/*      $NetBSD: vfs_bio.c,v 1.308 2026/05/03 16:02:36 thorpej Exp $    */

/*-
 * Copyright (c) 2007, 2008, 2009, 2019, 2020 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Andrew Doran, and by Wasabi Systems, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*-
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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 University 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 REGENTS 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 REGENTS 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.
 *
 *      @(#)vfs_bio.c   8.6 (Berkeley) 1/11/94
 */

/*-
 * Copyright (c) 1994 Christopher G. Demetriou
 *
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
 *
 *      @(#)vfs_bio.c   8.6 (Berkeley) 1/11/94
 */

/*
 * The buffer cache subsystem.
 *
 * Some references:
 *      Bach: The Design of the UNIX Operating System (Prentice Hall, 1986)
 *      Leffler, et al.: The Design and Implementation of the 4.3BSD
 *              UNIX Operating System (Addison Welley, 1989)
 *
 * Locking
 *
 * There are three locks:
 * - bufcache_lock: protects global buffer cache state.
 * - BC_BUSY: a long term per-buffer lock.
 * - buf_t::b_objlock: lock on completion (biowait vs biodone).
 *
 * For buffers associated with vnodes (a most common case) b_objlock points
 * to the vnode_t::v_interlock.  Otherwise, it points to generic buffer_lock.
 *
 * Lock order:
 *      bufcache_lock ->
 *              buf_t::b_objlock
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.308 2026/05/03 16:02:36 thorpej Exp $");

#ifdef _KERNEL_OPT
#include "opt_biohist.h"
#include "opt_bufcache.h"
#include "opt_dtrace.h"
#endif

#include <sys/param.h>
#include <sys/types.h>

#include <sys/bitops.h>
#include <sys/buf.h>
#include <sys/conf.h>
#include <sys/cprng.h>
#include <sys/cpu.h>
#include <sys/fstrans.h>
#include <sys/intr.h>
#include <sys/kauth.h>
#include <sys/kernel.h>
#include <sys/mount.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/sdt.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/vnode.h>
#include <sys/wapbl.h>

#include <uvm/uvm.h>    /* extern struct uvm uvm */

#include <miscfs/specfs/specdev.h>

SDT_PROVIDER_DEFINE(io);

SDT_PROBE_DEFINE4(io, kernel, , bbusy__start,
    "struct buf *"/*bp*/,
    "bool"/*intr*/, "int"/*timo*/, "kmutex_t *"/*interlock*/);
SDT_PROBE_DEFINE5(io, kernel, , bbusy__done,
    "struct buf *"/*bp*/,
    "bool"/*intr*/,
    "int"/*timo*/,
    "kmutex_t *"/*interlock*/,
    "int"/*error*/);
SDT_PROBE_DEFINE0(io, kernel, , getnewbuf__start);
SDT_PROBE_DEFINE1(io, kernel, , getnewbuf__done,  "struct buf *"/*bp*/);
SDT_PROBE_DEFINE3(io, kernel, , getblk__start,
    "struct vnode *"/*vp*/, "daddr_t"/*blkno*/, "int"/*size*/);
SDT_PROBE_DEFINE4(io, kernel, , getblk__done,
    "struct vnode *"/*vp*/, "daddr_t"/*blkno*/, "int"/*size*/,
    "struct buf *"/*bp*/);
SDT_PROBE_DEFINE2(io, kernel, , brelse, "struct buf *"/*bp*/, "int"/*set*/);
SDT_PROBE_DEFINE1(io, kernel, , wait__start, "struct buf *"/*bp*/);
SDT_PROBE_DEFINE1(io, kernel, , wait__done, "struct buf *"/*bp*/);

#ifndef BUFPAGES
# define BUFPAGES 0
#endif

#ifdef BUFCACHE
# if (BUFCACHE < 5) || (BUFCACHE > 95)
#  error BUFCACHE is not between 5 and 95
# endif
#else
# define BUFCACHE 15
#endif

u_int   nbuf;                   /* desired number of buffer headers */
u_int   bufpages = BUFPAGES;    /* optional hardwired count */
u_int   bufcache = BUFCACHE;    /* max % of RAM to use for buffer cache */

/*
 * Definitions for the buffer free lists.
 */
#define BQUEUES         3               /* number of free buffer queues */

#define BQ_LOCKED       0               /* super-blocks &c */
#define BQ_LRU          1               /* lru, useful buffers */
#define BQ_AGE          2               /* rubbish */

struct bqueue {
        TAILQ_HEAD(, buf) bq_queue;
        uint64_t bq_bytes;
        buf_t *bq_marker;
};
static struct bqueue bufqueues[BQUEUES] __cacheline_aligned;

/* Function prototypes */
static void buf_setwm(void);
static int buf_trim(void);
static void *bufpool_page_alloc(struct pool *, int);
static void bufpool_page_free(struct pool *, void *);
static buf_t *bio_doread(struct vnode *, daddr_t, int, int);
static buf_t *getnewbuf(int, int, int);
static int buf_lotsfree(void);
static int buf_canrelease(void);
static u_long buf_mempoolidx(u_long);
static u_long buf_roundsize(u_long);
static void *buf_alloc(size_t);
static void buf_mrelease(void *, size_t);
static void binsheadfree(buf_t *, struct bqueue *);
static void binstailfree(buf_t *, struct bqueue *);
#ifdef DEBUG
static int checkfreelist(buf_t *, struct bqueue *, int);
#endif
static void biointr(void *);
static void biodone2(buf_t *);
static void sysctl_kern_buf_setup(void);
static void sysctl_vm_buf_setup(void);

/* Initialization for biohist */

#include <sys/biohist.h>

BIOHIST_DEFINE(biohist);

void
biohist_init(void)
{

        BIOHIST_INIT(biohist, BIOHIST_SIZE);
}

/*
 * Definitions for the buffer hash lists.
 */
#define BUFHASH(dvp, lbn)       \
        (&bufhashtbl[(((long)(dvp) >> 8) + (int)(lbn)) & bufhash])
LIST_HEAD(bufhashhdr, buf) *bufhashtbl, invalhash;
u_long  bufhash;

static int     bufhash_stats(struct hashstat_sysctl *, bool);

static kcondvar_t needbuffer_cv;

/*
 * Buffer queue lock.
 */
kmutex_t bufcache_lock __cacheline_aligned;
kmutex_t buffer_lock __cacheline_aligned;

/* Software ISR for completed transfers. */
static void *biodone_sih;

/* Buffer pool for I/O buffers. */
static pool_cache_t buf_cache;
static pool_cache_t bufio_cache;

#define MEMPOOL_INDEX_OFFSET (ilog2(DEV_BSIZE)) /* smallest pool is 512 bytes */
#define NMEMPOOLS (ilog2(MAXBSIZE) - MEMPOOL_INDEX_OFFSET + 1)
__CTASSERT((1 << (NMEMPOOLS + MEMPOOL_INDEX_OFFSET - 1)) == MAXBSIZE);

/* Buffer memory pools */
static struct pool bmempools[NMEMPOOLS];

static struct vm_map *buf_map;

/*
 * Buffer memory pool allocator.
 */
static void *
bufpool_page_alloc(struct pool *pp, int flags)
{

        return (void *)uvm_km_alloc(buf_map,
            MAXBSIZE, MAXBSIZE,
            ((flags & PR_WAITOK) ? 0 : UVM_KMF_NOWAIT|UVM_KMF_TRYLOCK)
            | UVM_KMF_WIRED);
}

static void
bufpool_page_free(struct pool *pp, void *v)
{

        uvm_km_free(buf_map, (vaddr_t)v, MAXBSIZE, UVM_KMF_WIRED);
}

static struct pool_allocator bufmempool_allocator = {
        .pa_alloc = bufpool_page_alloc,
        .pa_free = bufpool_page_free,
        .pa_pagesz = MAXBSIZE,
};

/* Buffer memory management variables */
u_long bufmem_valimit;
u_long bufmem_hiwater;
u_long bufmem_lowater;
u_long bufmem;

/*
 * MD code can call this to set a hard limit on the amount
 * of virtual memory used by the buffer cache.
 */
int
buf_setvalimit(vsize_t sz)
{

        /* We need to accommodate at least NMEMPOOLS of MAXBSIZE each */
        if (sz < NMEMPOOLS * MAXBSIZE)
                return SET_ERROR(EINVAL);

        bufmem_valimit = sz;
        return 0;
}

static void
buf_setwm(void)
{

        bufmem_hiwater = buf_memcalc();
        /* lowater is approx. 2% of memory (with bufcache = 15) */
#define BUFMEM_WMSHIFT  3
#define BUFMEM_HIWMMIN  (64 * 1024 << BUFMEM_WMSHIFT)
        if (bufmem_hiwater < BUFMEM_HIWMMIN)
                /* Ensure a reasonable minimum value */
                bufmem_hiwater = BUFMEM_HIWMMIN;
        bufmem_lowater = bufmem_hiwater >> BUFMEM_WMSHIFT;
}

#ifdef DEBUG
int debug_verify_freelist = 0;
static int
checkfreelist(buf_t *bp, struct bqueue *dp, int ison)
{
        buf_t *b;

        if (!debug_verify_freelist)
                return 1;

        TAILQ_FOREACH(b, &dp->bq_queue, b_freelist) {
                if (b == bp)
                        return ison ? 1 : 0;
        }

        return ison ? 0 : 1;
}
#endif

/*
 * Insq/Remq for the buffer hash lists.
 * Call with buffer queue locked.
 */
static void
binsheadfree(buf_t *bp, struct bqueue *dp)
{

        KASSERT(mutex_owned(&bufcache_lock));
        KASSERT(bp->b_freelistindex == -1);
        TAILQ_INSERT_HEAD(&dp->bq_queue, bp, b_freelist);
        dp->bq_bytes += bp->b_bufsize;
        bp->b_freelistindex = dp - bufqueues;
}

static void
binstailfree(buf_t *bp, struct bqueue *dp)
{

        KASSERT(mutex_owned(&bufcache_lock));
        KASSERTMSG(bp->b_freelistindex == -1, "double free of buffer? "
            "bp=%p, b_freelistindex=%d\n", bp, bp->b_freelistindex);
        TAILQ_INSERT_TAIL(&dp->bq_queue, bp, b_freelist);
        dp->bq_bytes += bp->b_bufsize;
        bp->b_freelistindex = dp - bufqueues;
}

void
bremfree(buf_t *bp)
{
        struct bqueue *dp;
        int bqidx = bp->b_freelistindex;

        KASSERT(mutex_owned(&bufcache_lock));

        KASSERT(bqidx != -1);
        dp = &bufqueues[bqidx];
        KDASSERT(checkfreelist(bp, dp, 1));
        KASSERT(dp->bq_bytes >= bp->b_bufsize);
        TAILQ_REMOVE(&dp->bq_queue, bp, b_freelist);
        dp->bq_bytes -= bp->b_bufsize;

        /* For the sysctl helper. */
        if (bp == dp->bq_marker)
                dp->bq_marker = NULL;

#if defined(DIAGNOSTIC)
        bp->b_freelistindex = -1;
#endif /* defined(DIAGNOSTIC) */
}

/*
 * note that for some ports this is used by pmap bootstrap code to
 * determine kva size.
 */
u_long
buf_memcalc(void)
{
        u_long n;
        vsize_t mapsz = 0;

        /*
         * Determine the upper bound of memory to use for buffers.
         *
         *      - If bufpages is specified, use that as the number
         *        pages.
         *
         *      - Otherwise, use bufcache as the percentage of
         *        physical memory.
         */
        if (bufpages != 0) {
                n = bufpages;
        } else {
                if (bufcache < 5) {
                        printf("forcing bufcache %d -> 5", bufcache);
                        bufcache = 5;
                }
                if (bufcache > 95) {
                        printf("forcing bufcache %d -> 95", bufcache);
                        bufcache = 95;
                }
                if (buf_map != NULL)
                        mapsz = vm_map_max(buf_map) - vm_map_min(buf_map);
                n = calc_cache_size(mapsz, bufcache,
                    (buf_map != kernel_map) ? 100 : BUFCACHE_VA_MAXPCT)
                    / PAGE_SIZE;
        }

        n <<= PAGE_SHIFT;
        if (bufmem_valimit != 0 && n > bufmem_valimit)
                n = bufmem_valimit;

        return n;
}

/*
 * Initialize buffers and hash links for buffers.
 */
void
bufinit(void)
{
        struct bqueue *dp;
        int use_std;
        u_int i;

        biodone_vfs = biodone;

        mutex_init(&bufcache_lock, MUTEX_DEFAULT, IPL_NONE);
        mutex_init(&buffer_lock, MUTEX_DEFAULT, IPL_NONE);
        cv_init(&needbuffer_cv, "needbuf");

        if (bufmem_valimit != 0) {
                vaddr_t minaddr = 0, maxaddr;
                buf_map = uvm_km_suballoc(kernel_map, &minaddr, &maxaddr,
                    bufmem_valimit, 0, false, 0);
                if (buf_map == NULL)
                        panic("bufinit: cannot allocate submap");
        } else
                buf_map = kernel_map;

        /*
         * Initialize buffer cache memory parameters.
         */
        bufmem = 0;
        buf_setwm();

        /* On "small" machines use small pool page sizes where possible */
        use_std = (physmem < atop(16*1024*1024));

        /*
         * Also use them on systems that can map the pool pages using
         * a direct-mapped segment.
         */
#ifdef PMAP_MAP_POOLPAGE
        use_std = 1;
#endif

        buf_cache = pool_cache_init(sizeof(buf_t), 0, 0, 0,
            "bufpl", NULL, IPL_SOFTBIO, NULL, NULL, NULL);
        bufio_cache = pool_cache_init(sizeof(buf_t), 0, 0, 0,
            "biopl", NULL, IPL_BIO, NULL, NULL, NULL);

        for (i = 0; i < NMEMPOOLS; i++) {
                struct pool_allocator *pa;
                struct pool *pp = &bmempools[i];
                u_int size = 1 << (i + MEMPOOL_INDEX_OFFSET);
                char *name = kmem_alloc(8, KM_SLEEP); /* XXX: never freed */

                if (__predict_false(size >= 1048576))
                        (void)snprintf(name, 8, "buf%um", size / 1048576);
                else if (__predict_true(size >= 1024))
                        (void)snprintf(name, 8, "buf%uk", size / 1024);
                else
                        (void)snprintf(name, 8, "buf%ub", size);
                pa = (size <= PAGE_SIZE && use_std)
                    ? &pool_allocator_nointr
                    : &bufmempool_allocator;
                pool_init(pp, size, DEV_BSIZE, 0, 0, name, pa, IPL_NONE);
                pool_setlowat(pp, 1);
                pool_sethiwat(pp, 1);
        }

        /* Initialize the buffer queues */
        for (dp = bufqueues; dp < &bufqueues[BQUEUES]; dp++) {
                TAILQ_INIT(&dp->bq_queue);
                dp->bq_bytes = 0;
        }

        /*
         * Estimate hash table size based on the amount of memory we
         * intend to use for the buffer cache. The average buffer
         * size is dependent on our clients (i.e. filesystems).
         *
         * For now, use an empirical 3K per buffer.
         */
        nbuf = (bufmem_hiwater / 1024) / 3;
        bufhashtbl = hashinit(nbuf, HASH_LIST, true, &bufhash);

        sysctl_kern_buf_setup();
        sysctl_vm_buf_setup();
        hashstat_register("bufhash", bufhash_stats);
}

void
bufinit2(void)
{

        biodone_sih = softint_establish(SOFTINT_BIO | SOFTINT_MPSAFE, biointr,
            NULL);
        if (biodone_sih == NULL)
                panic("bufinit2: can't establish soft interrupt");
}

static int
buf_lotsfree(void)
{
        u_long guess;

        /* Always allocate if less than the low water mark. */
        if (bufmem < bufmem_lowater)
                return 1;

        /* Never allocate if greater than the high water mark. */
        if (bufmem > bufmem_hiwater)
                return 0;

        /* If there's anything on the AGE list, it should be eaten. */
        if (TAILQ_FIRST(&bufqueues[BQ_AGE].bq_queue) != NULL)
                return 0;

        /*
         * The probability of getting a new allocation is inversely
         * proportional  to the current size of the cache above
         * the low water mark.  Divide the total first to avoid overflows
         * in the product.
         */
        guess = cprng_fast32() % 16;

        if ((bufmem_hiwater - bufmem_lowater) / 16 * guess >=
            (bufmem - bufmem_lowater))
                return 1;

        /* Otherwise don't allocate. */
        return 0;
}

/*
 * Return estimate of bytes we think need to be
 * released to help resolve low memory conditions.
 *
 * => called with bufcache_lock held.
 */
static int
buf_canrelease(void)
{
        int pagedemand, ninvalid = 0;

        KASSERT(mutex_owned(&bufcache_lock));

        if (bufmem < bufmem_lowater)
                return 0;

        if (bufmem > bufmem_hiwater)
                return bufmem - bufmem_hiwater;

        ninvalid += bufqueues[BQ_AGE].bq_bytes;

        pagedemand = uvmexp.freetarg - uvm_availmem(false);
        if (pagedemand < 0)
                return ninvalid;
        return MAX(ninvalid, MIN(2 * MAXBSIZE,
            MIN((bufmem - bufmem_lowater) / 16, pagedemand * PAGE_SIZE)));
}

/*
 * Buffer memory allocation helper functions
 */
static u_long
buf_mempoolidx(u_long size)
{
        u_int n = 0;

        size -= 1;
        size >>= MEMPOOL_INDEX_OFFSET;
        while (size) {
                size >>= 1;
                n += 1;
        }
        if (n >= NMEMPOOLS)
                panic("buf mem pool index %d", n);
        return n;
}

static u_long
buf_roundsize(u_long size)
{

        /* Round up to nearest power of 2 */
        return (1 << (buf_mempoolidx(size) + MEMPOOL_INDEX_OFFSET));
}

static void *
buf_alloc(size_t size)
{
        u_int n = buf_mempoolidx(size);
        void *addr;

        while (1) {
                addr = pool_get(&bmempools[n], PR_NOWAIT);
                if (addr != NULL)
                        break;

                /* No memory, see if we can free some. If so, try again */
                mutex_enter(&bufcache_lock);
                if (buf_drain(1) > 0) {
                        mutex_exit(&bufcache_lock);
                        continue;
                }

                if (uvm_lwp_is_pagedaemon(curlwp)) {
                        mutex_exit(&bufcache_lock);
                        return NULL;
                }

                /* Wait for buffers to arrive on the LRU queue */
                cv_timedwait(&needbuffer_cv, &bufcache_lock, hz / 4);
                mutex_exit(&bufcache_lock);
        }

        return addr;
}

static void
buf_mrelease(void *addr, size_t size)
{

        pool_put(&bmempools[buf_mempoolidx(size)], addr);
}

/*
 * bread()/breadn() helper.
 */
static buf_t *
bio_doread(struct vnode *vp, daddr_t blkno, int size, int async)
{
        buf_t *bp;
        struct mount *mp;

        bp = getblk(vp, blkno, size, 0, 0);

        /*
         * getblk() may return NULL if we are the pagedaemon.
         */
        if (bp == NULL) {
                KASSERT(uvm_lwp_is_pagedaemon(curlwp));
                return NULL;
        }

        /*
         * If buffer does not have data valid, start a read.
         * Note that if buffer is BC_INVAL, getblk() won't return it.
         * Therefore, it's valid if its I/O has completed or been delayed.
         */
        if (!ISSET(bp->b_oflags, (BO_DONE | BO_DELWRI))) {
                /* Start I/O for the buffer. */
                SET(bp->b_flags, B_READ | async);
                if (async)
                        BIO_SETPRIO(bp, BPRIO_TIMELIMITED);
                else
                        BIO_SETPRIO(bp, BPRIO_TIMECRITICAL);
                VOP_STRATEGY(vp, bp);

                /* Pay for the read. */
                curlwp->l_ru.ru_inblock++;
        } else if (async)
                brelse(bp, 0);

        if (vp->v_type == VBLK)
                mp = spec_node_getmountedfs(vp);
        else
                mp = vp->v_mount;

        /*
         * Collect statistics on synchronous and asynchronous reads.
         * Reads from block devices are charged to their associated
         * filesystem (if any).
         */
        if (mp != NULL) {
                if (async == 0)
                        mp->mnt_stat.f_syncreads++;
                else
                        mp->mnt_stat.f_asyncreads++;
        }

        return bp;
}

/*
 * Read a disk block.
 * This algorithm described in Bach (p.54).
 */
int
bread(struct vnode *vp, daddr_t blkno, int size, int flags, buf_t **bpp)
{
        buf_t *bp;
        int error;

        BIOHIST_FUNC(__func__); BIOHIST_CALLED(biohist);

        /* Get buffer for block. */
        bp = *bpp = bio_doread(vp, blkno, size, 0);
        if (bp == NULL)
                return SET_ERROR(ENOMEM);

        /* Wait for the read to complete, and return result. */
        error = biowait(bp);
        if (error == 0 && (flags & B_MODIFY) != 0)
                error = fscow_run(bp, true);
        if (error) {
                brelse(bp, 0);
                *bpp = NULL;
        }

        return error;
}

/*
 * Read-ahead multiple disk blocks. The first is sync, the rest async.
 * Trivial modification to the breada algorithm presented in Bach (p.55).
 */
int
breadn(struct vnode *vp, daddr_t blkno, int size, daddr_t *rablks,
    int *rasizes, int nrablks, int flags, buf_t **bpp)
{
        buf_t *bp;
        int error, i;

        BIOHIST_FUNC(__func__); BIOHIST_CALLED(biohist);

        bp = *bpp = bio_doread(vp, blkno, size, 0);
        if (bp == NULL)
                return SET_ERROR(ENOMEM);

        /*
         * For each of the read-ahead blocks, start a read, if necessary.
         */
        mutex_enter(&bufcache_lock);
        for (i = 0; i < nrablks; i++) {
                /* If it's in the cache, just go on to next one. */
                if (incore(vp, rablks[i]))
                        continue;

                /* Get a buffer for the read-ahead block */
                mutex_exit(&bufcache_lock);
                (void) bio_doread(vp, rablks[i], rasizes[i], B_ASYNC);
                mutex_enter(&bufcache_lock);
        }
        mutex_exit(&bufcache_lock);

        /* Otherwise, we had to start a read for it; wait until it's valid. */
        error = biowait(bp);
        if (error == 0 && (flags & B_MODIFY) != 0)
                error = fscow_run(bp, true);
        if (error) {
                brelse(bp, 0);
                *bpp = NULL;
        }

        return error;
}

/*
 * Block write.  Described in Bach (p.56)
 */
int
bwrite(buf_t *bp)
{
        int rv, sync, wasdelayed;
        struct vnode *vp;
        struct mount *mp;

        BIOHIST_FUNC(__func__); BIOHIST_CALLARGS(biohist, "bp=%#jx",
            (uintptr_t)bp, 0, 0, 0);

        KASSERT(ISSET(bp->b_cflags, BC_BUSY));
        KASSERT(!cv_has_waiters(&bp->b_done));

        vp = bp->b_vp;

        /*
         * dholland 20160728 AFAICT vp==NULL must be impossible as it
         * will crash upon reaching VOP_STRATEGY below... see further
         * analysis on tech-kern.
         */
        KASSERTMSG(vp != NULL, "bwrite given buffer with null vnode");

        if (vp != NULL) {
                KASSERT(bp->b_objlock == vp->v_interlock);
                if (vp->v_type == VBLK)
                        mp = spec_node_getmountedfs(vp);
                else
                        mp = vp->v_mount;
        } else {
                mp = NULL;
        }

        if (mp && mp->mnt_wapbl) {
                if (bp->b_iodone != mp->mnt_wapbl_op->wo_wapbl_biodone) {
                        bdwrite(bp);
                        return 0;
                }
        }

        /*
         * Remember buffer type, to switch on it later.  If the write was
         * synchronous, but the file system was mounted with MNT_ASYNC,
         * convert it to a delayed write.
         * XXX note that this relies on delayed tape writes being converted
         * to async, not sync writes (which is safe, but ugly).
         */
        sync = !ISSET(bp->b_flags, B_ASYNC);
        if (sync && mp != NULL && ISSET(mp->mnt_flag, MNT_ASYNC)) {
                bdwrite(bp);
                return 0;
        }

        /*
         * Collect statistics on synchronous and asynchronous writes.
         * Writes to block devices are charged to their associated
         * filesystem (if any).
         */
        if (mp != NULL) {
                if (sync)
                        mp->mnt_stat.f_syncwrites++;
                else
                        mp->mnt_stat.f_asyncwrites++;
        }

        /*
         * Pay for the I/O operation and make sure the buf is on the correct
         * vnode queue.
         */
        bp->b_error = 0;
        wasdelayed = ISSET(bp->b_oflags, BO_DELWRI);
        CLR(bp->b_flags, B_READ);
        if (wasdelayed) {
                mutex_enter(&bufcache_lock);
                mutex_enter(bp->b_objlock);
                CLR(bp->b_oflags, BO_DONE | BO_DELWRI);
                reassignbuf(bp, bp->b_vp);
                /* Wake anyone trying to busy the buffer via vnode's lists. */
                cv_broadcast(&bp->b_busy);
                mutex_exit(&bufcache_lock);
        } else {
                curlwp->l_ru.ru_oublock++;
                mutex_enter(bp->b_objlock);
                CLR(bp->b_oflags, BO_DONE | BO_DELWRI);
        }
        if (vp != NULL)
                vp->v_numoutput++;
        mutex_exit(bp->b_objlock);

        /* Initiate disk write. */
        if (sync)
                BIO_SETPRIO(bp, BPRIO_TIMECRITICAL);
        else
                BIO_SETPRIO(bp, BPRIO_TIMELIMITED);

        VOP_STRATEGY(vp, bp);

        if (sync) {
                /* If I/O was synchronous, wait for it to complete. */
                rv = biowait(bp);

                /* Release the buffer. */
                brelse(bp, 0);

                return rv;
        } else {
                return 0;
        }
}

int
vn_bwrite(void *v)
{
        struct vop_bwrite_args *ap = v;

        return bwrite(ap->a_bp);
}

/*
 * Delayed write.
 *
 * The buffer is marked dirty, but is not queued for I/O.
 * This routine should be used when the buffer is expected
 * to be modified again soon, typically a small write that
 * partially fills a buffer.
 *
 * NB: magnetic tapes cannot be delayed; they must be
 * written in the order that the writes are requested.
 *
 * Described in Leffler, et al. (pp. 208-213).
 */
void
bdwrite(buf_t *bp)
{

        BIOHIST_FUNC(__func__); BIOHIST_CALLARGS(biohist, "bp=%#jx",
            (uintptr_t)bp, 0, 0, 0);

        KASSERT(bp->b_vp == NULL || bp->b_vp->v_tag != VT_UFS ||
            bp->b_vp->v_type == VBLK || ISSET(bp->b_flags, B_COWDONE));
        KASSERT(ISSET(bp->b_cflags, BC_BUSY));
        KASSERT(!cv_has_waiters(&bp->b_done));

        /* If this is a tape block, write the block now. */
        if (bdev_type(bp->b_dev) == D_TAPE) {
                bawrite(bp);
                return;
        }

        if (wapbl_vphaswapbl(bp->b_vp)) {
                struct mount *mp = wapbl_vptomp(bp->b_vp);

                if (bp->b_iodone != mp->mnt_wapbl_op->wo_wapbl_biodone) {
                        WAPBL_ADD_BUF(mp, bp);
                }
        }

        /*
         * If the block hasn't been seen before:
         *      (1) Mark it as having been seen,
         *      (2) Charge for the write,
         *      (3) Make sure it's on its vnode's correct block list.
         */
        KASSERT(bp->b_vp == NULL || bp->b_objlock == bp->b_vp->v_interlock);

        if (!ISSET(bp->b_oflags, BO_DELWRI)) {
                mutex_enter(&bufcache_lock);
                mutex_enter(bp->b_objlock);
                SET(bp->b_oflags, BO_DELWRI);
                curlwp->l_ru.ru_oublock++;
                reassignbuf(bp, bp->b_vp);
                /* Wake anyone trying to busy the buffer via vnode's lists. */
                cv_broadcast(&bp->b_busy);
                mutex_exit(&bufcache_lock);
        } else {
                mutex_enter(bp->b_objlock);
        }
        /* Otherwise, the "write" is done, so mark and release the buffer. */
        CLR(bp->b_oflags, BO_DONE);
        mutex_exit(bp->b_objlock);

        brelse(bp, 0);
}

/*
 * Asynchronous block write; just an asynchronous bwrite().
 */
void
bawrite(buf_t *bp)
{

        KASSERT(ISSET(bp->b_cflags, BC_BUSY));
        KASSERT(bp->b_vp != NULL);

        SET(bp->b_flags, B_ASYNC);
        VOP_BWRITE(bp->b_vp, bp);
}

/*
 * Release a buffer on to the free lists.
 * Described in Bach (p. 46).
 */
void
brelsel(buf_t *bp, int set)
{
        struct bqueue *bufq;
        struct vnode *vp;

        SDT_PROBE2(io, kernel, , brelse,  bp, set);

        KASSERT(bp != NULL);
        KASSERT(mutex_owned(&bufcache_lock));
        KASSERT(!cv_has_waiters(&bp->b_done));

        SET(bp->b_cflags, set);

        KASSERT(ISSET(bp->b_cflags, BC_BUSY));
        KASSERT(bp->b_iodone == NULL);

        /* Wake up any processes waiting for any buffer to become free. */
        cv_signal(&needbuffer_cv);

        /* Wake up any proceeses waiting for _this_ buffer to become free */
        if (ISSET(bp->b_cflags, BC_WANTED))
                CLR(bp->b_cflags, BC_WANTED|BC_AGE);

        /* If it's clean clear the copy-on-write flag. */
        if (ISSET(bp->b_flags, B_COWDONE)) {
                mutex_enter(bp->b_objlock);
                if (!ISSET(bp->b_oflags, BO_DELWRI))
                        CLR(bp->b_flags, B_COWDONE);
                mutex_exit(bp->b_objlock);
        }

        /*
         * Determine which queue the buffer should be on, then put it there.
         */

        /* If it's locked, don't report an error; try again later. */
        if (ISSET(bp->b_flags, B_LOCKED))
                bp->b_error = 0;

        /* If it's not cacheable, or an error, mark it invalid. */
        if (ISSET(bp->b_cflags, BC_NOCACHE) || bp->b_error != 0)
                SET(bp->b_cflags, BC_INVAL);

        if (ISSET(bp->b_cflags, BC_VFLUSH)) {
                /*
                 * This is a delayed write buffer that was just flushed to
                 * disk.  It is still on the LRU queue.  If it's become
                 * invalid, then we need to move it to a different queue;
                 * otherwise leave it in its current position.
                 */
                CLR(bp->b_cflags, BC_VFLUSH);
                if (!ISSET(bp->b_cflags, BC_INVAL|BC_AGE) &&
                    !ISSET(bp->b_flags, B_LOCKED) && bp->b_error == 0) {
                        KDASSERT(checkfreelist(bp, &bufqueues[BQ_LRU], 1));
                        goto already_queued;
                } else {
                        bremfree(bp);
                }
        }

        KDASSERT(checkfreelist(bp, &bufqueues[BQ_AGE], 0));
        KDASSERT(checkfreelist(bp, &bufqueues[BQ_LRU], 0));
        KDASSERT(checkfreelist(bp, &bufqueues[BQ_LOCKED], 0));

        if ((bp->b_bufsize <= 0) || ISSET(bp->b_cflags, BC_INVAL)) {
                /*
                 * If it's invalid or empty, dissociate it from its vnode
                 * and put on the head of the appropriate queue.
                 */
                if (ISSET(bp->b_flags, B_LOCKED)) {
                        if (wapbl_vphaswapbl(vp = bp->b_vp)) {
                                struct mount *mp = wapbl_vptomp(vp);

                                KASSERT(bp->b_iodone !=
                                    mp->mnt_wapbl_op->wo_wapbl_biodone);
                                WAPBL_REMOVE_BUF(mp, bp);
                        }
                }

                mutex_enter(bp->b_objlock);
                CLR(bp->b_oflags, BO_DONE|BO_DELWRI);
                if ((vp = bp->b_vp) != NULL) {
                        KASSERT(bp->b_objlock == vp->v_interlock);
                        reassignbuf(bp, bp->b_vp);
                        brelvp(bp);
                        mutex_exit(vp->v_interlock);
                } else {
                        KASSERT(bp->b_objlock == &buffer_lock);
                        mutex_exit(bp->b_objlock);
                }
                /* We want to dispose of the buffer, so wake everybody. */
                cv_broadcast(&bp->b_busy);
                if (bp->b_bufsize <= 0)
                        /* no data */
                        goto already_queued;
                else
                        /* invalid data */
                        bufq = &bufqueues[BQ_AGE];
                binsheadfree(bp, bufq);
        } else  {
                /*
                 * It has valid data.  Put it on the end of the appropriate
                 * queue, so that it'll stick around for as long as possible.
                 * If buf is AGE, but has dependencies, must put it on last
                 * bufqueue to be scanned, ie LRU. This protects against the
                 * livelock where BQ_AGE only has buffers with dependencies,
                 * and we thus never get to the dependent buffers in BQ_LRU.
                 */
                if (ISSET(bp->b_flags, B_LOCKED)) {
                        /* locked in core */
                        bufq = &bufqueues[BQ_LOCKED];
                } else if (!ISSET(bp->b_cflags, BC_AGE)) {
                        /* valid data */
                        bufq = &bufqueues[BQ_LRU];
                } else {
                        /* stale but valid data */
                        bufq = &bufqueues[BQ_AGE];
                }
                binstailfree(bp, bufq);
        }
already_queued:
        /* Unlock the buffer. */
        CLR(bp->b_cflags, BC_AGE|BC_BUSY|BC_NOCACHE);
        CLR(bp->b_flags, B_ASYNC);

        /*
         * Wake only the highest priority waiter on the lock, in order to
         * prevent a thundering herd: many LWPs simultaneously awakening and
         * competing for the buffer's lock.  Testing in 2019 revealed this
         * to reduce contention on bufcache_lock tenfold during a kernel
         * compile.  Here and elsewhere, when the buffer is changing
         * identity, being disposed of, or moving from one list to another,
         * we wake all lock requestors.
         */
        if (bp->b_bufsize <= 0) {
                cv_broadcast(&bp->b_busy);
                buf_destroy(bp);
#ifdef DEBUG
                memset((char *)bp, 0, sizeof(*bp));
#endif
                pool_cache_put(buf_cache, bp);
        } else
                cv_signal(&bp->b_busy);
}

void
brelse(buf_t *bp, int set)
{

        mutex_enter(&bufcache_lock);
        brelsel(bp, set);
        mutex_exit(&bufcache_lock);
}

/*
 * Determine if a block is in the cache.
 * Just look on what would be its hash chain.  If it's there, return
 * a pointer to it, unless it's marked invalid.  If it's marked invalid,
 * we normally don't return the buffer, unless the caller explicitly
 * wants us to.
 */
buf_t *
incore(struct vnode *vp, daddr_t blkno)
{
        buf_t *bp;

        KASSERT(mutex_owned(&bufcache_lock));

        /* Search hash chain */
        LIST_FOREACH(bp, BUFHASH(vp, blkno), b_hash) {
                if (bp->b_lblkno == blkno && bp->b_vp == vp &&
                    !ISSET(bp->b_cflags, BC_INVAL)) {
                        KASSERT(bp->b_objlock == vp->v_interlock);
                        return (bp);
                }
        }

        return NULL;
}

/*
 * Get a block of requested size that is associated with
 * a given vnode and block offset. If it is found in the
 * block cache, mark it as having been found, make it busy
 * and return it. Otherwise, return an empty block of the
 * correct size. It is up to the caller to insure that the
 * cached blocks be of the correct size.
 */
buf_t *
getblk(struct vnode *vp, daddr_t blkno, int size, int slpflag, int slptimeo)
{
        int err, preserve;
        buf_t *bp;

        mutex_enter(&bufcache_lock);
        SDT_PROBE3(io, kernel, , getblk__start,  vp, blkno, size);
loop:
        bp = incore(vp, blkno);
        if (bp != NULL) {
                err = bbusy(bp, ((slpflag & PCATCH) != 0), slptimeo, NULL);
                if (err != 0) {
                        if (err == EPASSTHROUGH)
                                goto loop;
                        mutex_exit(&bufcache_lock);
                        SDT_PROBE4(io, kernel, , getblk__done,
                            vp, blkno, size, NULL);
                        return NULL;
                }
                KASSERT(!cv_has_waiters(&bp->b_done));
#ifdef DIAGNOSTIC
                if (ISSET(bp->b_oflags, BO_DONE|BO_DELWRI) &&
                    bp->b_bcount < size && vp->v_type != VBLK)
                        panic("getblk: block size invariant failed");
#endif
                bremfree(bp);
                preserve = 1;
        } else {
                if ((bp = getnewbuf(slpflag, slptimeo, 0)) == NULL)
                        goto loop;

                if (incore(vp, blkno) != NULL) {
                        /* The block has come into memory in the meantime. */
                        brelsel(bp, 0);
                        goto loop;
                }

                LIST_INSERT_HEAD(BUFHASH(vp, blkno), bp, b_hash);
                bp->b_blkno = bp->b_lblkno = bp->b_rawblkno = blkno;
                mutex_enter(vp->v_interlock);
                bgetvp(vp, bp);
                mutex_exit(vp->v_interlock);
                preserve = 0;
        }
        mutex_exit(&bufcache_lock);

        /*
         * LFS can't track total size of B_LOCKED buffer (locked_queue_bytes)
         * if we re-size buffers here.
         */
        if (ISSET(bp->b_flags, B_LOCKED)) {
                KASSERT(bp->b_bufsize >= size);
        } else {
                if (allocbuf(bp, size, preserve)) {
                        mutex_enter(&bufcache_lock);
                        LIST_REMOVE(bp, b_hash);
                        brelsel(bp, BC_INVAL);
                        mutex_exit(&bufcache_lock);
                        SDT_PROBE4(io, kernel, , getblk__done,
                            vp, blkno, size, NULL);
                        return NULL;
                }
        }
        BIO_SETPRIO(bp, BPRIO_DEFAULT);
        SDT_PROBE4(io, kernel, , getblk__done,  vp, blkno, size, bp);
        return bp;
}

/*
 * Get an empty, disassociated buffer of given size.
 */
buf_t *
geteblk(int size)
{
        buf_t *bp;
        int error __diagused;

        mutex_enter(&bufcache_lock);
        while ((bp = getnewbuf(0, 0, 0)) == NULL)
                continue;

        SET(bp->b_cflags, BC_INVAL);
        LIST_INSERT_HEAD(&invalhash, bp, b_hash);
        mutex_exit(&bufcache_lock);
        BIO_SETPRIO(bp, BPRIO_DEFAULT);
        error = allocbuf(bp, size, 0);
        KASSERT(error == 0);
        return bp;
}

/*
 * Expand or contract the actual memory allocated to a buffer.
 *
 * If the buffer shrinks, data is lost, so it's up to the
 * caller to have written it out *first*; this routine will not
 * start a write.  If the buffer grows, it's the callers
 * responsibility to fill out the buffer's additional contents.
 */
int
allocbuf(buf_t *bp, int size, int preserve)
{
        void *addr;
        vsize_t oldsize, desired_size;
        int oldcount;
        int delta;

        desired_size = buf_roundsize(size);
        if (desired_size > MAXBSIZE)
                printf("allocbuf: buffer larger than MAXBSIZE requested");

        oldcount = bp->b_bcount;

        bp->b_bcount = size;

        oldsize = bp->b_bufsize;
        if (oldsize == desired_size) {
                /*
                 * Do not short cut the WAPBL resize, as the buffer length
                 * could still have changed and this would corrupt the
                 * tracking of the transaction length.
                 */
                goto out;
        }

        /*
         * If we want a buffer of a different size, re-allocate the
         * buffer's memory; copy old content only if needed.
         */
        addr = buf_alloc(desired_size);
        if (addr == NULL)
                return SET_ERROR(ENOMEM);
        if (preserve)
                memcpy(addr, bp->b_data, MIN(oldsize,desired_size));
        if (bp->b_data != NULL)
                buf_mrelease(bp->b_data, oldsize);
        bp->b_data = addr;
        bp->b_bufsize = desired_size;

        /*
         * Update overall buffer memory counter (protected by bufcache_lock)
         */
        delta = (long)desired_size - (long)oldsize;

        mutex_enter(&bufcache_lock);
        if ((bufmem += delta) > bufmem_hiwater) {
                /*
                 * Need to trim overall memory usage.
                 */
                while (buf_canrelease()) {
                        if (preempt_needed()) {
                                mutex_exit(&bufcache_lock);
                                preempt();
                                mutex_enter(&bufcache_lock);
                        }
                        if (buf_trim() == 0)
                                break;
                }
        }
        mutex_exit(&bufcache_lock);

out:
        if (wapbl_vphaswapbl(bp->b_vp)) {
                WAPBL_RESIZE_BUF(wapbl_vptomp(bp->b_vp), bp,
                    oldsize, oldcount);
        }

        return 0;
}

/*
 * Find a buffer which is available for use.
 * Select something from a free list.
 * Preference is to AGE list, then LRU list.
 *
 * Called with the buffer queues locked.
 * Return buffer locked.
 */
static buf_t *
getnewbuf(int slpflag, int slptimeo, int from_bufq)
{
        buf_t *bp;
        struct vnode *vp;
        struct mount *transmp = NULL;

        SDT_PROBE0(io, kernel, , getnewbuf__start);

start:
        KASSERT(mutex_owned(&bufcache_lock));

        /*
         * Get a new buffer from the pool.
         */
        if (!from_bufq && buf_lotsfree()) {
                mutex_exit(&bufcache_lock);
                bp = pool_cache_get(buf_cache, PR_NOWAIT);
                if (bp != NULL) {
                        memset((char *)bp, 0, sizeof(*bp));
                        buf_init(bp);
                        SET(bp->b_cflags, BC_BUSY);     /* mark buffer busy */
                        mutex_enter(&bufcache_lock);
#if defined(DIAGNOSTIC)
                        bp->b_freelistindex = -1;
#endif /* defined(DIAGNOSTIC) */
                        SDT_PROBE1(io, kernel, , getnewbuf__done,  bp);
                        return bp;
                }
                mutex_enter(&bufcache_lock);
        }

        KASSERT(mutex_owned(&bufcache_lock));
        if ((bp = TAILQ_FIRST(&bufqueues[BQ_AGE].bq_queue)) != NULL) {
                KASSERT(!ISSET(bp->b_oflags, BO_DELWRI));
        } else {
                TAILQ_FOREACH(bp, &bufqueues[BQ_LRU].bq_queue, b_freelist) {
                        if (ISSET(bp->b_cflags, BC_VFLUSH) ||
                            !ISSET(bp->b_oflags, BO_DELWRI))
                                break;
                        if (fstrans_start_nowait(bp->b_vp->v_mount) == 0) {
                                KASSERT(transmp == NULL);
                                transmp = bp->b_vp->v_mount;
                                break;
                        }
                }
        }
        if (bp != NULL) {
                KASSERT(!ISSET(bp->b_cflags, BC_BUSY) ||
                    ISSET(bp->b_cflags, BC_VFLUSH));
                bremfree(bp);

                /* Buffer is no longer on free lists. */
                SET(bp->b_cflags, BC_BUSY);

                /* Wake anyone trying to lock the old identity. */
                cv_broadcast(&bp->b_busy);
        } else {
                /*
                 * XXX: !from_bufq should be removed.
                 */
                if (!from_bufq || !uvm_lwp_is_pagedaemon(curlwp)) {
                        /* wait for a free buffer of any kind */
                        if ((slpflag & PCATCH) != 0)
                                (void)cv_timedwait_sig(&needbuffer_cv,
                                    &bufcache_lock, slptimeo);
                        else
                                (void)cv_timedwait(&needbuffer_cv,
                                    &bufcache_lock, slptimeo);
                }
                SDT_PROBE1(io, kernel, , getnewbuf__done,  NULL);
                return NULL;
        }

#ifdef DIAGNOSTIC
        if (bp->b_bufsize <= 0)
                panic("buffer %p: on queue but empty", bp);
#endif

        if (ISSET(bp->b_cflags, BC_VFLUSH)) {
                /*
                 * This is a delayed write buffer being flushed to disk.  Make
                 * sure it gets aged out of the queue when it's finished, and
                 * leave it off the LRU queue.
                 */
                CLR(bp->b_cflags, BC_VFLUSH);
                SET(bp->b_cflags, BC_AGE);
                goto start;
        }

        KASSERT(ISSET(bp->b_cflags, BC_BUSY));
        KASSERT(!cv_has_waiters(&bp->b_done));

        /*
         * If buffer was a delayed write, start it and return NULL
         * (since we might sleep while starting the write).
         */
        if (ISSET(bp->b_oflags, BO_DELWRI)) {
                /*
                 * This buffer has gone through the LRU, so make sure it gets
                 * reused ASAP.
                 */
                SET(bp->b_cflags, BC_AGE);
                mutex_exit(&bufcache_lock);
                bawrite(bp);
                KASSERT(transmp != NULL);
                fstrans_done(transmp);
                mutex_enter(&bufcache_lock);
                SDT_PROBE1(io, kernel, , getnewbuf__done,  NULL);
                return NULL;
        }

        KASSERT(transmp == NULL);

        vp = bp->b_vp;

        /* clear out various other fields */
        bp->b_cflags = BC_BUSY;
        bp->b_oflags = 0;
        bp->b_flags = 0;
        bp->b_dev = NODEV;
        bp->b_blkno = 0;
        bp->b_lblkno = 0;
        bp->b_rawblkno = 0;
        bp->b_iodone = 0;
        bp->b_error = 0;
        bp->b_resid = 0;
        bp->b_bcount = 0;

        LIST_REMOVE(bp, b_hash);

        /* Disassociate us from our vnode, if we had one... */
        if (vp != NULL) {
                mutex_enter(vp->v_interlock);
                brelvp(bp);
                mutex_exit(vp->v_interlock);
        }

        SDT_PROBE1(io, kernel, , getnewbuf__done,  bp);
        return bp;
}

/*
 * Invalidate the specified buffer if it exists.
 */
void
binvalbuf(struct vnode *vp, daddr_t blkno)
{
        buf_t *bp;
        int err;

        mutex_enter(&bufcache_lock);

loop:
        bp = incore(vp, blkno);
        if (bp != NULL) {
                err = bbusy(bp, 0, 0, NULL);
                if (err == EPASSTHROUGH)
                        goto loop;
                bremfree(bp);
                if (ISSET(bp->b_oflags, BO_DELWRI)) {
                        SET(bp->b_cflags, BC_NOCACHE);
                        mutex_exit(&bufcache_lock);
                        bwrite(bp);
                } else {
                        brelsel(bp, BC_INVAL);
                        mutex_exit(&bufcache_lock);
                }
        } else
                mutex_exit(&bufcache_lock);
}

/*
 * Attempt to free an aged buffer off the queues.
 * Called with queue lock held.
 * Returns the amount of buffer memory freed.
 */
static int
buf_trim(void)
{
        buf_t *bp;
        long size;

        KASSERT(mutex_owned(&bufcache_lock));

        /* Instruct getnewbuf() to get buffers off the queues */
        if ((bp = getnewbuf(PCATCH, 1, 1)) == NULL)
                return 0;

        KASSERT((bp->b_cflags & BC_WANTED) == 0);
        size = bp->b_bufsize;
        bufmem -= size;
        if (size > 0) {
                buf_mrelease(bp->b_data, size);
                bp->b_bcount = bp->b_bufsize = 0;
        }
        /* brelse() will return the buffer to the global buffer pool */
        brelsel(bp, 0);
        return size;
}

int
buf_drain(int n)
{
        int size = 0, sz;

        KASSERT(mutex_owned(&bufcache_lock));

        while (size < n && bufmem > bufmem_lowater) {
                sz = buf_trim();
                if (sz <= 0)
                        break;
                size += sz;
        }

        return size;
}

/*
 * Wait for operations on the buffer to complete.
 * When they do, extract and return the I/O's error value.
 */
int
biowait(buf_t *bp)
{

        BIOHIST_FUNC(__func__);

        KASSERT(ISSET(bp->b_cflags, BC_BUSY));

        SDT_PROBE1(io, kernel, , wait__start, bp);

        mutex_enter(bp->b_objlock);

        BIOHIST_CALLARGS(biohist, "bp=%#jx, oflags=0x%jx, ret_addr=%#jx",
            (uintptr_t)bp, bp->b_oflags,
            (uintptr_t)__builtin_return_address(0), 0);

        while (!ISSET(bp->b_oflags, BO_DONE | BO_DELWRI)) {
                BIOHIST_LOG(biohist, "waiting bp=%#jx",
                    (uintptr_t)bp, 0, 0, 0);
                cv_wait(&bp->b_done, bp->b_objlock);
        }
        mutex_exit(bp->b_objlock);

        SDT_PROBE1(io, kernel, , wait__done, bp);

        BIOHIST_LOG(biohist, "return %jd", bp->b_error, 0, 0, 0);

        return bp->b_error;
}

/*
 * Mark I/O complete on a buffer.
 *
 * If a callback has been requested, e.g. the pageout
 * daemon, do so. Otherwise, awaken waiting processes.
 *
 * [ Leffler, et al., says on p.247:
 *      "This routine wakes up the blocked process, frees the buffer
 *      for an asynchronous write, or, for a request by the pagedaemon
 *      process, invokes a procedure specified in the buffer structure" ]
 *
 * In real life, the pagedaemon (or other system processes) wants
 * to do async stuff too, and doesn't want the buffer brelse()'d.
 * (for swap pager, that puts swap buffers on the free lists (!!!),
 * for the vn device, that puts allocated buffers on the free lists!)
 */
void
biodone(buf_t *bp)
{
        int s;

        BIOHIST_FUNC(__func__);

        KASSERT(!ISSET(bp->b_oflags, BO_DONE));

        if (cpu_intr_p()) {
                /* From interrupt mode: defer to a soft interrupt. */
                s = splvm();
                TAILQ_INSERT_TAIL(&curcpu()->ci_data.cpu_biodone, bp, b_actq);

                BIOHIST_CALLARGS(biohist, "bp=%#jx, softint scheduled",
                    (uintptr_t)bp, 0, 0, 0);
                softint_schedule(biodone_sih);
                splx(s);
        } else {
                /* Process now - the buffer may be freed soon. */
                biodone2(bp);
        }
}

SDT_PROBE_DEFINE1(io, kernel, , done, "struct buf *"/*bp*/);

static void
biodone2(buf_t *bp)
{
        void (*callout)(buf_t *);

        SDT_PROBE1(io, kernel, ,done, bp);

        BIOHIST_FUNC(__func__);
        BIOHIST_CALLARGS(biohist, "bp=%#jx", (uintptr_t)bp, 0, 0, 0);

        mutex_enter(bp->b_objlock);
        /* Note that the transfer is done. */
        if (ISSET(bp->b_oflags, BO_DONE))
                panic("biodone2 already");
        CLR(bp->b_flags, B_COWDONE);
        SET(bp->b_oflags, BO_DONE);
        BIO_SETPRIO(bp, BPRIO_DEFAULT);

        /* Wake up waiting writers. */
        if (!ISSET(bp->b_flags, B_READ))
                vwakeup(bp);

        if ((callout = bp->b_iodone) != NULL) {
                BIOHIST_LOG(biohist, "callout %#jx", (uintptr_t)callout,
                    0, 0, 0);

                /* Note callout done, then call out. */
                KASSERT(!cv_has_waiters(&bp->b_done));
                bp->b_iodone = NULL;
                mutex_exit(bp->b_objlock);
                (*callout)(bp);
        } else if (ISSET(bp->b_flags, B_ASYNC)) {
                /* If async, release. */
                BIOHIST_LOG(biohist, "async", 0, 0, 0, 0);
                KASSERT(!cv_has_waiters(&bp->b_done));
                mutex_exit(bp->b_objlock);
                brelse(bp, 0);
        } else {
                /* Otherwise just wake up waiters in biowait(). */
                BIOHIST_LOG(biohist, "wake-up", 0, 0, 0, 0);
                cv_broadcast(&bp->b_done);
                mutex_exit(bp->b_objlock);
        }
}

static void
biointr(void *cookie)
{
        struct cpu_info *ci;
        buf_t *bp;
        int s;

        BIOHIST_FUNC(__func__); BIOHIST_CALLED(biohist);

        ci = curcpu();

        s = splvm();
        while (!TAILQ_EMPTY(&ci->ci_data.cpu_biodone)) {
                KASSERT(curcpu() == ci);

                bp = TAILQ_FIRST(&ci->ci_data.cpu_biodone);
                TAILQ_REMOVE(&ci->ci_data.cpu_biodone, bp, b_actq);
                splx(s);

                BIOHIST_LOG(biohist, "bp=%#jx", (uintptr_t)bp, 0, 0, 0);
                biodone2(bp);

                s = splvm();
        }
        splx(s);
}

static void
sysctl_fillbuf(const buf_t *i, struct buf_sysctl *o)
{
        const bool allowaddr = get_expose_address(curproc);

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

        o->b_flags = i->b_flags | i->b_cflags | i->b_oflags;
        o->b_error = i->b_error;
        o->b_prio = i->b_prio;
        o->b_dev = i->b_dev;
        o->b_bufsize = i->b_bufsize;
        o->b_bcount = i->b_bcount;
        o->b_resid = i->b_resid;
        COND_SET_VALUE(o->b_addr, PTRTOUINT64(i->b_data), allowaddr);
        o->b_blkno = i->b_blkno;
        o->b_rawblkno = i->b_rawblkno;
        COND_SET_VALUE(o->b_iodone, PTRTOUINT64(i->b_iodone), allowaddr);
        COND_SET_VALUE(o->b_proc, PTRTOUINT64(i->b_proc), allowaddr);
        COND_SET_VALUE(o->b_vp, PTRTOUINT64(i->b_vp), allowaddr);
        COND_SET_VALUE(o->b_saveaddr, PTRTOUINT64(i->b_saveaddr), allowaddr);
        o->b_lblkno = i->b_lblkno;
}

static int
sysctl_dobuf(SYSCTLFN_ARGS)
{
        buf_t *bp;
        struct buf_sysctl bs;
        struct bqueue *bq;
        char *dp;
        u_int i, op, arg;
        size_t len, needed, elem_size, out_size;
        int error, elem_count, retries;

        if (namelen == 1 && name[0] == CTL_QUERY)
                return sysctl_query(SYSCTLFN_CALL(rnode));

        if (namelen != 4)
                return SET_ERROR(EINVAL);

        retries = 100;
retry:
        dp = oldp;
        len = (oldp != NULL) ? *oldlenp : 0;
        op = name[0];
        arg = name[1];
        elem_size = name[2];
        elem_count = name[3];
        out_size = MIN(sizeof(bs), elem_size);

        /*
         * at the moment, these are just "placeholders" to make the
         * API for retrieving kern.buf data more extensible in the
         * future.
         *
         * XXX kern.buf currently has "netbsd32" issues.  hopefully
         * these will be resolved at a later point.
         */
        if (op != KERN_BUF_ALL || arg != KERN_BUF_ALL ||
            elem_size < 1 || elem_count < 0)
                return SET_ERROR(EINVAL);

        if (oldp == NULL) {
                /* count only, don't run through the buffer queues */
                needed = pool_cache_nget(buf_cache) -
                    pool_cache_nput(buf_cache);
                *oldlenp = (needed + KERN_BUFSLOP) * elem_size;

                return 0;
        }

        error = 0;
        needed = 0;
        sysctl_unlock();
        mutex_enter(&bufcache_lock);
        for (i = 0; i < BQUEUES; i++) {
                bq = &bufqueues[i];
                TAILQ_FOREACH(bp, &bq->bq_queue, b_freelist) {
                        bq->bq_marker = bp;
                        if (len >= elem_size && elem_count > 0) {
                                sysctl_fillbuf(bp, &bs);
                                mutex_exit(&bufcache_lock);
                                error = copyout(&bs, dp, out_size);
                                mutex_enter(&bufcache_lock);
                                if (error)
                                        break;
                                if (bq->bq_marker != bp) {
                                        /*
                                         * This sysctl node is only for
                                         * statistics.  Retry; if the
                                         * queue keeps changing, then
                                         * bail out.
                                         */
                                        if (retries-- == 0) {
                                                error = SET_ERROR(EAGAIN);
                                                break;
                                        }
                                        mutex_exit(&bufcache_lock);
                                        sysctl_relock();
                                        goto retry;
                                }
                                dp += elem_size;
                                len -= elem_size;
                        }
                        needed += elem_size;
                        if (elem_count > 0 && elem_count != INT_MAX)
                                elem_count--;
                }
                if (error != 0)
                        break;
        }
        mutex_exit(&bufcache_lock);
        sysctl_relock();

        *oldlenp = needed;

        return error;
}

static int
sysctl_bufvm_update(SYSCTLFN_ARGS)
{
        int error, rv;
        struct sysctlnode node;
        unsigned int temp_bufcache;
        unsigned long temp_water;

        /* Take a copy of the supplied node and its data */
        node = *rnode;
        if (node.sysctl_data == &bufcache) {
                node.sysctl_data = &temp_bufcache;
                temp_bufcache = *(unsigned int *)rnode->sysctl_data;
        } else {
                node.sysctl_data = &temp_water;
                temp_water = *(unsigned long *)rnode->sysctl_data;
        }

        /* Update the copy */
        error = sysctl_lookup(SYSCTLFN_CALL(&node));
        if (error || newp == NULL)
                return error;

        if (rnode->sysctl_data == &bufcache) {
                if (temp_bufcache > 100)
                        return SET_ERROR(EINVAL);
                bufcache = temp_bufcache;
                buf_setwm();
        } else if (rnode->sysctl_data == &bufmem_lowater) {
                if (bufmem_hiwater - temp_water < 16)
                        return SET_ERROR(EINVAL);
                bufmem_lowater = temp_water;
        } else if (rnode->sysctl_data == &bufmem_hiwater) {
                if (temp_water - bufmem_lowater < 16)
                        return SET_ERROR(EINVAL);
                bufmem_hiwater = temp_water;
        } else
                return SET_ERROR(EINVAL);

        /* Drain until below new high water mark */
        sysctl_unlock();
        mutex_enter(&bufcache_lock);
        while (bufmem > bufmem_hiwater) {
                rv = buf_drain((bufmem - bufmem_hiwater) / (2 * 1024));
                if (rv <= 0)
                        break;
        }
        mutex_exit(&bufcache_lock);
        sysctl_relock();

        return 0;
}

static struct sysctllog *vfsbio_sysctllog;

static void
sysctl_kern_buf_setup(void)
{

        sysctl_createv(&vfsbio_sysctllog, 0, NULL, NULL,
            CTLFLAG_PERMANENT,
            CTLTYPE_NODE, "buf",
            SYSCTL_DESCR("Kernel buffer cache information"),
            sysctl_dobuf, 0, NULL, 0,
            CTL_KERN, KERN_BUF, CTL_EOL);
}

static void
sysctl_vm_buf_setup(void)
{

        sysctl_createv(&vfsbio_sysctllog, 0, NULL, NULL,
            CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
            CTLTYPE_INT, "bufcache",
            SYSCTL_DESCR("Percentage of physical memory to use for "
                "buffer cache"),
            sysctl_bufvm_update, 0, &bufcache, 0,
            CTL_VM, CTL_CREATE, CTL_EOL);
        sysctl_createv(&vfsbio_sysctllog, 0, NULL, NULL,
            CTLFLAG_PERMANENT|CTLFLAG_READONLY,
            CTLTYPE_LONG, "bufmem",
            SYSCTL_DESCR("Amount of kernel memory used by buffer cache"),
            NULL, 0, &bufmem, 0,
            CTL_VM, CTL_CREATE, CTL_EOL);
        sysctl_createv(&vfsbio_sysctllog, 0, NULL, NULL,
            CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
            CTLTYPE_LONG, "bufmem_lowater",
            SYSCTL_DESCR("Minimum amount of kernel memory to reserve for "
                "buffer cache"),
            sysctl_bufvm_update, 0, &bufmem_lowater, 0,
            CTL_VM, CTL_CREATE, CTL_EOL);
        sysctl_createv(&vfsbio_sysctllog, 0, NULL, NULL,
            CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
            CTLTYPE_LONG, "bufmem_hiwater",
            SYSCTL_DESCR("Maximum amount of kernel memory to use for "
                "buffer cache"),
            sysctl_bufvm_update, 0, &bufmem_hiwater, 0,
            CTL_VM, CTL_CREATE, CTL_EOL);
}

static int
bufhash_stats(struct hashstat_sysctl *hs, bool fill)
{
        buf_t *bp;
        uint64_t chain;

        strlcpy(hs->hash_name, "bufhash", sizeof(hs->hash_name));
        strlcpy(hs->hash_desc, "buffer hash", sizeof(hs->hash_desc));
        if (!fill)
                return 0;

        hs->hash_size = bufhash + 1;

        for (size_t i = 0; i < hs->hash_size; i++) {
                chain = 0;

                mutex_enter(&bufcache_lock);
                LIST_FOREACH(bp, &bufhashtbl[i], b_hash) {
                        chain++;
                }
                mutex_exit(&bufcache_lock);

                if (chain > 0) {
                        hs->hash_used++;
                        hs->hash_items += chain;
                        if (chain > hs->hash_maxchain)
                                hs->hash_maxchain = chain;
                }
                preempt_point();
        }

        return 0;
}

#ifdef DEBUG
/*
 * Print out statistics on the current allocation of the buffer pool.
 * Can be enabled to print out on every ``sync'' by setting "syncprt"
 * in vfs_syscalls.c using sysctl.
 */
void
vfs_bufstats(void)
{
        int i, j, count;
        buf_t *bp;
        struct bqueue *dp;
        int counts[MAXBSIZE / MIN_PAGE_SIZE + 1];
        static const char *bname[BQUEUES] = { "LOCKED", "LRU", "AGE" };

        for (dp = bufqueues, i = 0; dp < &bufqueues[BQUEUES]; dp++, i++) {
                count = 0;
                memset(counts, 0, sizeof(counts));
                TAILQ_FOREACH(bp, &dp->bq_queue, b_freelist) {
                        counts[bp->b_bufsize / PAGE_SIZE]++;
                        count++;
                }
                printf("%s: total-%d", bname[i], count);
                for (j = 0; j <= MAXBSIZE / PAGE_SIZE; j++)
                        if (counts[j] != 0)
                                printf(", %d-%d", j * PAGE_SIZE, counts[j]);
                printf("\n");
        }
}
#endif /* DEBUG */

/* ------------------------------ */

buf_t *
getiobuf(struct vnode *vp, bool waitok)
{
        buf_t *bp;

        bp = pool_cache_get(bufio_cache, (waitok ? PR_WAITOK : PR_NOWAIT));
        if (bp == NULL)
                return bp;

        buf_init(bp);

        if ((bp->b_vp = vp) != NULL) {
                bp->b_objlock = vp->v_interlock;
        } else {
                KASSERT(bp->b_objlock == &buffer_lock);
        }

        return bp;
}

void
putiobuf(buf_t *bp)
{

        buf_destroy(bp);
        pool_cache_put(bufio_cache, bp);
}

/*
 * nestiobuf_iodone: b_iodone callback for nested buffers.
 */

void
nestiobuf_iodone(buf_t *bp)
{
        buf_t *mbp = bp->b_private;
        int error;
        int donebytes;

        KASSERT(bp->b_bcount <= bp->b_bufsize);
        KASSERT(mbp != bp);

        error = bp->b_error;
        if (bp->b_error == 0 &&
            (bp->b_bcount < bp->b_bufsize || bp->b_resid > 0)) {
                /*
                 * Not all got transferred, raise an error. We have no way to
                 * propagate these conditions to mbp.
                 */
                error = SET_ERROR(EIO);
        }

        donebytes = bp->b_bufsize;

        putiobuf(bp);
        nestiobuf_done(mbp, donebytes, error);
}

/*
 * nestiobuf_setup: setup a "nested" buffer.
 *
 * => 'mbp' is a "master" buffer which is being divided into sub pieces.
 * => 'bp' should be a buffer allocated by getiobuf.
 * => 'offset' is a byte offset in the master buffer.
 * => 'size' is a size in bytes of this nested buffer.
 */

void
nestiobuf_setup(buf_t *mbp, buf_t *bp, int offset, size_t size)
{
        const int b_pass = mbp->b_flags & (B_READ|B_PHYS|B_RAW|B_MEDIA_FLAGS);
        struct vnode *vp = mbp->b_vp;

        KASSERT(mbp->b_bcount >= offset + size);
        bp->b_vp = vp;
        bp->b_dev = mbp->b_dev;
        bp->b_objlock = mbp->b_objlock;
        bp->b_cflags = BC_BUSY;
        bp->b_flags = B_ASYNC | b_pass;
        bp->b_iodone = nestiobuf_iodone;
        bp->b_data = (char *)mbp->b_data + offset;
        bp->b_resid = bp->b_bcount = size;
        bp->b_bufsize = bp->b_bcount;
        bp->b_private = mbp;
        BIO_COPYPRIO(bp, mbp);
        if (BUF_ISWRITE(bp) && vp != NULL) {
                mutex_enter(vp->v_interlock);
                vp->v_numoutput++;
                mutex_exit(vp->v_interlock);
        }
}

/*
 * nestiobuf_done: propagate completion to the master buffer.
 *
 * => 'donebytes' specifies how many bytes in the 'mbp' is completed.
 * => 'error' is an errno(2) that 'donebytes' has been completed with.
 */

void
nestiobuf_done(buf_t *mbp, int donebytes, int error)
{

        if (donebytes == 0) {
                return;
        }
        mutex_enter(mbp->b_objlock);
        KASSERT(mbp->b_resid >= donebytes);
        mbp->b_resid -= donebytes;
        if (error)
                mbp->b_error = error;
        if (mbp->b_resid == 0) {
                if (mbp->b_error)
                        mbp->b_resid = mbp->b_bcount;
                mutex_exit(mbp->b_objlock);
                biodone(mbp);
        } else
                mutex_exit(mbp->b_objlock);
}

void
buf_init(buf_t *bp)
{

        cv_init(&bp->b_busy, "biolock");
        cv_init(&bp->b_done, "biowait");
        bp->b_dev = NODEV;
        bp->b_error = 0;
        bp->b_flags = 0;
        bp->b_cflags = 0;
        bp->b_oflags = 0;
        bp->b_objlock = &buffer_lock;
        bp->b_iodone = NULL;
        bp->b_dev = NODEV;
        bp->b_vnbufs.le_next = NOLIST;
        BIO_SETPRIO(bp, BPRIO_DEFAULT);
}

void
buf_destroy(buf_t *bp)
{

        cv_destroy(&bp->b_done);
        cv_destroy(&bp->b_busy);
}

int
bbusy(buf_t *bp, bool intr, int timo, kmutex_t *interlock)
{
        int error;

        KASSERT(mutex_owned(&bufcache_lock));

        SDT_PROBE4(io, kernel, , bbusy__start,  bp, intr, timo, interlock);

        if ((bp->b_cflags & BC_BUSY) != 0) {
                if (uvm_lwp_is_pagedaemon(curlwp)) {
                        error = SET_ERROR(EDEADLK);
                        goto out;
                }
                bp->b_cflags |= BC_WANTED;
                if (interlock != NULL)
                        mutex_exit(interlock);
                if (intr) {
                        error = cv_timedwait_sig(&bp->b_busy, &bufcache_lock,
                            timo);
                } else {
                        error = cv_timedwait(&bp->b_busy, &bufcache_lock,
                            timo);
                }
                /*
                 * At this point the buffer may be gone: don't touch it
                 * again.  The caller needs to find it again and retry.
                 */
                if (interlock != NULL)
                        mutex_enter(interlock);
                if (error == 0)
                        error = SET_ERROR(EPASSTHROUGH);
        } else {
                bp->b_cflags |= BC_BUSY;
                error = 0;
        }

out:    SDT_PROBE5(io, kernel, , bbusy__done,
            bp, intr, timo, interlock, error);
        return error;
}

/*
 * Nothing outside this file should really need to know about nbuf,
 * but a few things still want to read it, so give them a way to do that.
 */
u_int
buf_nbuf(void)
{

        return nbuf;
}