Don't set I/O Scheduler for Partitions

[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.
 */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/vdev_disk.h>
#include <sys/vdev_impl.h>
#include <sys/fs/zfs.h>
#include <sys/zio.h>
#include <sys/sunldi.h>

char *zfs_vdev_scheduler = VDEV_SCHEDULER;

/*
 * Virtual device vector for disks.
 */
typedef struct dio_request {
        struct completion       dr_comp;        /* Completion for sync IO */
        atomic_t                dr_ref;         /* References */
        zio_t                   *dr_zio;        /* Parent ZIO */
        int                     dr_rw;          /* Read/Write */
        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 = MS_RDONLY;

        return mode;
}
#endif /* HAVE_OPEN_BDEV_EXCLUSIVE */

static uint64_t
bdev_capacity(struct block_device *bdev)
{
        struct hd_struct *part = bdev->bd_part;

        /* The partition capacity referenced by the block device */
        if (part)
               return part->nr_sects;

        /* Otherwise assume the full device capacity */
        return get_capacity(bdev->bd_disk);
}

static void
vdev_disk_error(zio_t *zio)
{
#ifdef ZFS_DEBUG
        printk("ZFS: zio error=%d type=%d offset=%llu size=%llu "
            "flags=%x delay=%llu\n", zio->io_error, zio->io_type,
            (u_longlong_t)zio->io_offset, (u_longlong_t)zio->io_size,
            zio->io_flags, (u_longlong_t)zio->io_delay);
#endif
}

/*
 * 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.
 *
 * Unfortunately we cannot directly call the elevator_switch() function
 * because it is not exported from the block layer.  This means we have
 * to use the sysfs interface and a user space upcall.  Pools will be
 * automatically imported on module load so we must do this at device
 * open time from the kernel.
 */
static int
vdev_elevator_switch(vdev_t *v, char *elevator)
{
        vdev_disk_t *vd = v->vdev_tsd;
        struct block_device *bdev = vd->vd_bdev;
        struct request_queue *q = bdev_get_queue(bdev);
        char *device = bdev->bd_disk->disk_name;
        char sh_path[] = "/bin/sh";
        char sh_cmd[128];
        char *argv[] = { sh_path, "-c", sh_cmd };
        char *envp[] = { NULL };
        int count = 0, error;

        /* Skip devices which are not whole disks (partitions) */
        if (!v->vdev_wholedisk)
                return (0);

        /* Skip devices without schedulers (loop, ram, dm, etc) */
        if (!q->elevator || !blk_queue_stackable(q))
                return (0);

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

        /*
         * Set the desired scheduler with a three attempt retry for
         * -EFAULT which has been observed to occur spuriously.
         */
        sprintf(sh_cmd, "%s \"%s\" >/sys/block/%s/queue/scheduler",
            "/bin/echo", elevator, device);

        while (++count <= 3) {
                error = call_usermodehelper(sh_path, argv, envp, 1);
                if ((error == 0) || (error != -EFAULT))
                       break;
        }

        if (error)
                printk("ZFS: Unable to set \"%s\" scheduler for %s (%s): %d\n",
                       elevator, v->vdev_path, device, error);

        return (error);
}

static int
vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *ashift)
{
        struct block_device *bdev;
        vdev_disk_t *vd;
        int mode, block_size;

        /* 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;
                return EINVAL;
        }

        vd = kmem_zalloc(sizeof(vdev_disk_t), KM_SLEEP);
        if (vd == NULL)
                return ENOMEM;

        /*
         * 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 recabled 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 tolerence to component failure.
         * Alternately 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 reorder due to probing order.
         * Devices in the wrong locations will be detected by the higher
         * level vdev validation.
         */
        mode = spa_mode(v->vdev_spa);
        bdev = vdev_bdev_open(v->vdev_path, vdev_bdev_mode(mode), vd);
        if (IS_ERR(bdev)) {
                kmem_free(vd, sizeof(vdev_disk_t));
                return -PTR_ERR(bdev);
        }

        v->vdev_tsd = vd;
        vd->vd_bdev = bdev;
        block_size =  vdev_bdev_block_size(bdev);

        /* We think the wholedisk property should always be set when this
         * function is called.  ASSERT here so if any legitimate cases exist
         * where it's not set, we'll find them during debugging.  If we never
         * hit the ASSERT, this and the following conditional statement can be
         * removed. */
        ASSERT3S(v->vdev_wholedisk, !=, -1ULL);

        /* The wholedisk property was initialized to -1 in vdev_alloc() if it
         * was unspecified.  In that case, check if this is a whole device.
         * When bdev->bd_contains == bdev we have a whole device and not simply
         * a partition. */
        if (v->vdev_wholedisk == -1ULL)
                v->vdev_wholedisk = (bdev->bd_contains == bdev);

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

        /* Physical volume size in bytes */
        *psize = bdev_capacity(bdev) * block_size;

        /* Based on the minimum sector size set the block size */
        *ashift = highbit(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 (vd == NULL)
                return;

        if (vd->vd_bdev != NULL)
                vdev_bdev_close(vd->vd_bdev,
                                vdev_bdev_mode(spa_mode(v->vdev_spa)));

        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) {
                init_completion(&dr->dr_comp);
                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 int
vdev_disk_dio_is_sync(dio_request_t *dr)
{
#ifdef HAVE_BIO_RW_SYNC
        /* BIO_RW_SYNC preferred interface from 2.6.12-2.6.29 */
        return (dr->dr_rw & (1 << BIO_RW_SYNC));
#else
# ifdef HAVE_BIO_RW_SYNCIO
        /* BIO_RW_SYNCIO preferred interface from 2.6.30-2.6.35 */
        return (dr->dr_rw & (1 << BIO_RW_SYNCIO));
# else
#  ifdef HAVE_REQ_SYNC
        /* REQ_SYNC preferred interface from 2.6.36-2.6.xx */
        return (dr->dr_rw & REQ_SYNC);
#  else
#   error "Unable to determine bio sync flag"
#  endif /* HAVE_REQ_SYNC */
# endif /* HAVE_BIO_RW_SYNC */
#endif /* HAVE_BIO_RW_SYNCIO */
}

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_delay = jiffies_to_msecs(
                            jiffies_64 - zio->io_delay);
                        zio->io_error = error;
                        ASSERT3S(zio->io_error, >=, 0);
                        if (zio->io_error)
                                vdev_disk_error(zio);
                        zio_interrupt(zio);
                }
        }

        return rc;
}

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

        /* Fatal error but print some useful debugging before asserting */
        if (dr == NULL)
                PANIC("dr == NULL, bio->bi_private == NULL\n"
                    "bi_next: %p, bi_flags: %lx, bi_rw: %lu, bi_vcnt: %d\n"
                    "bi_idx: %d, bi_size: %d, bi_end_io: %p, bi_cnt: %d\n",
                    bio->bi_next, bio->bi_flags, bio->bi_rw, bio->bi_vcnt,
                    bio->bi_idx, bio->bi_size, bio->bi_end_io,
                    atomic_read(&bio->bi_cnt));

#ifndef HAVE_2ARGS_BIO_END_IO_T
        if (bio->bi_size)
                return 1;
#endif /* HAVE_2ARGS_BIO_END_IO_T */

        if (error == 0 && !test_bit(BIO_UPTODATE, &bio->bi_flags))
                error = -EIO;

        if (dr->dr_error == 0)
                dr->dr_error = -error;

        /* Drop reference aquired by __vdev_disk_physio */
        rc = vdev_disk_dio_put(dr);

        /* Wake up synchronous waiter this is the last outstanding bio */
        if ((rc == 1) && vdev_disk_dio_is_sync(dr))
                complete(&dr->dr_comp);

        BIO_END_IO_RETURN(0);
}

static inline unsigned long
bio_nr_pages(void *bio_ptr, unsigned int bio_size)
{
        return ((((unsigned long)bio_ptr + bio_size + PAGE_SIZE - 1) >>
                PAGE_SHIFT) - ((unsigned long)bio_ptr >> PAGE_SHIFT));
}

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 (kmem_virt(bio_ptr))
                        page = vmalloc_to_page(bio_ptr);
                else
                        page = virt_to_page(bio_ptr);

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

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

        return bio_size;
}

static int
__vdev_disk_physio(struct block_device *bdev, zio_t *zio, caddr_t kbuf_ptr,
                   size_t kbuf_size, uint64_t kbuf_offset, int flags)
{
        dio_request_t *dr;
        caddr_t bio_ptr;
        uint64_t bio_offset;
        int bio_size, bio_count = 16;
        int i = 0, error = 0, block_size;

        ASSERT3U(kbuf_offset + kbuf_size, <=, bdev->bd_inode->i_size);

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

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

        dr->dr_zio = zio;
        dr->dr_rw = flags;
        block_size = vdev_bdev_block_size(bdev);

        /*
         * 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.
         */
        bio_ptr    = kbuf_ptr;
        bio_offset = kbuf_offset;
        bio_size   = kbuf_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;
                        printk("WARNING: Resized bio's/dio to %d\n",bio_count);
                        goto retry;
                }

                dr->dr_bio[i] = bio_alloc(GFP_NOIO,
                                          bio_nr_pages(bio_ptr, bio_size));
                if (dr->dr_bio[i] == NULL) {
                        vdev_disk_dio_free(dr);
                        return ENOMEM;
                }

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

                dr->dr_bio[i]->bi_bdev = bdev;
                dr->dr_bio[i]->bi_sector = bio_offset / block_size;
                dr->dr_bio[i]->bi_rw = dr->dr_rw;
                dr->dr_bio[i]->bi_end_io = vdev_disk_physio_completion;
                dr->dr_bio[i]->bi_private = dr;

                /* Remaining size is returned to become the new size */
                bio_size = bio_map(dr->dr_bio[i], bio_ptr, bio_size);

                /* Advance in buffer and construct another bio if needed */
                bio_ptr    += dr->dr_bio[i]->bi_size;
                bio_offset += dr->dr_bio[i]->bi_size;
        }

        /* Extra reference to protect dio_request during submit_bio */
        vdev_disk_dio_get(dr);
        if (zio)
                zio->io_delay = jiffies_64;

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

        /*
         * On synchronous blocking requests we wait for all bio the completion
         * callbacks to run.  We will be woken when the last callback runs
         * for this dio.  We are responsible for putting the last dio_request
         * reference will in turn put back the last bio references.  The
         * only synchronous consumer is vdev_disk_read_rootlabel() all other
         * IO originating from vdev_disk_io_start() is asynchronous.
         */
        if (vdev_disk_dio_is_sync(dr)) {
                wait_for_completion(&dr->dr_comp);
                error = dr->dr_error;
                ASSERT3S(atomic_read(&dr->dr_ref), ==, 1);
        }

        (void)vdev_disk_dio_put(dr);

        return error;
}

int
vdev_disk_physio(struct block_device *bdev, caddr_t kbuf,
                 size_t size, uint64_t offset, int flags)
{
        bio_set_flags_failfast(bdev, &flags);
        return __vdev_disk_physio(bdev, NULL, kbuf, size, offset, flags);
}

/* 2.6.24 API change */
#ifdef HAVE_BIO_EMPTY_BARRIER
BIO_END_IO_PROTO(vdev_disk_io_flush_completion, bio, size, rc)
{
        zio_t *zio = bio->bi_private;

        zio->io_delay = jiffies_to_msecs(jiffies_64 - zio->io_delay);
        zio->io_error = -rc;
        if (rc && (rc == -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);

        BIO_END_IO_RETURN(0);
}

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 ENXIO;

        bio = bio_alloc(GFP_KERNEL, 0);
        if (!bio)
                return ENOMEM;

        bio->bi_end_io = vdev_disk_io_flush_completion;
        bio->bi_private = zio;
        bio->bi_bdev = bdev;
        zio->io_delay = jiffies_64;
        submit_bio(WRITE_BARRIER, bio);

        return 0;
}
#else
static int
vdev_disk_io_flush(struct block_device *bdev, zio_t *zio)
{
        return ENOTSUP;
}
#endif /* HAVE_BIO_EMPTY_BARRIER */

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

        switch (zio->io_type) {
        case ZIO_TYPE_IOCTL:

                if (!vdev_readable(v)) {
                        zio->io_error = ENXIO;
                        return ZIO_PIPELINE_CONTINUE;
                }

                switch (zio->io_cmd) {
                case DKIOCFLUSHWRITECACHE:

                        if (zfs_nocacheflush)
                                break;

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

                        error = vdev_disk_io_flush(vd->vd_bdev, zio);
                        if (error == 0)
                                return ZIO_PIPELINE_STOP;

                        zio->io_error = error;
                        if (error == ENOTSUP)
                                v->vdev_nowritecache = B_TRUE;

                        break;

                default:
                        zio->io_error = ENOTSUP;
                }

                return ZIO_PIPELINE_CONTINUE;

        case ZIO_TYPE_WRITE:
                flags = WRITE;
                break;

        case ZIO_TYPE_READ:
                flags = READ;
                break;

        default:
                zio->io_error = ENOTSUP;
                return ZIO_PIPELINE_CONTINUE;
        }

        error = __vdev_disk_physio(vd->vd_bdev, zio, zio->io_data,
                                   zio->io_size, zio->io_offset, flags);
        if (error) {
                zio->io_error = error;
                return ZIO_PIPELINE_CONTINUE;
        }

        return ZIO_PIPELINE_STOP;
}

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 */
}

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

/*
 * Given the root disk device devid or pathname, read the label from
 * the device, and construct a configuration nvlist.
 */
int
vdev_disk_read_rootlabel(char *devpath, char *devid, nvlist_t **config)
{
        struct block_device *bdev;
        vdev_label_t *label;
        uint64_t s, size;
        int i;

        bdev = vdev_bdev_open(devpath, vdev_bdev_mode(FREAD), NULL);
        if (IS_ERR(bdev))
                return -PTR_ERR(bdev);

        s = bdev_capacity(bdev) * vdev_bdev_block_size(bdev);
        if (s == 0) {
                vdev_bdev_close(bdev, vdev_bdev_mode(FREAD));
                return EIO;
        }

        size = P2ALIGN_TYPED(s, sizeof(vdev_label_t), uint64_t);
        label = vmem_alloc(sizeof(vdev_label_t), KM_SLEEP);

        for (i = 0; i < VDEV_LABELS; i++) {
                uint64_t offset, state, txg = 0;

                /* read vdev label */
                offset = vdev_label_offset(size, i, 0);
                if (vdev_disk_physio(bdev, (caddr_t)label,
                    VDEV_SKIP_SIZE + VDEV_PHYS_SIZE, offset, READ_SYNC) != 0)
                        continue;

                if (nvlist_unpack(label->vl_vdev_phys.vp_nvlist,
                    sizeof (label->vl_vdev_phys.vp_nvlist), config, 0) != 0) {
                        *config = NULL;
                        continue;
                }

                if (nvlist_lookup_uint64(*config, ZPOOL_CONFIG_POOL_STATE,
                    &state) != 0 || state >= POOL_STATE_DESTROYED) {
                        nvlist_free(*config);
                        *config = NULL;
                        continue;
                }

                if (nvlist_lookup_uint64(*config, ZPOOL_CONFIG_POOL_TXG,
                    &txg) != 0 || txg == 0) {
                        nvlist_free(*config);
                        *config = NULL;
                        continue;
                }

                break;
        }

        vmem_free(label, sizeof(vdev_label_t));
        vdev_bdev_close(bdev, vdev_bdev_mode(FREAD));

        return 0;
}

module_param(zfs_vdev_scheduler, charp, 0644);
MODULE_PARM_DESC(zfs_vdev_scheduler, "IO Scheduler (noop)");