/*      $NetBSD: chfs_gc.c,v 1.12 2021/12/07 22:13:56 andvar Exp $      */

/*-
 * Copyright (c) 2010 Department of Software Engineering,
 *                    University of Szeged, Hungary
 * Copyright (c) 2010 Tamas Toth <ttoth@inf.u-szeged.hu>
 * Copyright (c) 2010 Adam Hoka <ahoka@NetBSD.org>
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by the Department of Software Engineering, University of Szeged, Hungary
 *
 * 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 AUTHOR ``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 AUTHOR 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/cprng.h>
#include "chfs.h"

void chfs_gc_release_inode(struct chfs_mount *,
    struct chfs_inode *);
struct chfs_inode *chfs_gc_fetch_inode(struct chfs_mount *,
    ino_t, uint32_t);
int chfs_check(struct chfs_mount *, struct chfs_vnode_cache *);
void chfs_clear_inode(struct chfs_mount *, struct chfs_inode *);


struct chfs_eraseblock *find_gc_block(struct chfs_mount *);
int chfs_gcollect_pristine(struct chfs_mount *,
    struct chfs_eraseblock *,
    struct chfs_vnode_cache *, struct chfs_node_ref *);
int chfs_gcollect_live(struct chfs_mount *,
    struct chfs_eraseblock *, struct chfs_node_ref *,
    struct chfs_inode *);
int chfs_gcollect_vnode(struct chfs_mount *, struct chfs_inode *);
int chfs_gcollect_dirent(struct chfs_mount *,
    struct chfs_eraseblock *, struct chfs_inode *,
    struct chfs_dirent *);
int chfs_gcollect_deletion_dirent(struct chfs_mount *,
    struct chfs_eraseblock *, struct chfs_inode *,
    struct chfs_dirent *);
int chfs_gcollect_dnode(struct chfs_mount *,
    struct chfs_eraseblock *, struct chfs_inode *,
    struct chfs_full_dnode *, uint32_t, uint32_t);

/* 
 * chfs_gc_trigger - wakes up GC thread, if it should run
 * Must be called with chm_lock_mountfields held. 
 */
void
chfs_gc_trigger(struct chfs_mount *chmp)
{
        struct garbage_collector_thread *gc = &chmp->chm_gc_thread;

        if (gc->gcth_running &&
            chfs_gc_thread_should_wake(chmp)) {
                cv_signal(&gc->gcth_wakeup);
        }
}


/* chfs_gc_thread - garbage collector's thread */
void
chfs_gc_thread(void *data)
{
        struct chfs_mount *chmp = data;
        struct garbage_collector_thread *gc = &chmp->chm_gc_thread;

        dbg_gc("[GC THREAD] thread started\n");

        mutex_enter(&chmp->chm_lock_mountfields);
        while (gc->gcth_running) {
                /* we must call chfs_gc_thread_should_wake with chm_lock_mountfields
                 * held, which is a bit awkwardly done here, but we can't really
                 * do it otherway with the current design...
                 */
                if (chfs_gc_thread_should_wake(chmp)) {
                        if (chfs_gcollect_pass(chmp) == ENOSPC) {
                                mutex_exit(&chmp->chm_lock_mountfields);
                                panic("No space for garbage collection\n");
                                /* XXX why break here? i have added a panic
                                 * here to see if it gets triggered -ahoka
                                 */
                                break;
                        }
                        /* XXX gcollect_pass drops the mutex */
                }

                cv_timedwait_sig(&gc->gcth_wakeup,
                    &chmp->chm_lock_mountfields, mstohz(100));
        }
        mutex_exit(&chmp->chm_lock_mountfields);

        dbg_gc("[GC THREAD] thread stopped\n");
        kthread_exit(0);
}

/* chfs_gc_thread_start - starts GC */
void
chfs_gc_thread_start(struct chfs_mount *chmp)
{
        struct garbage_collector_thread *gc = &chmp->chm_gc_thread;

        cv_init(&gc->gcth_wakeup, "chfsgccv");

        gc->gcth_running = true;
        kthread_create(PRI_NONE, /*KTHREAD_MPSAFE |*/ KTHREAD_MUSTJOIN,
            NULL, chfs_gc_thread, chmp, &gc->gcth_thread,
            "chfsgcth");
}

/* chfs_gc_thread_stop - stops GC */
void
chfs_gc_thread_stop(struct chfs_mount *chmp)
{
        struct garbage_collector_thread *gc = &chmp->chm_gc_thread;

        /* check if it is actually running */
        if (gc->gcth_running) {
                gc->gcth_running = false;
        } else {
                return;
        }
        cv_signal(&gc->gcth_wakeup);
        dbg_gc("[GC THREAD] stop signal sent\n");

        kthread_join(gc->gcth_thread);
#ifdef BROKEN_KTH_JOIN
        kpause("chfsthjoin", false, mstohz(1000), NULL);
#endif

        cv_destroy(&gc->gcth_wakeup);
}

/*
 * chfs_gc_thread_should_wake - checks if GC thread should wake up
 * Must be called with chm_lock_mountfields held.
 * Returns 1, if GC should wake up and 0 else.
 */
int
chfs_gc_thread_should_wake(struct chfs_mount *chmp)
{
        int nr_very_dirty = 0;
        struct chfs_eraseblock *cheb;
        uint32_t dirty;

        KASSERT(mutex_owned(&chmp->chm_lock_mountfields));

        /* Erase pending queue is not empty. */
        if (!TAILQ_EMPTY(&chmp->chm_erase_pending_queue)) {
                dbg_gc("erase_pending\n");
                return 1;
        }

        /* There is something unchecked in the filesystem. */
        if (chmp->chm_unchecked_size) {
                dbg_gc("unchecked\n");
                return 1;
        }

        dirty = chmp->chm_dirty_size - chmp->chm_nr_erasable_blocks *
            chmp->chm_ebh->eb_size;

        /* Number of free and erasable blocks are critical. */
        if (chmp->chm_nr_free_blocks + chmp->chm_nr_erasable_blocks <
            chmp->chm_resv_blocks_gctrigger && (dirty > chmp->chm_nospc_dirty)) {
                dbg_gc("free: %d + erasable: %d < resv: %d\n",
                    chmp->chm_nr_free_blocks, chmp->chm_nr_erasable_blocks,
                    chmp->chm_resv_blocks_gctrigger);
                dbg_gc("dirty: %d > nospc_dirty: %d\n",
                    dirty, chmp->chm_nospc_dirty);

                return 1;
        }

        /* There are too much very dirty blocks. */
        TAILQ_FOREACH(cheb, &chmp->chm_very_dirty_queue, queue) {
                nr_very_dirty++;
                if (nr_very_dirty == chmp->chm_vdirty_blocks_gctrigger) {
                        dbg_gc("nr_very_dirty\n");
                        return 1;
                }
        }

        /* Everything is OK, GC shouldn't run. */
        return 0;
}

/* chfs_gc_release_inode - does nothing yet */
void
chfs_gc_release_inode(struct chfs_mount *chmp,
    struct chfs_inode *ip)
{
        dbg_gc("release inode\n");
}

/* chfs_gc_fetch_inode - assign the given inode to the GC */
struct chfs_inode *
chfs_gc_fetch_inode(struct chfs_mount *chmp, ino_t vno,
    uint32_t unlinked)
{
        struct vnode *vp = NULL;
        struct chfs_vnode_cache *vc;
        struct chfs_inode *ip;
        dbg_gc("fetch inode %llu\n", (unsigned long long)vno);

        if (unlinked) {
                dbg_gc("unlinked\n");
                vp = chfs_vnode_lookup(chmp, vno);
                if (!vp) {
                        mutex_enter(&chmp->chm_lock_vnocache);
                        vc = chfs_vnode_cache_get(chmp, vno);
                        if (!vc) {
                                mutex_exit(&chmp->chm_lock_vnocache);
                                return NULL;
                        }
                        mutex_exit(&chmp->chm_lock_vnocache);
                        if (vc->state != VNO_STATE_CHECKEDABSENT) {
                                /* XXX why do we need the delay here?! */
                                KASSERT(mutex_owned(&chmp->chm_lock_mountfields));
                                cv_timedwait_sig(
                                        &chmp->chm_gc_thread.gcth_wakeup,
                                        &chmp->chm_lock_mountfields, mstohz(50));
                        }
                        return NULL;
                }
        } else {
                dbg_gc("vnode lookup\n");
                vp = chfs_vnode_lookup(chmp, vno);
        }
        dbg_gc("vp to ip\n");
        ip = VTOI(vp);
        KASSERT(ip);
        vrele(vp);

        return ip;
}

extern rb_tree_ops_t frag_rbtree_ops;

/* chfs_check - checks an inode with minimal initialization */
int
chfs_check(struct chfs_mount *chmp, struct  chfs_vnode_cache *chvc)
{
        KASSERT(mutex_owned(&chmp->chm_lock_vnocache));

        struct chfs_inode *ip;
        struct vnode *vp;
        int ret;

        /* Get a new inode. */
        ip = pool_get(&chfs_inode_pool, PR_WAITOK);
        if (!ip) {
                return ENOMEM;
        }

        vp = kmem_zalloc(sizeof(struct vnode), KM_SLEEP);

        /* Minimal initialization. */
        ip->chvc = chvc;
        ip->vp = vp;

        vp->v_data = ip;

        rb_tree_init(&ip->fragtree, &frag_rbtree_ops);
        TAILQ_INIT(&ip->dents);

        /* Build the node. */
        mutex_exit(&chmp->chm_lock_vnocache);
        ret = chfs_read_inode_internal(chmp, ip);
        mutex_enter(&chmp->chm_lock_vnocache);
        if (!ret) {
                chfs_clear_inode(chmp, ip);
        }

        /* Release inode. */
        pool_put(&chfs_inode_pool, ip);

        return ret;
}

/* chfs_clear_inode - kills a minimal inode */
void
chfs_clear_inode(struct chfs_mount *chmp, struct chfs_inode *ip)
{
        KASSERT(mutex_owned(&chmp->chm_lock_vnocache));

        struct chfs_dirent *fd, *tmpfd;
        struct chfs_vnode_cache *chvc;
        struct chfs_node_ref *nref;

        chvc = ip->chvc;
        /* shouldnt this be: */
        //bool deleted = (chvc && !(chvc->pvno || chvc->nlink));
        int deleted = (chvc && !(chvc->pvno | chvc->nlink));

        /* Set actual state. */
        if (chvc && chvc->state != VNO_STATE_CHECKING) {
                chvc->state = VNO_STATE_CLEARING;
        }

        /* Remove vnode information. */
        while (deleted && chvc->v != (struct chfs_node_ref *)chvc) {
                nref = chvc->v;
                chfs_remove_and_obsolete(chmp, chvc, nref, &chvc->v);
        }

        /* Destroy data. */
        chfs_kill_fragtree(chmp, &ip->fragtree);

        /* Clear dirents. */
        TAILQ_FOREACH_SAFE(fd, &ip->dents, fds, tmpfd) {
                chfs_free_dirent(fd);
        }

        /* Remove node from vnode cache. */
        if (chvc && chvc->state == VNO_STATE_CHECKING) {
                chvc->state = VNO_STATE_CHECKEDABSENT;
                if ((struct chfs_vnode_cache *)chvc->v == chvc &&
                    (struct chfs_vnode_cache *)chvc->dirents == chvc &&
                    (struct chfs_vnode_cache *)chvc->dnode == chvc)
                        chfs_vnode_cache_remove(chmp, chvc);
        }
}

/* find_gc_block - finds the next block for GC */
struct chfs_eraseblock *
find_gc_block(struct chfs_mount *chmp)
{
        struct chfs_eraseblock *ret;
        struct chfs_eraseblock_queue *nextqueue;

        KASSERT(mutex_owned(&chmp->chm_lock_mountfields));

        /* Get a random number. */
        uint32_t n = cprng_fast32() % 128;

again:
        /* Find an eraseblock queue. */
    if (n<50 && !TAILQ_EMPTY(&chmp->chm_erase_pending_queue)) {
                dbg_gc("Picking block from erase_pending_queue to GC next\n");
                nextqueue = &chmp->chm_erase_pending_queue;
        } else if (n<110 && !TAILQ_EMPTY(&chmp->chm_very_dirty_queue) ) {
                dbg_gc("Picking block from very_dirty_queue to GC next\n");
                nextqueue = &chmp->chm_very_dirty_queue;
        } else if (n<126 && !TAILQ_EMPTY(&chmp->chm_dirty_queue) ) {
                dbg_gc("Picking block from dirty_queue to GC next\n");
                nextqueue = &chmp->chm_dirty_queue;
        } else if (!TAILQ_EMPTY(&chmp->chm_clean_queue)) {
                dbg_gc("Picking block from clean_queue to GC next\n");
                nextqueue = &chmp->chm_clean_queue;
        } else if (!TAILQ_EMPTY(&chmp->chm_dirty_queue)) {
                dbg_gc("Picking block from dirty_queue to GC next"
                    " (clean_queue was empty)\n");
                nextqueue = &chmp->chm_dirty_queue;
        } else if (!TAILQ_EMPTY(&chmp->chm_very_dirty_queue)) {
                dbg_gc("Picking block from very_dirty_queue to GC next"
                    " (clean_queue and dirty_queue were empty)\n");
                nextqueue = &chmp->chm_very_dirty_queue;
        } else if (!TAILQ_EMPTY(&chmp->chm_erase_pending_queue)) {
                dbg_gc("Picking block from erase_pending_queue to GC next"
                    " (clean_queue and {very_,}dirty_queue were empty)\n");
                nextqueue = &chmp->chm_erase_pending_queue;
        } else if (!TAILQ_EMPTY(&chmp->chm_erasable_pending_wbuf_queue)) {
                dbg_gc("Synching wbuf in order to reuse "
                    "erasable_pendig_wbuf_queue blocks\n");
                rw_enter(&chmp->chm_lock_wbuf, RW_WRITER);
                chfs_flush_pending_wbuf(chmp);
                rw_exit(&chmp->chm_lock_wbuf);
                goto again;
        } else {
                dbg_gc("CHFS: no clean, dirty _or_ erasable"
                    " blocks to GC from! Where are they all?\n");
                return NULL;
        }

        /* Get the first block of the queue. */
        ret = TAILQ_FIRST(nextqueue);
        if (chmp->chm_nextblock) {
                dbg_gc("nextblock num: %u - gcblock num: %u\n",
                    chmp->chm_nextblock->lnr, ret->lnr);
                if (ret == chmp->chm_nextblock)
                        goto again;
        }
        TAILQ_REMOVE(nextqueue, ret, queue);

        /* Set GC block. */
        chmp->chm_gcblock = ret;
        /* Set GC node. */
        ret->gc_node = ret->first_node;

        if (!ret->gc_node) {
                dbg_gc("Oops! ret->gc_node at LEB: %u is NULL\n", ret->lnr);
                panic("CHFS BUG - one LEB's gc_node is NULL\n");
        }

        /* TODO wasted size? */
        return ret;
}

/* chfs_gcollect_pass - this is the main function of GC */
int
chfs_gcollect_pass(struct chfs_mount *chmp)
{
        struct chfs_vnode_cache *vc;
        struct chfs_eraseblock *eb;
        struct chfs_node_ref *nref;
        uint32_t gcblock_dirty;
        struct chfs_inode *ip;
        ino_t vno, pvno;
        uint32_t nlink;
        int ret = 0;

        KASSERT(mutex_owned(&chmp->chm_lock_mountfields));

        /* Check all vnodes. */
        for (;;) {
                mutex_enter(&chmp->chm_lock_sizes);

                /* Check unchecked size. */
                dbg_gc("unchecked size == %u\n", chmp->chm_unchecked_size);
                if (!chmp->chm_unchecked_size)
                        break;

                /* Compare vnode number to the maximum. */
                if (chmp->chm_checked_vno > chmp->chm_max_vno) {
                        mutex_exit(&chmp->chm_lock_sizes);
                        dbg_gc("checked_vno (#%llu) > max_vno (#%llu)\n",
                            (unsigned long long)chmp->chm_checked_vno,
                            (unsigned long long)chmp->chm_max_vno);
                        return ENOSPC;
                }

                mutex_exit(&chmp->chm_lock_sizes);

                mutex_enter(&chmp->chm_lock_vnocache);
                dbg_gc("checking vno #%llu\n",
                        (unsigned long long)chmp->chm_checked_vno);
                dbg_gc("get vnode cache\n");

                /* OK, Get and check the vnode cache. */
                vc = chfs_vnode_cache_get(chmp, chmp->chm_checked_vno++);

                if (!vc) {
                        dbg_gc("!vc\n");
                        mutex_exit(&chmp->chm_lock_vnocache);
                        continue;
                }

                if ((vc->pvno | vc->nlink) == 0) {
                        dbg_gc("(pvno | nlink) == 0\n");
                        mutex_exit(&chmp->chm_lock_vnocache);
                        continue;
                }

                /* Find out the state of the vnode. */
                dbg_gc("switch\n");
                switch (vc->state) {
                case VNO_STATE_CHECKEDABSENT:
                        /* FALLTHROUGH */
                case VNO_STATE_PRESENT:
                        mutex_exit(&chmp->chm_lock_vnocache);
                        continue;

                case VNO_STATE_GC:
                        /* FALLTHROUGH */
                case VNO_STATE_CHECKING:
                        mutex_exit(&chmp->chm_lock_vnocache);
                        dbg_gc("VNO_STATE GC or CHECKING\n");
                        panic("CHFS BUG - vc state gc or checking\n");

                case VNO_STATE_READING:
                        chmp->chm_checked_vno--;
                        mutex_exit(&chmp->chm_lock_vnocache);
                        /* XXX why do we need the delay here?! */
                        kpause("chvncrea", true, mstohz(50), NULL);

                        return 0;

                default:
                        mutex_exit(&chmp->chm_lock_vnocache);
                        dbg_gc("default\n");
                        panic("CHFS BUG - vc state is other what we"
                            " checked\n");

                case VNO_STATE_UNCHECKED:
                        ;
                }

                /* We found an unchecked vnode. */

                vc->state = VNO_STATE_CHECKING;

                /* XXX check if this is too heavy to call under
                 * chm_lock_vnocache
                 */
                ret = chfs_check(chmp, vc);
                vc->state = VNO_STATE_CHECKEDABSENT;

                mutex_exit(&chmp->chm_lock_vnocache);
                return ret;
        }

        /* Get GC block. */
        eb = chmp->chm_gcblock;

        if (!eb) {
                eb = find_gc_block(chmp);
        }

        if (!eb) {
                dbg_gc("!eb\n");
                if (!TAILQ_EMPTY(&chmp->chm_erase_pending_queue)) {
                        mutex_exit(&chmp->chm_lock_sizes);
                        return EAGAIN;
                }
                mutex_exit(&chmp->chm_lock_sizes);
                return EIO;
        }

        if (!eb->used_size) {
                dbg_gc("!eb->used_size\n");
                goto eraseit;
        }

        /* Get GC node. */
        nref = eb->gc_node;
        gcblock_dirty = eb->dirty_size;

        /* Find a node which wasn't obsoleted yet.
         * Obsoleted nodes will be simply deleted after the whole block has checked. */
        while(CHFS_REF_OBSOLETE(nref)) {
#ifdef DBG_MSG_GC
                if (nref == chmp->chm_blocks[nref->nref_lnr].last_node) {
                        dbg_gc("THIS NODE IS THE LAST NODE OF ITS EB\n");
                }
#endif
                nref = node_next(nref);
                if (!nref) {
                        eb->gc_node = nref;
                        mutex_exit(&chmp->chm_lock_sizes);
                        panic("CHFS BUG - nref is NULL)\n");
                }
        }

        /* We found a "not obsoleted" node. */
        eb->gc_node = nref;
        KASSERT(nref->nref_lnr == chmp->chm_gcblock->lnr);

        /* Check if node is in any chain. */
        if (!nref->nref_next) {
                /* This node is not in any chain. Simply collect it, or obsolete. */
                mutex_exit(&chmp->chm_lock_sizes);
                if (CHFS_REF_FLAGS(nref) == CHFS_PRISTINE_NODE_MASK) {
                        chfs_gcollect_pristine(chmp, eb, NULL, nref);
                } else {
                        chfs_mark_node_obsolete(chmp, nref);
                }
                goto lock_size;
        }

        mutex_exit(&chmp->chm_lock_sizes);

        mutex_enter(&chmp->chm_lock_vnocache);

        dbg_gc("nref lnr: %u - offset: %u\n", nref->nref_lnr, nref->nref_offset);
        vc = chfs_nref_to_vc(nref);

        /* Check the state of the node. */
        dbg_gc("switch\n");
        switch(vc->state) {
        case VNO_STATE_CHECKEDABSENT:
                        if (CHFS_REF_FLAGS(nref) == CHFS_PRISTINE_NODE_MASK) {
                                vc->state = VNO_STATE_GC;
                        }
                        break;

        case VNO_STATE_PRESENT:
                        break;

        case VNO_STATE_UNCHECKED:
                        /* FALLTHROUGH */
        case VNO_STATE_CHECKING:
                        /* FALLTHROUGH */
        case VNO_STATE_GC:
                        mutex_exit(&chmp->chm_lock_vnocache);
                        panic("CHFS BUG - vc state unchecked,"
                                " checking or gc (vno #%llu, num #%d)\n",
                                (unsigned long long)vc->vno, vc->state);

        case VNO_STATE_READING:
                        /* Node is in use at this time. */
                        mutex_exit(&chmp->chm_lock_vnocache);
                        kpause("chvncrea", true, mstohz(50), NULL);
                        return 0;
        }

        if (vc->state == VNO_STATE_GC) {
                dbg_gc("vc->state == VNO_STATE_GC\n");
                vc->state = VNO_STATE_CHECKEDABSENT;
                mutex_exit(&chmp->chm_lock_vnocache);
                ret = chfs_gcollect_pristine(chmp, eb, NULL, nref);

                //TODO wake_up(&chmp->chm_vnocache_wq);
                if (ret != EBADF)
                        goto test_gcnode;
                mutex_enter(&chmp->chm_lock_vnocache);
        }

        /* Collect living node. */
        vno = vc->vno;
        pvno = vc->pvno;
        nlink = vc->nlink;
        mutex_exit(&chmp->chm_lock_vnocache);

        ip = chfs_gc_fetch_inode(chmp, vno, !(pvno | nlink));

        if (!ip) {
                dbg_gc("!ip\n");
                ret = 0;
                goto lock_size;
        }

        chfs_gcollect_live(chmp, eb, nref, ip);

        chfs_gc_release_inode(chmp, ip);

test_gcnode:
        if (eb->dirty_size == gcblock_dirty &&
            !CHFS_REF_OBSOLETE(eb->gc_node)) {
                dbg_gc("ERROR collecting node at %u failed.\n",
                    CHFS_GET_OFS(eb->gc_node->nref_offset));

                ret = ENOSPC;
        }

lock_size:
        KASSERT(mutex_owned(&chmp->chm_lock_mountfields));
        mutex_enter(&chmp->chm_lock_sizes);
eraseit:
        dbg_gc("eraseit\n");

        if (chmp->chm_gcblock) {
        /* This is only for debugging. */
                dbg_gc("eb used size = %u\n", chmp->chm_gcblock->used_size);
                dbg_gc("eb free size = %u\n", chmp->chm_gcblock->free_size);
                dbg_gc("eb dirty size = %u\n", chmp->chm_gcblock->dirty_size);
                dbg_gc("eb unchecked size = %u\n",
                    chmp->chm_gcblock->unchecked_size);
                dbg_gc("eb wasted size = %u\n", chmp->chm_gcblock->wasted_size);

                KASSERT(chmp->chm_gcblock->used_size + chmp->chm_gcblock->free_size +
                    chmp->chm_gcblock->dirty_size +
                    chmp->chm_gcblock->unchecked_size +
                    chmp->chm_gcblock->wasted_size == chmp->chm_ebh->eb_size);

        }

        /* Check the state of GC block. */
        if (chmp->chm_gcblock && chmp->chm_gcblock->dirty_size +
            chmp->chm_gcblock->wasted_size == chmp->chm_ebh->eb_size) {
                dbg_gc("Block at leb #%u completely obsoleted by GC, "
                    "Moving to erase_pending_queue\n", chmp->chm_gcblock->lnr);
                TAILQ_INSERT_TAIL(&chmp->chm_erase_pending_queue,
                    chmp->chm_gcblock, queue);
                chmp->chm_gcblock = NULL;
                chmp->chm_nr_erasable_blocks++;
                if (!TAILQ_EMPTY(&chmp->chm_erase_pending_queue)) {
                        ret = chfs_remap_leb(chmp);
                }
        }

        mutex_exit(&chmp->chm_lock_sizes);
        dbg_gc("return\n");
        return ret;
}


/* chfs_gcollect_pristine - collects a pristine node */
int
chfs_gcollect_pristine(struct chfs_mount *chmp, struct chfs_eraseblock *cheb,
    struct chfs_vnode_cache *chvc, struct chfs_node_ref *nref)
{
        struct chfs_node_ref *newnref;
        struct chfs_flash_node_hdr *nhdr;
        struct chfs_flash_vnode *fvnode;
        struct chfs_flash_dirent_node *fdirent;
        struct chfs_flash_data_node *fdata;
        int ret, retries = 0;
        uint32_t ofs, crc;
        size_t totlen = chfs_nref_len(chmp, cheb, nref);
        char *data;
        struct iovec vec;
        size_t retlen;

        dbg_gc("gcollect_pristine\n");

        data = kmem_alloc(totlen, KM_SLEEP);
        ofs = CHFS_GET_OFS(nref->nref_offset);

        /* Read header. */
        ret = chfs_read_leb(chmp, nref->nref_lnr, data, ofs, totlen, &retlen);
        if (ret) {
                dbg_gc("reading error\n");
                goto err_out;
        }
        if (retlen != totlen) {
                dbg_gc("read size error\n");
                ret = EIO;
                goto err_out;
        }
        nhdr = (struct chfs_flash_node_hdr *)data;

        /* Check the header. */
        if (le16toh(nhdr->magic) != CHFS_FS_MAGIC_BITMASK) {
                dbg_gc("node header magic number error\n");
                ret = EBADF;
                goto err_out;
        }
        crc = crc32(0, (uint8_t *)nhdr, CHFS_NODE_HDR_SIZE - 4);
        if (crc != le32toh(nhdr->hdr_crc)) {
                dbg_gc("node header crc error\n");
                ret = EBADF;
                goto err_out;
        }

        /* Read the remaining parts. */
        switch(le16toh(nhdr->type)) {
        case CHFS_NODETYPE_VNODE:
                /* vnode information node */
                        fvnode = (struct chfs_flash_vnode *)data;
                crc = crc32(0, (uint8_t *)fvnode, sizeof(struct chfs_flash_vnode) - 4);
                if (crc != le32toh(fvnode->node_crc)) {
                                dbg_gc("vnode crc error\n");
                                ret = EBADF;
                                goto err_out;
                        }
                        break;
        case CHFS_NODETYPE_DIRENT:
                /* dirent node */
                        fdirent = (struct chfs_flash_dirent_node *)data;
                crc = crc32(0, (uint8_t *)fdirent, sizeof(struct chfs_flash_dirent_node) - 4);
                if (crc != le32toh(fdirent->node_crc)) {
                                dbg_gc("dirent crc error\n");
                                ret = EBADF;
                                goto err_out;
                        }
                crc = crc32(0, fdirent->name, fdirent->nsize);
                if (crc != le32toh(fdirent->name_crc)) {
                                dbg_gc("dirent name crc error\n");
                                ret = EBADF;
                                goto err_out;
                        }
                        break;
        case CHFS_NODETYPE_DATA:
                /* data node */
                        fdata = (struct chfs_flash_data_node *)data;
                crc = crc32(0, (uint8_t *)fdata, sizeof(struct chfs_flash_data_node) - 4);
                if (crc != le32toh(fdata->node_crc)) {
                                dbg_gc("data node crc error\n");
                                ret = EBADF;
                                goto err_out;
                        }
                        break;
        default:
                /* unknown node */
                        if (chvc) {
                                dbg_gc("unknown node have vnode cache\n");
                                ret = EBADF;
                                goto err_out;
                        }
        }
        /* CRC's OK, write node to its new place */
retry:
        ret = chfs_reserve_space_gc(chmp, totlen);
        if (ret)
                goto err_out;

        newnref = chfs_alloc_node_ref(chmp->chm_nextblock);
        if (!newnref) {
                ret = ENOMEM;
                goto err_out;
        }

        ofs = chmp->chm_ebh->eb_size - chmp->chm_nextblock->free_size;
        newnref->nref_offset = ofs;

        /* write out the whole node */
        vec.iov_base = (void *)data;
        vec.iov_len = totlen;
        mutex_enter(&chmp->chm_lock_sizes);
        ret = chfs_write_wbuf(chmp, &vec, 1, ofs, &retlen);

        if (ret || retlen != totlen) {
                /* error while writing */
                chfs_err("error while writing out to the media\n");
                chfs_err("err: %d | size: %zu | retlen : %zu\n",
                    ret, totlen, retlen);

                chfs_change_size_dirty(chmp, chmp->chm_nextblock, totlen);
                if (retries) {
                        mutex_exit(&chmp->chm_lock_sizes);
                        ret = EIO;
                        goto err_out;
                }

                /* try again */
                retries++;
                mutex_exit(&chmp->chm_lock_sizes);
                goto retry;
        }

        /* update vnode information */
        mutex_exit(&chmp->chm_lock_sizes);
        //TODO should we set free_size?
        mutex_enter(&chmp->chm_lock_vnocache);
        chfs_add_vnode_ref_to_vc(chmp, chvc, newnref);
        mutex_exit(&chmp->chm_lock_vnocache);
        ret = 0;
        /* FALLTHROUGH */
err_out:
        kmem_free(data, totlen);
        return ret;
}


/* chfs_gcollect_live - collects a living node */
int
chfs_gcollect_live(struct chfs_mount *chmp,
    struct chfs_eraseblock *cheb, struct chfs_node_ref *nref,
    struct chfs_inode *ip)
{
        struct chfs_node_frag *frag;
        struct chfs_full_dnode *fn = NULL;
        int start = 0, end = 0, nrfrags = 0;
        struct chfs_dirent *fd = NULL;
        int ret = 0;
        bool is_dirent;

        dbg_gc("gcollect_live\n");

        if (chmp->chm_gcblock != cheb) {
                dbg_gc("GC block is no longer gcblock. Restart.\n");
                goto upnout;
        }

        if (CHFS_REF_OBSOLETE(nref)) {
                dbg_gc("node to be GC'd was obsoleted in the meantime.\n");
                goto upnout;
        }

        /* It's a vnode? */
        if (ip->chvc->v == nref) {
                chfs_gcollect_vnode(chmp, ip);
                goto upnout;
        }

        /* Find data node. */
        dbg_gc("find full dnode\n");
        for(frag = frag_first(&ip->fragtree);
            frag; frag = frag_next(&ip->fragtree, frag)) {
                if (frag->node && frag->node->nref == nref) {
                        fn = frag->node;
                        end = frag->ofs + frag->size;
                        if (!nrfrags++)
                                start = frag->ofs;
                        if (nrfrags == frag->node->frags)
                                break;
                }
        }

        /* It's a pristine node, or dnode (or hole? XXX have we hole nodes?) */
        if (fn) {
                if (CHFS_REF_FLAGS(nref) == CHFS_PRISTINE_NODE_MASK) {
                        ret = chfs_gcollect_pristine(chmp,
                            cheb, ip->chvc, nref);
                        if (!ret) {
                                frag->node->nref = ip->chvc->v;
                        }
                        if (ret != EBADF)
                                goto upnout;
                }
                ret = chfs_gcollect_dnode(chmp, cheb, ip, fn, start, end);
                goto upnout;
        }

        /* Is it a dirent? */
        dbg_gc("find full dirent\n");
        is_dirent = false;
        TAILQ_FOREACH(fd, &ip->dents, fds) {
                if (fd->nref == nref) {
                        is_dirent = true;
                        break;
                }
        }

        if (is_dirent && fd->vno) {
                /* Living dirent. */
                ret = chfs_gcollect_dirent(chmp, cheb, ip, fd);
        } else if (is_dirent) {
                /* Already deleted dirent. */
                ret = chfs_gcollect_deletion_dirent(chmp, cheb, ip, fd);
        } else {
                dbg_gc("Nref at leb #%u offset 0x%08x wasn't in node list"
                    " for ino #%llu\n",
                    nref->nref_lnr, CHFS_GET_OFS(nref->nref_offset),
                    (unsigned long long)ip->ino);
                if (CHFS_REF_OBSOLETE(nref)) {
                        dbg_gc("But it's obsolete so we don't mind"
                            " too much.\n");
                }
        }

upnout:
        return ret;
}

/* chfs_gcollect_vnode - collects a vnode information node */
int
chfs_gcollect_vnode(struct chfs_mount *chmp, struct chfs_inode *ip)
{
        int ret;
        dbg_gc("gcollect_vnode\n");

        /* Simply write the new vnode information to the flash
         * with GC's space allocation */
        ret = chfs_write_flash_vnode(chmp, ip, ALLOC_GC);

        return ret;
}

/* chfs_gcollect_dirent - collects a dirent */
int
chfs_gcollect_dirent(struct chfs_mount *chmp,
    struct chfs_eraseblock *cheb, struct chfs_inode *parent,
    struct chfs_dirent *fd)
{
        struct vnode *vnode = NULL;
        struct chfs_inode *ip;
        dbg_gc("gcollect_dirent\n");

        /* Find vnode. */
        vnode = chfs_vnode_lookup(chmp, fd->vno);

        /* XXX maybe KASSERT or panic on this? */
        if (vnode == NULL) {
                return ENOENT;
        }

        ip = VTOI(vnode);
        vrele(vnode);

        /* Remove and obsolete the previous version. */
        mutex_enter(&chmp->chm_lock_vnocache);
        chfs_remove_and_obsolete(chmp, parent->chvc, fd->nref,
                &parent->chvc->dirents);
        mutex_exit(&chmp->chm_lock_vnocache);

        /* Write the new dirent to the flash. */
        return chfs_write_flash_dirent(chmp,
            parent, ip, fd, fd->vno, ALLOC_GC);
}

/* 
 * chfs_gcollect_deletion_dirent -
 * collects a dirent what was marked as deleted
 */
int
chfs_gcollect_deletion_dirent(struct chfs_mount *chmp,
    struct chfs_eraseblock *cheb, struct chfs_inode *parent,
    struct chfs_dirent *fd)
{
        struct chfs_flash_dirent_node chfdn;
        struct chfs_node_ref *nref;
        size_t retlen, name_len, nref_len;
        uint32_t name_crc;

        int ret;

        dbg_gc("gcollect_deletion_dirent\n");

        /* Check node. */
        name_len = strlen(fd->name);
        name_crc = crc32(0, fd->name, name_len);

        nref_len = chfs_nref_len(chmp, cheb, fd->nref);

        /* XXX This was a noop  (void)chfs_vnode_lookup(chmp, fd->vno); */

        /* Find it in parent dirents. */
        for (nref = parent->chvc->dirents;
             nref != (void*)parent->chvc;
             nref = nref->nref_next) {

                if (!CHFS_REF_OBSOLETE(nref))
                        continue;

                /* if node refs have different length, skip */
                if (chfs_nref_len(chmp, NULL, nref) != nref_len)
                        continue;

                if (CHFS_GET_OFS(nref->nref_offset) ==
                    CHFS_GET_OFS(fd->nref->nref_offset)) {
                        continue;
                }

                /* read it from flash */
                ret = chfs_read_leb(chmp,
                    nref->nref_lnr, (void*)&chfdn, CHFS_GET_OFS(nref->nref_offset),
                    nref_len, &retlen);

                if (ret) {
                        dbg_gc("Read error: %d\n", ret);
                        continue;
                }

                if (retlen != nref_len) {
                        dbg_gc("Error reading node:"
                            " read: %zu instead of: %zu\n", retlen, nref_len);
                        continue;
                }

                /* if node type doesn't match, skip */
                if (le16toh(chfdn.type) != CHFS_NODETYPE_DIRENT)
                        continue;

                /* if crc doesn't match, skip */
                if (le32toh(chfdn.name_crc) != name_crc)
                        continue;

                /* if length of name different, or this is an another deletion
                 * dirent, skip
                 */
                if (chfdn.nsize != name_len || !le64toh(chfdn.vno))
                        continue;

                /* check actual name */
                if (memcmp(chfdn.name, fd->name, name_len))
                        continue;

                mutex_enter(&chmp->chm_lock_vnocache);
                chfs_remove_and_obsolete(chmp, parent->chvc, fd->nref,
                        &parent->chvc->dirents);
                mutex_exit(&chmp->chm_lock_vnocache);
                return chfs_write_flash_dirent(chmp,
                    parent, NULL, fd, fd->vno, ALLOC_GC);
        }

        /* Simply remove it from the parent dirents. */
        TAILQ_REMOVE(&parent->dents, fd, fds);
        chfs_free_dirent(fd);
        return 0;
}

/* chfs_gcollect_dnode - */
int
chfs_gcollect_dnode(struct chfs_mount *chmp,
    struct chfs_eraseblock *orig_cheb, struct chfs_inode *ip,
    struct chfs_full_dnode *fn, uint32_t orig_start, uint32_t orig_end)
{
        struct chfs_node_ref *nref;
        struct chfs_full_dnode *newfn;
        struct chfs_flash_data_node *fdnode;
        int ret = 0, retries = 0;
        uint32_t totlen;
        char *data = NULL;
        struct iovec vec;
        size_t retlen;
        dbg_gc("gcollect_dnode\n");

        //TODO merge frags

        KASSERT(orig_cheb->lnr == fn->nref->nref_lnr);
        totlen = chfs_nref_len(chmp, orig_cheb, fn->nref);
        data = kmem_alloc(totlen, KM_SLEEP);

        /* Read the node from the flash. */
        ret = chfs_read_leb(chmp, fn->nref->nref_lnr, data, fn->nref->nref_offset,
            totlen, &retlen);

        fdnode = (struct chfs_flash_data_node *)data;
        fdnode->version = htole64(++ip->chvc->highest_version);
        fdnode->node_crc = htole32(crc32(0, (uint8_t *)fdnode,
                sizeof(*fdnode) - 4));

        vec.iov_base = (void *)data;
        vec.iov_len = totlen;

retry:
        /* Set the next block where we can write. */
        ret = chfs_reserve_space_gc(chmp, totlen);
        if (ret)
                goto out;

        nref = chfs_alloc_node_ref(chmp->chm_nextblock);
        if (!nref) {
                ret = ENOMEM;
                goto out;
        }

        mutex_enter(&chmp->chm_lock_sizes);

        nref->nref_offset = chmp->chm_ebh->eb_size - chmp->chm_nextblock->free_size;
        KASSERT(nref->nref_offset % 4 == 0);
        chfs_change_size_free(chmp, chmp->chm_nextblock, -totlen);

        /* Write it to the writebuffer. */
        ret = chfs_write_wbuf(chmp, &vec, 1, nref->nref_offset, &retlen);
        if (ret || retlen != totlen) {
                /* error during writing */
                chfs_err("error while writing out to the media\n");
                chfs_err("err: %d | size: %d | retlen : %zu\n",
                    ret, totlen, retlen);
                chfs_change_size_dirty(chmp, chmp->chm_nextblock, totlen);
                if (retries) {
                        ret = EIO;
                        mutex_exit(&chmp->chm_lock_sizes);
                        goto out;
                }

                /* try again */
                retries++;
                mutex_exit(&chmp->chm_lock_sizes);
                goto retry;
        }

        dbg_gc("new nref lnr: %u - offset: %u\n", nref->nref_lnr, nref->nref_offset);

        chfs_change_size_used(chmp, &chmp->chm_blocks[nref->nref_lnr], totlen);
        mutex_exit(&chmp->chm_lock_sizes);
        KASSERT(chmp->chm_blocks[nref->nref_lnr].used_size <= chmp->chm_ebh->eb_size);

        /* Set fields of the new node. */
        newfn = chfs_alloc_full_dnode();
        newfn->nref = nref;
        newfn->ofs = fn->ofs;
        newfn->size = fn->size;
        newfn->frags = 0;

        mutex_enter(&chmp->chm_lock_vnocache);
        /* Remove every part of the old node. */
        chfs_remove_frags_of_node(chmp, &ip->fragtree, fn->nref);
        chfs_remove_and_obsolete(chmp, ip->chvc, fn->nref, &ip->chvc->dnode);

        /* Add the new nref to inode. */
        chfs_add_full_dnode_to_inode(chmp, ip, newfn);
        chfs_add_node_to_list(chmp,
            ip->chvc, newfn->nref, &ip->chvc->dnode);
        mutex_exit(&chmp->chm_lock_vnocache);

out:
        kmem_free(data, totlen);
        return ret;
}