING;

    // if there are people still waiting, sleep for 10ms to
    // let them clean up and get out of there.  however we
    // also don't want to get stuck forever so if they don't
    // exit after 5 seconds we're tearing things down anyway.
    while(fseh->watcher->blockers && counter++ < 500) {
        // issue wakeup in case anyone is blocked waiting for an event
        // do this each time we wakeup in case the blocker missed
        // the wakeup due to the unprotected test of WATCHER_CLOSING
        // and decision to tsleep in fmod_watch... this bit of 
        // latency is a decent tradeoff against not having to
        // take and drop a lock in fmod_watch
        fsevents_wakeup(fseh->watcher);

        tsleep((caddr_t)fseh->watcher, PRIBIO, "watcher-close", 1);
    }

    return 0;
}


static int
fseventsopen(__unused dev_t dev, __unused int flag, __unused int mode, __unused struct proc *p)
{
    if (!is_suser()) {
        return EPERM;
    }
    
    return 0;
}

static int
fseventsclose(__unused dev_t dev, __unused int flag, __unused int mode, __unused struct proc *p)
{
    return 0;
}

static int
fseventsread(__unused dev_t dev, __unused struct uio *uio, __unused int ioflag)
{
    return EIO;
}


static int
parse_buffer_and_add_events(const char *buffer, int bufsize, vfs_context_t ctx, long *remainder)
{
    const fse_info *finfo, *dest_finfo;
    const char *path, *ptr, *dest_path, *event_start=buffer;
    int path_len, type, dest_path_len, err = 0;


    ptr = buffer;
    while ((ptr+sizeof(int)+sizeof(fse_info)+1) < buffer+bufsize) {
        type = *(const int *)ptr;
        if (type < 0 || type >= FSE_MAX_EVENTS) {
            err = EINVAL;
            break;
        }

        ptr += sizeof(int);
        
        finfo = (const fse_info *)ptr;
        ptr += sizeof(fse_info);

        path = ptr;
        while(ptr < buffer+bufsize && *ptr != '\0') {
            ptr++;
        }

        if (ptr >= buffer+bufsize) {
            break;
        }

        ptr++;   // advance over the trailing '\0'

        path_len = ptr - path;

        if (type != FSE_RENAME && type != FSE_EXCHANGE) {
            event_start = ptr;   // record where the next event starts

            err = add_fsevent(type, ctx, FSE_ARG_STRING, path_len, path, FSE_ARG_FINFO, finfo, FSE_ARG_DONE);
            if (err) {
                break;
            }
            continue;
        }

        //
        // if we're here we have to slurp up the destination finfo
        // and path so that we can pass them to the add_fsevent()
        // call.  basically it's a copy of the above code.
        //
        dest_finfo = (const fse_info *)ptr;
        ptr += sizeof(fse_info);

        dest_path = ptr;
        while(ptr < buffer+bufsize && *ptr != '\0') {
            ptr++;
        }

        if (ptr >= buffer+bufsize) {
            break;
        }

        ptr++;               // advance over the trailing '\0'
        event_start = ptr;   // record where the next event starts

        dest_path_len = ptr - dest_path;
        //
        // If the destination inode number is non-zero, generate a rename
        // with both source and destination FSE_ARG_FINFO. Otherwise generate
        // a rename with only one FSE_ARG_FINFO. If you need to inject an
        // exchange with an inode of zero, just make that inode (and its path)
        // come in as the first one, not the second.
        //
        if (dest_finfo->ino) {
                err = add_fsevent(type, ctx,
                                  FSE_ARG_STRING, path_len,      path,      FSE_ARG_FINFO, finfo,
                                  FSE_ARG_STRING, dest_path_len, dest_path, FSE_ARG_FINFO, dest_finfo,
                                  FSE_ARG_DONE);
        } else {
                err = add_fsevent(type, ctx,
                                  FSE_ARG_STRING, path_len,      path,      FSE_ARG_FINFO, finfo,
                                  FSE_ARG_STRING, dest_path_len, dest_path,
                                  FSE_ARG_DONE);
        }

        if (err) {
            break;
        }

    }

    // if the last event wasn't complete, set the remainder
    // to be the last event start boundary.
    //
    *remainder = (long)((buffer+bufsize) - event_start);

    return err;
}


//
// Note: this buffer size can not ever be less than
//       2*MAXPATHLEN + 2*sizeof(fse_info) + sizeof(int)
//       because that is the max size for a single event.
//       I made it 4k to be a "nice" size.  making it
//       smaller is not a good idea.
//
#define WRITE_BUFFER_SIZE  4096
char *write_buffer=NULL;

static int
fseventswrite(__unused dev_t dev, struct uio *uio, __unused int ioflag)
{
    int error=0, count;
    vfs_context_t ctx = vfs_context_current();
    long offset=0, remainder;

    lck_mtx_lock(&event_writer_lock);

    if (write_buffer == NULL) {
        if (kmem_alloc(kernel_map, (vm_offset_t *)&write_buffer, WRITE_BUFFER_SIZE)) {
            lck_mtx_unlock(&event_writer_lock);
            return ENOMEM;
        }
    }

    //
    // this loop copies in and processes the events written.
    // it takes care to copy in reasonable size chunks and
    // process them.  if there is an event that spans a chunk
    // boundary we're careful to copy those bytes down to the
    // beginning of the buffer and read the next chunk in just
    // after it.
    //
    while(uio_resid(uio)) {
        if (uio_resid(uio) > (WRITE_BUFFER_SIZE-offset)) {
            count = WRITE_BUFFER_SIZE - offset;
        } else {
            count = uio_resid(uio);
        }

        error = uiomove(write_buffer+offset, count, uio);
        if (error) {
            break;
        }

        // printf("fsevents: write: copied in %d bytes (offset: %ld)\n", count, offset);
        error = parse_buffer_and_add_events(write_buffer, offset+count, ctx, &remainder);
        if (error) {
            break;
        }           

        //
        // if there's any remainder, copy it down to the beginning
        // of the buffer so that it will get processed the next time
        // through the loop.  note that the remainder always starts
        // at an event boundary.
        //
        if (remainder != 0) {
            // printf("fsevents: write: an event spanned a %d byte boundary.  remainder: %ld\n",
            //  WRITE_BUFFER_SIZE, remainder);
            memmove(write_buffer, (write_buffer+count+offset) - remainder, remainder);
            offset = remainder;
        } else {
            offset = 0;
        }
    }

    lck_mtx_unlock(&event_writer_lock);

    return error;
}


static struct fileops fsevents_fops = {
    fseventsf_read,
    fseventsf_write,
    fseventsf_ioctl,
    fseventsf_select,
    fseventsf_close,
    fseventsf_kqfilter,
    fseventsf_drain
};

typedef struct ext_fsevent_clone_args {
    user_addr_t  event_list;
    int32_t      num_events;
    int32_t      event_queue_depth;
    user_addr_t  fd;
} ext_fsevent_clone_args;

typedef struct old_fsevent_clone_args {
    uint32_t  event_list;
    int32_t  num_events;
    int32_t  event_queue_depth;
    uint32_t  fd;
} old_fsevent_clone_args;

#define OLD_FSEVENTS_CLONE      _IOW('s', 1, old_fsevent_clone_args)

static int
fseventsioctl(__unused dev_t dev, u_long cmd, caddr_t data, __unused int flag, struct proc *p)
{
    struct fileproc *f;
    int fd, error;
    fsevent_handle *fseh = NULL;
    ext_fsevent_clone_args *fse_clone_args, _fse_clone;
    int8_t *event_list;
    int is64bit = proc_is64bit(p);

    switch (cmd) {
        case OLD_FSEVENTS_CLONE: {
            old_fsevent_clone_args *old_args = (old_fsevent_clone_args *)data;

            fse_clone_args = &_fse_clone;
            memset(fse_clone_args, 0, sizeof(ext_fsevent_clone_args));

            fse_clone_args->event_list        = CAST_USER_ADDR_T(old_args->event_list);
            fse_clone_args->num_events        = old_args->num_events;
            fse_clone_args->event_queue_depth = old_args->event_queue_depth;
            fse_clone_args->fd                = CAST_USER_ADDR_T(old_args->fd);
            goto handle_clone;
        }
            
        case FSEVENTS_CLONE:
            if (is64bit) {
                fse_clone_args = (ext_fsevent_clone_args *)data;
            } else {
                fsevent_clone_args *ufse_clone = (fsevent_clone_args *)data;
                
                fse_clone_args = &_fse_clone;
                memset(fse_clone_args, 0, sizeof(ext_fsevent_clone_args));

                fse_clone_args->event_list        = CAST_USER_ADDR_T(ufse_clone->event_list);
                fse_clone_args->num_events        = ufse_clone->num_events;
                fse_clone_args->event_queue_depth = ufse_clone->event_queue_depth;
                fse_clone_args->fd                = CAST_USER_ADDR_T(ufse_clone->fd);
            }

        handle_clone:
            if (fse_clone_args->num_events < 0 || fse_clone_args->num_events > 4096) {
                return EINVAL;
            }

            MALLOC(fseh, fsevent_handle *, sizeof(fsevent_handle),
                   M_TEMP, M_WAITOK);
            if (fseh == NULL) {
                return ENOMEM;
            }
            memset(fseh, 0, sizeof(fsevent_handle));
            
            klist_init(&fseh->knotes);

            MALLOC(event_list, int8_t *,
                   fse_clone_args->num_events * sizeof(int8_t),
                   M_TEMP, M_WAITOK);
            if (event_list == NULL) {
                FREE(fseh, M_TEMP);
                return ENOMEM;
            }
    
            error = copyin(fse_clone_args->event_list,
                           (void *)event_list,
                           fse_clone_args->num_events * sizeof(int8_t));
            if (error) {
                FREE(event_list, M_TEMP);
                FREE(fseh, M_TEMP);
                return error;
            }
    
            error = add_watcher(event_list,
                                fse_clone_args->num_events,
                                fse_clone_args->event_queue_depth,
                                &fseh->watcher);
            if (error) {
                FREE(event_list, M_TEMP);
                FREE(fseh, M_TEMP);
                return error;
            }

            // connect up the watcher with this fsevent_handle
            fseh->watcher->fseh = fseh;

            error = falloc(p, &f, &fd, vfs_context_current());
            if (error) {
                FREE(event_list, M_TEMP);
                FREE(fseh, M_TEMP);
                return (error);
            }
            proc_fdlock(p);
            f->f_fglob->fg_flag = FREAD | FWRITE;
            f->f_fglob->fg_type = DTYPE_FSEVENTS;
            f->f_fglob->fg_ops = &fsevents_fops;
            f->f_fglob->fg_data = (caddr_t) fseh;
            proc_fdunlock(p);
            error = copyout((void *)&fd, fse_clone_args->fd, sizeof(int32_t));
            if (error != 0) {
                fp_free(p, fd, f);
            } else {
                proc_fdlock(p);
                procfdtbl_releasefd(p, fd, NULL);
                fp_drop(p, fd, f, 1);
                proc_fdunlock(p);
            }
            break;

        default:
            error = EINVAL;
            break;
    }

    return error;
}

static void
fsevents_wakeup(fs_event_watcher *watcher)
{
    selwakeup(&watcher->fseh->si);
    KNOTE(&watcher->fseh->knotes, NOTE_WRITE|NOTE_NONE);
    wakeup((caddr_t)watcher);
}


/*
 * A struct describing which functions will get invoked for certain
 * actions.
 */
static struct cdevsw fsevents_cdevsw =
{
    fseventsopen,               /* open */
    fseventsclose,              /* close */
    fseventsread,               /* read */
    fseventswrite,              /* write */
    fseventsioctl,              /* ioctl */
    (stop_fcn_t *)&nulldev,     /* stop */
    (reset_fcn_t *)&nulldev,    /* reset */
    NULL,                       /* tty's */
    eno_select,                 /* select */
    eno_mmap,                   /* mmap */
    eno_strat,                  /* strategy */
    eno_getc,                   /* getc */
    eno_putc,                   /* putc */
    0                           /* type */
};


/*
 * Called to initialize our device,
 * and to register ourselves with devfs
 */

void
fsevents_init(void)
{
    int ret;

    if (fsevents_installed) {
        return;
    } 

    fsevents_installed = 1;

    ret = cdevsw_add(-1, &fsevents_cdevsw);
    if (ret < 0) {
        fsevents_installed = 0;
        return;
    }

    devfs_make_node(makedev (ret, 0), DEVFS_CHAR,
                    UID_ROOT, GID_WHEEL, 0644, "fsevents", 0);

    fsevents_internal_init();
}


char *
get_pathbuff(void)
{
    char *path;

    MALLOC_ZONE(path, char *, MAXPATHLEN, M_NAMEI, M_WAITOK);
    return path;
}

void
release_pathbuff(char *path)
{

    if (path == NULL) {
        return;
    }
    FREE_ZONE(path, MAXPATHLEN, M_NAMEI);
}

int
get_fse_info(struct vnode *vp, fse_info *fse, __unused vfs_context_t ctx)
{
    struct vnode_attr va;

    VATTR_INIT(&va);
    VATTR_WANTED(&va, va_fsid);
    VATTR_WANTED(&va, va_fileid);
    VATTR_WANTED(&va, va_mode);
    VATTR_WANTED(&va, va_uid);
    VATTR_WANTED(&va, va_gid);
    if (vp->v_flag & VISHARDLINK) {
        if (vp->v_type == VDIR) {
            VATTR_WANTED(&va, va_dirlinkcount);
        } else {
            VATTR_WANTED(&va, va_nlink);
        }
    }
    
    if (vnode_getattr(vp, &va, vfs_context_kernel()) != 0) {
        memset(fse, 0, sizeof(fse_info));
        return -1;
    }
    
    fse->ino  = (ino64_t)va.va_fileid;
    fse->dev  = (dev_t)va.va_fsid;
    fse->mode = (int32_t)vnode_vttoif(vnode_vtype(vp)) | va.va_mode;
    fse->uid  = (uid_t)va.va_uid;
    fse->gid  = (gid_t)va.va_gid;
    if (vp->v_flag & VISHARDLINK) {
        fse->mode |= FSE_MODE_HLINK;
        if (vp->v_type == VDIR) {
            fse->nlink = (uint64_t)va.va_dirlinkcount;
        } else {
            fse->nlink = (uint64_t)va.va_nlink;
        }
    }    

    return 0;
}

void
create_fsevent_from_kevent(vnode_t vp, uint32_t kevents, struct vnode_attr *vap)
{
    int fsevent_type=FSE_CONTENT_MODIFIED, len;   // the default is the most pessimistic
    char pathbuf[MAXPATHLEN];
    fse_info fse;

    
    if (kevents & VNODE_EVENT_DELETE) {
        fsevent_type = FSE_DELETE;
    } else if (kevents & (VNODE_EVENT_EXTEND|VNODE_EVENT_WRITE)) {
        fsevent_type = FSE_CONTENT_MODIFIED;
    } else if (kevents & VNODE_EVENT_LINK) {
        fsevent_type = FSE_CREATE_FILE;
    } else if (kevents & VNODE_EVENT_RENAME) {
        fsevent_type = FSE_CREATE_FILE;    // XXXdbg - should use FSE_RENAME but we don't have the destination info;
    } else if (kevents & (VNODE_EVENT_FILE_CREATED|VNODE_EVENT_FILE_REMOVED|VNODE_EVENT_DIR_CREATED|VNODE_EVENT_DIR_REMOVED)) {
        fsevent_type = FSE_STAT_CHANGED;  // XXXdbg - because vp is a dir and the thing created/removed lived inside it
    } else {   // a catch all for VNODE_EVENT_PERMS, VNODE_EVENT_ATTRIB and anything else
        fsevent_type = FSE_STAT_CHANGED;
    }

    // printf("convert_kevent: kevents 0x%x fsevent type 0x%x (for %s)\n", kevents, fsevent_type, vp->v_name ? vp->v_name : "(no-name)");

    fse.dev = vap->va_fsid;
    fse.ino = vap->va_fileid;
    fse.mode = vnode_vttoif(vnode_vtype(vp)) | (uint32_t)vap->va_mode;
    if (vp->v_flag & VISHARDLINK) {
        fse.mode |= FSE_MODE_HLINK;
        if (vp->v_type == VDIR) {
            fse.nlink = vap->va_dirlinkcount;
        } else {
            fse.nlink = vap->va_nlink;
        }
    }

    if (vp->v_type == VDIR) {
        fse.mode |= FSE_REMOTE_DIR_EVENT;       
    }
    

    fse.uid = vap->va_uid;
    fse.gid = vap->va_gid;

    len = sizeof(pathbuf);
    if (vn_getpath(vp, pathbuf, &len) == 0) {
        add_fsevent(fsevent_type, vfs_context_current(), FSE_ARG_STRING, len, pathbuf, FSE_ARG_FINFO, &fse, FSE_ARG_DONE);
    }
    return;
}

#else /* CONFIG_FSE */
/*
 * The get_pathbuff and release_pathbuff routines are used in places not
 * related to fsevents, and it's a handy abstraction, so define trivial
 * versions that don't cache a pool of buffers.  This way, we don't have
 * to conditionalize the callers, and they still get the advantage of the
 * pool of buffers if CONFIG_FSE is turned on.
 */
char *
get_pathbuff(void)
{
        char *path;
        MALLOC_ZONE(path, char *, MAXPATHLEN, M_NAMEI, M_WAITOK);
        return path;
}

void
release_pathbuff(char *path)
{
        FREE_ZONE(path, MAXPATHLEN, M_NAMEI);
}
#endif /* CONFIG_FSE */