Get rid of space_map_update() for ms_synced_length

[mirror_zfs.git] / module / 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 http://www.opensolaris.org/os/licensing.
 * 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, 2018 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/abd.h>
#include <sys/fs/zfs.h>
#include <sys/zio.h>
#include <linux/mod_compat.h>
#include <linux/msdos_fs.h>
#include <linux/vfs_compat.h>

char *zfs_vdev_scheduler = VDEV_SCHEDULER;
static void *zfs_vdev_holder = VDEV_HOLDER;

/* 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[0];     /* Attached bio's */
} dio_request_t;


#ifdef HAVE_OPEN_BDEV_EXCLUSIVE
static fmode_t
vdev_bdev_mode(int smode)
{
        fmode_t mode = 0;

        ASSERT3S(smode & (FREAD | FWRITE), !=, 0);

        if (smode & FREAD)
                mode |= FMODE_READ;

        if (smode & FWRITE)
                mode |= FMODE_WRITE;

        return (mode);
}
#else
static int
vdev_bdev_mode(int smode)
{
        int mode = 0;

        ASSERT3S(smode & (FREAD | FWRITE), !=, 0);

        if ((smode & FREAD) && !(smode & FWRITE))
                mode = SB_RDONLY;

        return (mode);
}
#endif /* HAVE_OPEN_BDEV_EXCLUSIVE */

/*
 * 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));
}

/*
 * 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().
 */
static uint64_t
bdev_max_capacity(struct block_device *bdev, uint64_t wholedisk)
{
        uint64_t psize;
        int64_t available;

        if (wholedisk && bdev->bd_part != NULL && bdev != bdev->bd_contains) {
                /*
                 * 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.
                 */
                available = i_size_read(bdev->bd_contains->bd_inode) -
                    ((EFI_MIN_RESV_SIZE + NEW_START_BLOCK +
                    PARTITION_END_ALIGNMENT) << SECTOR_BITS);
                if (available > 0)
                        psize = available;
                else
                        psize = 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=%x\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);
}

/*
 * Use the Linux 'noop' elevator for zfs managed block devices.  This
 * strikes the ideal balance by allowing the zfs elevator to do all
 * request ordering and prioritization.  While allowing the Linux
 * elevator to do the maximum front/back merging allowed by the
 * physical device.  This yields the largest possible requests for
 * the device with the lowest total overhead.
 */
static void
vdev_elevator_switch(vdev_t *v, char *elevator)
{
        vdev_disk_t *vd = v->vdev_tsd;
        struct request_queue *q;
        char *device;
        int error;

        for (int c = 0; c < v->vdev_children; c++)
                vdev_elevator_switch(v->vdev_child[c], elevator);

        if (!v->vdev_ops->vdev_op_leaf || vd->vd_bdev == NULL)
                return;

        q = bdev_get_queue(vd->vd_bdev);
        device = vd->vd_bdev->bd_disk->disk_name;

        /*
         * Skip devices which are not whole disks (partitions).
         * Device-mapper devices are excepted since they may be whole
         * disks despite the vdev_wholedisk flag, in which case we can
         * and should switch the elevator. If the device-mapper device
         * does not have an elevator (i.e. dm-raid, dm-crypt, etc.) the
         * "Skip devices without schedulers" check below will fail.
         */
        if (!v->vdev_wholedisk && strncmp(device, "dm-", 3) != 0)
                return;

        /* Leave existing scheduler when set to "none" */
        if ((strncmp(elevator, "none", 4) == 0) && (strlen(elevator) == 4))
                return;

        /*
         * The elevator_change() function was available in kernels from
         * 2.6.36 to 4.11.  When not available fall back to using the user
         * mode helper functionality to set the elevator via sysfs.  This
         * requires /bin/echo and sysfs to be mounted which may not be true
         * early in the boot process.
         */
#ifdef HAVE_ELEVATOR_CHANGE
        error = elevator_change(q, elevator);
#else
#define SET_SCHEDULER_CMD \
        "exec 0</dev/null " \
        "     1>/sys/block/%s/queue/scheduler " \
        "     2>/dev/null; " \
        "echo %s"

        char *argv[] = { "/bin/sh", "-c", NULL, NULL };
        char *envp[] = { NULL };

        argv[2] = kmem_asprintf(SET_SCHEDULER_CMD, device, elevator);
        error = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
        strfree(argv[2]);
#endif /* HAVE_ELEVATOR_CHANGE */
        if (error) {
                zfs_dbgmsg("Unable to set \"%s\" scheduler for %s (%s): %d\n",
                    elevator, v->vdev_path, device, error);
        }
}

static int
vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *max_psize,
    uint64_t *ashift)
{
        struct block_device *bdev;
        fmode_t mode = vdev_bdev_mode(spa_mode(v->vdev_spa));
        int count = 0, block_size;
        int bdev_retry_count = 50;
        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 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 count 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->bd_contains) {
                                bdevname(bdev->bd_contains, disk_name + 5);
                                reread_part = B_TRUE;
                        }

                        vdev_bdev_close(bdev, mode);
                }

                if (reread_part) {
                        bdev = vdev_bdev_open(disk_name, mode, zfs_vdev_holder);
                        if (!IS_ERR(bdev)) {
                                int error = vdev_bdev_reread_part(bdev);
                                vdev_bdev_close(bdev, mode);
                                if (error == 0)
                                        bdev_retry_count = 100;
                        }
                }
        } 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.
         */
        bdev = ERR_PTR(-ENXIO);
        while (IS_ERR(bdev) && count < bdev_retry_count) {
                bdev = vdev_bdev_open(v->vdev_path, mode, zfs_vdev_holder);
                if (unlikely(PTR_ERR(bdev) == -ENOENT)) {
                        schedule_timeout(MSEC_TO_TICK(10));
                        count++;
                } else if (IS_ERR(bdev)) {
                        break;
                }
        }

        if (IS_ERR(bdev)) {
                int error = -PTR_ERR(bdev);
                vdev_dbgmsg(v, "open error=%d count=%d\n", error, count);
                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 */
        block_size = vdev_bdev_block_size(vd->vd_bdev);

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

        /* 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 */
        *ashift = highbit64(MAX(block_size, SPA_MINBLOCKSIZE)) - 1;

        /* Try to set the io scheduler elevator algorithm */
        (void) vdev_elevator_switch(v, zfs_vdev_scheduler);

        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_bdev_close(vd->vd_bdev,
                    vdev_bdev_mode(spa_mode(v->vdev_spa)));
        }

        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;
        int i;

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

                for (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 int
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);
                }
        }

        return (rc);
}

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

        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 */
        rc = vdev_disk_dio_put(dr);
}

static unsigned int
bio_map(struct bio *bio, void *bio_ptr, unsigned int bio_size)
{
        unsigned int offset, size, i;
        struct page *page;

        offset = offset_in_page(bio_ptr);
        for (i = 0; i < bio->bi_max_vecs; i++) {
                size = PAGE_SIZE - offset;

                if (bio_size <= 0)
                        break;

                if (size > bio_size)
                        size = bio_size;

                if (is_vmalloc_addr(bio_ptr))
                        page = vmalloc_to_page(bio_ptr);
                else
                        page = virt_to_page(bio_ptr);

                /*
                 * Some network related block device uses tcp_sendpage, which
                 * doesn't behave well when using 0-count page, this is a
                 * safety net to catch them.
                 */
                ASSERT3S(page_count(page), >, 0);

                if (bio_add_page(bio, page, size, offset) != size)
                        break;

                bio_ptr  += size;
                bio_size -= size;
                offset = 0;
        }

        return (bio_size);
}

static unsigned int
bio_map_abd_off(struct bio *bio, abd_t *abd, unsigned int size, size_t off)
{
        if (abd_is_linear(abd))
                return (bio_map(bio, ((char *)abd_to_buf(abd)) + off, size));

        return (abd_scatter_bio_map_off(bio, abd, size, off));
}

static inline void
vdev_submit_bio_impl(struct bio *bio)
{
#ifdef HAVE_1ARG_SUBMIT_BIO
        submit_bio(bio);
#else
        submit_bio(0, bio);
#endif
}

#ifdef HAVE_BIO_SET_DEV
#if defined(CONFIG_BLK_CGROUP) && defined(HAVE_BIO_SET_DEV_GPL_ONLY)
/*
 * 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)
{
        struct request_queue *q = bio->bi_disk->queue;

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

        if (blkg_tryget(q->root_blkg))
                bio->bi_blkg = q->root_blkg;
}
#define bio_associate_blkg vdev_bio_associate_blkg
#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 */

static inline void
vdev_submit_bio(struct bio *bio)
{
#ifdef HAVE_CURRENT_BIO_TAIL
        struct bio **bio_tail = current->bio_tail;
        current->bio_tail = NULL;
        vdev_submit_bio_impl(bio);
        current->bio_tail = bio_tail;
#else
        struct bio_list *bio_list = current->bio_list;
        current->bio_list = NULL;
        vdev_submit_bio_impl(bio);
        current->bio_list = bio_list;
#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, bio_count = 16;
        int i = 0, error = 0;
#if defined(HAVE_BLK_QUEUE_HAVE_BLK_PLUG)
        struct blk_plug plug;
#endif
        /*
         * 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",
                    io_offset, io_size, i_size_read(bdev->bd_inode));
                return (SET_ERROR(EIO));
        }

retry:
        dr = vdev_disk_dio_alloc(bio_count);
        if (dr == NULL)
                return (SET_ERROR(ENOMEM));

        if (zio && !(zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)))
                bio_set_flags_failfast(bdev, &flags);

        dr->dr_zio = zio;

        /*
         * When the IO size exceeds the maximum bio size for the request
         * queue we are forced to break the IO in multiple bio's and wait
         * for them all to complete.  Ideally, all pool users will set
         * their volume block size to match the maximum request size and
         * the common case will be one bio per vdev IO request.
         */

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

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

                /*
                 * By default only 'bio_count' bio's per dio are allowed.
                 * However, if we find ourselves in a situation where more
                 * are needed we allocate a larger dio and warn the user.
                 */
                if (dr->dr_bio_count == i) {
                        vdev_disk_dio_free(dr);
                        bio_count *= 2;
                        goto retry;
                }

                /* bio_alloc() with __GFP_WAIT never returns NULL */
                dr->dr_bio[i] = bio_alloc(GFP_NOIO,
                    MIN(abd_nr_pages_off(zio->io_abd, bio_size, abd_offset),
                    BIO_MAX_PAGES));
                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_set_dev(dr->dr_bio[i], bdev);
                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 = bio_map_abd_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 defined(HAVE_BLK_QUEUE_HAVE_BLK_PLUG)
        if (dr->dr_bio_count > 1)
                blk_start_plug(&plug);
#endif

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

#if defined(HAVE_BLK_QUEUE_HAVE_BLK_PLUG)
        if (dr->dr_bio_count > 1)
                blk_finish_plug(&plug);
#endif

        (void) 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 = bio_alloc(GFP_NOIO, 0);
        /* bio_alloc() with __GFP_WAIT never returns NULL */
        if (unlikely(bio == NULL))
                return (SET_ERROR(ENOMEM));

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

        return (0);
}

static void
vdev_disk_io_start(zio_t *zio)
{
        vdev_t *v = zio->io_vd;
        vdev_disk_t *vd = v->vdev_tsd;
        int rw, flags, 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;
#if defined(HAVE_BLK_QUEUE_HAVE_BIO_RW_UNPLUG)
                flags = (1 << BIO_RW_UNPLUG);
#elif defined(REQ_UNPLUG)
                flags = REQ_UNPLUG;
#else
                flags = 0;
#endif
                break;

        case ZIO_TYPE_READ:
                rw = READ;
#if defined(HAVE_BLK_QUEUE_HAVE_BIO_RW_UNPLUG)
                flags = (1 << BIO_RW_UNPLUG);
#elif defined(REQ_UNPLUG)
                flags = REQ_UNPLUG;
#else
                flags = 0;
#endif
                break;

        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, flags);
        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 (check_disk_change(vd->vd_bdev)) {
                        vdev_bdev_invalidate(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;

        /* XXX: Implement me as a vnode lookup for the device */
        vd->vdev_name_vp = NULL;
        vd->vdev_devid_vp = NULL;
}

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 */
}

static int
param_set_vdev_scheduler(const char *val, zfs_kernel_param_t *kp)
{
        spa_t *spa = NULL;
        char *p;

        if (val == NULL)
                return (SET_ERROR(-EINVAL));

        if ((p = strchr(val, '\n')) != NULL)
                *p = '\0';

        if (spa_mode_global != 0) {
                mutex_enter(&spa_namespace_lock);
                while ((spa = spa_next(spa)) != NULL) {
                        if (spa_state(spa) != POOL_STATE_ACTIVE ||
                            !spa_writeable(spa) || spa_suspended(spa))
                                continue;

                        spa_open_ref(spa, FTAG);
                        mutex_exit(&spa_namespace_lock);
                        vdev_elevator_switch(spa->spa_root_vdev, (char *)val);
                        mutex_enter(&spa_namespace_lock);
                        spa_close(spa, FTAG);
                }
                mutex_exit(&spa_namespace_lock);
        }

        return (param_set_charp(val, kp));
}

vdev_ops_t vdev_disk_ops = {
        vdev_disk_open,
        vdev_disk_close,
        vdev_default_asize,
        vdev_disk_io_start,
        vdev_disk_io_done,
        NULL,
        NULL,
        vdev_disk_hold,
        vdev_disk_rele,
        NULL,
        vdev_default_xlate,
        VDEV_TYPE_DISK,         /* name of this vdev type */
        B_TRUE                  /* leaf vdev */
};

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");