flush: only detect lack of flush support in one place

[zfs.git] / module / os / linux / zfs / vdev_disk.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or https://opensource.org/licenses/CDDL-1.0.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (C) 2008-2010 Lawrence Livermore National Security, LLC.
 * Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
 * Rewritten for Linux by Brian Behlendorf <behlendorf1@llnl.gov>.
 * LLNL-CODE-403049.
 * Copyright (c) 2012, 2019 by Delphix. All rights reserved.
 * Copyright (c) 2023, 2024, Klara Inc.
 */

#include <sys/zfs_context.h>
#include <sys/spa_impl.h>
#include <sys/vdev_disk.h>
#include <sys/vdev_impl.h>
#include <sys/vdev_trim.h>
#include <sys/abd.h>
#include <sys/fs/zfs.h>
#include <sys/zio.h>
#include <linux/blkpg.h>
#include <linux/msdos_fs.h>
#include <linux/vfs_compat.h>
#include <linux/blk-cgroup.h>

/*
 * Linux 6.8.x uses a bdev_handle as an instance/refcount for an underlying
 * block_device. Since it carries the block_device inside, its convenient to
 * just use the handle as a proxy.
 *
 * Linux 6.9.x uses a file for the same purpose.
 *
 * For pre-6.8, we just emulate this with a cast, since we don't need any of
 * the other fields inside the handle.
 */
#if defined(HAVE_BDEV_OPEN_BY_PATH)
typedef struct bdev_handle zfs_bdev_handle_t;
#define BDH_BDEV(bdh)           ((bdh)->bdev)
#define BDH_IS_ERR(bdh)         (IS_ERR(bdh))
#define BDH_PTR_ERR(bdh)        (PTR_ERR(bdh))
#define BDH_ERR_PTR(err)        (ERR_PTR(err))
#elif defined(HAVE_BDEV_FILE_OPEN_BY_PATH)
typedef struct file zfs_bdev_handle_t;
#define BDH_BDEV(bdh)           (file_bdev(bdh))
#define BDH_IS_ERR(bdh)         (IS_ERR(bdh))
#define BDH_PTR_ERR(bdh)        (PTR_ERR(bdh))
#define BDH_ERR_PTR(err)        (ERR_PTR(err))
#else
typedef void zfs_bdev_handle_t;
#define BDH_BDEV(bdh)           ((struct block_device *)bdh)
#define BDH_IS_ERR(bdh)         (IS_ERR(BDH_BDEV(bdh)))
#define BDH_PTR_ERR(bdh)        (PTR_ERR(BDH_BDEV(bdh)))
#define BDH_ERR_PTR(err)        (ERR_PTR(err))
#endif

typedef struct vdev_disk {
        zfs_bdev_handle_t               *vd_bdh;
        krwlock_t                       vd_lock;
} vdev_disk_t;

/*
 * Maximum number of segments to add to a bio (min 4). If this is higher than
 * the maximum allowed by the device queue or the kernel itself, it will be
 * clamped. Setting it to zero will cause the kernel's ideal size to be used.
 */
uint_t zfs_vdev_disk_max_segs = 0;

/*
 * Unique identifier for the exclusive vdev holder.
 */
static void *zfs_vdev_holder = VDEV_HOLDER;

/*
 * Wait up to zfs_vdev_open_timeout_ms milliseconds before determining the
 * device is missing. The missing path may be transient since the links
 * can be briefly removed and recreated in response to udev events.
 */
static uint_t zfs_vdev_open_timeout_ms = 1000;

/*
 * Size of the "reserved" partition, in blocks.
 */
#define EFI_MIN_RESV_SIZE       (16 * 1024)

/*
 * BIO request failfast mask.
 */

static unsigned int zfs_vdev_failfast_mask = 1;

/*
 * Convert SPA mode flags into bdev open mode flags.
 */
#ifdef HAVE_BLK_MODE_T
typedef blk_mode_t vdev_bdev_mode_t;
#define VDEV_BDEV_MODE_READ     BLK_OPEN_READ
#define VDEV_BDEV_MODE_WRITE    BLK_OPEN_WRITE
#define VDEV_BDEV_MODE_EXCL     BLK_OPEN_EXCL
#define VDEV_BDEV_MODE_MASK     (BLK_OPEN_READ|BLK_OPEN_WRITE|BLK_OPEN_EXCL)
#else
typedef fmode_t vdev_bdev_mode_t;
#define VDEV_BDEV_MODE_READ     FMODE_READ
#define VDEV_BDEV_MODE_WRITE    FMODE_WRITE
#define VDEV_BDEV_MODE_EXCL     FMODE_EXCL
#define VDEV_BDEV_MODE_MASK     (FMODE_READ|FMODE_WRITE|FMODE_EXCL)
#endif

static vdev_bdev_mode_t
vdev_bdev_mode(spa_mode_t smode)
{
        ASSERT3U(smode, !=, SPA_MODE_UNINIT);
        ASSERT0(smode & ~(SPA_MODE_READ|SPA_MODE_WRITE));

        vdev_bdev_mode_t bmode = VDEV_BDEV_MODE_EXCL;

        if (smode & SPA_MODE_READ)
                bmode |= VDEV_BDEV_MODE_READ;

        if (smode & SPA_MODE_WRITE)
                bmode |= VDEV_BDEV_MODE_WRITE;

        ASSERT(bmode & VDEV_BDEV_MODE_MASK);
        ASSERT0(bmode & ~VDEV_BDEV_MODE_MASK);

        return (bmode);
}

/*
 * Returns the usable capacity (in bytes) for the partition or disk.
 */
static uint64_t
bdev_capacity(struct block_device *bdev)
{
#ifdef HAVE_BDEV_NR_BYTES
        return (bdev_nr_bytes(bdev));
#else
        return (i_size_read(bdev->bd_inode));
#endif
}

#if !defined(HAVE_BDEV_WHOLE)
static inline struct block_device *
bdev_whole(struct block_device *bdev)
{
        return (bdev->bd_contains);
}
#endif

#if defined(HAVE_BDEVNAME)
#define vdev_bdevname(bdev, name)       bdevname(bdev, name)
#else
static inline void
vdev_bdevname(struct block_device *bdev, char *name)
{
        snprintf(name, BDEVNAME_SIZE, "%pg", bdev);
}
#endif

/*
 * Returns the maximum expansion capacity of the block device (in bytes).
 *
 * It is possible to expand a vdev when it has been created as a wholedisk
 * and the containing block device has increased in capacity.  Or when the
 * partition containing the pool has been manually increased in size.
 *
 * This function is only responsible for calculating the potential expansion
 * size so it can be reported by 'zpool list'.  The efi_use_whole_disk() is
 * responsible for verifying the expected partition layout in the wholedisk
 * case, and updating the partition table if appropriate.  Once the partition
 * size has been increased the additional capacity will be visible using
 * bdev_capacity().
 *
 * The returned maximum expansion capacity is always expected to be larger, or
 * at the very least equal, to its usable capacity to prevent overestimating
 * the pool expandsize.
 */
static uint64_t
bdev_max_capacity(struct block_device *bdev, uint64_t wholedisk)
{
        uint64_t psize;
        int64_t available;

        if (wholedisk && bdev != bdev_whole(bdev)) {
                /*
                 * When reporting maximum expansion capacity for a wholedisk
                 * deduct any capacity which is expected to be lost due to
                 * alignment restrictions.  Over reporting this value isn't
                 * harmful and would only result in slightly less capacity
                 * than expected post expansion.
                 * The estimated available space may be slightly smaller than
                 * bdev_capacity() for devices where the number of sectors is
                 * not a multiple of the alignment size and the partition layout
                 * is keeping less than PARTITION_END_ALIGNMENT bytes after the
                 * "reserved" EFI partition: in such cases return the device
                 * usable capacity.
                 */
                available = bdev_capacity(bdev_whole(bdev)) -
                    ((EFI_MIN_RESV_SIZE + NEW_START_BLOCK +
                    PARTITION_END_ALIGNMENT) << SECTOR_BITS);
                psize = MAX(available, bdev_capacity(bdev));
        } else {
                psize = bdev_capacity(bdev);
        }

        return (psize);
}

static void
vdev_disk_error(zio_t *zio)
{
        /*
         * This function can be called in interrupt context, for instance while
         * handling IRQs coming from a misbehaving disk device; use printk()
         * which is safe from any context.
         */
        printk(KERN_WARNING "zio pool=%s vdev=%s error=%d type=%d "
            "offset=%llu size=%llu flags=%llu\n", spa_name(zio->io_spa),
            zio->io_vd->vdev_path, zio->io_error, zio->io_type,
            (u_longlong_t)zio->io_offset, (u_longlong_t)zio->io_size,
            zio->io_flags);
}

static void
vdev_disk_kobj_evt_post(vdev_t *v)
{
        vdev_disk_t *vd = v->vdev_tsd;
        if (vd && vd->vd_bdh) {
                spl_signal_kobj_evt(BDH_BDEV(vd->vd_bdh));
        } else {
                vdev_dbgmsg(v, "vdev_disk_t is NULL for VDEV:%s\n",
                    v->vdev_path);
        }
}

static zfs_bdev_handle_t *
vdev_blkdev_get_by_path(const char *path, spa_mode_t smode, void *holder)
{
        vdev_bdev_mode_t bmode = vdev_bdev_mode(smode);

#if defined(HAVE_BDEV_FILE_OPEN_BY_PATH)
        return (bdev_file_open_by_path(path, bmode, holder, NULL));
#elif defined(HAVE_BDEV_OPEN_BY_PATH)
        return (bdev_open_by_path(path, bmode, holder, NULL));
#elif defined(HAVE_BLKDEV_GET_BY_PATH_4ARG)
        return (blkdev_get_by_path(path, bmode, holder, NULL));
#else
        return (blkdev_get_by_path(path, bmode, holder));
#endif
}

static void
vdev_blkdev_put(zfs_bdev_handle_t *bdh, spa_mode_t smode, void *holder)
{
#if defined(HAVE_BDEV_RELEASE)
        return (bdev_release(bdh));
#elif defined(HAVE_BLKDEV_PUT_HOLDER)
        return (blkdev_put(BDH_BDEV(bdh), holder));
#elif defined(HAVE_BLKDEV_PUT)
        return (blkdev_put(BDH_BDEV(bdh), vdev_bdev_mode(smode)));
#else
        fput(bdh);
#endif
}

static int
vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *max_psize,
    uint64_t *logical_ashift, uint64_t *physical_ashift)
{
        zfs_bdev_handle_t *bdh;
        spa_mode_t smode = spa_mode(v->vdev_spa);
        hrtime_t timeout = MSEC2NSEC(zfs_vdev_open_timeout_ms);
        vdev_disk_t *vd;

        /* Must have a pathname and it must be absolute. */
        if (v->vdev_path == NULL || v->vdev_path[0] != '/') {
                v->vdev_stat.vs_aux = VDEV_AUX_BAD_LABEL;
                vdev_dbgmsg(v, "invalid vdev_path");
                return (SET_ERROR(EINVAL));
        }

        /*
         * Reopen the device if it is currently open.  When expanding a
         * partition force re-scanning the partition table if userland
         * did not take care of this already. We need to do this while closed
         * in order to get an accurate updated block device size.  Then
         * since udev may need to recreate the device links increase the
         * open retry timeout before reporting the device as unavailable.
         */
        vd = v->vdev_tsd;
        if (vd) {
                char disk_name[BDEVNAME_SIZE + 6] = "/dev/";
                boolean_t reread_part = B_FALSE;

                rw_enter(&vd->vd_lock, RW_WRITER);
                bdh = vd->vd_bdh;
                vd->vd_bdh = NULL;

                if (bdh) {
                        struct block_device *bdev = BDH_BDEV(bdh);
                        if (v->vdev_expanding && bdev != bdev_whole(bdev)) {
                                vdev_bdevname(bdev_whole(bdev), disk_name + 5);
                                /*
                                 * If userland has BLKPG_RESIZE_PARTITION,
                                 * then it should have updated the partition
                                 * table already. We can detect this by
                                 * comparing our current physical size
                                 * with that of the device. If they are
                                 * the same, then we must not have
                                 * BLKPG_RESIZE_PARTITION or it failed to
                                 * update the partition table online. We
                                 * fallback to rescanning the partition
                                 * table from the kernel below. However,
                                 * if the capacity already reflects the
                                 * updated partition, then we skip
                                 * rescanning the partition table here.
                                 */
                                if (v->vdev_psize == bdev_capacity(bdev))
                                        reread_part = B_TRUE;
                        }

                        vdev_blkdev_put(bdh, smode, zfs_vdev_holder);
                }

                if (reread_part) {
                        bdh = vdev_blkdev_get_by_path(disk_name, smode,
                            zfs_vdev_holder);
                        if (!BDH_IS_ERR(bdh)) {
                                int error =
                                    vdev_bdev_reread_part(BDH_BDEV(bdh));
                                vdev_blkdev_put(bdh, smode, zfs_vdev_holder);
                                if (error == 0) {
                                        timeout = MSEC2NSEC(
                                            zfs_vdev_open_timeout_ms * 2);
                                }
                        }
                }
        } else {
                vd = kmem_zalloc(sizeof (vdev_disk_t), KM_SLEEP);

                rw_init(&vd->vd_lock, NULL, RW_DEFAULT, NULL);
                rw_enter(&vd->vd_lock, RW_WRITER);
        }

        /*
         * Devices are always opened by the path provided at configuration
         * time.  This means that if the provided path is a udev by-id path
         * then drives may be re-cabled without an issue.  If the provided
         * path is a udev by-path path, then the physical location information
         * will be preserved.  This can be critical for more complicated
         * configurations where drives are located in specific physical
         * locations to maximize the systems tolerance to component failure.
         *
         * Alternatively, you can provide your own udev rule to flexibly map
         * the drives as you see fit.  It is not advised that you use the
         * /dev/[hd]d devices which may be reordered due to probing order.
         * Devices in the wrong locations will be detected by the higher
         * level vdev validation.
         *
         * The specified paths may be briefly removed and recreated in
         * response to udev events.  This should be exceptionally unlikely
         * because the zpool command makes every effort to verify these paths
         * have already settled prior to reaching this point.  Therefore,
         * a ENOENT failure at this point is highly likely to be transient
         * and it is reasonable to sleep and retry before giving up.  In
         * practice delays have been observed to be on the order of 100ms.
         *
         * When ERESTARTSYS is returned it indicates the block device is
         * a zvol which could not be opened due to the deadlock detection
         * logic in zvol_open().  Extend the timeout and retry the open
         * subsequent attempts are expected to eventually succeed.
         */
        hrtime_t start = gethrtime();
        bdh = BDH_ERR_PTR(-ENXIO);
        while (BDH_IS_ERR(bdh) && ((gethrtime() - start) < timeout)) {
                bdh = vdev_blkdev_get_by_path(v->vdev_path, smode,
                    zfs_vdev_holder);
                if (unlikely(BDH_PTR_ERR(bdh) == -ENOENT)) {
                        /*
                         * There is no point of waiting since device is removed
                         * explicitly
                         */
                        if (v->vdev_removed)
                                break;

                        schedule_timeout_interruptible(MSEC_TO_TICK(10));
                } else if (unlikely(BDH_PTR_ERR(bdh) == -ERESTARTSYS)) {
                        timeout = MSEC2NSEC(zfs_vdev_open_timeout_ms * 10);
                        continue;
                } else if (BDH_IS_ERR(bdh)) {
                        break;
                }
        }

        if (BDH_IS_ERR(bdh)) {
                int error = -BDH_PTR_ERR(bdh);
                vdev_dbgmsg(v, "open error=%d timeout=%llu/%llu", error,
                    (u_longlong_t)(gethrtime() - start),
                    (u_longlong_t)timeout);
                vd->vd_bdh = NULL;
                v->vdev_tsd = vd;
                rw_exit(&vd->vd_lock);
                return (SET_ERROR(error));
        } else {
                vd->vd_bdh = bdh;
                v->vdev_tsd = vd;
                rw_exit(&vd->vd_lock);
        }

        struct block_device *bdev = BDH_BDEV(vd->vd_bdh);

        /*  Determine the physical block size */
        int physical_block_size = bdev_physical_block_size(bdev);

        /*  Determine the logical block size */
        int logical_block_size = bdev_logical_block_size(bdev);

        /*
         * If the device has a write cache, clear the nowritecache flag,
         * so that we start issuing flush requests again.
         */
        v->vdev_nowritecache = !zfs_bdev_has_write_cache(bdev);

        /* Set when device reports it supports TRIM. */
        v->vdev_has_trim = bdev_discard_supported(bdev);

        /* Set when device reports it supports secure TRIM. */
        v->vdev_has_securetrim = bdev_secure_discard_supported(bdev);

        /* Inform the ZIO pipeline that we are non-rotational */
        v->vdev_nonrot = blk_queue_nonrot(bdev_get_queue(bdev));

        /* Physical volume size in bytes for the partition */
        *psize = bdev_capacity(bdev);

        /* Physical volume size in bytes including possible expansion space */
        *max_psize = bdev_max_capacity(bdev, v->vdev_wholedisk);

        /* Based on the minimum sector size set the block size */
        *physical_ashift = highbit64(MAX(physical_block_size,
            SPA_MINBLOCKSIZE)) - 1;

        *logical_ashift = highbit64(MAX(logical_block_size,
            SPA_MINBLOCKSIZE)) - 1;

        return (0);
}

static void
vdev_disk_close(vdev_t *v)
{
        vdev_disk_t *vd = v->vdev_tsd;

        if (v->vdev_reopening || vd == NULL)
                return;

        if (vd->vd_bdh != NULL)
                vdev_blkdev_put(vd->vd_bdh, spa_mode(v->vdev_spa),
                    zfs_vdev_holder);

        rw_destroy(&vd->vd_lock);
        kmem_free(vd, sizeof (vdev_disk_t));
        v->vdev_tsd = NULL;
}

/*
 * preempt_schedule_notrace is GPL-only which breaks the ZFS build, so
 * replace it with preempt_schedule under the following condition:
 */
#if defined(CONFIG_ARM64) && \
    defined(CONFIG_PREEMPTION) && \
    defined(CONFIG_BLK_CGROUP)
#define preempt_schedule_notrace(x) preempt_schedule(x)
#endif

/*
 * As for the Linux 5.18 kernel bio_alloc() expects a block_device struct
 * as an argument removing the need to set it with bio_set_dev().  This
 * removes the need for all of the following compatibility code.
 */
#if !defined(HAVE_BIO_ALLOC_4ARG)

#if defined(CONFIG_BLK_CGROUP) && defined(HAVE_BIO_SET_DEV_GPL_ONLY)
/*
 * The Linux 5.5 kernel updated percpu_ref_tryget() which is inlined by
 * blkg_tryget() to use rcu_read_lock() instead of rcu_read_lock_sched().
 * As a side effect the function was converted to GPL-only.  Define our
 * own version when needed which uses rcu_read_lock_sched().
 *
 * The Linux 5.17 kernel split linux/blk-cgroup.h into a private and a public
 * part, moving blkg_tryget into the private one. Define our own version.
 */
#if defined(HAVE_BLKG_TRYGET_GPL_ONLY) || !defined(HAVE_BLKG_TRYGET)
static inline bool
vdev_blkg_tryget(struct blkcg_gq *blkg)
{
        struct percpu_ref *ref = &blkg->refcnt;
        unsigned long __percpu *count;
        bool rc;

        rcu_read_lock_sched();

        if (__ref_is_percpu(ref, &count)) {
                this_cpu_inc(*count);
                rc = true;
        } else {
#ifdef ZFS_PERCPU_REF_COUNT_IN_DATA
                rc = atomic_long_inc_not_zero(&ref->data->count);
#else
                rc = atomic_long_inc_not_zero(&ref->count);
#endif
        }

        rcu_read_unlock_sched();

        return (rc);
}
#else
#define vdev_blkg_tryget(bg)    blkg_tryget(bg)
#endif
#ifdef HAVE_BIO_SET_DEV_MACRO
/*
 * The Linux 5.0 kernel updated the bio_set_dev() macro so it calls the
 * GPL-only bio_associate_blkg() symbol thus inadvertently converting
 * the entire macro.  Provide a minimal version which always assigns the
 * request queue's root_blkg to the bio.
 */
static inline void
vdev_bio_associate_blkg(struct bio *bio)
{
#if defined(HAVE_BIO_BDEV_DISK)
        struct request_queue *q = bio->bi_bdev->bd_disk->queue;
#else
        struct request_queue *q = bio->bi_disk->queue;
#endif

        ASSERT3P(q, !=, NULL);
        ASSERT3P(bio->bi_blkg, ==, NULL);

        if (q->root_blkg && vdev_blkg_tryget(q->root_blkg))
                bio->bi_blkg = q->root_blkg;
}

#define bio_associate_blkg vdev_bio_associate_blkg
#else
static inline void
vdev_bio_set_dev(struct bio *bio, struct block_device *bdev)
{
#if defined(HAVE_BIO_BDEV_DISK)
        struct request_queue *q = bdev->bd_disk->queue;
#else
        struct request_queue *q = bio->bi_disk->queue;
#endif
        bio_clear_flag(bio, BIO_REMAPPED);
        if (bio->bi_bdev != bdev)
                bio_clear_flag(bio, BIO_THROTTLED);
        bio->bi_bdev = bdev;

        ASSERT3P(q, !=, NULL);
        ASSERT3P(bio->bi_blkg, ==, NULL);

        if (q->root_blkg && vdev_blkg_tryget(q->root_blkg))
                bio->bi_blkg = q->root_blkg;
}
#define bio_set_dev             vdev_bio_set_dev
#endif
#endif
#endif /* !HAVE_BIO_ALLOC_4ARG */

static inline void
vdev_submit_bio(struct bio *bio)
{
        struct bio_list *bio_list = current->bio_list;
        current->bio_list = NULL;
        (void) submit_bio(bio);
        current->bio_list = bio_list;
}

static inline struct bio *
vdev_bio_alloc(struct block_device *bdev, gfp_t gfp_mask,
    unsigned short nr_vecs)
{
        struct bio *bio;

#ifdef HAVE_BIO_ALLOC_4ARG
        bio = bio_alloc(bdev, nr_vecs, 0, gfp_mask);
#else
        bio = bio_alloc(gfp_mask, nr_vecs);
        if (likely(bio != NULL))
                bio_set_dev(bio, bdev);
#endif

        return (bio);
}

static inline uint_t
vdev_bio_max_segs(struct block_device *bdev)
{
        /*
         * Smallest of the device max segs and the tuneable max segs. Minimum
         * 4, so there's room to finish split pages if they come up.
         */
        const uint_t dev_max_segs = queue_max_segments(bdev_get_queue(bdev));
        const uint_t tune_max_segs = (zfs_vdev_disk_max_segs > 0) ?
            MAX(4, zfs_vdev_disk_max_segs) : dev_max_segs;
        const uint_t max_segs = MIN(tune_max_segs, dev_max_segs);

#ifdef HAVE_BIO_MAX_SEGS
        return (bio_max_segs(max_segs));
#else
        return (MIN(max_segs, BIO_MAX_PAGES));
#endif
}

static inline uint_t
vdev_bio_max_bytes(struct block_device *bdev)
{
        return (queue_max_sectors(bdev_get_queue(bdev)) << 9);
}


/*
 * Virtual block IO object (VBIO)
 *
 * Linux block IO (BIO) objects have a limit on how many data segments (pages)
 * they can hold. Depending on how they're allocated and structured, a large
 * ZIO can require more than one BIO to be submitted to the kernel, which then
 * all have to complete before we can return the completed ZIO back to ZFS.
 *
 * A VBIO is a wrapper around multiple BIOs, carrying everything needed to
 * translate a ZIO down into the kernel block layer and back again.
 *
 * Note that these are only used for data ZIOs (read/write). Meta-operations
 * (flush/trim) don't need multiple BIOs and so can just make the call
 * directly.
 */
typedef struct {
        zio_t           *vbio_zio;      /* parent zio */

        struct block_device *vbio_bdev; /* blockdev to submit bios to */

        abd_t           *vbio_abd;      /* abd carrying borrowed linear buf */

        uint_t          vbio_max_segs;  /* max segs per bio */

        uint_t          vbio_max_bytes; /* max bytes per bio */
        uint_t          vbio_lbs_mask;  /* logical block size mask */

        uint64_t        vbio_offset;    /* start offset of next bio */

        struct bio      *vbio_bio;      /* pointer to the current bio */
        int             vbio_flags;     /* bio flags */
} vbio_t;

static vbio_t *
vbio_alloc(zio_t *zio, struct block_device *bdev, int flags)
{
        vbio_t *vbio = kmem_zalloc(sizeof (vbio_t), KM_SLEEP);

        vbio->vbio_zio = zio;
        vbio->vbio_bdev = bdev;
        vbio->vbio_abd = NULL;
        vbio->vbio_max_segs = vdev_bio_max_segs(bdev);
        vbio->vbio_max_bytes = vdev_bio_max_bytes(bdev);
        vbio->vbio_lbs_mask = ~(bdev_logical_block_size(bdev)-1);
        vbio->vbio_offset = zio->io_offset;
        vbio->vbio_bio = NULL;
        vbio->vbio_flags = flags;

        return (vbio);
}

static void vbio_completion(struct bio *bio);

static int
vbio_add_page(vbio_t *vbio, struct page *page, uint_t size, uint_t offset)
{
        struct bio *bio = vbio->vbio_bio;
        uint_t ssize;

        while (size > 0) {
                if (bio == NULL) {
                        /* New BIO, allocate and set up */
                        bio = vdev_bio_alloc(vbio->vbio_bdev, GFP_NOIO,
                            vbio->vbio_max_segs);
                        VERIFY(bio);

                        BIO_BI_SECTOR(bio) = vbio->vbio_offset >> 9;
                        bio_set_op_attrs(bio,
                            vbio->vbio_zio->io_type == ZIO_TYPE_WRITE ?
                            WRITE : READ, vbio->vbio_flags);

                        if (vbio->vbio_bio) {
                                bio_chain(vbio->vbio_bio, bio);
                                vdev_submit_bio(vbio->vbio_bio);
                        }
                        vbio->vbio_bio = bio;
                }

                /*
                 * Only load as much of the current page data as will fit in
                 * the space left in the BIO, respecting lbs alignment. Older
                 * kernels will error if we try to overfill the BIO, while
                 * newer ones will accept it and split the BIO. This ensures
                 * everything works on older kernels, and avoids an additional
                 * overhead on the new.
                 */
                ssize = MIN(size, (vbio->vbio_max_bytes - BIO_BI_SIZE(bio)) &
                    vbio->vbio_lbs_mask);
                if (ssize > 0 &&
                    bio_add_page(bio, page, ssize, offset) == ssize) {
                        /* Accepted, adjust and load any remaining. */
                        size -= ssize;
                        offset += ssize;
                        continue;
                }

                /* No room, set up for a new BIO and loop */
                vbio->vbio_offset += BIO_BI_SIZE(bio);

                /* Signal new BIO allocation wanted */
                bio = NULL;
        }

        return (0);
}

/* Iterator callback to submit ABD pages to the vbio. */
static int
vbio_fill_cb(struct page *page, size_t off, size_t len, void *priv)
{
        vbio_t *vbio = priv;
        return (vbio_add_page(vbio, page, len, off));
}

/* Create some BIOs, fill them with data and submit them */
static void
vbio_submit(vbio_t *vbio, abd_t *abd, uint64_t size)
{
        /*
         * We plug so we can submit the BIOs as we go and only unplug them when
         * they are fully created and submitted. This is important; if we don't
         * plug, then the kernel may start executing earlier BIOs while we're
         * still creating and executing later ones, and if the device goes
         * away while that's happening, older kernels can get confused and
         * trample memory.
         */
        struct blk_plug plug;
        blk_start_plug(&plug);

        (void) abd_iterate_page_func(abd, 0, size, vbio_fill_cb, vbio);
        ASSERT(vbio->vbio_bio);

        vbio->vbio_bio->bi_end_io = vbio_completion;
        vbio->vbio_bio->bi_private = vbio;

        /*
         * Once submitted, vbio_bio now owns vbio (through bi_private) and we
         * can't touch it again. The bio may complete and vbio_completion() be
         * called and free the vbio before this task is run again, so we must
         * consider it invalid from this point.
         */
        vdev_submit_bio(vbio->vbio_bio);

        blk_finish_plug(&plug);
}

/* IO completion callback */
static void
vbio_completion(struct bio *bio)
{
        vbio_t *vbio = bio->bi_private;
        zio_t *zio = vbio->vbio_zio;

        ASSERT(zio);

        /* Capture and log any errors */
        zio->io_error = bi_status_to_errno(bio->bi_status);
        ASSERT3U(zio->io_error, >=, 0);

        if (zio->io_error)
                vdev_disk_error(zio);

        /* Return the BIO to the kernel */
        bio_put(bio);

        /*
         * We're likely in an interrupt context so we can't do ABD/memory work
         * here; instead we stash vbio on the zio and take care of it in the
         * done callback.
         */
        ASSERT3P(zio->io_bio, ==, NULL);
        zio->io_bio = vbio;

        zio_delay_interrupt(zio);
}

/*
 * Iterator callback to count ABD pages and check their size & alignment.
 *
 * On Linux, each BIO segment can take a page pointer, and an offset+length of
 * the data within that page. A page can be arbitrarily large ("compound"
 * pages) but we still have to ensure the data portion is correctly sized and
 * aligned to the logical block size, to ensure that if the kernel wants to
 * split the BIO, the two halves will still be properly aligned.
 *
 * NOTE: if you change this function, change the copy in
 * tests/zfs-tests/tests/functional/vdev_disk/page_alignment.c, and add test
 * data there to validate the change you're making.
 */
typedef struct {
        size_t  blocksize;
        int     seen_first;
        int     seen_last;
} vdev_disk_check_alignment_t;

static int
vdev_disk_check_alignment_cb(struct page *page, size_t off, size_t len,
    void *priv)
{
        (void) page;
        vdev_disk_check_alignment_t *s = priv;

        /*
         * The cardinal rule: a single on-disk block must never cross an
         * physical (order-0) page boundary, as the kernel expects to be able
         * to split at both LBS and page boundaries.
         *
         * This implies various alignment rules for the blocks in this
         * (possibly compound) page, which we can check for.
         */

        /*
         * If the previous page did not end on a page boundary, then we
         * can't proceed without creating a hole.
         */
        if (s->seen_last)
                return (1);

        /* This page must contain only whole LBS-sized blocks. */
        if (!IS_P2ALIGNED(len, s->blocksize))
                return (1);

        /*
         * If this is not the first page in the ABD, then the data must start
         * on a page-aligned boundary (so the kernel can split on page
         * boundaries without having to deal with a hole). If it is, then
         * it can start on LBS-alignment.
         */
        if (s->seen_first) {
                if (!IS_P2ALIGNED(off, PAGESIZE))
                        return (1);
        } else {
                if (!IS_P2ALIGNED(off, s->blocksize))
                        return (1);
                s->seen_first = 1;
        }

        /*
         * If this data does not end on a page-aligned boundary, then this
         * must be the last page in the ABD, for the same reason.
         */
        s->seen_last = !IS_P2ALIGNED(off+len, PAGESIZE);

        return (0);
}

/*
 * Check if we can submit the pages in this ABD to the kernel as-is. Returns
 * the number of pages, or 0 if it can't be submitted like this.
 */
static boolean_t
vdev_disk_check_alignment(abd_t *abd, uint64_t size, struct block_device *bdev)
{
        vdev_disk_check_alignment_t s = {
            .blocksize = bdev_logical_block_size(bdev),
        };

        if (abd_iterate_page_func(abd, 0, size,
            vdev_disk_check_alignment_cb, &s))
                return (B_FALSE);

        return (B_TRUE);
}

static int
vdev_disk_io_rw(zio_t *zio)
{
        vdev_t *v = zio->io_vd;
        vdev_disk_t *vd = v->vdev_tsd;
        struct block_device *bdev = BDH_BDEV(vd->vd_bdh);
        int flags = 0;

        /*
         * Accessing outside the block device is never allowed.
         */
        if (zio->io_offset + zio->io_size > bdev_capacity(bdev)) {
                vdev_dbgmsg(zio->io_vd,
                    "Illegal access %llu size %llu, device size %llu",
                    (u_longlong_t)zio->io_offset,
                    (u_longlong_t)zio->io_size,
                    (u_longlong_t)bdev_capacity(bdev));
                return (SET_ERROR(EIO));
        }

        if (!(zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)) &&
            v->vdev_failfast == B_TRUE) {
                bio_set_flags_failfast(bdev, &flags, zfs_vdev_failfast_mask & 1,
                    zfs_vdev_failfast_mask & 2, zfs_vdev_failfast_mask & 4);
        }

        /*
         * Check alignment of the incoming ABD. If any part of it would require
         * submitting a page that is not aligned to both the logical block size
         * and the page size, then we take a copy into a new memory region with
         * correct alignment.  This should be impossible on a 512b LBS. On
         * larger blocks, this can happen at least when a small number of
         * blocks (usually 1) are allocated from a shared slab, or when
         * abnormally-small data regions (eg gang headers) are mixed into the
         * same ABD as larger allocations (eg aggregations).
         */
        abd_t *abd = zio->io_abd;
        if (!vdev_disk_check_alignment(abd, zio->io_size, bdev)) {
                /* Allocate a new memory region with guaranteed alignment */
                abd = abd_alloc_for_io(zio->io_size,
                    zio->io_abd->abd_flags & ABD_FLAG_META);

                /* If we're writing copy our data into it */
                if (zio->io_type == ZIO_TYPE_WRITE)
                        abd_copy(abd, zio->io_abd, zio->io_size);

                /*
                 * False here would mean the new allocation has an invalid
                 * alignment too, which would mean that abd_alloc() is not
                 * guaranteeing this, or our logic in
                 * vdev_disk_check_alignment() is wrong. In either case,
                 * something in seriously wrong and its not safe to continue.
                 */
                VERIFY(vdev_disk_check_alignment(abd, zio->io_size, bdev));
        }

        /* Allocate vbio, with a pointer to the borrowed ABD if necessary */
        vbio_t *vbio = vbio_alloc(zio, bdev, flags);
        if (abd != zio->io_abd)
                vbio->vbio_abd = abd;

        /* Fill it with data pages and submit it to the kernel */
        vbio_submit(vbio, abd, zio->io_size);
        return (0);
}

/* ========== */

/*
 * This is the classic, battle-tested BIO submission code. Until we're totally
 * sure that the new code is safe and correct in all cases, this will remain
 * available and can be enabled by setting zfs_vdev_disk_classic=1 at module
 * load time.
 *
 * These functions have been renamed to vdev_classic_* to make it clear what
 * they belong to, but their implementations are unchanged.
 */

/*
 * Virtual device vector for disks.
 */
typedef struct dio_request {
        zio_t                   *dr_zio;        /* Parent ZIO */
        atomic_t                dr_ref;         /* References */
        int                     dr_error;       /* Bio error */
        int                     dr_bio_count;   /* Count of bio's */
        struct bio              *dr_bio[];      /* Attached bio's */
} dio_request_t;

static dio_request_t *
vdev_classic_dio_alloc(int bio_count)
{
        dio_request_t *dr = kmem_zalloc(sizeof (dio_request_t) +
            sizeof (struct bio *) * bio_count, KM_SLEEP);
        atomic_set(&dr->dr_ref, 0);
        dr->dr_bio_count = bio_count;
        dr->dr_error = 0;

        for (int i = 0; i < dr->dr_bio_count; i++)
                dr->dr_bio[i] = NULL;

        return (dr);
}

static void
vdev_classic_dio_free(dio_request_t *dr)
{
        int i;

        for (i = 0; i < dr->dr_bio_count; i++)
                if (dr->dr_bio[i])
                        bio_put(dr->dr_bio[i]);

        kmem_free(dr, sizeof (dio_request_t) +
            sizeof (struct bio *) * dr->dr_bio_count);
}

static void
vdev_classic_dio_get(dio_request_t *dr)
{
        atomic_inc(&dr->dr_ref);
}

static void
vdev_classic_dio_put(dio_request_t *dr)
{
        int rc = atomic_dec_return(&dr->dr_ref);

        /*
         * Free the dio_request when the last reference is dropped and
         * ensure zio_interpret is called only once with the correct zio
         */
        if (rc == 0) {
                zio_t *zio = dr->dr_zio;
                int error = dr->dr_error;

                vdev_classic_dio_free(dr);

                if (zio) {
                        zio->io_error = error;
                        ASSERT3S(zio->io_error, >=, 0);
                        if (zio->io_error)
                                vdev_disk_error(zio);

                        zio_delay_interrupt(zio);
                }
        }
}

static void
vdev_classic_physio_completion(struct bio *bio)
{
        dio_request_t *dr = bio->bi_private;

        if (dr->dr_error == 0) {
                dr->dr_error = bi_status_to_errno(bio->bi_status);
        }

        /* Drop reference acquired by vdev_classic_physio */
        vdev_classic_dio_put(dr);
}

static inline unsigned int
vdev_classic_bio_max_segs(zio_t *zio, int bio_size, uint64_t abd_offset)
{
        unsigned long nr_segs = abd_nr_pages_off(zio->io_abd,
            bio_size, abd_offset);

#ifdef HAVE_BIO_MAX_SEGS
        return (bio_max_segs(nr_segs));
#else
        return (MIN(nr_segs, BIO_MAX_PAGES));
#endif
}

static int
vdev_classic_physio(zio_t *zio)
{
        vdev_t *v = zio->io_vd;
        vdev_disk_t *vd = v->vdev_tsd;
        struct block_device *bdev = BDH_BDEV(vd->vd_bdh);
        size_t io_size = zio->io_size;
        uint64_t io_offset = zio->io_offset;
        int rw = zio->io_type == ZIO_TYPE_READ ? READ : WRITE;
        int flags = 0;

        dio_request_t *dr;
        uint64_t abd_offset;
        uint64_t bio_offset;
        int bio_size;
        int bio_count = 16;
        int error = 0;
        struct blk_plug plug;
        unsigned short nr_vecs;

        /*
         * Accessing outside the block device is never allowed.
         */
        if (io_offset + io_size > bdev_capacity(bdev)) {
                vdev_dbgmsg(zio->io_vd,
                    "Illegal access %llu size %llu, device size %llu",
                    (u_longlong_t)io_offset,
                    (u_longlong_t)io_size,
                    (u_longlong_t)bdev_capacity(bdev));
                return (SET_ERROR(EIO));
        }

retry:
        dr = vdev_classic_dio_alloc(bio_count);

        if (!(zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)) &&
            zio->io_vd->vdev_failfast == B_TRUE) {
                bio_set_flags_failfast(bdev, &flags, zfs_vdev_failfast_mask & 1,
                    zfs_vdev_failfast_mask & 2, zfs_vdev_failfast_mask & 4);
        }

        dr->dr_zio = zio;

        /*
         * Since bio's can have up to BIO_MAX_PAGES=256 iovec's, each of which
         * is at least 512 bytes and at most PAGESIZE (typically 4K), one bio
         * can cover at least 128KB and at most 1MB.  When the required number
         * of iovec's exceeds this, we are forced to break the IO in multiple
         * bio's and wait for them all to complete.  This is likely if the
         * recordsize property is increased beyond 1MB.  The default
         * bio_count=16 should typically accommodate the maximum-size zio of
         * 16MB.
         */

        abd_offset = 0;
        bio_offset = io_offset;
        bio_size = io_size;
        for (int i = 0; i <= dr->dr_bio_count; i++) {

                /* Finished constructing bio's for given buffer */
                if (bio_size <= 0)
                        break;

                /*
                 * If additional bio's are required, we have to retry, but
                 * this should be rare - see the comment above.
                 */
                if (dr->dr_bio_count == i) {
                        vdev_classic_dio_free(dr);
                        bio_count *= 2;
                        goto retry;
                }

                nr_vecs = vdev_classic_bio_max_segs(zio, bio_size, abd_offset);
                dr->dr_bio[i] = vdev_bio_alloc(bdev, GFP_NOIO, nr_vecs);
                if (unlikely(dr->dr_bio[i] == NULL)) {
                        vdev_classic_dio_free(dr);
                        return (SET_ERROR(ENOMEM));
                }

                /* Matching put called by vdev_classic_physio_completion */
                vdev_classic_dio_get(dr);

                BIO_BI_SECTOR(dr->dr_bio[i]) = bio_offset >> 9;
                dr->dr_bio[i]->bi_end_io = vdev_classic_physio_completion;
                dr->dr_bio[i]->bi_private = dr;
                bio_set_op_attrs(dr->dr_bio[i], rw, flags);

                /* Remaining size is returned to become the new size */
                bio_size = abd_bio_map_off(dr->dr_bio[i], zio->io_abd,
                    bio_size, abd_offset);

                /* Advance in buffer and construct another bio if needed */
                abd_offset += BIO_BI_SIZE(dr->dr_bio[i]);
                bio_offset += BIO_BI_SIZE(dr->dr_bio[i]);
        }

        /* Extra reference to protect dio_request during vdev_submit_bio */
        vdev_classic_dio_get(dr);

        if (dr->dr_bio_count > 1)
                blk_start_plug(&plug);

        /* Submit all bio's associated with this dio */
        for (int i = 0; i < dr->dr_bio_count; i++) {
                if (dr->dr_bio[i])
                        vdev_submit_bio(dr->dr_bio[i]);
        }

        if (dr->dr_bio_count > 1)
                blk_finish_plug(&plug);

        vdev_classic_dio_put(dr);

        return (error);
}

/* ========== */

static void
vdev_disk_io_flush_completion(struct bio *bio)
{
        zio_t *zio = bio->bi_private;
        zio->io_error = bi_status_to_errno(bio->bi_status);
        if (zio->io_error == EOPNOTSUPP || zio->io_error == ENOTTY)
                zio->io_error = SET_ERROR(ENOTSUP);

        bio_put(bio);
        ASSERT3S(zio->io_error, >=, 0);
        if (zio->io_error)
                vdev_disk_error(zio);
        zio_interrupt(zio);
}

static int
vdev_disk_io_flush(struct block_device *bdev, zio_t *zio)
{
        struct request_queue *q;
        struct bio *bio;

        q = bdev_get_queue(bdev);
        if (!q)
                return (SET_ERROR(ENXIO));

        bio = vdev_bio_alloc(bdev, GFP_NOIO, 0);
        if (unlikely(bio == NULL))
                return (SET_ERROR(ENOMEM));

        bio->bi_end_io = vdev_disk_io_flush_completion;
        bio->bi_private = zio;
        bio_set_flush(bio);
        vdev_submit_bio(bio);
        invalidate_bdev(bdev);

        return (0);
}

static void
vdev_disk_discard_end_io(struct bio *bio)
{
        zio_t *zio = bio->bi_private;
        zio->io_error = bi_status_to_errno(bio->bi_status);

        bio_put(bio);
        if (zio->io_error)
                vdev_disk_error(zio);
        zio_interrupt(zio);
}

/*
 * Wrappers for the different secure erase and discard APIs. We use async
 * when available; in this case, *biop is set to the last bio in the chain.
 */
static int
vdev_bdev_issue_secure_erase(zfs_bdev_handle_t *bdh, sector_t sector,
    sector_t nsect, struct bio **biop)
{
        *biop = NULL;
        int error;

#if defined(HAVE_BLKDEV_ISSUE_SECURE_ERASE)
        error = blkdev_issue_secure_erase(BDH_BDEV(bdh),
            sector, nsect, GFP_NOFS);
#elif defined(HAVE_BLKDEV_ISSUE_DISCARD_ASYNC_FLAGS)
        error = __blkdev_issue_discard(BDH_BDEV(bdh),
            sector, nsect, GFP_NOFS, BLKDEV_DISCARD_SECURE, biop);
#elif defined(HAVE_BLKDEV_ISSUE_DISCARD_FLAGS)
        error = blkdev_issue_discard(BDH_BDEV(bdh),
            sector, nsect, GFP_NOFS, BLKDEV_DISCARD_SECURE);
#else
#error "unsupported kernel"
#endif

        return (error);
}

static int
vdev_bdev_issue_discard(zfs_bdev_handle_t *bdh, sector_t sector,
    sector_t nsect, struct bio **biop)
{
        *biop = NULL;
        int error;

#if defined(HAVE_BLKDEV_ISSUE_DISCARD_ASYNC_FLAGS)
        error = __blkdev_issue_discard(BDH_BDEV(bdh),
            sector, nsect, GFP_NOFS, 0, biop);
#elif defined(HAVE_BLKDEV_ISSUE_DISCARD_ASYNC_NOFLAGS)
        error = __blkdev_issue_discard(BDH_BDEV(bdh),
            sector, nsect, GFP_NOFS, biop);
#elif defined(HAVE_BLKDEV_ISSUE_DISCARD_FLAGS)
        error = blkdev_issue_discard(BDH_BDEV(bdh),
            sector, nsect, GFP_NOFS, 0);
#elif defined(HAVE_BLKDEV_ISSUE_DISCARD_NOFLAGS)
        error = blkdev_issue_discard(BDH_BDEV(bdh),
            sector, nsect, GFP_NOFS);
#else
#error "unsupported kernel"
#endif

        return (error);
}

/*
 * Entry point for TRIM ops. This calls the right wrapper for secure erase or
 * discard, and then does the appropriate finishing work for error vs success
 * and async vs sync.
 */
static int
vdev_disk_io_trim(zio_t *zio)
{
        int error;
        struct bio *bio;

        zfs_bdev_handle_t *bdh = ((vdev_disk_t *)zio->io_vd->vdev_tsd)->vd_bdh;
        sector_t sector = zio->io_offset >> 9;
        sector_t nsects = zio->io_size >> 9;

        if (zio->io_trim_flags & ZIO_TRIM_SECURE)
                error = vdev_bdev_issue_secure_erase(bdh, sector, nsects, &bio);
        else
                error = vdev_bdev_issue_discard(bdh, sector, nsects, &bio);

        if (error != 0)
                return (SET_ERROR(-error));

        if (bio == NULL) {
                /*
                 * This was a synchronous op that completed successfully, so
                 * return it to ZFS immediately.
                 */
                zio_interrupt(zio);
        } else {
                /*
                 * This was an asynchronous op; set up completion callback and
                 * issue it.
                 */
                bio->bi_private = zio;
                bio->bi_end_io = vdev_disk_discard_end_io;
                vdev_submit_bio(bio);
        }

        return (0);
}

int (*vdev_disk_io_rw_fn)(zio_t *zio) = NULL;

static void
vdev_disk_io_start(zio_t *zio)
{
        vdev_t *v = zio->io_vd;
        vdev_disk_t *vd = v->vdev_tsd;
        int error;

        /*
         * If the vdev is closed, it's likely in the REMOVED or FAULTED state.
         * Nothing to be done here but return failure.
         */
        if (vd == NULL) {
                zio->io_error = ENXIO;
                zio_interrupt(zio);
                return;
        }

        rw_enter(&vd->vd_lock, RW_READER);

        /*
         * If the vdev is closed, it's likely due to a failed reopen and is
         * in the UNAVAIL state.  Nothing to be done here but return failure.
         */
        if (vd->vd_bdh == NULL) {
                rw_exit(&vd->vd_lock);
                zio->io_error = ENXIO;
                zio_interrupt(zio);
                return;
        }

        switch (zio->io_type) {
        case ZIO_TYPE_FLUSH:

                if (!vdev_readable(v)) {
                        /* Drive not there, can't flush */
                        error = SET_ERROR(ENXIO);
                } else if (zfs_nocacheflush) {
                        /* Flushing disabled by operator, declare success */
                        error = 0;
                } else if (v->vdev_nowritecache) {
                        /* This vdev not capable of flushing */
                        error = SET_ERROR(ENOTSUP);
                } else {
                        /*
                         * Issue the flush. If successful, the response will
                         * be handled in the completion callback, so we're done.
                         */
                        error = vdev_disk_io_flush(BDH_BDEV(vd->vd_bdh), zio);
                        if (error == 0) {
                                rw_exit(&vd->vd_lock);
                                return;
                        }
                }

                /* Couldn't issue the flush, so set the error and return it */
                rw_exit(&vd->vd_lock);
                zio->io_error = error;
                zio_execute(zio);
                return;

        case ZIO_TYPE_TRIM:
                error = vdev_disk_io_trim(zio);
                rw_exit(&vd->vd_lock);
                if (error) {
                        zio->io_error = error;
                        zio_execute(zio);
                }
                return;

        case ZIO_TYPE_READ:
        case ZIO_TYPE_WRITE:
                zio->io_target_timestamp = zio_handle_io_delay(zio);
                error = vdev_disk_io_rw_fn(zio);
                rw_exit(&vd->vd_lock);
                if (error) {
                        zio->io_error = error;
                        zio_interrupt(zio);
                }
                return;

        default:
                /*
                 * Getting here means our parent vdev has made a very strange
                 * request of us, and shouldn't happen. Assert here to force a
                 * crash in dev builds, but in production return the IO
                 * unhandled. The pool will likely suspend anyway but that's
                 * nicer than crashing the kernel.
                 */
                ASSERT3S(zio->io_type, ==, -1);

                rw_exit(&vd->vd_lock);
                zio->io_error = SET_ERROR(ENOTSUP);
                zio_interrupt(zio);
                return;
        }

        __builtin_unreachable();
}

static void
vdev_disk_io_done(zio_t *zio)
{
        /* If this was a read or write, we need to clean up the vbio */
        if (zio->io_bio != NULL) {
                vbio_t *vbio = zio->io_bio;
                zio->io_bio = NULL;

                /*
                 * If we copied the ABD before issuing it, clean up and return
                 * the copy to the ADB, with changes if appropriate.
                 */
                if (vbio->vbio_abd != NULL) {
                        if (zio->io_type == ZIO_TYPE_READ)
                                abd_copy(zio->io_abd, vbio->vbio_abd,
                                    zio->io_size);

                        abd_free(vbio->vbio_abd);
                        vbio->vbio_abd = NULL;
                }

                /* Final cleanup */
                kmem_free(vbio, sizeof (vbio_t));
        }

        /*
         * If the device returned EIO, we revalidate the media.  If it is
         * determined the media has changed this triggers the asynchronous
         * removal of the device from the configuration.
         */
        if (zio->io_error == EIO) {
                vdev_t *v = zio->io_vd;
                vdev_disk_t *vd = v->vdev_tsd;

                if (!zfs_check_disk_status(BDH_BDEV(vd->vd_bdh))) {
                        invalidate_bdev(BDH_BDEV(vd->vd_bdh));
                        v->vdev_remove_wanted = B_TRUE;
                        spa_async_request(zio->io_spa, SPA_ASYNC_REMOVE);
                }
        }
}

static void
vdev_disk_hold(vdev_t *vd)
{
        ASSERT(spa_config_held(vd->vdev_spa, SCL_STATE, RW_WRITER));

        /* We must have a pathname, and it must be absolute. */
        if (vd->vdev_path == NULL || vd->vdev_path[0] != '/')
                return;

        /*
         * Only prefetch path and devid info if the device has
         * never been opened.
         */
        if (vd->vdev_tsd != NULL)
                return;

}

static void
vdev_disk_rele(vdev_t *vd)
{
        ASSERT(spa_config_held(vd->vdev_spa, SCL_STATE, RW_WRITER));

        /* XXX: Implement me as a vnode rele for the device */
}

/*
 * BIO submission method. See comment above about vdev_classic.
 * Set zfs_vdev_disk_classic=0 for new, =1 for classic
 */
static uint_t zfs_vdev_disk_classic = 0;        /* default new */

/* Set submission function from module parameter */
static int
vdev_disk_param_set_classic(const char *buf, zfs_kernel_param_t *kp)
{
        int err = param_set_uint(buf, kp);
        if (err < 0)
                return (SET_ERROR(err));

        vdev_disk_io_rw_fn =
            zfs_vdev_disk_classic ? vdev_classic_physio : vdev_disk_io_rw;

        printk(KERN_INFO "ZFS: forcing %s BIO submission\n",
            zfs_vdev_disk_classic ? "classic" : "new");

        return (0);
}

/*
 * At first use vdev use, set the submission function from the default value if
 * it hasn't been set already.
 */
static int
vdev_disk_init(spa_t *spa, nvlist_t *nv, void **tsd)
{
        (void) spa;
        (void) nv;
        (void) tsd;

        if (vdev_disk_io_rw_fn == NULL)
                vdev_disk_io_rw_fn = zfs_vdev_disk_classic ?
                    vdev_classic_physio : vdev_disk_io_rw;

        return (0);
}

vdev_ops_t vdev_disk_ops = {
        .vdev_op_init = vdev_disk_init,
        .vdev_op_fini = NULL,
        .vdev_op_open = vdev_disk_open,
        .vdev_op_close = vdev_disk_close,
        .vdev_op_asize = vdev_default_asize,
        .vdev_op_min_asize = vdev_default_min_asize,
        .vdev_op_min_alloc = NULL,
        .vdev_op_io_start = vdev_disk_io_start,
        .vdev_op_io_done = vdev_disk_io_done,
        .vdev_op_state_change = NULL,
        .vdev_op_need_resilver = NULL,
        .vdev_op_hold = vdev_disk_hold,
        .vdev_op_rele = vdev_disk_rele,
        .vdev_op_remap = NULL,
        .vdev_op_xlate = vdev_default_xlate,
        .vdev_op_rebuild_asize = NULL,
        .vdev_op_metaslab_init = NULL,
        .vdev_op_config_generate = NULL,
        .vdev_op_nparity = NULL,
        .vdev_op_ndisks = NULL,
        .vdev_op_type = VDEV_TYPE_DISK,         /* name of this vdev type */
        .vdev_op_leaf = B_TRUE,                 /* leaf vdev */
        .vdev_op_kobj_evt_post = vdev_disk_kobj_evt_post
};

/*
 * The zfs_vdev_scheduler module option has been deprecated. Setting this
 * value no longer has any effect.  It has not yet been entirely removed
 * to allow the module to be loaded if this option is specified in the
 * /etc/modprobe.d/zfs.conf file.  The following warning will be logged.
 */
static int
param_set_vdev_scheduler(const char *val, zfs_kernel_param_t *kp)
{
        int error = param_set_charp(val, kp);
        if (error == 0) {
                printk(KERN_INFO "The 'zfs_vdev_scheduler' module option "
                    "is not supported.\n");
        }

        return (error);
}

static const char *zfs_vdev_scheduler = "unused";
module_param_call(zfs_vdev_scheduler, param_set_vdev_scheduler,
    param_get_charp, &zfs_vdev_scheduler, 0644);
MODULE_PARM_DESC(zfs_vdev_scheduler, "I/O scheduler");

int
param_set_min_auto_ashift(const char *buf, zfs_kernel_param_t *kp)
{
        uint_t val;
        int error;

        error = kstrtouint(buf, 0, &val);
        if (error < 0)
                return (SET_ERROR(error));

        if (val < ASHIFT_MIN || val > zfs_vdev_max_auto_ashift)
                return (SET_ERROR(-EINVAL));

        error = param_set_uint(buf, kp);
        if (error < 0)
                return (SET_ERROR(error));

        return (0);
}

int
param_set_max_auto_ashift(const char *buf, zfs_kernel_param_t *kp)
{
        uint_t val;
        int error;

        error = kstrtouint(buf, 0, &val);
        if (error < 0)
                return (SET_ERROR(error));

        if (val > ASHIFT_MAX || val < zfs_vdev_min_auto_ashift)
                return (SET_ERROR(-EINVAL));

        error = param_set_uint(buf, kp);
        if (error < 0)
                return (SET_ERROR(error));

        return (0);
}

ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, open_timeout_ms, UINT, ZMOD_RW,
        "Timeout before determining that a device is missing");

ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, failfast_mask, UINT, ZMOD_RW,
        "Defines failfast mask: 1 - device, 2 - transport, 4 - driver");

ZFS_MODULE_PARAM(zfs_vdev_disk, zfs_vdev_disk_, max_segs, UINT, ZMOD_RW,
        "Maximum number of data segments to add to an IO request (min 4)");

ZFS_MODULE_PARAM_CALL(zfs_vdev_disk, zfs_vdev_disk_, classic,
    vdev_disk_param_set_classic, param_get_uint, ZMOD_RD,
        "Use classic BIO submission method");