sys/vfs/hammer2: Fix double count of hammer2_iod_file_{read,write}

[dragonfly.git] / sys / vfs / hammer2 / hammer2_strategy.c

/*
 * Copyright (c) 2011-2018 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@dragonflybsd.org>
 * by Venkatesh Srinivas <vsrinivas@dragonflybsd.org>
 * by Daniel Flores (GSOC 2013 - mentored by Matthew Dillon, compression)
 *
 * 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.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 * This module handles low level logical file I/O (strategy) which backs
 * the logical buffer cache.
 *
 * [De]compression, zero-block, check codes, and buffer cache operations
 * for file data is handled here.
 *
 * Live dedup makes its home here as well.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/buf.h>
#include <sys/proc.h>
#include <sys/mount.h>
#include <sys/vnode.h>
#include <sys/objcache.h>

#include "hammer2.h"
#include "hammer2_lz4.h"

#include "zlib/hammer2_zlib.h"

struct objcache *cache_buffer_read;
struct objcache *cache_buffer_write;

/*
 * Strategy code (async logical file buffer I/O from system)
 *
 * Except for the transaction init (which should normally not block),
 * we essentially run the strategy operation asynchronously via a XOP.
 *
 * WARNING! The XOP deals with buffer synchronization.  It is not synchronized
 *          to the current cpu.
 *
 * XXX This isn't supposed to be able to deadlock against vfs_sync vfsync()
 *     calls but it has in the past when multiple flushes are queued.
 *
 * XXX We currently terminate the transaction once we get a quorum, otherwise
 *     the frontend can stall, but this can leave the remaining nodes with
 *     a potential flush conflict.  We need to delay flushes on those nodes
 *     until running transactions complete separately from the normal
 *     transaction sequencing.  FIXME TODO.
 */
static int hammer2_strategy_read(struct vop_strategy_args *ap);
static int hammer2_strategy_write(struct vop_strategy_args *ap);
static void hammer2_strategy_read_completion(hammer2_chain_t *focus,
                                const char *data, struct bio *bio);

static hammer2_off_t hammer2_dedup_lookup(hammer2_dev_t *hmp,
                        char **datap, int pblksize);

int
hammer2_vop_strategy(struct vop_strategy_args *ap)
{
        struct bio *biop;
        struct buf *bp;
        int error;

        biop = ap->a_bio;
        bp = biop->bio_buf;

        switch(bp->b_cmd) {
        case BUF_CMD_READ:
                error = hammer2_strategy_read(ap);
                break;
        case BUF_CMD_WRITE:
                error = hammer2_strategy_write(ap);
                break;
        default:
                bp->b_error = error = EINVAL;
                bp->b_flags |= B_ERROR;
                biodone(biop);
                break;
        }
        return (error);
}

/*
 * Return the largest contiguous physical disk range for the logical
 * request, in bytes.
 *
 * (struct vnode *vp, off_t loffset, off_t *doffsetp, int *runp, int *runb)
 *
 * Basically disabled, the logical buffer write thread has to deal with
 * buffers one-at-a-time.  Note that this should not prevent cluster_read()
 * from reading-ahead, it simply prevents it from trying form a single
 * cluster buffer for the logical request.  H2 already uses 64KB buffers!
 */
int
hammer2_vop_bmap(struct vop_bmap_args *ap)
{
        *ap->a_doffsetp = NOOFFSET;
        if (ap->a_runp)
                *ap->a_runp = 0;
        if (ap->a_runb)
                *ap->a_runb = 0;
        return (EOPNOTSUPP);
}

/****************************************************************************
 *                              READ SUPPORT                                *
 ****************************************************************************/
/*
 * Callback used in read path in case that a block is compressed with LZ4.
 */
static
void
hammer2_decompress_LZ4_callback(const char *data, u_int bytes, struct bio *bio)
{
        struct buf *bp;
        char *compressed_buffer;
        int compressed_size;
        int result;

        bp = bio->bio_buf;

#if 0
        if bio->bio_caller_info2.index &&
              bio->bio_caller_info1.uvalue32 !=
              crc32(bp->b_data, bp->b_bufsize) --- return error
#endif

        KKASSERT(bp->b_bufsize <= HAMMER2_PBUFSIZE);
        compressed_size = *(const int *)data;
        KKASSERT((uint32_t)compressed_size <= bytes - sizeof(int));

        compressed_buffer = objcache_get(cache_buffer_read, M_INTWAIT);
        result = LZ4_decompress_safe(__DECONST(char *, &data[sizeof(int)]),
                                     compressed_buffer,
                                     compressed_size,
                                     bp->b_bufsize);
        if (result < 0) {
                kprintf("READ PATH: Error during decompression."
                        "bio %016jx/%d\n",
                        (intmax_t)bio->bio_offset, bytes);
                /* make sure it isn't random garbage */
                bzero(compressed_buffer, bp->b_bufsize);
        }
        KKASSERT(result <= bp->b_bufsize);
        bcopy(compressed_buffer, bp->b_data, bp->b_bufsize);
        if (result < bp->b_bufsize)
                bzero(bp->b_data + result, bp->b_bufsize - result);
        objcache_put(cache_buffer_read, compressed_buffer);
        bp->b_resid = 0;
        bp->b_flags |= B_AGE;
}

/*
 * Callback used in read path in case that a block is compressed with ZLIB.
 * It is almost identical to LZ4 callback, so in theory they can be unified,
 * but we didn't want to make changes in bio structure for that.
 */
static
void
hammer2_decompress_ZLIB_callback(const char *data, u_int bytes, struct bio *bio)
{
        struct buf *bp;
        char *compressed_buffer;
        z_stream strm_decompress;
        int result;
        int ret;

        bp = bio->bio_buf;

        KKASSERT(bp->b_bufsize <= HAMMER2_PBUFSIZE);
        strm_decompress.avail_in = 0;
        strm_decompress.next_in = Z_NULL;

        ret = inflateInit(&strm_decompress);

        if (ret != Z_OK)
                kprintf("HAMMER2 ZLIB: Fatal error in inflateInit.\n");

        compressed_buffer = objcache_get(cache_buffer_read, M_INTWAIT);
        strm_decompress.next_in = __DECONST(char *, data);

        /* XXX supply proper size, subset of device bp */
        strm_decompress.avail_in = bytes;
        strm_decompress.next_out = compressed_buffer;
        strm_decompress.avail_out = bp->b_bufsize;

        ret = inflate(&strm_decompress, Z_FINISH);
        if (ret != Z_STREAM_END) {
                kprintf("HAMMER2 ZLIB: Fatal error during decompression.\n");
                bzero(compressed_buffer, bp->b_bufsize);
        }
        bcopy(compressed_buffer, bp->b_data, bp->b_bufsize);
        result = bp->b_bufsize - strm_decompress.avail_out;
        if (result < bp->b_bufsize)
                bzero(bp->b_data + result, strm_decompress.avail_out);
        objcache_put(cache_buffer_read, compressed_buffer);
        ret = inflateEnd(&strm_decompress);

        bp->b_resid = 0;
        bp->b_flags |= B_AGE;
}

/*
 * Logical buffer I/O, async read.
 */
static
int
hammer2_strategy_read(struct vop_strategy_args *ap)
{
        hammer2_xop_strategy_t *xop;
        struct bio *bio;
        hammer2_inode_t *ip;
        hammer2_key_t lbase;

        bio = ap->a_bio;
        ip = VTOI(ap->a_vp);

        lbase = bio->bio_offset;
        KKASSERT(((int)lbase & HAMMER2_PBUFMASK) == 0);

        xop = hammer2_xop_alloc(ip, HAMMER2_XOP_STRATEGY);
        xop->finished = 0;
        xop->bio = bio;
        xop->lbase = lbase;
        hammer2_mtx_init(&xop->lock, "h2bior");
        hammer2_xop_start(&xop->head, &hammer2_strategy_read_desc);
        /* asynchronous completion */

        return(0);
}

/*
 * Per-node XOP (threaded), do a synchronous lookup of the chain and
 * its data.  The frontend is asynchronous, so we are also responsible
 * for racing to terminate the frontend.
 */
void
hammer2_xop_strategy_read(hammer2_xop_t *arg, void *scratch, int clindex)
{
        hammer2_xop_strategy_t *xop = &arg->xop_strategy;
        hammer2_chain_t *parent;
        hammer2_chain_t *chain;
        hammer2_chain_t *focus;
        hammer2_key_t key_dummy;
        hammer2_key_t lbase;
        struct bio *bio;
        struct buf *bp;
        const char *data;
        int error;

        /*
         * Note that we can race completion of the bio supplied by
         * the front-end so we cannot access it until we determine
         * that we are the ones finishing it up.
         */
        lbase = xop->lbase;

        /*
         * This is difficult to optimize.  The logical buffer might be
         * partially dirty (contain dummy zero-fill pages), which would
         * mess up our crc calculation if we were to try a direct read.
         * So for now we always double-buffer through the underlying
         * storage.
         *
         * If not for the above problem we could conditionalize on
         * (1) 64KB buffer, (2) one chain (not multi-master) and
         * (3) !hammer2_double_buffer, and issue a direct read into the
         * logical buffer.
         */
        parent = hammer2_inode_chain(xop->head.ip1, clindex,
                                     HAMMER2_RESOLVE_ALWAYS |
                                     HAMMER2_RESOLVE_SHARED);
        if (parent) {
                chain = hammer2_chain_lookup(&parent, &key_dummy,
                                             lbase, lbase,
                                             &error,
                                             HAMMER2_LOOKUP_ALWAYS |
                                             HAMMER2_LOOKUP_SHARED);
                if (chain)
                        error = chain->error;
        } else {
                error = HAMMER2_ERROR_EIO;
                chain = NULL;
        }
        error = hammer2_xop_feed(&xop->head, chain, clindex, error);
        if (chain) {
                hammer2_chain_unlock(chain);
                hammer2_chain_drop(chain);
        }
        if (parent) {
                hammer2_chain_unlock(parent);
                hammer2_chain_drop(parent);
        }
        chain = NULL;   /* safety */
        parent = NULL;  /* safety */

        /*
         * Race to finish the frontend.  First-to-complete.  bio is only
         * valid if we are determined to be the ones able to complete
         * the operation.
         */
        if (xop->finished)
                return;
        hammer2_mtx_ex(&xop->lock);
        if (xop->finished) {
                hammer2_mtx_unlock(&xop->lock);
                return;
        }
        bio = xop->bio;
        bp = bio->bio_buf;
        bkvasync(bp);

        /*
         * Async operation has not completed and we now own the lock.
         * Determine if we can complete the operation by issuing the
         * frontend collection non-blocking.
         *
         * H2 double-buffers the data, setting B_NOTMETA on the logical
         * buffer hints to the OS that the logical buffer should not be
         * swapcached (since the device buffer can be).
         *
         * Also note that even for compressed data we would rather the
         * kernel cache/swapcache device buffers more and (decompressed)
         * logical buffers less, since that will significantly improve
         * the amount of end-user data that can be cached.
         *
         * NOTE: The chain->data for xop->head.cluster.focus will be
         *       synchronized to the current cpu by xop_collect(),
         *       but other chains in the cluster might not be.
         */
        error = hammer2_xop_collect(&xop->head, HAMMER2_XOP_COLLECT_NOWAIT);

        switch(error) {
        case 0:
                xop->finished = 1;
                hammer2_mtx_unlock(&xop->lock);
                bp->b_flags |= B_NOTMETA;
                focus = xop->head.cluster.focus;
                data = hammer2_xop_gdata(&xop->head)->buf;
                hammer2_strategy_read_completion(focus, data, xop->bio);
                hammer2_xop_pdata(&xop->head);
                biodone(bio);
                hammer2_xop_retire(&xop->head, HAMMER2_XOPMASK_VOP);
                break;
        case HAMMER2_ERROR_ENOENT:
                xop->finished = 1;
                hammer2_mtx_unlock(&xop->lock);
                bp->b_flags |= B_NOTMETA;
                bp->b_resid = 0;
                bp->b_error = 0;
                bzero(bp->b_data, bp->b_bcount);
                biodone(bio);
                hammer2_xop_retire(&xop->head, HAMMER2_XOPMASK_VOP);
                break;
        case HAMMER2_ERROR_EINPROGRESS:
                hammer2_mtx_unlock(&xop->lock);
                break;
        default:
                kprintf("xop_strategy_read: error %08x loff=%016jx\n",
                        error, (intmax_t)bp->b_loffset);
                xop->finished = 1;
                hammer2_mtx_unlock(&xop->lock);
                bp->b_flags |= B_ERROR;
                bp->b_error = EIO;
                biodone(bio);
                hammer2_xop_retire(&xop->head, HAMMER2_XOPMASK_VOP);
                break;
        }
}

static
void
hammer2_strategy_read_completion(hammer2_chain_t *focus, const char *data,
                                 struct bio *bio)
{
        struct buf *bp = bio->bio_buf;

        if (focus->bref.type == HAMMER2_BREF_TYPE_INODE) {
                /*
                 * Copy from in-memory inode structure.
                 */
                bcopy(((const hammer2_inode_data_t *)data)->u.data,
                      bp->b_data, HAMMER2_EMBEDDED_BYTES);
                bzero(bp->b_data + HAMMER2_EMBEDDED_BYTES,
                      bp->b_bcount - HAMMER2_EMBEDDED_BYTES);
                bp->b_resid = 0;
                bp->b_error = 0;
        } else if (focus->bref.type == HAMMER2_BREF_TYPE_DATA) {
                /*
                 * Data is on-media, record for live dedup.  Release the
                 * chain (try to free it) when done.  The data is still
                 * cached by both the buffer cache in front and the
                 * block device behind us.  This leaves more room in the
                 * LRU chain cache for meta-data chains which we really
                 * want to retain.
                 *
                 * NOTE: Deduplication cannot be safely recorded for
                 *       records without a check code.
                 */
                hammer2_dedup_record(focus, NULL, data);
                atomic_set_int(&focus->flags, HAMMER2_CHAIN_RELEASE);

                /*
                 * Decompression and copy.
                 */
                switch (HAMMER2_DEC_COMP(focus->bref.methods)) {
                case HAMMER2_COMP_LZ4:
                        hammer2_decompress_LZ4_callback(data, focus->bytes,
                                                        bio);
                        /* b_resid set by call */
                        break;
                case HAMMER2_COMP_ZLIB:
                        hammer2_decompress_ZLIB_callback(data, focus->bytes,
                                                         bio);
                        /* b_resid set by call */
                        break;
                case HAMMER2_COMP_NONE:
                        KKASSERT(focus->bytes <= bp->b_bcount);
                        bcopy(data, bp->b_data, focus->bytes);
                        if (focus->bytes < bp->b_bcount) {
                                bzero(bp->b_data + focus->bytes,
                                      bp->b_bcount - focus->bytes);
                        }
                        bp->b_resid = 0;
                        bp->b_error = 0;
                        break;
                default:
                        panic("hammer2_strategy_read_completion: "
                              "unknown compression type");
                }
        } else {
                panic("hammer2_strategy_read_completion: unknown bref type");
        }
}

/****************************************************************************
 *                              WRITE SUPPORT                               *
 ****************************************************************************/

/*
 * Functions for compression in threads,
 * from hammer2_vnops.c
 */
static void hammer2_write_file_core(char *data, hammer2_inode_t *ip,
                                hammer2_chain_t **parentp,
                                hammer2_key_t lbase, int ioflag, int pblksize,
                                hammer2_tid_t mtid, int *errorp);
static void hammer2_compress_and_write(char *data, hammer2_inode_t *ip,
                                hammer2_chain_t **parentp,
                                hammer2_key_t lbase, int ioflag, int pblksize,
                                hammer2_tid_t mtid, int *errorp,
                                int comp_algo, int check_algo);
static void hammer2_zero_check_and_write(char *data, hammer2_inode_t *ip,
                                hammer2_chain_t **parentp,
                                hammer2_key_t lbase, int ioflag, int pblksize,
                                hammer2_tid_t mtid, int *errorp,
                                int check_algo);
static int test_block_zeros(const char *buf, size_t bytes);
static void zero_write(char *data, hammer2_inode_t *ip,
                                hammer2_chain_t **parentp,
                                hammer2_key_t lbase,
                                hammer2_tid_t mtid, int *errorp);
static void hammer2_write_bp(hammer2_chain_t *chain, char *data,
                                int ioflag, int pblksize,
                                hammer2_tid_t mtid, int *errorp,
                                int check_algo);

int
hammer2_strategy_write(struct vop_strategy_args *ap)
{
        hammer2_xop_strategy_t *xop;
        hammer2_pfs_t *pmp;
        struct bio *bio;
        hammer2_inode_t *ip;

        bio = ap->a_bio;
        ip = VTOI(ap->a_vp);
        pmp = ip->pmp;

        atomic_set_int(&ip->flags, HAMMER2_INODE_DIRTYDATA);
        hammer2_lwinprog_ref(pmp);
        hammer2_trans_assert_strategy(pmp);
        hammer2_trans_init(pmp, HAMMER2_TRANS_BUFCACHE);

        xop = hammer2_xop_alloc(ip, HAMMER2_XOP_MODIFYING |
                                    HAMMER2_XOP_STRATEGY);
        xop->finished = 0;
        xop->bio = bio;
        xop->lbase = bio->bio_offset;
        hammer2_mtx_init(&xop->lock, "h2biow");
        hammer2_xop_start(&xop->head, &hammer2_strategy_write_desc);
        /* asynchronous completion */

        hammer2_lwinprog_wait(pmp, hammer2_flush_pipe);

        return(0);
}

/*
 * Per-node XOP (threaded).  Write the logical buffer to the media.
 *
 * This is a bit problematic because there may be multiple target and
 * any of them may be able to release the bp.  In addition, if our
 * particulr target is offline we don't want to block the bp (and thus
 * the frontend).  To accomplish this we copy the data to the per-thr
 * scratch buffer.
 */
void
hammer2_xop_strategy_write(hammer2_xop_t *arg, void *scratch, int clindex)
{
        hammer2_xop_strategy_t *xop = &arg->xop_strategy;
        hammer2_chain_t *parent;
        hammer2_key_t lbase;
        hammer2_inode_t *ip;
        struct bio *bio;
        struct buf *bp;
        int error;
        int lblksize;
        int pblksize;
        char *bio_data;

        /*
         * We can only access the bp/bio if the frontend has not yet
         * completed.
         */
        if (xop->finished)
                return;
        hammer2_mtx_sh(&xop->lock);
        if (xop->finished) {
                hammer2_mtx_unlock(&xop->lock);
                return;
        }

        lbase = xop->lbase;
        bio = xop->bio;                 /* ephermal */
        bp = bio->bio_buf;              /* ephermal */
        ip = xop->head.ip1;             /* retained by ref */
        bio_data = scratch;

        /* hammer2_trans_init(parent->hmp->spmp, HAMMER2_TRANS_BUFCACHE); */

        lblksize = hammer2_calc_logical(ip, bio->bio_offset, &lbase, NULL);
        pblksize = hammer2_calc_physical(ip, lbase);
        bkvasync(bp);
        KKASSERT(lblksize <= MAXPHYS);
        bcopy(bp->b_data, bio_data, lblksize);

        hammer2_mtx_unlock(&xop->lock);
        bp = NULL;      /* safety, illegal to access after unlock */
        bio = NULL;     /* safety, illegal to access after unlock */

        /*
         * Actual operation
         */
        parent = hammer2_inode_chain(ip, clindex, HAMMER2_RESOLVE_ALWAYS);
        hammer2_write_file_core(bio_data, ip, &parent,
                                lbase, IO_ASYNC, pblksize,
                                xop->head.mtid, &error);
        if (parent) {
                hammer2_chain_unlock(parent);
                hammer2_chain_drop(parent);
                parent = NULL;  /* safety */
        }
        hammer2_xop_feed(&xop->head, NULL, clindex, error);

        /*
         * Try to complete the operation on behalf of the front-end.
         */
        if (xop->finished)
                return;
        hammer2_mtx_ex(&xop->lock);
        if (xop->finished) {
                hammer2_mtx_unlock(&xop->lock);
                return;
        }

        /*
         * Async operation has not completed and we now own the lock.
         * Determine if we can complete the operation by issuing the
         * frontend collection non-blocking.
         *
         * H2 double-buffers the data, setting B_NOTMETA on the logical
         * buffer hints to the OS that the logical buffer should not be
         * swapcached (since the device buffer can be).
         */
        error = hammer2_xop_collect(&xop->head, HAMMER2_XOP_COLLECT_NOWAIT);

        if (error == HAMMER2_ERROR_EINPROGRESS) {
                hammer2_mtx_unlock(&xop->lock);
                return;
        }

        /*
         * Async operation has completed.
         */
        xop->finished = 1;
        hammer2_mtx_unlock(&xop->lock);

        bio = xop->bio;         /* now owned by us */
        bp = bio->bio_buf;      /* now owned by us */

        if (error == HAMMER2_ERROR_ENOENT || error == 0) {
                bp->b_flags |= B_NOTMETA;
                bp->b_resid = 0;
                bp->b_error = 0;
                biodone(bio);
        } else {
                kprintf("xop_strategy_write: error %d loff=%016jx\n",
                        error, (intmax_t)bp->b_loffset);
                bp->b_flags |= B_ERROR;
                bp->b_error = EIO;
                biodone(bio);
        }
        hammer2_xop_retire(&xop->head, HAMMER2_XOPMASK_VOP);
        hammer2_trans_assert_strategy(ip->pmp);
        hammer2_lwinprog_drop(ip->pmp);
        hammer2_trans_done(ip->pmp, HAMMER2_TRANS_BUFCACHE);
}

/*
 * Wait for pending I/O to complete
 */
void
hammer2_bioq_sync(hammer2_pfs_t *pmp)
{
        hammer2_lwinprog_wait(pmp, 0);
}

/*
 * Assign physical storage at (cparent, lbase), returning a suitable chain
 * and setting *errorp appropriately.
 *
 * If no error occurs, the returned chain will be in a modified state.
 *
 * If an error occurs, the returned chain may or may not be NULL.  If
 * not-null any chain->error (if not 0) will also be rolled up into *errorp.
 * So the caller only needs to test *errorp.
 *
 * cparent can wind up being anything.
 *
 * If datap is not NULL, *datap points to the real data we intend to write.
 * If we can dedup the storage location we set *datap to NULL to indicate
 * to the caller that a dedup occurred.
 *
 * NOTE: Special case for data embedded in inode.
 */
static
hammer2_chain_t *
hammer2_assign_physical(hammer2_inode_t *ip, hammer2_chain_t **parentp,
                        hammer2_key_t lbase, int pblksize,
                        hammer2_tid_t mtid, char **datap, int *errorp)
{
        hammer2_chain_t *chain;
        hammer2_key_t key_dummy;
        hammer2_off_t dedup_off;
        int pradix = hammer2_getradix(pblksize);

        /*
         * Locate the chain associated with lbase, return a locked chain.
         * However, do not instantiate any data reference (which utilizes a
         * device buffer) because we will be using direct IO via the
         * logical buffer cache buffer.
         */
        KKASSERT(pblksize >= HAMMER2_ALLOC_MIN);

        chain = hammer2_chain_lookup(parentp, &key_dummy,
                                     lbase, lbase,
                                     errorp,
                                     HAMMER2_LOOKUP_NODATA);

        /*
         * The lookup code should not return a DELETED chain to us, unless
         * its a short-file embedded in the inode.  Then it is possible for
         * the lookup to return a deleted inode.
         */
        if (chain && (chain->flags & HAMMER2_CHAIN_DELETED) &&
            chain->bref.type != HAMMER2_BREF_TYPE_INODE) {
                kprintf("assign physical deleted chain @ "
                        "%016jx (%016jx.%02x) ip %016jx\n",
                        lbase, chain->bref.data_off, chain->bref.type,
                        ip->meta.inum);
                Debugger("bleh");
        }

        if (chain == NULL) {
                /*
                 * We found a hole, create a new chain entry.
                 *
                 * NOTE: DATA chains are created without device backing
                 *       store (nor do we want any).
                 */
                dedup_off = hammer2_dedup_lookup((*parentp)->hmp, datap,
                                                 pblksize);
                *errorp |= hammer2_chain_create(parentp, &chain, NULL, ip->pmp,
                                       HAMMER2_ENC_CHECK(ip->meta.check_algo) |
                                       HAMMER2_ENC_COMP(HAMMER2_COMP_NONE),
                                                lbase, HAMMER2_PBUFRADIX,
                                                HAMMER2_BREF_TYPE_DATA,
                                                pblksize, mtid,
                                                dedup_off, 0);
                if (chain == NULL)
                        goto failed;
                /*ip->delta_dcount += pblksize;*/
        } else if (chain->error == 0) {
                switch (chain->bref.type) {
                case HAMMER2_BREF_TYPE_INODE:
                        /*
                         * The data is embedded in the inode, which requires
                         * a bit more finess.
                         */
                        *errorp |= hammer2_chain_modify_ip(ip, chain, mtid, 0);
                        break;
                case HAMMER2_BREF_TYPE_DATA:
                        dedup_off = hammer2_dedup_lookup(chain->hmp, datap,
                                                         pblksize);
                        if (chain->bytes != pblksize) {
                                *errorp |= hammer2_chain_resize(chain,
                                                     mtid, dedup_off,
                                                     pradix,
                                                     HAMMER2_MODIFY_OPTDATA);
                                if (*errorp)
                                        break;
                        }

                        /*
                         * DATA buffers must be marked modified whether the
                         * data is in a logical buffer or not.  We also have
                         * to make this call to fixup the chain data pointers
                         * after resizing in case this is an encrypted or
                         * compressed buffer.
                         */
                        *errorp |= hammer2_chain_modify(chain, mtid, dedup_off,
                                                        HAMMER2_MODIFY_OPTDATA);
                        break;
                default:
                        panic("hammer2_assign_physical: bad type");
                        /* NOT REACHED */
                        break;
                }
        } else {
                *errorp = chain->error;
        }
        atomic_set_int(&ip->flags, HAMMER2_INODE_DIRTYDATA);
failed:
        return (chain);
}

/*
 * hammer2_write_file_core()
 *
 * The core write function which determines which path to take
 * depending on compression settings.  We also have to locate the
 * related chains so we can calculate and set the check data for
 * the blockref.
 */
static
void
hammer2_write_file_core(char *data, hammer2_inode_t *ip,
                        hammer2_chain_t **parentp,
                        hammer2_key_t lbase, int ioflag, int pblksize,
                        hammer2_tid_t mtid, int *errorp)
{
        hammer2_chain_t *chain;
        char *bdata;

        *errorp = 0;

        switch(HAMMER2_DEC_ALGO(ip->meta.comp_algo)) {
        case HAMMER2_COMP_NONE:
                /*
                 * We have to assign physical storage to the buffer
                 * we intend to dirty or write now to avoid deadlocks
                 * in the strategy code later.
                 *
                 * This can return NOOFFSET for inode-embedded data.
                 * The strategy code will take care of it in that case.
                 */
                bdata = data;
                chain = hammer2_assign_physical(ip, parentp, lbase, pblksize,
                                                mtid, &bdata, errorp);
                if (*errorp) {
                        /* skip modifications */
                } else if (chain->bref.type == HAMMER2_BREF_TYPE_INODE) {
                        hammer2_inode_data_t *wipdata;

                        wipdata = &chain->data->ipdata;
                        KKASSERT(wipdata->meta.op_flags &
                                 HAMMER2_OPFLAG_DIRECTDATA);
                        bcopy(data, wipdata->u.data, HAMMER2_EMBEDDED_BYTES);
                        ++hammer2_iod_file_wembed;
                } else if (bdata == NULL) {
                        /*
                         * Copy of data already present on-media.
                         */
                        chain->bref.methods =
                                HAMMER2_ENC_COMP(HAMMER2_COMP_NONE) +
                                HAMMER2_ENC_CHECK(ip->meta.check_algo);
                        hammer2_chain_setcheck(chain, data);
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                } else {
                        hammer2_write_bp(chain, data, ioflag, pblksize,
                                         mtid, errorp, ip->meta.check_algo);
                }
                if (chain) {
                        hammer2_chain_unlock(chain);
                        hammer2_chain_drop(chain);
                }
                break;
        case HAMMER2_COMP_AUTOZERO:
                /*
                 * Check for zero-fill only
                 */
                hammer2_zero_check_and_write(data, ip, parentp,
                                             lbase, ioflag, pblksize,
                                             mtid, errorp,
                                             ip->meta.check_algo);
                break;
        case HAMMER2_COMP_LZ4:
        case HAMMER2_COMP_ZLIB:
        default:
                /*
                 * Check for zero-fill and attempt compression.
                 */
                hammer2_compress_and_write(data, ip, parentp,
                                           lbase, ioflag, pblksize,
                                           mtid, errorp,
                                           ip->meta.comp_algo,
                                           ip->meta.check_algo);
                break;
        }
}

/*
 * Helper
 *
 * Generic function that will perform the compression in compression
 * write path. The compression algorithm is determined by the settings
 * obtained from inode.
 */
static
void
hammer2_compress_and_write(char *data, hammer2_inode_t *ip,
        hammer2_chain_t **parentp,
        hammer2_key_t lbase, int ioflag, int pblksize,
        hammer2_tid_t mtid, int *errorp, int comp_algo, int check_algo)
{
        hammer2_chain_t *chain;
        int comp_size;
        int comp_block_size;
        char *comp_buffer;
        char *bdata;

        /*
         * An all-zeros write creates a hole unless the check code
         * is disabled.  When the check code is disabled all writes
         * are done in-place, including any all-zeros writes.
         *
         * NOTE: A snapshot will still force a copy-on-write
         *       (see the HAMMER2_CHECK_NONE in hammer2_chain.c).
         */
        if (check_algo != HAMMER2_CHECK_NONE &&
            test_block_zeros(data, pblksize)) {
                zero_write(data, ip, parentp, lbase, mtid, errorp);
                return;
        }

        /*
         * Compression requested.  Try to compress the block.  We store
         * the data normally if we cannot sufficiently compress it.
         *
         * We have a heuristic to detect files which are mostly
         * uncompressable and avoid the compression attempt in that
         * case.  If the compression heuristic is turned off, we always
         * try to compress.
         */
        comp_size = 0;
        comp_buffer = NULL;

        KKASSERT(pblksize / 2 <= 32768);

        if (ip->comp_heuristic < 8 || (ip->comp_heuristic & 7) == 0 ||
            hammer2_always_compress) {
                z_stream strm_compress;
                int comp_level;
                int ret;

                switch(HAMMER2_DEC_ALGO(comp_algo)) {
                case HAMMER2_COMP_LZ4:
                        /*
                         * We need to prefix with the size, LZ4
                         * doesn't do it for us.  Add the related
                         * overhead.
                         *
                         * NOTE: The LZ4 code seems to assume at least an
                         *       8-byte buffer size granularity and may
                         *       overrun the buffer if given a 4-byte
                         *       granularity.
                         */
                        comp_buffer = objcache_get(cache_buffer_write,
                                                   M_INTWAIT);
                        comp_size = LZ4_compress_limitedOutput(
                                        data,
                                        &comp_buffer[sizeof(int)],
                                        pblksize,
                                        pblksize / 2 - sizeof(int64_t));
                        *(int *)comp_buffer = comp_size;
                        if (comp_size)
                                comp_size += sizeof(int);
                        break;
                case HAMMER2_COMP_ZLIB:
                        comp_level = HAMMER2_DEC_LEVEL(comp_algo);
                        if (comp_level == 0)
                                comp_level = 6; /* default zlib compression */
                        else if (comp_level < 6)
                                comp_level = 6;
                        else if (comp_level > 9)
                                comp_level = 9;
                        ret = deflateInit(&strm_compress, comp_level);
                        if (ret != Z_OK) {
                                kprintf("HAMMER2 ZLIB: fatal error "
                                        "on deflateInit.\n");
                        }

                        comp_buffer = objcache_get(cache_buffer_write,
                                                   M_INTWAIT);
                        strm_compress.next_in = data;
                        strm_compress.avail_in = pblksize;
                        strm_compress.next_out = comp_buffer;
                        strm_compress.avail_out = pblksize / 2;
                        ret = deflate(&strm_compress, Z_FINISH);
                        if (ret == Z_STREAM_END) {
                                comp_size = pblksize / 2 -
                                            strm_compress.avail_out;
                        } else {
                                comp_size = 0;
                        }
                        ret = deflateEnd(&strm_compress);
                        break;
                default:
                        kprintf("Error: Unknown compression method.\n");
                        kprintf("Comp_method = %d.\n", comp_algo);
                        break;
                }
        }

        if (comp_size == 0) {
                /*
                 * compression failed or turned off
                 */
                comp_block_size = pblksize;     /* safety */
                if (++ip->comp_heuristic > 128)
                        ip->comp_heuristic = 8;
        } else {
                /*
                 * compression succeeded
                 */
                ip->comp_heuristic = 0;
                if (comp_size <= 1024) {
                        comp_block_size = 1024;
                } else if (comp_size <= 2048) {
                        comp_block_size = 2048;
                } else if (comp_size <= 4096) {
                        comp_block_size = 4096;
                } else if (comp_size <= 8192) {
                        comp_block_size = 8192;
                } else if (comp_size <= 16384) {
                        comp_block_size = 16384;
                } else if (comp_size <= 32768) {
                        comp_block_size = 32768;
                } else {
                        panic("hammer2: WRITE PATH: "
                              "Weird comp_size value.");
                        /* NOT REACHED */
                        comp_block_size = pblksize;
                }

                /*
                 * Must zero the remainder or dedup (which operates on a
                 * physical block basis) will not find matches.
                 */
                if (comp_size < comp_block_size) {
                        bzero(comp_buffer + comp_size,
                              comp_block_size - comp_size);
                }
        }

        /*
         * Assign physical storage, bdata will be set to NULL if a live-dedup
         * was successful.
         */
        bdata = comp_size ? comp_buffer : data;
        chain = hammer2_assign_physical(ip, parentp, lbase, comp_block_size,
                                        mtid, &bdata, errorp);

        if (*errorp) {
                goto done;
        }

        if (chain->bref.type == HAMMER2_BREF_TYPE_INODE) {
                hammer2_inode_data_t *wipdata;

                *errorp = hammer2_chain_modify_ip(ip, chain, mtid, 0);
                if (*errorp == 0) {
                        wipdata = &chain->data->ipdata;
                        KKASSERT(wipdata->meta.op_flags &
                                 HAMMER2_OPFLAG_DIRECTDATA);
                        bcopy(data, wipdata->u.data, HAMMER2_EMBEDDED_BYTES);
                        ++hammer2_iod_file_wembed;
                }
        } else if (bdata == NULL) {
                /*
                 * Live deduplication, a copy of the data is already present
                 * on the media.
                 */
                if (comp_size) {
                        chain->bref.methods =
                                HAMMER2_ENC_COMP(comp_algo) +
                                HAMMER2_ENC_CHECK(check_algo);
                } else {
                        chain->bref.methods =
                                HAMMER2_ENC_COMP(
                                        HAMMER2_COMP_NONE) +
                                HAMMER2_ENC_CHECK(check_algo);
                }
                bdata = comp_size ? comp_buffer : data;
                hammer2_chain_setcheck(chain, bdata);
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
        } else {
                hammer2_io_t *dio;

                KKASSERT(chain->flags & HAMMER2_CHAIN_MODIFIED);

                switch(chain->bref.type) {
                case HAMMER2_BREF_TYPE_INODE:
                        panic("hammer2_compress_and_write: unexpected inode\n");
                        break;
                case HAMMER2_BREF_TYPE_DATA:
                        /*
                         * Optimize out the read-before-write
                         * if possible.
                         */
                        *errorp = hammer2_io_newnz(chain->hmp,
                                                   chain->bref.type,
                                                   chain->bref.data_off,
                                                   chain->bytes,
                                                   &dio);
                        if (*errorp) {
                                hammer2_io_brelse(&dio);
                                kprintf("hammer2: WRITE PATH: "
                                        "dbp bread error\n");
                                break;
                        }
                        bdata = hammer2_io_data(dio, chain->bref.data_off);

                        /*
                         * When loading the block make sure we don't
                         * leave garbage after the compressed data.
                         */
                        if (comp_size) {
                                chain->bref.methods =
                                        HAMMER2_ENC_COMP(comp_algo) +
                                        HAMMER2_ENC_CHECK(check_algo);
                                bcopy(comp_buffer, bdata, comp_block_size);
                        } else {
                                chain->bref.methods =
                                        HAMMER2_ENC_COMP(
                                                HAMMER2_COMP_NONE) +
                                        HAMMER2_ENC_CHECK(check_algo);
                                bcopy(data, bdata, pblksize);
                        }

                        /*
                         * The flush code doesn't calculate check codes for
                         * file data (doing so can result in excessive I/O),
                         * so we do it here.
                         */
                        hammer2_chain_setcheck(chain, bdata);

                        /*
                         * Device buffer is now valid, chain is no longer in
                         * the initial state.
                         *
                         * (No blockref table worries with file data)
                         */
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                        hammer2_dedup_record(chain, dio, bdata);

                        /* Now write the related bdp. */
                        if (ioflag & IO_SYNC) {
                                /*
                                 * Synchronous I/O requested.
                                 */
                                hammer2_io_bwrite(&dio);
                        /*
                        } else if ((ioflag & IO_DIRECT) &&
                                   loff + n == pblksize) {
                                hammer2_io_bdwrite(&dio);
                        */
                        } else if (ioflag & IO_ASYNC) {
                                hammer2_io_bawrite(&dio);
                        } else {
                                hammer2_io_bdwrite(&dio);
                        }
                        break;
                default:
                        panic("hammer2_compress_and_write: bad chain type %d\n",
                                chain->bref.type);
                        /* NOT REACHED */
                        break;
                }
        }
done:
        if (chain) {
                hammer2_chain_unlock(chain);
                hammer2_chain_drop(chain);
        }
        if (comp_buffer)
                objcache_put(cache_buffer_write, comp_buffer);
}

/*
 * Helper
 *
 * Function that performs zero-checking and writing without compression,
 * it corresponds to default zero-checking path.
 */
static
void
hammer2_zero_check_and_write(char *data, hammer2_inode_t *ip,
        hammer2_chain_t **parentp,
        hammer2_key_t lbase, int ioflag, int pblksize,
        hammer2_tid_t mtid, int *errorp,
        int check_algo)
{
        hammer2_chain_t *chain;
        char *bdata;

        if (check_algo != HAMMER2_CHECK_NONE &&
            test_block_zeros(data, pblksize)) {
                /*
                 * An all-zeros write creates a hole unless the check code
                 * is disabled.  When the check code is disabled all writes
                 * are done in-place, including any all-zeros writes.
                 *
                 * NOTE: A snapshot will still force a copy-on-write
                 *       (see the HAMMER2_CHECK_NONE in hammer2_chain.c).
                 */
                zero_write(data, ip, parentp, lbase, mtid, errorp);
        } else {
                /*
                 * Normal write (bdata set to NULL if de-duplicated)
                 */
                bdata = data;
                chain = hammer2_assign_physical(ip, parentp, lbase, pblksize,
                                                mtid, &bdata, errorp);
                if (*errorp) {
                        /* do nothing */
                } else if (bdata) {
                        hammer2_write_bp(chain, data, ioflag, pblksize,
                                         mtid, errorp, check_algo);
                } else {
                        /* dedup occurred */
                        chain->bref.methods =
                                HAMMER2_ENC_COMP(HAMMER2_COMP_NONE) +
                                HAMMER2_ENC_CHECK(check_algo);
                        hammer2_chain_setcheck(chain, data);
                        atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                }
                if (chain) {
                        hammer2_chain_unlock(chain);
                        hammer2_chain_drop(chain);
                }
        }
}

/*
 * Helper
 *
 * A function to test whether a block of data contains only zeros,
 * returns TRUE (non-zero) if the block is all zeros.
 */
static
int
test_block_zeros(const char *buf, size_t bytes)
{
        size_t i;

        for (i = 0; i < bytes; i += sizeof(long)) {
                if (*(const long *)(buf + i) != 0)
                        return (0);
        }
        return (1);
}

/*
 * Helper
 *
 * Function to "write" a block that contains only zeros.
 */
static
void
zero_write(char *data, hammer2_inode_t *ip,
           hammer2_chain_t **parentp,
           hammer2_key_t lbase, hammer2_tid_t mtid, int *errorp)
{
        hammer2_chain_t *chain;
        hammer2_key_t key_dummy;

        chain = hammer2_chain_lookup(parentp, &key_dummy,
                                     lbase, lbase,
                                     errorp,
                                     HAMMER2_LOOKUP_NODATA);
        if (chain) {
                if (chain->bref.type == HAMMER2_BREF_TYPE_INODE) {
                        hammer2_inode_data_t *wipdata;

                        if (*errorp == 0) {
                                *errorp = hammer2_chain_modify_ip(ip, chain,
                                                                  mtid, 0);
                        }
                        if (*errorp == 0) {
                                wipdata = &chain->data->ipdata;
                                KKASSERT(wipdata->meta.op_flags &
                                         HAMMER2_OPFLAG_DIRECTDATA);
                                bzero(wipdata->u.data, HAMMER2_EMBEDDED_BYTES);
                                ++hammer2_iod_file_wembed;
                        }
                } else {
                        /* chain->error ok for deletion */
                        hammer2_chain_delete(*parentp, chain,
                                             mtid, HAMMER2_DELETE_PERMANENT);
                        ++hammer2_iod_file_wzero;
                }
                atomic_set_int(&ip->flags, HAMMER2_INODE_DIRTYDATA);
                hammer2_chain_unlock(chain);
                hammer2_chain_drop(chain);
        } else {
                ++hammer2_iod_file_wzero;
        }
}

/*
 * Helper
 *
 * Function to write the data as it is, without performing any sort of
 * compression. This function is used in path without compression and
 * default zero-checking path.
 */
static
void
hammer2_write_bp(hammer2_chain_t *chain, char *data, int ioflag,
                 int pblksize,
                 hammer2_tid_t mtid, int *errorp, int check_algo)
{
        hammer2_inode_data_t *wipdata;
        hammer2_io_t *dio;
        char *bdata;
        int error;

        error = 0;      /* XXX TODO below */

        KKASSERT(chain->flags & HAMMER2_CHAIN_MODIFIED);

        switch(chain->bref.type) {
        case HAMMER2_BREF_TYPE_INODE:
                wipdata = &chain->data->ipdata;
                KKASSERT(wipdata->meta.op_flags & HAMMER2_OPFLAG_DIRECTDATA);
                bcopy(data, wipdata->u.data, HAMMER2_EMBEDDED_BYTES);
                error = 0;
                ++hammer2_iod_file_wembed;
                break;
        case HAMMER2_BREF_TYPE_DATA:
                error = hammer2_io_newnz(chain->hmp,
                                         chain->bref.type,
                                         chain->bref.data_off,
                                         chain->bytes, &dio);
                if (error) {
                        hammer2_io_bqrelse(&dio);
                        kprintf("hammer2: WRITE PATH: "
                                "dbp bread error\n");
                        break;
                }
                bdata = hammer2_io_data(dio, chain->bref.data_off);

                chain->bref.methods = HAMMER2_ENC_COMP(HAMMER2_COMP_NONE) +
                                      HAMMER2_ENC_CHECK(check_algo);
                bcopy(data, bdata, chain->bytes);

                /*
                 * The flush code doesn't calculate check codes for
                 * file data (doing so can result in excessive I/O),
                 * so we do it here.
                 */
                hammer2_chain_setcheck(chain, bdata);

                /*
                 * Device buffer is now valid, chain is no longer in
                 * the initial state.
                 *
                 * (No blockref table worries with file data)
                 */
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_INITIAL);
                hammer2_dedup_record(chain, dio, bdata);

                if (ioflag & IO_SYNC) {
                        /*
                         * Synchronous I/O requested.
                         */
                        hammer2_io_bwrite(&dio);
                /*
                } else if ((ioflag & IO_DIRECT) &&
                           loff + n == pblksize) {
                        hammer2_io_bdwrite(&dio);
                */
                } else if (ioflag & IO_ASYNC) {
                        hammer2_io_bawrite(&dio);
                } else {
                        hammer2_io_bdwrite(&dio);
                }
                break;
        default:
                panic("hammer2_write_bp: bad chain type %d\n",
                      chain->bref.type);
                /* NOT REACHED */
                error = 0;
                break;
        }
        *errorp = error;
}

/*
 * LIVE DEDUP HEURISTICS
 *
 * Record media and crc information for possible dedup operation.  Note
 * that the dedup mask bits must also be set in the related DIO for a dedup
 * to be fully validated (which is handled in the freemap allocation code).
 *
 * WARNING! This code is SMP safe but the heuristic allows SMP collisions.
 *          All fields must be loaded into locals and validated.
 *
 * WARNING! Should only be used for file data and directory entries,
 *          hammer2_chain_modify() only checks for the dedup case on data
 *          chains.  Also, dedup data can only be recorded for committed
 *          chains (so NOT strategy writes which can undergo further
 *          modification after the fact!).
 */
void
hammer2_dedup_record(hammer2_chain_t *chain, hammer2_io_t *dio,
                     const char *data)
{
        hammer2_dev_t *hmp;
        hammer2_dedup_t *dedup;
        uint64_t crc;
        uint64_t mask;
        int best = 0;
        int i;
        int dticks;

        /*
         * We can only record a dedup if we have media data to test against.
         * If dedup is not enabled, return early, which allows a chain to
         * remain marked MODIFIED (which might have benefits in special
         * situations, though typically it does not).
         */
        if (hammer2_dedup_enable == 0)
                return;
        if (dio == NULL) {
                dio = chain->dio;
                if (dio == NULL)
                        return;
        }

        hmp = chain->hmp;

        switch(HAMMER2_DEC_CHECK(chain->bref.methods)) {
        case HAMMER2_CHECK_ISCSI32:
                /*
                 * XXX use the built-in crc (the dedup lookup sequencing
                 * needs to be fixed so the check code is already present
                 * when dedup_lookup is called)
                 */
#if 0
                crc = (uint64_t)(uint32_t)chain->bref.check.iscsi32.value;
#endif
                crc = XXH64(data, chain->bytes, XXH_HAMMER2_SEED);
                break;
        case HAMMER2_CHECK_XXHASH64:
                crc = chain->bref.check.xxhash64.value;
                break;
        case HAMMER2_CHECK_SHA192:
                /*
                 * XXX use the built-in crc (the dedup lookup sequencing
                 * needs to be fixed so the check code is already present
                 * when dedup_lookup is called)
                 */
#if 0
                crc = ((uint64_t *)chain->bref.check.sha192.data)[0] ^
                      ((uint64_t *)chain->bref.check.sha192.data)[1] ^
                      ((uint64_t *)chain->bref.check.sha192.data)[2];
#endif
                crc = XXH64(data, chain->bytes, XXH_HAMMER2_SEED);
                break;
        default:
                /*
                 * Cannot dedup without a check code
                 *
                 * NOTE: In particular, CHECK_NONE allows a sector to be
                 *       overwritten without copy-on-write, recording
                 *       a dedup block for a CHECK_NONE object would be
                 *       a disaster!
                 */
                return;
        }

        atomic_set_int(&chain->flags, HAMMER2_CHAIN_DEDUPABLE);

        dedup = &hmp->heur_dedup[crc & (HAMMER2_DEDUP_HEUR_MASK & ~3)];
        for (i = 0; i < 4; ++i) {
                if (dedup[i].data_crc == crc) {
                        best = i;
                        break;
                }
                dticks = (int)(dedup[i].ticks - dedup[best].ticks);
                if (dticks < 0 || dticks > hz * 60 * 30)
                        best = i;
        }
        dedup += best;
        if (hammer2_debug & 0x40000) {
                kprintf("REC %04x %016jx %016jx\n",
                        (int)(dedup - hmp->heur_dedup),
                        crc,
                        chain->bref.data_off);
        }
        dedup->ticks = ticks;
        dedup->data_off = chain->bref.data_off;
        dedup->data_crc = crc;

        /*
         * Set the valid bits for the dedup only after we know the data
         * buffer has been updated.  The alloc bits were set (and the valid
         * bits cleared) when the media was allocated.
         *
         * This is done in two stages becuase the bulkfree code can race
         * the gap between allocation and data population.  Both masks must
         * be set before a bcmp/dedup operation is able to use the block.
         */
        mask = hammer2_dedup_mask(dio, chain->bref.data_off, chain->bytes);
        atomic_set_64(&dio->dedup_valid, mask);

#if 0
        /*
         * XXX removed. MODIFIED is an integral part of the flush code,
         * lets not just clear it
         */
        /*
         * Once we record the dedup the chain must be marked clean to
         * prevent reuse of the underlying block.   Remember that this
         * write occurs when the buffer cache is flushed (i.e. on sync(),
         * fsync(), filesystem periodic sync, or when the kernel needs to
         * flush a buffer), and not whenever the user write()s.
         */
        if (chain->flags & HAMMER2_CHAIN_MODIFIED) {
                atomic_clear_int(&chain->flags, HAMMER2_CHAIN_MODIFIED);
                atomic_add_long(&hammer2_count_modified_chains, -1);
                if (chain->pmp)
                        hammer2_pfs_memory_wakeup(chain->pmp, -1);
        }
#endif
}

static
hammer2_off_t
hammer2_dedup_lookup(hammer2_dev_t *hmp, char **datap, int pblksize)
{
        hammer2_dedup_t *dedup;
        hammer2_io_t *dio;
        hammer2_off_t off;
        uint64_t crc;
        uint64_t mask;
        char *data;
        char *dtmp;
        int i;

        if (hammer2_dedup_enable == 0)
                return 0;
        data = *datap;
        if (data == NULL)
                return 0;

        /*
         * XXX use the built-in crc (the dedup lookup sequencing
         * needs to be fixed so the check code is already present
         * when dedup_lookup is called)
         */
        crc = XXH64(data, pblksize, XXH_HAMMER2_SEED);
        dedup = &hmp->heur_dedup[crc & (HAMMER2_DEDUP_HEUR_MASK & ~3)];

        if (hammer2_debug & 0x40000) {
                kprintf("LOC %04x/4 %016jx\n",
                        (int)(dedup - hmp->heur_dedup),
                        crc);
        }

        for (i = 0; i < 4; ++i) {
                off = dedup[i].data_off;
                cpu_ccfence();
                if (dedup[i].data_crc != crc)
                        continue;
                if ((1 << (int)(off & HAMMER2_OFF_MASK_RADIX)) != pblksize)
                        continue;
                dio = hammer2_io_getquick(hmp, off, pblksize);
                if (dio) {
                        dtmp = hammer2_io_data(dio, off),
                        mask = hammer2_dedup_mask(dio, off, pblksize);
                        if ((dio->dedup_alloc & mask) == mask &&
                            (dio->dedup_valid & mask) == mask &&
                            bcmp(data, dtmp, pblksize) == 0) {
                                if (hammer2_debug & 0x40000) {
                                        kprintf("DEDUP SUCCESS %016jx\n",
                                                (intmax_t)off);
                                }
                                hammer2_io_putblk(&dio);
                                *datap = NULL;
                                dedup[i].ticks = ticks;   /* update use */
                                atomic_add_long(&hammer2_iod_file_wdedup,
                                                pblksize);

                                return off;             /* RETURN */
                        }
                        hammer2_io_putblk(&dio);
                }
        }
        return 0;
}

/*
 * Poof.  Races are ok, if someone gets in and reuses a dedup offset
 * before or while we are clearing it they will also recover the freemap
 * entry (set it to fully allocated), so a bulkfree race can only set it
 * to a possibly-free state.
 *
 * XXX ok, well, not really sure races are ok but going to run with it
 *     for the moment.
 */
void
hammer2_dedup_clear(hammer2_dev_t *hmp)
{
        int i;

        for (i = 0; i < HAMMER2_DEDUP_HEUR_SIZE; ++i) {
                hmp->heur_dedup[i].data_off = 0;
                hmp->heur_dedup[i].ticks = ticks - 1;
        }
}