ZIL: Call brt_pending_add() replaying TX_CLONE_RANGE

[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.
 */

#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>
#ifdef HAVE_LINUX_BLK_CGROUP_HEADER
#include <linux/blk-cgroup.h>
#endif

typedef struct vdev_disk {
        struct block_device             *vd_bdev;
        krwlock_t                       vd_lock;
} vdev_disk_t;

/*
 * 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)

/*
 * 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;

/*
 * BIO request failfast mask.
 */

static unsigned int zfs_vdev_failfast_mask = 1;

#ifdef HAVE_BLK_MODE_T
static blk_mode_t
#else
static fmode_t
#endif
vdev_bdev_mode(spa_mode_t spa_mode)
{
#ifdef HAVE_BLK_MODE_T
        blk_mode_t mode = 0;

        if (spa_mode & SPA_MODE_READ)
                mode |= BLK_OPEN_READ;

        if (spa_mode & SPA_MODE_WRITE)
                mode |= BLK_OPEN_WRITE;
#else
        fmode_t mode = 0;

        if (spa_mode & SPA_MODE_READ)
                mode |= FMODE_READ;

        if (spa_mode & SPA_MODE_WRITE)
                mode |= FMODE_WRITE;
#endif

        return (mode);
}

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

#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 = i_size_read(bdev_whole(bdev)->bd_inode) -
                    ((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_bdev) {
                spl_signal_kobj_evt(vd->vd_bdev);
        } else {
                vdev_dbgmsg(v, "vdev_disk_t is NULL for VDEV:%s\n",
                    v->vdev_path);
        }
}

#if !defined(HAVE_BLKDEV_GET_BY_PATH_4ARG)
/*
 * Define a dummy struct blk_holder_ops for kernel versions
 * prior to 6.5.
 */
struct blk_holder_ops {};
#endif

static struct block_device *
vdev_blkdev_get_by_path(const char *path, spa_mode_t mode, void *holder,
    const struct blk_holder_ops *hops)
{
#ifdef HAVE_BLKDEV_GET_BY_PATH_4ARG
        return (blkdev_get_by_path(path,
            vdev_bdev_mode(mode) | BLK_OPEN_EXCL, holder, hops));
#else
        return (blkdev_get_by_path(path,
            vdev_bdev_mode(mode) | FMODE_EXCL, holder));
#endif
}

static void
vdev_blkdev_put(struct block_device *bdev, spa_mode_t mode, void *holder)
{
#ifdef HAVE_BLKDEV_PUT_HOLDER
        return (blkdev_put(bdev, holder));
#else
        return (blkdev_put(bdev, vdev_bdev_mode(mode) | FMODE_EXCL));
#endif
}

static int
vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *max_psize,
    uint64_t *logical_ashift, uint64_t *physical_ashift)
{
        struct block_device *bdev;
#ifdef HAVE_BLK_MODE_T
        blk_mode_t mode = vdev_bdev_mode(spa_mode(v->vdev_spa));
#else
        fmode_t mode = vdev_bdev_mode(spa_mode(v->vdev_spa));
#endif
        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);
                bdev = vd->vd_bdev;
                vd->vd_bdev = NULL;

                if (bdev) {
                        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(bdev, mode, zfs_vdev_holder);
                }

                if (reread_part) {
                        bdev = vdev_blkdev_get_by_path(disk_name, mode,
                            zfs_vdev_holder, NULL);
                        if (!IS_ERR(bdev)) {
                                int error = vdev_bdev_reread_part(bdev);
                                vdev_blkdev_put(bdev, mode, 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();
        bdev = ERR_PTR(-ENXIO);
        while (IS_ERR(bdev) && ((gethrtime() - start) < timeout)) {
                bdev = vdev_blkdev_get_by_path(v->vdev_path, mode,
                    zfs_vdev_holder, NULL);
                if (unlikely(PTR_ERR(bdev) == -ENOENT)) {
                        /*
                         * There is no point of waiting since device is removed
                         * explicitly
                         */
                        if (v->vdev_removed)
                                break;

                        schedule_timeout(MSEC_TO_TICK(10));
                } else if (unlikely(PTR_ERR(bdev) == -ERESTARTSYS)) {
                        timeout = MSEC2NSEC(zfs_vdev_open_timeout_ms * 10);
                        continue;
                } else if (IS_ERR(bdev)) {
                        break;
                }
        }

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

        /*  Determine the physical block size */
        int physical_block_size = bdev_physical_block_size(vd->vd_bdev);

        /*  Determine the logical block size */
        int logical_block_size = bdev_logical_block_size(vd->vd_bdev);

        /* Clear the nowritecache bit, causes vdev_reopen() to try again. */
        v->vdev_nowritecache = B_FALSE;

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

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

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

        /* Physical volume size in bytes for the partition */
        *psize = bdev_capacity(vd->vd_bdev);

        /* Physical volume size in bytes including possible expansion space */
        *max_psize = bdev_max_capacity(vd->vd_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_bdev != NULL) {
                vdev_blkdev_put(vd->vd_bdev, spa_mode(v->vdev_spa),
                    zfs_vdev_holder);
        }

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

static dio_request_t *
vdev_disk_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_disk_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_disk_dio_get(dio_request_t *dr)
{
        atomic_inc(&dr->dr_ref);
}

static void
vdev_disk_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_disk_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);
                }
        }
}

BIO_END_IO_PROTO(vdev_disk_physio_completion, bio, error)
{
        dio_request_t *dr = bio->bi_private;

        if (dr->dr_error == 0) {
#ifdef HAVE_1ARG_BIO_END_IO_T
                dr->dr_error = BIO_END_IO_ERROR(bio);
#else
                if (error)
                        dr->dr_error = -(error);
                else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
                        dr->dr_error = EIO;
#endif
        }

        /* Drop reference acquired by __vdev_disk_physio */
        vdev_disk_dio_put(dr);
}

static inline void
vdev_submit_bio_impl(struct bio *bio)
{
#ifdef HAVE_1ARG_SUBMIT_BIO
        (void) submit_bio(bio);
#else
        (void) submit_bio(bio_data_dir(bio), bio);
#endif
}

/*
 * 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)

#ifdef HAVE_BIO_SET_DEV
#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
#else
/*
 * Provide a bio_set_dev() helper macro for pre-Linux 4.14 kernels.
 */
static inline void
bio_set_dev(struct bio *bio, struct block_device *bdev)
{
        bio->bi_bdev = bdev;
}
#endif /* HAVE_BIO_SET_DEV */
#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;
        vdev_submit_bio_impl(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 unsigned int
vdev_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_disk_physio(struct block_device *bdev, zio_t *zio,
    size_t io_size, uint64_t io_offset, int rw, int flags)
{
        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->bd_inode->i_size) {
                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)i_size_read(bdev->bd_inode));
                return (SET_ERROR(EIO));
        }

retry:
        dr = vdev_disk_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_disk_dio_free(dr);
                        bio_count *= 2;
                        goto retry;
                }

                nr_vecs = vdev_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_disk_dio_free(dr);
                        return (SET_ERROR(ENOMEM));
                }

                /* Matching put called by vdev_disk_physio_completion */
                vdev_disk_dio_get(dr);

                BIO_BI_SECTOR(dr->dr_bio[i]) = bio_offset >> 9;
                dr->dr_bio[i]->bi_end_io = vdev_disk_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_disk_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_disk_dio_put(dr);

        return (error);
}

BIO_END_IO_PROTO(vdev_disk_io_flush_completion, bio, error)
{
        zio_t *zio = bio->bi_private;
#ifdef HAVE_1ARG_BIO_END_IO_T
        zio->io_error = BIO_END_IO_ERROR(bio);
#else
        zio->io_error = -error;
#endif

        if (zio->io_error && (zio->io_error == EOPNOTSUPP))
                zio->io_vd->vdev_nowritecache = B_TRUE;

        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 int
vdev_disk_io_trim(zio_t *zio)
{
        vdev_t *v = zio->io_vd;
        vdev_disk_t *vd = v->vdev_tsd;

#if defined(HAVE_BLKDEV_ISSUE_SECURE_ERASE)
        if (zio->io_trim_flags & ZIO_TRIM_SECURE) {
                return (-blkdev_issue_secure_erase(vd->vd_bdev,
                    zio->io_offset >> 9, zio->io_size >> 9, GFP_NOFS));
        } else {
                return (-blkdev_issue_discard(vd->vd_bdev,
                    zio->io_offset >> 9, zio->io_size >> 9, GFP_NOFS));
        }
#elif defined(HAVE_BLKDEV_ISSUE_DISCARD)
        unsigned long trim_flags = 0;
#if defined(BLKDEV_DISCARD_SECURE)
        if (zio->io_trim_flags & ZIO_TRIM_SECURE)
                trim_flags |= BLKDEV_DISCARD_SECURE;
#endif
        return (-blkdev_issue_discard(vd->vd_bdev,
            zio->io_offset >> 9, zio->io_size >> 9, GFP_NOFS, trim_flags));
#else
#error "Unsupported kernel"
#endif
}

static void
vdev_disk_io_start(zio_t *zio)
{
        vdev_t *v = zio->io_vd;
        vdev_disk_t *vd = v->vdev_tsd;
        int rw, 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_bdev == NULL) {
                rw_exit(&vd->vd_lock);
                zio->io_error = ENXIO;
                zio_interrupt(zio);
                return;
        }

        switch (zio->io_type) {
        case ZIO_TYPE_IOCTL:

                if (!vdev_readable(v)) {
                        rw_exit(&vd->vd_lock);
                        zio->io_error = SET_ERROR(ENXIO);
                        zio_interrupt(zio);
                        return;
                }

                switch (zio->io_cmd) {
                case DKIOCFLUSHWRITECACHE:

                        if (zfs_nocacheflush)
                                break;

                        if (v->vdev_nowritecache) {
                                zio->io_error = SET_ERROR(ENOTSUP);
                                break;
                        }

                        error = vdev_disk_io_flush(vd->vd_bdev, zio);
                        if (error == 0) {
                                rw_exit(&vd->vd_lock);
                                return;
                        }

                        zio->io_error = error;

                        break;

                default:
                        zio->io_error = SET_ERROR(ENOTSUP);
                }

                rw_exit(&vd->vd_lock);
                zio_execute(zio);
                return;
        case ZIO_TYPE_WRITE:
                rw = WRITE;
                break;

        case ZIO_TYPE_READ:
                rw = READ;
                break;

        case ZIO_TYPE_TRIM:
                zio->io_error = vdev_disk_io_trim(zio);
                rw_exit(&vd->vd_lock);
                zio_interrupt(zio);
                return;

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

        zio->io_target_timestamp = zio_handle_io_delay(zio);
        error = __vdev_disk_physio(vd->vd_bdev, zio,
            zio->io_size, zio->io_offset, rw, 0);
        rw_exit(&vd->vd_lock);

        if (error) {
                zio->io_error = error;
                zio_interrupt(zio);
                return;
        }
}

static void
vdev_disk_io_done(zio_t *zio)
{
        /*
         * 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(vd->vd_bdev)) {
                        invalidate_bdev(vd->vd_bdev);
                        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 */
}

vdev_ops_t vdev_disk_ops = {
        .vdev_op_init = NULL,
        .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");