/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2011, Bryan Venteicher <bryanv@FreeBSD.org>
 * All rights reserved.
 *
 * 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 unmodified, this list of conditions, and the following
 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/* Driver for VirtIO block devices. */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/bio.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/msan.h>
#include <sys/sglist.h>
#include <sys/sysctl.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/queue.h>

#include <geom/geom.h>
#include <geom/geom_disk.h>

#include <machine/bus.h>
#include <machine/resource.h>
#include <sys/bus.h>
#include <sys/rman.h>

#include <dev/virtio/virtio.h>
#include <dev/virtio/virtqueue.h>
#include <dev/virtio/block/virtio_blk.h>

#include "virtio_if.h"

struct vtblk_request {
        struct vtblk_softc              *vbr_sc;
        bus_dmamap_t                     vbr_mapp;

        struct virtio_blk_outhdr        *vbr_hdr;
        vm_paddr_t                       vbr_hdr_paddr;
        bus_dmamap_t                     vbr_hdr_mapp;
        uint8_t                         *vbr_ack;
        vm_paddr_t                       vbr_ack_paddr;
        bus_dmamap_t                     vbr_ack_mapp;

        /* Fields after this point are zeroed for each request. */
        struct bio                      *vbr_bp;
        uint8_t                          vbr_requeue_on_error;
        uint8_t                          vbr_busdma_wait;
        int                              vbr_error;
        TAILQ_ENTRY(vtblk_request)       vbr_link;
};

enum vtblk_cache_mode {
        VTBLK_CACHE_WRITETHROUGH,
        VTBLK_CACHE_WRITEBACK,
        VTBLK_CACHE_MAX
};

struct vtblk_softc {
        device_t                 vtblk_dev;
        struct mtx               vtblk_mtx;
        struct mtx               vtblk_hdr_mtx;
        struct mtx               vtblk_ack_mtx;
        uint64_t                 vtblk_features;
        uint32_t                 vtblk_flags;
#define VTBLK_FLAG_INDIRECT     0x0001
#define VTBLK_FLAG_DETACH       0x0002
#define VTBLK_FLAG_SUSPEND      0x0004
#define VTBLK_FLAG_BARRIER      0x0008
#define VTBLK_FLAG_WCE_CONFIG   0x0010
#define VTBLK_FLAG_BUSDMA_WAIT  0x0020
#define VTBLK_FLAG_BUSDMA_ALIGN 0x0040

        struct virtqueue        *vtblk_vq;
        struct sglist           *vtblk_sglist;
        bus_dma_tag_t            vtblk_dmat;
        bus_dma_tag_t            vtblk_hdr_dmat;
        bus_dma_tag_t            vtblk_ack_dmat;
        struct disk             *vtblk_disk;

        struct bio_queue_head    vtblk_bioq;
        TAILQ_HEAD(, vtblk_request)
                                 vtblk_req_free;
        TAILQ_HEAD(, vtblk_request)
                                 vtblk_req_ready;
        struct vtblk_request    *vtblk_req_ordered;

        int                      vtblk_max_nsegs;
        int                      vtblk_request_count;
        enum vtblk_cache_mode    vtblk_write_cache;

        struct bio_queue         vtblk_dump_queue;
        struct vtblk_request     vtblk_dump_request;
};

static struct virtio_feature_desc vtblk_feature_desc[] = {
        { VIRTIO_BLK_F_BARRIER,         "HostBarrier"   },
        { VIRTIO_BLK_F_SIZE_MAX,        "MaxSegSize"    },
        { VIRTIO_BLK_F_SEG_MAX,         "MaxNumSegs"    },
        { VIRTIO_BLK_F_GEOMETRY,        "DiskGeometry"  },
        { VIRTIO_BLK_F_RO,              "ReadOnly"      },
        { VIRTIO_BLK_F_BLK_SIZE,        "BlockSize"     },
        { VIRTIO_BLK_F_SCSI,            "SCSICmds"      },
        { VIRTIO_BLK_F_FLUSH,           "FlushCmd"      },
        { VIRTIO_BLK_F_TOPOLOGY,        "Topology"      },
        { VIRTIO_BLK_F_CONFIG_WCE,      "ConfigWCE"     },
        { VIRTIO_BLK_F_MQ,              "Multiqueue"    },
        { VIRTIO_BLK_F_DISCARD,         "Discard"       },
        { VIRTIO_BLK_F_WRITE_ZEROES,    "WriteZeros"    },

        { 0, NULL }
};

static int      vtblk_modevent(module_t, int, void *);

static int      vtblk_probe(device_t);
static int      vtblk_attach(device_t);
static int      vtblk_detach(device_t);
static int      vtblk_suspend(device_t);
static int      vtblk_resume(device_t);
static int      vtblk_shutdown(device_t);
static int      vtblk_attach_completed(device_t);
static int      vtblk_config_change(device_t);

static int      vtblk_open(struct disk *);
static int      vtblk_close(struct disk *);
static int      vtblk_ioctl(struct disk *, u_long, void *, int,
                    struct thread *);
static int      vtblk_dump(void *, void *, off_t, size_t);
static void     vtblk_strategy(struct bio *);

static int      vtblk_negotiate_features(struct vtblk_softc *);
static int      vtblk_setup_features(struct vtblk_softc *);
static int      vtblk_maximum_segments(struct vtblk_softc *,
                    struct virtio_blk_config *);
static int      vtblk_alloc_virtqueue(struct vtblk_softc *);
static void     vtblk_resize_disk(struct vtblk_softc *, uint64_t);
static void     vtblk_alloc_disk(struct vtblk_softc *,
                    struct virtio_blk_config *);
static void     vtblk_create_disk(struct vtblk_softc *);

static int      vtblk_request_prealloc(struct vtblk_softc *);
static void     vtblk_request_free(struct vtblk_softc *);
static struct vtblk_request *
                vtblk_request_dequeue(struct vtblk_softc *);
static void     vtblk_request_enqueue(struct vtblk_softc *,
                    struct vtblk_request *);
static struct vtblk_request *
                vtblk_request_next_ready(struct vtblk_softc *);
static void     vtblk_request_requeue_ready(struct vtblk_softc *,
                    struct vtblk_request *);
static struct vtblk_request *
                vtblk_request_next(struct vtblk_softc *);
static struct vtblk_request *
                vtblk_request_bio(struct vtblk_softc *);
static int      vtblk_request_execute(struct vtblk_request *, int);
static void     vtblk_request_execute_cb(void *,
                    bus_dma_segment_t *, int, int);
static int      vtblk_request_error(struct vtblk_request *);

static void     vtblk_queue_completed(struct vtblk_softc *,
                    struct bio_queue *);
static void     vtblk_done_completed(struct vtblk_softc *,
                    struct bio_queue *);
static void     vtblk_drain_vq(struct vtblk_softc *);
static void     vtblk_drain(struct vtblk_softc *);

static void     vtblk_startio(struct vtblk_softc *);
static void     vtblk_bio_done(struct vtblk_softc *, struct bio *, int);

static void     vtblk_read_config(struct vtblk_softc *,
                    struct virtio_blk_config *);
static void     vtblk_ident(struct vtblk_softc *);
static int      vtblk_poll_request(struct vtblk_softc *,
                    struct vtblk_request *);
static int      vtblk_quiesce(struct vtblk_softc *);
static void     vtblk_vq_intr(void *);
static void     vtblk_stop(struct vtblk_softc *);

static void     vtblk_dump_quiesce(struct vtblk_softc *);
static int      vtblk_dump_write(struct vtblk_softc *, void *, off_t, size_t);
static int      vtblk_dump_flush(struct vtblk_softc *);
static void     vtblk_dump_complete(struct vtblk_softc *);

static void     vtblk_set_write_cache(struct vtblk_softc *, int);
static int      vtblk_write_cache_enabled(struct vtblk_softc *sc,
                    struct virtio_blk_config *);
static int      vtblk_write_cache_sysctl(SYSCTL_HANDLER_ARGS);

static void     vtblk_setup_sysctl(struct vtblk_softc *);
static int      vtblk_tunable_int(struct vtblk_softc *, const char *, int);

#define vtblk_modern(_sc) (((_sc)->vtblk_features & VIRTIO_F_VERSION_1) != 0)
#define vtblk_htog16(_sc, _val) virtio_htog16(vtblk_modern(_sc), _val)
#define vtblk_htog32(_sc, _val) virtio_htog32(vtblk_modern(_sc), _val)
#define vtblk_htog64(_sc, _val) virtio_htog64(vtblk_modern(_sc), _val)
#define vtblk_gtoh16(_sc, _val) virtio_gtoh16(vtblk_modern(_sc), _val)
#define vtblk_gtoh32(_sc, _val) virtio_gtoh32(vtblk_modern(_sc), _val)
#define vtblk_gtoh64(_sc, _val) virtio_gtoh64(vtblk_modern(_sc), _val)

/* Tunables. */
static int vtblk_no_ident = 0;
TUNABLE_INT("hw.vtblk.no_ident", &vtblk_no_ident);
static int vtblk_writecache_mode = -1;
TUNABLE_INT("hw.vtblk.writecache_mode", &vtblk_writecache_mode);

#define VTBLK_COMMON_FEATURES \
    (VIRTIO_BLK_F_SIZE_MAX              | \
     VIRTIO_BLK_F_SEG_MAX               | \
     VIRTIO_BLK_F_GEOMETRY              | \
     VIRTIO_BLK_F_RO                    | \
     VIRTIO_BLK_F_BLK_SIZE              | \
     VIRTIO_BLK_F_FLUSH                 | \
     VIRTIO_BLK_F_TOPOLOGY              | \
     VIRTIO_BLK_F_CONFIG_WCE            | \
     VIRTIO_BLK_F_DISCARD               | \
     VIRTIO_RING_F_INDIRECT_DESC)

#define VTBLK_MODERN_FEATURES   (VTBLK_COMMON_FEATURES)
#define VTBLK_LEGACY_FEATURES   (VIRTIO_BLK_F_BARRIER | VTBLK_COMMON_FEATURES)

#define VTBLK_MTX(_sc)          &(_sc)->vtblk_mtx
#define VTBLK_LOCK_INIT(_sc, _name) \
                                mtx_init(VTBLK_MTX((_sc)), (_name), \
                                    "VirtIO Block Lock", MTX_DEF)
#define VTBLK_LOCK(_sc)         mtx_lock(VTBLK_MTX((_sc)))
#define VTBLK_UNLOCK(_sc)       mtx_unlock(VTBLK_MTX((_sc)))
#define VTBLK_LOCK_DESTROY(_sc) mtx_destroy(VTBLK_MTX((_sc)))
#define VTBLK_LOCK_ASSERT(_sc)  mtx_assert(VTBLK_MTX((_sc)), MA_OWNED)
#define VTBLK_LOCK_ASSERT_NOTOWNED(_sc) \
                                mtx_assert(VTBLK_MTX((_sc)), MA_NOTOWNED)

#define VTBLK_DISK_NAME         "vtbd"
#define VTBLK_QUIESCE_TIMEOUT   (30 * hz)
#define VTBLK_BSIZE             512

/*
 * Each block request uses at least two segments - one for the header
 * and one for the status.
 */
#define VTBLK_MIN_SEGMENTS      2

static device_method_t vtblk_methods[] = {
        /* Device methods. */
        DEVMETHOD(device_probe,         vtblk_probe),
        DEVMETHOD(device_attach,        vtblk_attach),
        DEVMETHOD(device_detach,        vtblk_detach),
        DEVMETHOD(device_suspend,       vtblk_suspend),
        DEVMETHOD(device_resume,        vtblk_resume),
        DEVMETHOD(device_shutdown,      vtblk_shutdown),

        /* VirtIO methods. */
        DEVMETHOD(virtio_attach_completed, vtblk_attach_completed),
        DEVMETHOD(virtio_config_change, vtblk_config_change),

        DEVMETHOD_END
};

static driver_t vtblk_driver = {
        "vtblk",
        vtblk_methods,
        sizeof(struct vtblk_softc)
};

VIRTIO_DRIVER_MODULE(virtio_blk, vtblk_driver, vtblk_modevent, NULL);
MODULE_VERSION(virtio_blk, 1);
MODULE_DEPEND(virtio_blk, virtio, 1, 1, 1);

VIRTIO_SIMPLE_PNPINFO(virtio_blk, VIRTIO_ID_BLOCK, "VirtIO Block Adapter");

static int
vtblk_modevent(module_t mod, int type, void *unused)
{
        int error;

        error = 0;

        switch (type) {
        case MOD_LOAD:
        case MOD_QUIESCE:
        case MOD_UNLOAD:
        case MOD_SHUTDOWN:
                break;
        default:
                error = EOPNOTSUPP;
                break;
        }

        return (error);
}

static int
vtblk_probe(device_t dev)
{
        return (VIRTIO_SIMPLE_PROBE(dev, virtio_blk));
}

static int
vtblk_attach(device_t dev)
{
        struct vtblk_softc *sc;
        struct virtio_blk_config blkcfg;
        int error;

        sc = device_get_softc(dev);
        sc->vtblk_dev = dev;
        virtio_set_feature_desc(dev, vtblk_feature_desc);

        VTBLK_LOCK_INIT(sc, device_get_nameunit(dev));
        bioq_init(&sc->vtblk_bioq);
        TAILQ_INIT(&sc->vtblk_dump_queue);
        TAILQ_INIT(&sc->vtblk_req_free);
        TAILQ_INIT(&sc->vtblk_req_ready);

        vtblk_setup_sysctl(sc);

        error = vtblk_setup_features(sc);
        if (error) {
                device_printf(dev, "cannot setup features\n");
                goto fail;
        }

        vtblk_read_config(sc, &blkcfg);

        /*
         * With the current sglist(9) implementation, it is not easy
         * for us to support a maximum segment size as adjacent
         * segments are coalesced. For now, just make sure it's larger
         * than the maximum supported transfer size.
         */
        if (virtio_with_feature(dev, VIRTIO_BLK_F_SIZE_MAX)) {
                if (blkcfg.size_max < maxphys) {
                        error = ENOTSUP;
                        device_printf(dev, "host requires unsupported "
                            "maximum segment size feature\n");
                        goto fail;
                }
        }

        sc->vtblk_max_nsegs = vtblk_maximum_segments(sc, &blkcfg);
        if (sc->vtblk_max_nsegs <= VTBLK_MIN_SEGMENTS) {
                error = EINVAL;
                device_printf(dev, "fewer than minimum number of segments "
                    "allowed: %d\n", sc->vtblk_max_nsegs);
                goto fail;
        }

        sc->vtblk_sglist = sglist_alloc(sc->vtblk_max_nsegs, M_NOWAIT);
        if (sc->vtblk_sglist == NULL) {
                error = ENOMEM;
                device_printf(dev, "cannot allocate sglist\n");
                goto fail;
        }

        /*
         * If vtblk_max_nsegs == VTBLK_MIN_SEGMENTS + 1, the device only
         * supports a single data segment; in that case we need busdma to
         * align to a page boundary so we can send a *contiguous* page size
         * request to the host.
         */
        if (sc->vtblk_max_nsegs == VTBLK_MIN_SEGMENTS + 1)
                sc->vtblk_flags |= VTBLK_FLAG_BUSDMA_ALIGN;
        error = bus_dma_tag_create(
            bus_get_dma_tag(dev),                       /* parent */
            (sc->vtblk_flags & VTBLK_FLAG_BUSDMA_ALIGN) ? PAGE_SIZE : 1,
            0,                                          /* boundary */
            BUS_SPACE_MAXADDR,                          /* lowaddr */
            BUS_SPACE_MAXADDR,                          /* highaddr */
            NULL, NULL,                                 /* filter, filterarg */
            maxphys,                                    /* max request size */
            sc->vtblk_max_nsegs - VTBLK_MIN_SEGMENTS,   /* max # segments */
            maxphys,                                    /* maxsegsize */
            BUS_DMA_COHERENT,                           /* flags */
            busdma_lock_mutex,                          /* lockfunc */
            &sc->vtblk_mtx,                             /* lockarg */
            &sc->vtblk_dmat);
        if (error) {
                device_printf(dev, "cannot create bus dma tag\n");
                goto fail;
        }

        error = bus_dma_tag_create(
            bus_get_dma_tag(dev),                       /* parent */
            (sc->vtblk_flags & VTBLK_FLAG_BUSDMA_ALIGN) ? PAGE_SIZE :
                sizeof(struct virtio_blk_outhdr),       /* alignment */
            0,                                          /* boundary */
            BUS_SPACE_MAXADDR,                          /* lowaddr */
            BUS_SPACE_MAXADDR,                          /* highaddr */
            NULL, NULL,                                 /* filter, filterarg */
            sizeof(struct virtio_blk_outhdr),           /* max request size */
            1,                                          /* max # segments */
            sizeof(struct virtio_blk_outhdr),           /* maxsegsize */
            BUS_DMA_COHERENT,                           /* flags */
            busdma_lock_mutex,                          /* lockfunc */
            &sc->vtblk_hdr_mtx,                         /* lockarg */
            &sc->vtblk_hdr_dmat);
        if (error) {
                device_printf(dev, "cannot create hdr bus dma tag\n");
                goto fail;
        }

        error = bus_dma_tag_create(
            bus_get_dma_tag(dev),                       /* parent */
            (sc->vtblk_flags & VTBLK_FLAG_BUSDMA_ALIGN) ? PAGE_SIZE :
                sizeof(uint8_t),                        /* alignment */
            0,                                          /* boundary */
            BUS_SPACE_MAXADDR,                          /* lowaddr */
            BUS_SPACE_MAXADDR,                          /* highaddr */
            NULL, NULL,                                 /* filter, filterarg */
            sizeof(uint8_t),                            /* max request size */
            1,                                          /* max # segments */
            sizeof(uint8_t),                            /* maxsegsize */
            BUS_DMA_COHERENT,                           /* flags */
            busdma_lock_mutex,                          /* lockfunc */
            &sc->vtblk_ack_mtx,                         /* lockarg */
            &sc->vtblk_ack_dmat);
        if (error) {
                device_printf(dev, "cannot create ack bus dma tag\n");
                goto fail;
        }

#ifdef __powerpc__
        /*
         * Virtio uses physical addresses rather than bus addresses, so we
         * need to ask busdma to skip the iommu physical->bus mapping.  At
         * present, this is only a thing on the powerpc architectures.
         */
        bus_dma_tag_set_iommu(sc->vtblk_dmat, NULL, NULL);
        bus_dma_tag_set_iommu(sc->vtblk_hdr_dmat, NULL, NULL);
        bus_dma_tag_set_iommu(sc->vtblk_ack_dmat, NULL, NULL);
#endif

        error = vtblk_alloc_virtqueue(sc);
        if (error) {
                device_printf(dev, "cannot allocate virtqueue\n");
                goto fail;
        }

        error = vtblk_request_prealloc(sc);
        if (error) {
                device_printf(dev, "cannot preallocate requests\n");
                goto fail;
        }

        vtblk_alloc_disk(sc, &blkcfg);

        error = virtio_setup_intr(dev, INTR_TYPE_BIO | INTR_ENTROPY);
        if (error) {
                device_printf(dev, "cannot setup virtqueue interrupt\n");
                goto fail;
        }

        virtqueue_enable_intr(sc->vtblk_vq);

fail:
        if (error)
                vtblk_detach(dev);

        return (error);
}

static int
vtblk_detach(device_t dev)
{
        struct vtblk_softc *sc;

        sc = device_get_softc(dev);

        VTBLK_LOCK(sc);
        sc->vtblk_flags |= VTBLK_FLAG_DETACH;
        if (device_is_attached(dev))
                vtblk_stop(sc);
        VTBLK_UNLOCK(sc);

        vtblk_drain(sc);

        if (sc->vtblk_disk != NULL) {
                disk_destroy(sc->vtblk_disk);
                sc->vtblk_disk = NULL;
        }

        if (sc->vtblk_ack_dmat != NULL) {
                bus_dma_tag_destroy(sc->vtblk_ack_dmat);
                sc->vtblk_ack_dmat = NULL;
        }

        if (sc->vtblk_hdr_dmat != NULL) {
                bus_dma_tag_destroy(sc->vtblk_hdr_dmat);
                sc->vtblk_hdr_dmat = NULL;
        }

        if (sc->vtblk_dmat != NULL) {
                bus_dma_tag_destroy(sc->vtblk_dmat);
                sc->vtblk_dmat = NULL;
        }

        if (sc->vtblk_sglist != NULL) {
                sglist_free(sc->vtblk_sglist);
                sc->vtblk_sglist = NULL;
        }

        VTBLK_LOCK_DESTROY(sc);

        return (0);
}

static int
vtblk_suspend(device_t dev)
{
        struct vtblk_softc *sc;
        int error;

        sc = device_get_softc(dev);

        VTBLK_LOCK(sc);
        sc->vtblk_flags |= VTBLK_FLAG_SUSPEND;
        /* XXX BMV: virtio_stop(), etc needed here? */
        error = vtblk_quiesce(sc);
        if (error)
                sc->vtblk_flags &= ~VTBLK_FLAG_SUSPEND;
        VTBLK_UNLOCK(sc);

        return (error);
}

static int
vtblk_resume(device_t dev)
{
        struct vtblk_softc *sc;

        sc = device_get_softc(dev);

        VTBLK_LOCK(sc);
        /* XXX BMV: virtio_reinit(), etc needed here? */
        sc->vtblk_flags &= ~VTBLK_FLAG_SUSPEND;
        vtblk_startio(sc);
        VTBLK_UNLOCK(sc);

        return (0);
}

static int
vtblk_shutdown(device_t dev)
{

        return (0);
}

static int
vtblk_attach_completed(device_t dev)
{
        struct vtblk_softc *sc;

        sc = device_get_softc(dev);

        /*
         * Create disk after attach as VIRTIO_BLK_T_GET_ID can only be
         * processed after the device acknowledged
         * VIRTIO_CONFIG_STATUS_DRIVER_OK.
         */
        vtblk_create_disk(sc);
        return (0);
}

static int
vtblk_config_change(device_t dev)
{
        struct vtblk_softc *sc;
        struct virtio_blk_config blkcfg;
        uint64_t capacity;

        sc = device_get_softc(dev);

        vtblk_read_config(sc, &blkcfg);

        /* Capacity is always in 512-byte units. */
        capacity = blkcfg.capacity * VTBLK_BSIZE;

        if (sc->vtblk_disk->d_mediasize != capacity)
                vtblk_resize_disk(sc, capacity);

        return (0);
}

static int
vtblk_open(struct disk *dp)
{
        struct vtblk_softc *sc;

        if ((sc = dp->d_drv1) == NULL)
                return (ENXIO);

        return (sc->vtblk_flags & VTBLK_FLAG_DETACH ? ENXIO : 0);
}

static int
vtblk_close(struct disk *dp)
{
        struct vtblk_softc *sc;

        if ((sc = dp->d_drv1) == NULL)
                return (ENXIO);

        return (0);
}

static int
vtblk_ioctl(struct disk *dp, u_long cmd, void *addr, int flag,
    struct thread *td)
{
        struct vtblk_softc *sc;

        if ((sc = dp->d_drv1) == NULL)
                return (ENXIO);

        return (ENOTTY);
}

static int
vtblk_dump(void *arg, void *virtual, off_t offset, size_t length)
{
        struct disk *dp;
        struct vtblk_softc *sc;
        int error;

        dp = arg;
        error = 0;

        if ((sc = dp->d_drv1) == NULL)
                return (ENXIO);

        VTBLK_LOCK(sc);

        vtblk_dump_quiesce(sc);

        if (length > 0)
                error = vtblk_dump_write(sc, virtual, offset, length);
        if (error || (virtual == NULL && offset == 0))
                vtblk_dump_complete(sc);

        VTBLK_UNLOCK(sc);

        return (error);
}

static void
vtblk_strategy(struct bio *bp)
{
        struct vtblk_softc *sc;

        if ((sc = bp->bio_disk->d_drv1) == NULL) {
                vtblk_bio_done(NULL, bp, EINVAL);
                return;
        }

        if ((bp->bio_cmd != BIO_READ) && (bp->bio_cmd != BIO_WRITE) &&
            (bp->bio_cmd != BIO_FLUSH) && (bp->bio_cmd != BIO_DELETE)) {
                vtblk_bio_done(sc, bp, EOPNOTSUPP);
                return;
        }

        VTBLK_LOCK(sc);

        if (sc->vtblk_flags & VTBLK_FLAG_DETACH) {
                VTBLK_UNLOCK(sc);
                vtblk_bio_done(sc, bp, ENXIO);
                return;
        }

        bioq_insert_tail(&sc->vtblk_bioq, bp);
        vtblk_startio(sc);

        VTBLK_UNLOCK(sc);
}

static int
vtblk_negotiate_features(struct vtblk_softc *sc)
{
        device_t dev;
        uint64_t features;

        dev = sc->vtblk_dev;
        features = virtio_bus_is_modern(dev) ? VTBLK_MODERN_FEATURES :
            VTBLK_LEGACY_FEATURES;

        sc->vtblk_features = virtio_negotiate_features(dev, features);
        return (virtio_finalize_features(dev));
}

static int
vtblk_setup_features(struct vtblk_softc *sc)
{
        device_t dev;
        int error;

        dev = sc->vtblk_dev;

        error = vtblk_negotiate_features(sc);
        if (error)
                return (error);

        if (virtio_with_feature(dev, VIRTIO_RING_F_INDIRECT_DESC))
                sc->vtblk_flags |= VTBLK_FLAG_INDIRECT;
        if (virtio_with_feature(dev, VIRTIO_BLK_F_CONFIG_WCE))
                sc->vtblk_flags |= VTBLK_FLAG_WCE_CONFIG;

        /* Legacy. */
        if (virtio_with_feature(dev, VIRTIO_BLK_F_BARRIER))
                sc->vtblk_flags |= VTBLK_FLAG_BARRIER;

        return (0);
}

static int
vtblk_maximum_segments(struct vtblk_softc *sc,
    struct virtio_blk_config *blkcfg)
{
        device_t dev;
        int nsegs;

        dev = sc->vtblk_dev;
        nsegs = VTBLK_MIN_SEGMENTS;

        if (virtio_with_feature(dev, VIRTIO_BLK_F_SEG_MAX)) {
                nsegs += MIN(blkcfg->seg_max, maxphys / PAGE_SIZE + 1);
                if (sc->vtblk_flags & VTBLK_FLAG_INDIRECT)
                        nsegs = MIN(nsegs, VIRTIO_MAX_INDIRECT);
        } else
                nsegs += 1;

        return (nsegs);
}

static int
vtblk_alloc_virtqueue(struct vtblk_softc *sc)
{
        device_t dev;
        struct vq_alloc_info vq_info;
        int indir_segs;

        dev = sc->vtblk_dev;

        indir_segs = 0;
        if (sc->vtblk_flags & VTBLK_FLAG_INDIRECT)
                indir_segs = sc->vtblk_max_nsegs;
        VQ_ALLOC_INFO_INIT(&vq_info, indir_segs,
            vtblk_vq_intr, sc, &sc->vtblk_vq,
            "%s request", device_get_nameunit(dev));

        return (virtio_alloc_virtqueues(dev, 1, &vq_info));
}

static void
vtblk_resize_disk(struct vtblk_softc *sc, uint64_t new_capacity)
{
        device_t dev;
        struct disk *dp;
        int error;

        dev = sc->vtblk_dev;
        dp = sc->vtblk_disk;

        dp->d_mediasize = new_capacity;
        if (bootverbose) {
                device_printf(dev, "resized to %juMB (%ju %u byte sectors)\n",
                    (uintmax_t) dp->d_mediasize >> 20,
                    (uintmax_t) dp->d_mediasize / dp->d_sectorsize,
                    dp->d_sectorsize);
        }

        error = disk_resize(dp, M_NOWAIT);
        if (error) {
                device_printf(dev,
                    "disk_resize(9) failed, error: %d\n", error);
        }
}

static void
vtblk_alloc_disk(struct vtblk_softc *sc, struct virtio_blk_config *blkcfg)
{
        device_t dev;
        struct disk *dp;

        dev = sc->vtblk_dev;

        sc->vtblk_disk = dp = disk_alloc();
        dp->d_open = vtblk_open;
        dp->d_close = vtblk_close;
        dp->d_ioctl = vtblk_ioctl;
        dp->d_strategy = vtblk_strategy;
        dp->d_name = VTBLK_DISK_NAME;
        dp->d_unit = device_get_unit(dev);
        dp->d_drv1 = sc;
        dp->d_flags = DISKFLAG_UNMAPPED_BIO | DISKFLAG_DIRECT_COMPLETION;
        dp->d_hba_vendor = virtio_get_vendor(dev);
        dp->d_hba_device = virtio_get_device(dev);
        dp->d_hba_subvendor = virtio_get_subvendor(dev);
        dp->d_hba_subdevice = virtio_get_subdevice(dev);
        strlcpy(dp->d_attachment, device_get_nameunit(dev),
            sizeof(dp->d_attachment));

        if (virtio_with_feature(dev, VIRTIO_BLK_F_RO))
                dp->d_flags |= DISKFLAG_WRITE_PROTECT;
        else {
                if (virtio_with_feature(dev, VIRTIO_BLK_F_FLUSH))
                        dp->d_flags |= DISKFLAG_CANFLUSHCACHE;
                dp->d_dump = vtblk_dump;
        }

        /* Capacity is always in 512-byte units. */
        dp->d_mediasize = blkcfg->capacity * VTBLK_BSIZE;

        if (virtio_with_feature(dev, VIRTIO_BLK_F_BLK_SIZE))
                dp->d_sectorsize = blkcfg->blk_size;
        else
                dp->d_sectorsize = VTBLK_BSIZE;

        /*
         * The VirtIO maximum I/O size is given in terms of segments.
         * However, FreeBSD limits I/O size by logical buffer size, not
         * by physically contiguous pages. Therefore, we have to assume
         * no pages are contiguous. This may impose an artificially low
         * maximum I/O size. But in practice, since QEMU advertises 128
         * segments, this gives us a maximum IO size of 125 * PAGE_SIZE,
         * which is typically greater than maxphys. Eventually we should
         * just advertise maxphys and split buffers that are too big.
         *
         * If we're not asking busdma to align data to page boundaries, the
         * maximum I/O size is reduced by PAGE_SIZE in order to accommodate
         * unaligned I/Os.
         */
        dp->d_maxsize = (sc->vtblk_max_nsegs - VTBLK_MIN_SEGMENTS) *
            PAGE_SIZE;
        if ((sc->vtblk_flags & VTBLK_FLAG_BUSDMA_ALIGN) == 0)
                dp->d_maxsize -= PAGE_SIZE;

        if (virtio_with_feature(dev, VIRTIO_BLK_F_GEOMETRY)) {
                dp->d_fwsectors = blkcfg->geometry.sectors;
                dp->d_fwheads = blkcfg->geometry.heads;
        }

        if (virtio_with_feature(dev, VIRTIO_BLK_F_TOPOLOGY) &&
            blkcfg->topology.physical_block_exp > 0) {
                dp->d_stripesize = dp->d_sectorsize *
                    (1 << blkcfg->topology.physical_block_exp);
                dp->d_stripeoffset = (dp->d_stripesize -
                    blkcfg->topology.alignment_offset * dp->d_sectorsize) %
                    dp->d_stripesize;
        }

        if (virtio_with_feature(dev, VIRTIO_BLK_F_DISCARD)) {
                dp->d_flags |= DISKFLAG_CANDELETE;
                dp->d_delmaxsize = blkcfg->max_discard_sectors * VTBLK_BSIZE;
        }

        if (vtblk_write_cache_enabled(sc, blkcfg) != 0)
                sc->vtblk_write_cache = VTBLK_CACHE_WRITEBACK;
        else
                sc->vtblk_write_cache = VTBLK_CACHE_WRITETHROUGH;
}

static void
vtblk_create_disk(struct vtblk_softc *sc)
{
        struct disk *dp;

        dp = sc->vtblk_disk;

        vtblk_ident(sc);

        device_printf(sc->vtblk_dev, "%juMB (%ju %u byte sectors)\n",
            (uintmax_t) dp->d_mediasize >> 20,
            (uintmax_t) dp->d_mediasize / dp->d_sectorsize,
            dp->d_sectorsize);

        disk_create(dp, DISK_VERSION);
}

static void
vtblk_ack_load_callback(void *arg, bus_dma_segment_t *segs, int nsegs,
    int error)
{
        struct vtblk_request *req;

        if (error != 0)
                return;

        KASSERT(nsegs == 1, ("%s: %d segments returned!", __func__, nsegs));

        req = (struct vtblk_request *)arg;
        req->vbr_ack_paddr = segs[0].ds_addr;
}

static void
vtblk_hdr_load_callback(void *arg, bus_dma_segment_t *segs, int nsegs,
    int error)
{
        struct vtblk_request *req;

        if (error != 0)
                return;

        KASSERT(nsegs == 1, ("%s: %d segments returned!", __func__, nsegs));

        req = (struct vtblk_request *)arg;
        req->vbr_hdr_paddr = segs[0].ds_addr;
}

static int
vtblk_create_request(struct vtblk_softc *sc, struct vtblk_request *req)
{
        req->vbr_sc = sc;

        if (bus_dmamap_create(sc->vtblk_dmat, 0, &req->vbr_mapp))
                goto error_free;

        if (bus_dmamem_alloc(sc->vtblk_hdr_dmat, (void **)&req->vbr_hdr,
            BUS_DMA_NOWAIT | BUS_DMA_ZERO | BUS_DMA_COHERENT,
            &req->vbr_hdr_mapp))
                goto error_destroy;

        if (bus_dmamem_alloc(sc->vtblk_ack_dmat, (void **)&req->vbr_ack,
            BUS_DMA_NOWAIT | BUS_DMA_ZERO | BUS_DMA_COHERENT,
            &req->vbr_ack_mapp))
                goto error_hdr_free;

        MPASS(sglist_count(req->vbr_hdr, sizeof(*req->vbr_hdr)) == 1);
        MPASS(sglist_count(req->vbr_ack, sizeof(*req->vbr_ack)) == 1);

        if (bus_dmamap_load(sc->vtblk_hdr_dmat, req->vbr_hdr_mapp,
            req->vbr_hdr, sizeof(struct virtio_blk_outhdr),
            vtblk_hdr_load_callback, req, BUS_DMA_NOWAIT))
                goto error_ack_free;

        if (bus_dmamap_load(sc->vtblk_ack_dmat, req->vbr_ack_mapp,
            req->vbr_ack, sizeof(uint8_t), vtblk_ack_load_callback,
            req, BUS_DMA_NOWAIT))
                goto error_hdr_unload;

        return (0);

error_hdr_unload:
        bus_dmamap_unload(sc->vtblk_hdr_dmat, req->vbr_hdr_mapp);
error_ack_free:
        bus_dmamem_free(sc->vtblk_ack_dmat, req->vbr_ack, req->vbr_ack_mapp);
error_hdr_free:
        bus_dmamem_free(sc->vtblk_hdr_dmat, req->vbr_hdr, req->vbr_hdr_mapp);
error_destroy:
        bus_dmamap_destroy(sc->vtblk_dmat, req->vbr_mapp);
error_free:

        return (ENOMEM);
}

static int
vtblk_request_prealloc(struct vtblk_softc *sc)
{
        struct vtblk_request *req;
        int i, nreqs;
        int error;

        nreqs = virtqueue_size(sc->vtblk_vq);

        /*
         * Preallocate sufficient requests to keep the virtqueue full. Each
         * request consumes VTBLK_MIN_SEGMENTS or more descriptors so reduce
         * the number allocated when indirect descriptors are not available.
         */
        if ((sc->vtblk_flags & VTBLK_FLAG_INDIRECT) == 0)
                nreqs /= VTBLK_MIN_SEGMENTS;

        for (i = 0; i < nreqs; i++) {
                req = malloc(sizeof(struct vtblk_request), M_DEVBUF, M_NOWAIT);
                if (req == NULL)
                        return (ENOMEM);

                error = vtblk_create_request(sc, req);
                if (error) {
                        free(req, M_DEVBUF);
                        return (error);
                }

                sc->vtblk_request_count++;
                vtblk_request_enqueue(sc, req);
        }

        error = vtblk_create_request(sc, &sc->vtblk_dump_request);

        return (error);
}

static void
vtblk_request_free(struct vtblk_softc *sc)
{
        struct vtblk_request *req;

        MPASS(TAILQ_EMPTY(&sc->vtblk_req_ready));

        while ((req = vtblk_request_dequeue(sc)) != NULL) {
                sc->vtblk_request_count--;
                bus_dmamap_unload(sc->vtblk_ack_dmat, req->vbr_ack_mapp);
                bus_dmamem_free(sc->vtblk_ack_dmat, req->vbr_ack,
                    req->vbr_ack_mapp);
                bus_dmamap_unload(sc->vtblk_hdr_dmat, req->vbr_hdr_mapp);
                bus_dmamem_free(sc->vtblk_hdr_dmat, req->vbr_hdr,
                    req->vbr_hdr_mapp);
                bus_dmamap_destroy(sc->vtblk_dmat, req->vbr_mapp);
        }

        KASSERT(sc->vtblk_request_count == 0,
            ("%s: leaked %d requests", __func__, sc->vtblk_request_count));
}

static struct vtblk_request *
vtblk_request_dequeue(struct vtblk_softc *sc)
{
        struct vtblk_request *req;

        req = TAILQ_FIRST(&sc->vtblk_req_free);
        if (req != NULL) {
                TAILQ_REMOVE(&sc->vtblk_req_free, req, vbr_link);
                bzero(req->vbr_hdr, sizeof(struct virtio_blk_outhdr));
                *req->vbr_ack = 0;
                bzero(&req->vbr_bp, sizeof(struct vtblk_request) -
                    offsetof(struct vtblk_request, vbr_bp));
        }

        return (req);
}

static void
vtblk_request_enqueue(struct vtblk_softc *sc, struct vtblk_request *req)
{

        TAILQ_INSERT_HEAD(&sc->vtblk_req_free, req, vbr_link);
}

static struct vtblk_request *
vtblk_request_next_ready(struct vtblk_softc *sc)
{
        struct vtblk_request *req;

        req = TAILQ_FIRST(&sc->vtblk_req_ready);
        if (req != NULL)
                TAILQ_REMOVE(&sc->vtblk_req_ready, req, vbr_link);

        return (req);
}

static void
vtblk_request_requeue_ready(struct vtblk_softc *sc, struct vtblk_request *req)
{

        /* NOTE: Currently, there will be at most one request in the queue. */
        TAILQ_INSERT_HEAD(&sc->vtblk_req_ready, req, vbr_link);
}

static struct vtblk_request *
vtblk_request_next(struct vtblk_softc *sc)
{
        struct vtblk_request *req;

        req = vtblk_request_next_ready(sc);
        if (req != NULL)
                return (req);

        return (vtblk_request_bio(sc));
}

static struct vtblk_request *
vtblk_request_bio(struct vtblk_softc *sc)
{
        struct bio_queue_head *bioq;
        struct vtblk_request *req;
        struct bio *bp;

        bioq = &sc->vtblk_bioq;

        if (bioq_first(bioq) == NULL)
                return (NULL);

        req = vtblk_request_dequeue(sc);
        if (req == NULL)
                return (NULL);

        bp = bioq_takefirst(bioq);
        req->vbr_bp = bp;
        *req->vbr_ack = -1;
        req->vbr_hdr->ioprio = vtblk_gtoh32(sc, 1);

        switch (bp->bio_cmd) {
        case BIO_FLUSH:
                req->vbr_hdr->type = vtblk_gtoh32(sc, VIRTIO_BLK_T_FLUSH);
                req->vbr_hdr->sector = 0;
                break;
        case BIO_READ:
                req->vbr_hdr->type = vtblk_gtoh32(sc, VIRTIO_BLK_T_IN);
                req->vbr_hdr->sector = vtblk_gtoh64(sc, bp->bio_offset /
                    VTBLK_BSIZE);
                break;
        case BIO_WRITE:
                req->vbr_hdr->type = vtblk_gtoh32(sc, VIRTIO_BLK_T_OUT);
                req->vbr_hdr->sector = vtblk_gtoh64(sc, bp->bio_offset /
                    VTBLK_BSIZE);
                break;
        case BIO_DELETE:
                req->vbr_hdr->type = vtblk_gtoh32(sc, VIRTIO_BLK_T_DISCARD);
                req->vbr_hdr->sector = vtblk_gtoh64(sc, bp->bio_offset /
                    VTBLK_BSIZE);
                break;
        default:
                panic("%s: bio with unhandled cmd: %d", __func__, bp->bio_cmd);
        }

        if (bp->bio_flags & BIO_ORDERED)
                req->vbr_hdr->type |= vtblk_gtoh32(sc, VIRTIO_BLK_T_BARRIER);

        return (req);
}

static int
vtblk_request_execute(struct vtblk_request *req, int flags)
{
        struct vtblk_softc *sc = req->vbr_sc;
        struct bio *bp = req->vbr_bp;
        int error = 0;

        /*
         * Call via bus_dmamap_load_bio or directly depending on whether we
         * have a buffer we need to map.  If we don't have a busdma map,
         * try to perform the I/O directly and hope that it works (this will
         * happen when dumping).
         */
        if ((req->vbr_mapp != NULL) &&
            (bp->bio_cmd == BIO_READ || bp->bio_cmd == BIO_WRITE)) {
                error = bus_dmamap_load_bio(sc->vtblk_dmat, req->vbr_mapp,
                    req->vbr_bp, vtblk_request_execute_cb, req, flags);
                if (error == EINPROGRESS) {
                        req->vbr_busdma_wait = 1;
                        sc->vtblk_flags |= VTBLK_FLAG_BUSDMA_WAIT;
                }
        } else {
                vtblk_request_execute_cb(req, NULL, 0, 0);
        }

        return (error ? error : req->vbr_error);
}

static void
vtblk_request_execute_cb(void * callback_arg, bus_dma_segment_t * segs,
    int nseg, int error)
{
        struct vtblk_request *req;
        struct vtblk_softc *sc;
        struct virtqueue *vq;
        struct sglist *sg;
        struct bio *bp;
        int ordered, readable, writable, i;

        req = (struct vtblk_request *)callback_arg;
        sc = req->vbr_sc;
        vq = sc->vtblk_vq;
        sg = sc->vtblk_sglist;
        bp = req->vbr_bp;
        ordered = 0;
        writable = 0;

        /*
         * If we paused request queueing while we waited for busdma to call us
         * asynchronously, unpause it now; this request made it through so we
         * don't need to worry about others getting ahead of us.  (Note that we
         * hold the device mutex so nothing will happen until after we return
         * anyway.)
         */
        if (req->vbr_busdma_wait)
                sc->vtblk_flags &= ~VTBLK_FLAG_BUSDMA_WAIT;

        /* Fail on errors from busdma. */
        if (error)
                goto out1;

        /*
         * Some hosts (such as bhyve) do not implement the barrier feature,
         * so we emulate it in the driver by allowing the barrier request
         * to be the only one in flight.
         */
        if ((sc->vtblk_flags & VTBLK_FLAG_BARRIER) == 0) {
                if (sc->vtblk_req_ordered != NULL) {
                        error = EBUSY;
                        goto out;
                }
                if (bp->bio_flags & BIO_ORDERED) {
                        if (!virtqueue_empty(vq)) {
                                error = EBUSY;
                                goto out;
                        }
                        ordered = 1;
                        req->vbr_hdr->type &= vtblk_gtoh32(sc,
                                ~VIRTIO_BLK_T_BARRIER);
                }
        }

        bus_dmamap_sync(sc->vtblk_hdr_dmat, req->vbr_hdr_mapp,
            BUS_DMASYNC_PREWRITE);

        sglist_reset(sg);
        sglist_append_phys(sg, req->vbr_hdr_paddr,
            sizeof(struct virtio_blk_outhdr));

        if (bp->bio_cmd == BIO_READ || bp->bio_cmd == BIO_WRITE) {
                /*
                 * We cast bus_addr_t to vm_paddr_t here; since we skip the
                 * iommu mapping (see vtblk_attach) this should be safe.
                 */
                for (i = 0; i < nseg; i++) {
                        error = sglist_append_phys(sg,
                            (vm_paddr_t)segs[i].ds_addr, segs[i].ds_len);
                        if (error || sg->sg_nseg == sg->sg_maxseg) {
                                panic("%s: bio %p data buffer too big %d",
                                    __func__, bp, error);
                        }
                }

                /* Special handling for dump, which bypasses busdma. */
                if (req->vbr_mapp == NULL) {
                        error = sglist_append_bio(sg, bp);
                        if (error || sg->sg_nseg == sg->sg_maxseg) {
                                panic("%s: bio %p data buffer too big %d",
                                    __func__, bp, error);
                        }
                }

                /* BIO_READ means the host writes into our buffer. */
                if (bp->bio_cmd == BIO_READ)
                        writable = sg->sg_nseg - 1;
        } else if (bp->bio_cmd == BIO_DELETE) {
                struct virtio_blk_discard_write_zeroes *discard;

                discard = malloc(sizeof(*discard), M_DEVBUF, M_NOWAIT | M_ZERO);
                if (discard == NULL) {
                        error = ENOMEM;
                        goto out;
                }

                bp->bio_driver1 = discard;
                discard->sector = vtblk_gtoh64(sc, bp->bio_offset / VTBLK_BSIZE);
                discard->num_sectors = vtblk_gtoh32(sc, bp->bio_bcount / VTBLK_BSIZE);
                error = sglist_append(sg, discard, sizeof(*discard));
                if (error || sg->sg_nseg == sg->sg_maxseg) {
                        panic("%s: bio %p data buffer too big %d",
                            __func__, bp, error);
                }
        }

        bus_dmamap_sync(sc->vtblk_ack_dmat, req->vbr_ack_mapp,
            BUS_DMASYNC_PREREAD);

        writable++;
        sglist_append_phys(sg, req->vbr_ack_paddr, sizeof(uint8_t));
        readable = sg->sg_nseg - writable;

        if (req->vbr_mapp != NULL) {
                switch (bp->bio_cmd) {
                case BIO_READ:
                        bus_dmamap_sync(sc->vtblk_dmat, req->vbr_mapp,
                            BUS_DMASYNC_PREREAD);
                        break;
                case BIO_WRITE:
                        bus_dmamap_sync(sc->vtblk_dmat, req->vbr_mapp,
                            BUS_DMASYNC_PREWRITE);
                        break;
                }
        }

        error = virtqueue_enqueue(vq, req, sg, readable, writable);
        if (error == 0 && ordered)
                sc->vtblk_req_ordered = req;

        /*
         * If we were called asynchronously, we need to notify the queue that
         * we've added a new request, since the notification from startio was
         * performed already.
         */
        if (error == 0 && req->vbr_busdma_wait)
                virtqueue_notify(vq);

out:
        if (error && (req->vbr_mapp != NULL))
                bus_dmamap_unload(sc->vtblk_dmat, req->vbr_mapp);
out1:
        if (error && req->vbr_requeue_on_error)
                vtblk_request_requeue_ready(sc, req);
        req->vbr_error = error;
}

static int
vtblk_request_error(struct vtblk_request *req)
{
        int error;

        bus_dmamap_sync(req->vbr_sc->vtblk_ack_dmat, req->vbr_ack_mapp,
            BUS_DMASYNC_POSTREAD);

        switch (*req->vbr_ack) {
        case VIRTIO_BLK_S_OK:
                error = 0;
                break;
        case VIRTIO_BLK_S_UNSUPP:
                error = ENOTSUP;
                break;
        default:
                error = EIO;
                break;
        }

        return (error);
}

static struct bio *
vtblk_queue_complete_one(struct vtblk_softc *sc, struct vtblk_request *req)
{
        struct bio *bp;

        if (sc->vtblk_req_ordered != NULL) {
                MPASS(sc->vtblk_req_ordered == req);
                sc->vtblk_req_ordered = NULL;
        }

        bp = req->vbr_bp;
        if (req->vbr_mapp != NULL) {
                switch (bp->bio_cmd) {
                case BIO_READ:
                        bus_dmamap_sync(sc->vtblk_dmat, req->vbr_mapp,
                            BUS_DMASYNC_POSTREAD);
                        bus_dmamap_unload(sc->vtblk_dmat, req->vbr_mapp);
                        break;
                case BIO_WRITE:
                        bus_dmamap_sync(sc->vtblk_dmat, req->vbr_mapp,
                            BUS_DMASYNC_POSTWRITE);
                        bus_dmamap_unload(sc->vtblk_dmat, req->vbr_mapp);
                        break;
                }
        }
        bp->bio_error = vtblk_request_error(req);
        return (bp);
}

static void
vtblk_queue_completed(struct vtblk_softc *sc, struct bio_queue *queue)
{
        struct vtblk_request *req;
        struct bio *bp;

        while ((req = virtqueue_dequeue(sc->vtblk_vq, NULL)) != NULL) {
                bp = vtblk_queue_complete_one(sc, req);

                TAILQ_INSERT_TAIL(queue, bp, bio_queue);
                vtblk_request_enqueue(sc, req);
        }
}

static void
vtblk_done_completed(struct vtblk_softc *sc, struct bio_queue *queue)
{
        struct bio *bp, *tmp;

        TAILQ_FOREACH_SAFE(bp, queue, bio_queue, tmp) {
                if (bp->bio_error != 0)
                        disk_err(bp, "hard error", -1, 1);
                vtblk_bio_done(sc, bp, bp->bio_error);
        }
}

static void
vtblk_drain_vq(struct vtblk_softc *sc)
{
        struct virtqueue *vq;
        struct vtblk_request *req;
        int last;

        vq = sc->vtblk_vq;
        last = 0;

        while ((req = virtqueue_drain(vq, &last)) != NULL) {
                vtblk_bio_done(sc, req->vbr_bp, ENXIO);
                vtblk_request_enqueue(sc, req);
        }

        sc->vtblk_req_ordered = NULL;
        KASSERT(virtqueue_empty(vq), ("virtqueue not empty"));
}

static void
vtblk_drain(struct vtblk_softc *sc)
{
        struct bio_queue_head *bioq;
        struct vtblk_request *req;
        struct bio *bp;

        bioq = &sc->vtblk_bioq;

        if (sc->vtblk_vq != NULL) {
                struct bio_queue queue;

                TAILQ_INIT(&queue);
                vtblk_queue_completed(sc, &queue);
                vtblk_done_completed(sc, &queue);

                vtblk_drain_vq(sc);
        }

        while ((req = vtblk_request_next_ready(sc)) != NULL) {
                vtblk_bio_done(sc, req->vbr_bp, ENXIO);
                vtblk_request_enqueue(sc, req);
        }

        while (bioq_first(bioq) != NULL) {
                bp = bioq_takefirst(bioq);
                vtblk_bio_done(sc, bp, ENXIO);
        }

        vtblk_request_free(sc);
}

static void
vtblk_startio(struct vtblk_softc *sc)
{
        struct virtqueue *vq;
        struct vtblk_request *req;
        int enq;

        VTBLK_LOCK_ASSERT(sc);
        vq = sc->vtblk_vq;
        enq = 0;

        if (sc->vtblk_flags & (VTBLK_FLAG_SUSPEND | VTBLK_FLAG_BUSDMA_WAIT))
                return;

        while (!virtqueue_full(vq)) {
                req = vtblk_request_next(sc);
                if (req == NULL)
                        break;

                req->vbr_requeue_on_error = 1;
                if (vtblk_request_execute(req, BUS_DMA_WAITOK))
                        break;

                enq++;
        }

        if (enq > 0)
                virtqueue_notify(vq);
}

static void
vtblk_bio_done(struct vtblk_softc *sc, struct bio *bp, int error)
{

        /* Because of GEOM direct dispatch, we cannot hold any locks. */
        if (sc != NULL)
                VTBLK_LOCK_ASSERT_NOTOWNED(sc);

        if (error) {
                bp->bio_resid = bp->bio_bcount;
                bp->bio_error = error;
                bp->bio_flags |= BIO_ERROR;
        } else {
                kmsan_mark_bio(bp, KMSAN_STATE_INITED);
        }

        if (bp->bio_driver1 != NULL) {
                free(bp->bio_driver1, M_DEVBUF);
                bp->bio_driver1 = NULL;
        }

        biodone(bp);
}

#define VTBLK_GET_CONFIG(_dev, _feature, _field, _cfg)                  \
        if (virtio_with_feature(_dev, _feature)) {                      \
                virtio_read_device_config(_dev,                         \
                    offsetof(struct virtio_blk_config, _field),         \
                    &(_cfg)->_field, sizeof((_cfg)->_field));           \
        }

static void
vtblk_read_config(struct vtblk_softc *sc, struct virtio_blk_config *blkcfg)
{
        device_t dev;

        dev = sc->vtblk_dev;

        bzero(blkcfg, sizeof(struct virtio_blk_config));

        /* The capacity is always available. */
        virtio_read_device_config(dev, offsetof(struct virtio_blk_config,
            capacity), &blkcfg->capacity, sizeof(blkcfg->capacity));

        /* Read the configuration if the feature was negotiated. */
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_SIZE_MAX, size_max, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_SEG_MAX, seg_max, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_GEOMETRY,
            geometry.cylinders, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_GEOMETRY,
            geometry.heads, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_GEOMETRY,
            geometry.sectors, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_BLK_SIZE, blk_size, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_TOPOLOGY,
            topology.physical_block_exp, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_TOPOLOGY,
            topology.alignment_offset, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_TOPOLOGY,
            topology.min_io_size, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_TOPOLOGY,
            topology.opt_io_size, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_CONFIG_WCE, wce, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_DISCARD, max_discard_sectors,
            blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_DISCARD, max_discard_seg, blkcfg);
        VTBLK_GET_CONFIG(dev, VIRTIO_BLK_F_DISCARD, discard_sector_alignment,
            blkcfg);
}

#undef VTBLK_GET_CONFIG

static void
vtblk_ident(struct vtblk_softc *sc)
{
        struct bio buf;
        struct disk *dp;
        struct vtblk_request *req;
        int len, error;

        dp = sc->vtblk_disk;
        len = MIN(VIRTIO_BLK_ID_BYTES, DISK_IDENT_SIZE);

        if (vtblk_tunable_int(sc, "no_ident", vtblk_no_ident) != 0)
                return;

        req = vtblk_request_dequeue(sc);
        if (req == NULL)
                return;

        *req->vbr_ack = -1;
        req->vbr_hdr->type = vtblk_gtoh32(sc, VIRTIO_BLK_T_GET_ID);
        req->vbr_hdr->ioprio = vtblk_gtoh32(sc, 1);
        req->vbr_hdr->sector = 0;

        req->vbr_bp = &buf;
        g_reset_bio(&buf);

        buf.bio_cmd = BIO_READ;
        buf.bio_data = dp->d_ident;
        buf.bio_bcount = len;

        VTBLK_LOCK(sc);
        error = vtblk_poll_request(sc, req);
        VTBLK_UNLOCK(sc);

        if (error) {
                device_printf(sc->vtblk_dev,
                    "error getting device identifier: %d\n", error);
        }
}

static int
vtblk_poll_request(struct vtblk_softc *sc, struct vtblk_request *req)
{
        struct vtblk_request *req1 __diagused;
        struct virtqueue *vq;
        struct bio *bp;
        int error;

        vq = sc->vtblk_vq;

        if (!virtqueue_empty(vq))
                return (EBUSY);

        error = vtblk_request_execute(req, BUS_DMA_NOWAIT);
        if (error)
                return (error);

        virtqueue_notify(vq);
        req1 = virtqueue_poll(vq, NULL);
        KASSERT(req == req1,
            ("%s: polling completed %p not %p", __func__, req1, req));

        bp = vtblk_queue_complete_one(sc, req);
        error = bp->bio_error;
        if (error && bootverbose) {
                device_printf(sc->vtblk_dev,
                    "%s: IO error: %d\n", __func__, error);
        }
        if (req != &sc->vtblk_dump_request)
                vtblk_request_enqueue(sc, req);

        return (error);
}

static int
vtblk_quiesce(struct vtblk_softc *sc)
{
        int error;

        VTBLK_LOCK_ASSERT(sc);
        error = 0;

        while (!virtqueue_empty(sc->vtblk_vq)) {
                if (mtx_sleep(&sc->vtblk_vq, VTBLK_MTX(sc), PRIBIO, "vtblkq",
                    VTBLK_QUIESCE_TIMEOUT) == EWOULDBLOCK) {
                        error = EBUSY;
                        break;
                }
        }

        return (error);
}

static void
vtblk_vq_intr(void *xsc)
{
        struct vtblk_softc *sc;
        struct virtqueue *vq;
        struct bio_queue queue;

        sc = xsc;
        vq = sc->vtblk_vq;
        TAILQ_INIT(&queue);

        VTBLK_LOCK(sc);

again:
        if (sc->vtblk_flags & VTBLK_FLAG_DETACH)
                goto out;

        vtblk_queue_completed(sc, &queue);
        vtblk_startio(sc);

        if (virtqueue_enable_intr(vq) != 0) {
                virtqueue_disable_intr(vq);
                goto again;
        }

        if (sc->vtblk_flags & VTBLK_FLAG_SUSPEND)
                wakeup(&sc->vtblk_vq);

out:
        VTBLK_UNLOCK(sc);
        vtblk_done_completed(sc, &queue);
}

static void
vtblk_stop(struct vtblk_softc *sc)
{

        virtqueue_disable_intr(sc->vtblk_vq);
        virtio_stop(sc->vtblk_dev);
}

static void
vtblk_dump_quiesce(struct vtblk_softc *sc)
{

        /*
         * Spin here until all the requests in-flight at the time of the
         * dump are completed and queued. The queued requests will be
         * biodone'd once the dump is finished.
         */
        while (!virtqueue_empty(sc->vtblk_vq))
                vtblk_queue_completed(sc, &sc->vtblk_dump_queue);
}

static int
vtblk_dump_write(struct vtblk_softc *sc, void *virtual, off_t offset,
    size_t length)
{
        struct bio buf;
        struct vtblk_request *req;

        req = &sc->vtblk_dump_request;
        req->vbr_sc = sc;
        *req->vbr_ack = -1;
        req->vbr_hdr->type = vtblk_gtoh32(sc, VIRTIO_BLK_T_OUT);
        req->vbr_hdr->ioprio = vtblk_gtoh32(sc, 1);
        req->vbr_hdr->sector = vtblk_gtoh64(sc, offset / VTBLK_BSIZE);

        req->vbr_bp = &buf;
        g_reset_bio(&buf);

        buf.bio_cmd = BIO_WRITE;
        buf.bio_data = virtual;
        buf.bio_bcount = length;

        return (vtblk_poll_request(sc, req));
}

static int
vtblk_dump_flush(struct vtblk_softc *sc)
{
        struct bio buf;
        struct vtblk_request *req;

        req = &sc->vtblk_dump_request;
        req->vbr_sc = sc;
        *req->vbr_ack = -1;
        req->vbr_hdr->type = vtblk_gtoh32(sc, VIRTIO_BLK_T_FLUSH);
        req->vbr_hdr->ioprio = vtblk_gtoh32(sc, 1);
        req->vbr_hdr->sector = 0;

        req->vbr_bp = &buf;
        g_reset_bio(&buf);

        buf.bio_cmd = BIO_FLUSH;

        return (vtblk_poll_request(sc, req));
}

static void
vtblk_dump_complete(struct vtblk_softc *sc)
{

        vtblk_dump_flush(sc);

        VTBLK_UNLOCK(sc);
        vtblk_done_completed(sc, &sc->vtblk_dump_queue);
        VTBLK_LOCK(sc);
}

static void
vtblk_set_write_cache(struct vtblk_softc *sc, int wc)
{

        /* Set either writeback (1) or writethrough (0) mode. */
        virtio_write_dev_config_1(sc->vtblk_dev,
            offsetof(struct virtio_blk_config, wce), wc);
}

static int
vtblk_write_cache_enabled(struct vtblk_softc *sc,
    struct virtio_blk_config *blkcfg)
{
        int wc;

        if (sc->vtblk_flags & VTBLK_FLAG_WCE_CONFIG) {
                wc = vtblk_tunable_int(sc, "writecache_mode",
                    vtblk_writecache_mode);
                if (wc >= 0 && wc < VTBLK_CACHE_MAX)
                        vtblk_set_write_cache(sc, wc);
                else
                        wc = blkcfg->wce;
        } else
                wc = virtio_with_feature(sc->vtblk_dev, VIRTIO_BLK_F_FLUSH);

        return (wc);
}

static int
vtblk_write_cache_sysctl(SYSCTL_HANDLER_ARGS)
{
        struct vtblk_softc *sc;
        int wc, error;

        sc = oidp->oid_arg1;
        wc = sc->vtblk_write_cache;

        error = sysctl_handle_int(oidp, &wc, 0, req);
        if (error || req->newptr == NULL)
                return (error);
        if ((sc->vtblk_flags & VTBLK_FLAG_WCE_CONFIG) == 0)
                return (EPERM);
        if (wc < 0 || wc >= VTBLK_CACHE_MAX)
                return (EINVAL);

        VTBLK_LOCK(sc);
        sc->vtblk_write_cache = wc;
        vtblk_set_write_cache(sc, sc->vtblk_write_cache);
        VTBLK_UNLOCK(sc);

        return (0);
}

static void
vtblk_setup_sysctl(struct vtblk_softc *sc)
{
        device_t dev;
        struct sysctl_ctx_list *ctx;
        struct sysctl_oid *tree;
        struct sysctl_oid_list *child;

        dev = sc->vtblk_dev;
        ctx = device_get_sysctl_ctx(dev);
        tree = device_get_sysctl_tree(dev);
        child = SYSCTL_CHILDREN(tree);

        SYSCTL_ADD_PROC(ctx, child, OID_AUTO, "writecache_mode",
            CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, sc, 0,
            vtblk_write_cache_sysctl, "I",
            "Write cache mode (writethrough (0) or writeback (1))");
}

static int
vtblk_tunable_int(struct vtblk_softc *sc, const char *knob, int def)
{
        char path[64];

        snprintf(path, sizeof(path),
            "hw.vtblk.%d.%s", device_get_unit(sc->vtblk_dev), knob);
        TUNABLE_INT_FETCH(path, &def);

        return (def);
}