9963 Seperate tunable for disabling ZIL vdev flush

[unleashed.git] / usr / src / uts / common / fs / 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) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
 * Copyright 2016 Nexenta Systems, Inc.  All rights reserved.
 * Copyright (c) 2013 Joyent, Inc.  All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/spa_impl.h>
#include <sys/refcount.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 <sys/sunldi.h>
#include <sys/efi_partition.h>
#include <sys/fm/fs/zfs.h>

/*
 * Tunable parameter for debugging or performance analysis. Setting this
 * will cause pool corruption on power loss if a volatile out-of-order
 * write cache is enabled.
 */
boolean_t zfs_nocacheflush = B_FALSE;

/*
 * Virtual device vector for disks.
 */

extern ldi_ident_t zfs_li;

static void vdev_disk_close(vdev_t *);

typedef struct vdev_disk_ldi_cb {
        list_node_t             lcb_next;
        ldi_callback_id_t       lcb_id;
} vdev_disk_ldi_cb_t;

static void
vdev_disk_alloc(vdev_t *vd)
{
        vdev_disk_t *dvd;

        dvd = vd->vdev_tsd = kmem_zalloc(sizeof (vdev_disk_t), KM_SLEEP);
        /*
         * Create the LDI event callback list.
         */
        list_create(&dvd->vd_ldi_cbs, sizeof (vdev_disk_ldi_cb_t),
            offsetof(vdev_disk_ldi_cb_t, lcb_next));
}

static void
vdev_disk_free(vdev_t *vd)
{
        vdev_disk_t *dvd = vd->vdev_tsd;
        vdev_disk_ldi_cb_t *lcb;

        if (dvd == NULL)
                return;

        /*
         * We have already closed the LDI handle. Clean up the LDI event
         * callbacks and free vd->vdev_tsd.
         */
        while ((lcb = list_head(&dvd->vd_ldi_cbs)) != NULL) {
                list_remove(&dvd->vd_ldi_cbs, lcb);
                (void) ldi_ev_remove_callbacks(lcb->lcb_id);
                kmem_free(lcb, sizeof (vdev_disk_ldi_cb_t));
        }
        list_destroy(&dvd->vd_ldi_cbs);
        kmem_free(dvd, sizeof (vdev_disk_t));
        vd->vdev_tsd = NULL;
}

/* ARGSUSED */
static int
vdev_disk_off_notify(ldi_handle_t lh, ldi_ev_cookie_t ecookie, void *arg,
    void *ev_data)
{
        vdev_t *vd = (vdev_t *)arg;
        vdev_disk_t *dvd = vd->vdev_tsd;

        /*
         * Ignore events other than offline.
         */
        if (strcmp(ldi_ev_get_type(ecookie), LDI_EV_OFFLINE) != 0)
                return (LDI_EV_SUCCESS);

        /*
         * All LDI handles must be closed for the state change to succeed, so
         * call on vdev_disk_close() to do this.
         *
         * We inform vdev_disk_close that it is being called from offline
         * notify context so it will defer cleanup of LDI event callbacks and
         * freeing of vd->vdev_tsd to the offline finalize or a reopen.
         */
        dvd->vd_ldi_offline = B_TRUE;
        vdev_disk_close(vd);

        /*
         * Now that the device is closed, request that the spa_async_thread
         * mark the device as REMOVED and notify FMA of the removal.
         */
        zfs_post_remove(vd->vdev_spa, vd);
        vd->vdev_remove_wanted = B_TRUE;
        spa_async_request(vd->vdev_spa, SPA_ASYNC_REMOVE);

        return (LDI_EV_SUCCESS);
}

/* ARGSUSED */
static void
vdev_disk_off_finalize(ldi_handle_t lh, ldi_ev_cookie_t ecookie,
    int ldi_result, void *arg, void *ev_data)
{
        vdev_t *vd = (vdev_t *)arg;

        /*
         * Ignore events other than offline.
         */
        if (strcmp(ldi_ev_get_type(ecookie), LDI_EV_OFFLINE) != 0)
                return;

        /*
         * We have already closed the LDI handle in notify.
         * Clean up the LDI event callbacks and free vd->vdev_tsd.
         */
        vdev_disk_free(vd);

        /*
         * Request that the vdev be reopened if the offline state change was
         * unsuccessful.
         */
        if (ldi_result != LDI_EV_SUCCESS) {
                vd->vdev_probe_wanted = B_TRUE;
                spa_async_request(vd->vdev_spa, SPA_ASYNC_PROBE);
        }
}

static ldi_ev_callback_t vdev_disk_off_callb = {
        .cb_vers = LDI_EV_CB_VERS,
        .cb_notify = vdev_disk_off_notify,
        .cb_finalize = vdev_disk_off_finalize
};

/* ARGSUSED */
static void
vdev_disk_dgrd_finalize(ldi_handle_t lh, ldi_ev_cookie_t ecookie,
    int ldi_result, void *arg, void *ev_data)
{
        vdev_t *vd = (vdev_t *)arg;

        /*
         * Ignore events other than degrade.
         */
        if (strcmp(ldi_ev_get_type(ecookie), LDI_EV_DEGRADE) != 0)
                return;

        /*
         * Degrade events always succeed. Mark the vdev as degraded.
         * This status is purely informative for the user.
         */
        (void) vdev_degrade(vd->vdev_spa, vd->vdev_guid, 0);
}

static ldi_ev_callback_t vdev_disk_dgrd_callb = {
        .cb_vers = LDI_EV_CB_VERS,
        .cb_notify = NULL,
        .cb_finalize = vdev_disk_dgrd_finalize
};

static void
vdev_disk_hold(vdev_t *vd)
{
        ddi_devid_t devid;
        char *minor;

        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;

        if (vd->vdev_wholedisk == -1ULL) {
                size_t len = strlen(vd->vdev_path) + 3;
                char *buf = kmem_alloc(len, KM_SLEEP);

                (void) snprintf(buf, len, "%ss0", vd->vdev_path);

                (void) ldi_vp_from_name(buf, &vd->vdev_name_vp);
                kmem_free(buf, len);
        }

        if (vd->vdev_name_vp == NULL)
                (void) ldi_vp_from_name(vd->vdev_path, &vd->vdev_name_vp);

        if (vd->vdev_devid != NULL &&
            ddi_devid_str_decode(vd->vdev_devid, &devid, &minor) == 0) {
                (void) ldi_vp_from_devid(devid, minor, &vd->vdev_devid_vp);
                ddi_devid_str_free(minor);
                ddi_devid_free(devid);
        }
}

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

        if (vd->vdev_name_vp) {
                VN_RELE_ASYNC(vd->vdev_name_vp,
                    dsl_pool_vnrele_taskq(vd->vdev_spa->spa_dsl_pool));
                vd->vdev_name_vp = NULL;
        }
        if (vd->vdev_devid_vp) {
                VN_RELE_ASYNC(vd->vdev_devid_vp,
                    dsl_pool_vnrele_taskq(vd->vdev_spa->spa_dsl_pool));
                vd->vdev_devid_vp = NULL;
        }
}

/*
 * We want to be loud in DEBUG kernels when DKIOCGMEDIAINFOEXT fails, or when
 * even a fallback to DKIOCGMEDIAINFO fails.
 */
#ifdef DEBUG
#define VDEV_DEBUG(...) cmn_err(CE_NOTE, __VA_ARGS__)
#else
#define VDEV_DEBUG(...) /* Nothing... */
#endif

static int
vdev_disk_open(vdev_t *vd, uint64_t *psize, uint64_t *max_psize,
    uint64_t *ashift)
{
        spa_t *spa = vd->vdev_spa;
        vdev_disk_t *dvd = vd->vdev_tsd;
        ldi_ev_cookie_t ecookie;
        vdev_disk_ldi_cb_t *lcb;
        union {
                struct dk_minfo_ext ude;
                struct dk_minfo ud;
        } dks;
        struct dk_minfo_ext *dkmext = &dks.ude;
        struct dk_minfo *dkm = &dks.ud;
        int error;
        dev_t dev;
        int otyp;
        boolean_t validate_devid = B_FALSE;
        ddi_devid_t devid;
        uint64_t capacity = 0, blksz = 0, pbsize;

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

        /*
         * Reopen the device if it's not currently open. Otherwise,
         * just update the physical size of the device.
         */
        if (dvd != NULL) {
                if (dvd->vd_ldi_offline && dvd->vd_lh == NULL) {
                        /*
                         * If we are opening a device in its offline notify
                         * context, the LDI handle was just closed. Clean
                         * up the LDI event callbacks and free vd->vdev_tsd.
                         */
                        vdev_disk_free(vd);
                } else {
                        ASSERT(vd->vdev_reopening);
                        goto skip_open;
                }
        }

        /*
         * Create vd->vdev_tsd.
         */
        vdev_disk_alloc(vd);
        dvd = vd->vdev_tsd;

        /*
         * When opening a disk device, we want to preserve the user's original
         * intent.  We always want to open the device by the path the user gave
         * us, even if it is one of multiple paths to the same device.  But we
         * also want to be able to survive disks being removed/recabled.
         * Therefore the sequence of opening devices is:
         *
         * 1. Try opening the device by path.  For legacy pools without the
         *    'whole_disk' property, attempt to fix the path by appending 's0'.
         *
         * 2. If the devid of the device matches the stored value, return
         *    success.
         *
         * 3. Otherwise, the device may have moved.  Try opening the device
         *    by the devid instead.
         */
        if (vd->vdev_devid != NULL) {
                if (ddi_devid_str_decode(vd->vdev_devid, &dvd->vd_devid,
                    &dvd->vd_minor) != 0) {
                        vd->vdev_stat.vs_aux = VDEV_AUX_BAD_LABEL;
                        vdev_dbgmsg(vd, "vdev_disk_open: invalid "
                            "vdev_devid '%s'", vd->vdev_devid);
                        return (SET_ERROR(EINVAL));
                }
        }

        error = EINVAL;         /* presume failure */

        if (vd->vdev_path != NULL) {

                if (vd->vdev_wholedisk == -1ULL) {
                        size_t len = strlen(vd->vdev_path) + 3;
                        char *buf = kmem_alloc(len, KM_SLEEP);

                        (void) snprintf(buf, len, "%ss0", vd->vdev_path);

                        error = ldi_open_by_name(buf, spa_mode(spa), kcred,
                            &dvd->vd_lh, zfs_li);
                        if (error == 0) {
                                spa_strfree(vd->vdev_path);
                                vd->vdev_path = buf;
                                vd->vdev_wholedisk = 1ULL;
                        } else {
                                kmem_free(buf, len);
                        }
                }

                /*
                 * If we have not yet opened the device, try to open it by the
                 * specified path.
                 */
                if (error != 0) {
                        error = ldi_open_by_name(vd->vdev_path, spa_mode(spa),
                            kcred, &dvd->vd_lh, zfs_li);
                }

                /*
                 * Compare the devid to the stored value.
                 */
                if (error == 0 && vd->vdev_devid != NULL &&
                    ldi_get_devid(dvd->vd_lh, &devid) == 0) {
                        if (ddi_devid_compare(devid, dvd->vd_devid) != 0) {
                                error = SET_ERROR(EINVAL);
                                (void) ldi_close(dvd->vd_lh, spa_mode(spa),
                                    kcred);
                                dvd->vd_lh = NULL;
                        }
                        ddi_devid_free(devid);
                }

                /*
                 * If we succeeded in opening the device, but 'vdev_wholedisk'
                 * is not yet set, then this must be a slice.
                 */
                if (error == 0 && vd->vdev_wholedisk == -1ULL)
                        vd->vdev_wholedisk = 0;
        }

        /*
         * If we were unable to open by path, or the devid check fails, open by
         * devid instead.
         */
        if (error != 0 && vd->vdev_devid != NULL) {
                error = ldi_open_by_devid(dvd->vd_devid, dvd->vd_minor,
                    spa_mode(spa), kcred, &dvd->vd_lh, zfs_li);
        }

        /*
         * If all else fails, then try opening by physical path (if available)
         * or the logical path (if we failed due to the devid check).  While not
         * as reliable as the devid, this will give us something, and the higher
         * level vdev validation will prevent us from opening the wrong device.
         */
        if (error) {
                if (vd->vdev_devid != NULL)
                        validate_devid = B_TRUE;

                if (vd->vdev_physpath != NULL &&
                    (dev = ddi_pathname_to_dev_t(vd->vdev_physpath)) != NODEV)
                        error = ldi_open_by_dev(&dev, OTYP_BLK, spa_mode(spa),
                            kcred, &dvd->vd_lh, zfs_li);

                /*
                 * Note that we don't support the legacy auto-wholedisk support
                 * as above.  This hasn't been used in a very long time and we
                 * don't need to propagate its oddities to this edge condition.
                 */
                if (error && vd->vdev_path != NULL)
                        error = ldi_open_by_name(vd->vdev_path, spa_mode(spa),
                            kcred, &dvd->vd_lh, zfs_li);
        }

        if (error) {
                vd->vdev_stat.vs_aux = VDEV_AUX_OPEN_FAILED;
                vdev_dbgmsg(vd, "vdev_disk_open: failed to open [error=%d]",
                    error);
                return (error);
        }

        /*
         * Now that the device has been successfully opened, update the devid
         * if necessary.
         */
        if (validate_devid && spa_writeable(spa) &&
            ldi_get_devid(dvd->vd_lh, &devid) == 0) {
                if (ddi_devid_compare(devid, dvd->vd_devid) != 0) {
                        char *vd_devid;

                        vd_devid = ddi_devid_str_encode(devid, dvd->vd_minor);
                        vdev_dbgmsg(vd, "vdev_disk_open: update devid from "
                            "'%s' to '%s'", vd->vdev_devid, vd_devid);
                        spa_strfree(vd->vdev_devid);
                        vd->vdev_devid = spa_strdup(vd_devid);
                        ddi_devid_str_free(vd_devid);
                }
                ddi_devid_free(devid);
        }

        /*
         * Once a device is opened, verify that the physical device path (if
         * available) is up to date.
         */
        if (ldi_get_dev(dvd->vd_lh, &dev) == 0 &&
            ldi_get_otyp(dvd->vd_lh, &otyp) == 0) {
                char *physpath, *minorname;

                physpath = kmem_alloc(MAXPATHLEN, KM_SLEEP);
                minorname = NULL;
                if (ddi_dev_pathname(dev, otyp, physpath) == 0 &&
                    ldi_get_minor_name(dvd->vd_lh, &minorname) == 0 &&
                    (vd->vdev_physpath == NULL ||
                    strcmp(vd->vdev_physpath, physpath) != 0)) {
                        if (vd->vdev_physpath)
                                spa_strfree(vd->vdev_physpath);
                        (void) strlcat(physpath, ":", MAXPATHLEN);
                        (void) strlcat(physpath, minorname, MAXPATHLEN);
                        vd->vdev_physpath = spa_strdup(physpath);
                }
                if (minorname)
                        kmem_free(minorname, strlen(minorname) + 1);
                kmem_free(physpath, MAXPATHLEN);
        }

        /*
         * Register callbacks for the LDI offline event.
         */
        if (ldi_ev_get_cookie(dvd->vd_lh, LDI_EV_OFFLINE, &ecookie) ==
            LDI_EV_SUCCESS) {
                lcb = kmem_zalloc(sizeof (vdev_disk_ldi_cb_t), KM_SLEEP);
                list_insert_tail(&dvd->vd_ldi_cbs, lcb);
                (void) ldi_ev_register_callbacks(dvd->vd_lh, ecookie,
                    &vdev_disk_off_callb, (void *) vd, &lcb->lcb_id);
        }

        /*
         * Register callbacks for the LDI degrade event.
         */
        if (ldi_ev_get_cookie(dvd->vd_lh, LDI_EV_DEGRADE, &ecookie) ==
            LDI_EV_SUCCESS) {
                lcb = kmem_zalloc(sizeof (vdev_disk_ldi_cb_t), KM_SLEEP);
                list_insert_tail(&dvd->vd_ldi_cbs, lcb);
                (void) ldi_ev_register_callbacks(dvd->vd_lh, ecookie,
                    &vdev_disk_dgrd_callb, (void *) vd, &lcb->lcb_id);
        }
skip_open:
        /*
         * Determine the actual size of the device.
         */
        if (ldi_get_size(dvd->vd_lh, psize) != 0) {
                vd->vdev_stat.vs_aux = VDEV_AUX_OPEN_FAILED;
                vdev_dbgmsg(vd, "vdev_disk_open: failed to get size");
                return (SET_ERROR(EINVAL));
        }

        *max_psize = *psize;

        /*
         * Determine the device's minimum transfer size.
         * If the ioctl isn't supported, assume DEV_BSIZE.
         */
        if ((error = ldi_ioctl(dvd->vd_lh, DKIOCGMEDIAINFOEXT,
            (intptr_t)dkmext, FKIOCTL, kcred, NULL)) == 0) {
                capacity = dkmext->dki_capacity - 1;
                blksz = dkmext->dki_lbsize;
                pbsize = dkmext->dki_pbsize;
        } else if ((error = ldi_ioctl(dvd->vd_lh, DKIOCGMEDIAINFO,
            (intptr_t)dkm, FKIOCTL, kcred, NULL)) == 0) {
                VDEV_DEBUG(
                    "vdev_disk_open(\"%s\"): fallback to DKIOCGMEDIAINFO\n",
                    vd->vdev_path);
                capacity = dkm->dki_capacity - 1;
                blksz = dkm->dki_lbsize;
                pbsize = blksz;
        } else {
                VDEV_DEBUG("vdev_disk_open(\"%s\"): "
                    "both DKIOCGMEDIAINFO{,EXT} calls failed, %d\n",
                    vd->vdev_path, error);
                pbsize = DEV_BSIZE;
        }

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

        if (vd->vdev_wholedisk == 1) {
                int wce = 1;

                if (error == 0) {
                        /*
                         * If we have the capability to expand, we'd have
                         * found out via success from DKIOCGMEDIAINFO{,EXT}.
                         * Adjust max_psize upward accordingly since we know
                         * we own the whole disk now.
                         */
                        *max_psize = capacity * blksz;
                }

                /*
                 * Since we own the whole disk, try to enable disk write
                 * caching.  We ignore errors because it's OK if we can't do it.
                 */
                (void) ldi_ioctl(dvd->vd_lh, DKIOCSETWCE, (intptr_t)&wce,
                    FKIOCTL, kcred, NULL);
        }

        /*
         * Clear the nowritecache bit, so that on a vdev_reopen() we will
         * try again.
         */
        vd->vdev_nowritecache = B_FALSE;

        return (0);
}

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

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

        if (dvd->vd_minor != NULL) {
                ddi_devid_str_free(dvd->vd_minor);
                dvd->vd_minor = NULL;
        }

        if (dvd->vd_devid != NULL) {
                ddi_devid_free(dvd->vd_devid);
                dvd->vd_devid = NULL;
        }

        if (dvd->vd_lh != NULL) {
                (void) ldi_close(dvd->vd_lh, spa_mode(vd->vdev_spa), kcred);
                dvd->vd_lh = NULL;
        }

        vd->vdev_delayed_close = B_FALSE;
        /*
         * If we closed the LDI handle due to an offline notify from LDI,
         * don't free vd->vdev_tsd or unregister the callbacks here;
         * the offline finalize callback or a reopen will take care of it.
         */
        if (dvd->vd_ldi_offline)
                return;

        vdev_disk_free(vd);
}

int
vdev_disk_physio(vdev_t *vd, caddr_t data,
    size_t size, uint64_t offset, int flags, boolean_t isdump)
{
        vdev_disk_t *dvd = vd->vdev_tsd;

        /*
         * If the vdev is closed, it's likely in the REMOVED or FAULTED state.
         * Nothing to be done here but return failure.
         */
        if (dvd == NULL || (dvd->vd_ldi_offline && dvd->vd_lh == NULL))
                return (EIO);

        ASSERT(vd->vdev_ops == &vdev_disk_ops);

        /*
         * If in the context of an active crash dump, use the ldi_dump(9F)
         * call instead of ldi_strategy(9F) as usual.
         */
        if (isdump) {
                ASSERT3P(dvd, !=, NULL);
                return (ldi_dump(dvd->vd_lh, data, lbtodb(offset),
                    lbtodb(size)));
        }

        return (vdev_disk_ldi_physio(dvd->vd_lh, data, size, offset, flags));
}

int
vdev_disk_ldi_physio(ldi_handle_t vd_lh, caddr_t data,
    size_t size, uint64_t offset, int flags)
{
        buf_t *bp;
        int error = 0;

        if (vd_lh == NULL)
                return (SET_ERROR(EINVAL));

        ASSERT(flags & B_READ || flags & B_WRITE);

        bp = getrbuf(KM_SLEEP);
        bp->b_flags = flags | B_BUSY | B_NOCACHE | B_FAILFAST;
        bp->b_bcount = size;
        bp->b_un.b_addr = (void *)data;
        bp->b_lblkno = lbtodb(offset);
        bp->b_bufsize = size;

        error = ldi_strategy(vd_lh, bp);
        ASSERT(error == 0);
        if ((error = biowait(bp)) == 0 && bp->b_resid != 0)
                error = SET_ERROR(EIO);
        freerbuf(bp);

        return (error);
}

static void
vdev_disk_io_intr(buf_t *bp)
{
        vdev_buf_t *vb = (vdev_buf_t *)bp;
        zio_t *zio = vb->vb_io;

        /*
         * The rest of the zio stack only deals with EIO, ECKSUM, and ENXIO.
         * Rather than teach the rest of the stack about other error
         * possibilities (EFAULT, etc), we normalize the error value here.
         */
        zio->io_error = (geterror(bp) != 0 ? EIO : 0);

        if (zio->io_error == 0 && bp->b_resid != 0)
                zio->io_error = SET_ERROR(EIO);

        if (zio->io_type == ZIO_TYPE_READ) {
                abd_return_buf_copy(zio->io_abd, bp->b_un.b_addr, zio->io_size);
        } else {
                abd_return_buf(zio->io_abd, bp->b_un.b_addr, zio->io_size);
        }

        kmem_free(vb, sizeof (vdev_buf_t));

        zio_delay_interrupt(zio);
}

static void
vdev_disk_ioctl_free(zio_t *zio)
{
        kmem_free(zio->io_vsd, sizeof (struct dk_callback));
}

static const zio_vsd_ops_t vdev_disk_vsd_ops = {
        vdev_disk_ioctl_free,
        zio_vsd_default_cksum_report
};

static void
vdev_disk_ioctl_done(void *zio_arg, int error)
{
        zio_t *zio = zio_arg;

        zio->io_error = error;

        zio_interrupt(zio);
}

static void
vdev_disk_io_start(zio_t *zio)
{
        vdev_t *vd = zio->io_vd;
        vdev_disk_t *dvd = vd->vdev_tsd;
        vdev_buf_t *vb;
        struct dk_callback *dkc;
        buf_t *bp;
        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 (dvd == NULL || (dvd->vd_ldi_offline && dvd->vd_lh == NULL)) {
                zio->io_error = ENXIO;
                zio_interrupt(zio);
                return;
        }

        if (zio->io_type == ZIO_TYPE_IOCTL) {
                /* XXPOLICY */
                if (!vdev_readable(vd)) {
                        zio->io_error = SET_ERROR(ENXIO);
                        zio_interrupt(zio);
                        return;
                }

                switch (zio->io_cmd) {

                case DKIOCFLUSHWRITECACHE:

                        if (zfs_nocacheflush)
                                break;

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

                        zio->io_vsd = dkc = kmem_alloc(sizeof (*dkc), KM_SLEEP);
                        zio->io_vsd_ops = &vdev_disk_vsd_ops;

                        dkc->dkc_callback = vdev_disk_ioctl_done;
                        dkc->dkc_flag = FLUSH_VOLATILE;
                        dkc->dkc_cookie = zio;

                        error = ldi_ioctl(dvd->vd_lh, zio->io_cmd,
                            (uintptr_t)dkc, FKIOCTL, kcred, NULL);

                        if (error == 0) {
                                /*
                                 * The ioctl will be done asychronously,
                                 * and will call vdev_disk_ioctl_done()
                                 * upon completion.
                                 */
                                return;
                        }

                        zio->io_error = error;

                        break;

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

                zio_execute(zio);
                return;
        }

        ASSERT(zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE);
        zio->io_target_timestamp = zio_handle_io_delay(zio);

        vb = kmem_alloc(sizeof (vdev_buf_t), KM_SLEEP);

        vb->vb_io = zio;
        bp = &vb->vb_buf;

        bioinit(bp);
        bp->b_flags = B_BUSY | B_NOCACHE |
            (zio->io_type == ZIO_TYPE_READ ? B_READ : B_WRITE);
        if (!(zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)))
                bp->b_flags |= B_FAILFAST;
        bp->b_bcount = zio->io_size;

        if (zio->io_type == ZIO_TYPE_READ) {
                bp->b_un.b_addr =
                    abd_borrow_buf(zio->io_abd, zio->io_size);
        } else {
                bp->b_un.b_addr =
                    abd_borrow_buf_copy(zio->io_abd, zio->io_size);
        }

        bp->b_lblkno = lbtodb(zio->io_offset);
        bp->b_bufsize = zio->io_size;
        bp->b_iodone = (int (*)())vdev_disk_io_intr;

        /* ldi_strategy() will return non-zero only on programming errors */
        VERIFY(ldi_strategy(dvd->vd_lh, bp) == 0);
}

static void
vdev_disk_io_done(zio_t *zio)
{
        vdev_t *vd = zio->io_vd;

        /*
         * If the device returned EIO, then attempt a DKIOCSTATE ioctl to see if
         * the device has been removed.  If this is the case, then we trigger an
         * asynchronous removal of the device. Otherwise, probe the device and
         * make sure it's still accessible.
         */
        if (zio->io_error == EIO && !vd->vdev_remove_wanted) {
                vdev_disk_t *dvd = vd->vdev_tsd;
                int state = DKIO_NONE;

                if (ldi_ioctl(dvd->vd_lh, DKIOCSTATE, (intptr_t)&state,
                    FKIOCTL, kcred, NULL) == 0 && state != DKIO_INSERTED) {
                        /*
                         * We post the resource as soon as possible, instead of
                         * when the async removal actually happens, because the
                         * DE is using this information to discard previous I/O
                         * errors.
                         */
                        zfs_post_remove(zio->io_spa, vd);
                        vd->vdev_remove_wanted = B_TRUE;
                        spa_async_request(zio->io_spa, SPA_ASYNC_REMOVE);
                } else if (!vd->vdev_delayed_close) {
                        vd->vdev_delayed_close = B_TRUE;
                }
        }
}

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,
        NULL,
        vdev_default_xlate,
        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)
{
        ldi_handle_t vd_lh;
        vdev_label_t *label;
        uint64_t s, size;
        int l;
        ddi_devid_t tmpdevid;
        int error = -1;
        char *minor_name;

        /*
         * Read the device label and build the nvlist.
         */
        if (devid != NULL && ddi_devid_str_decode(devid, &tmpdevid,
            &minor_name) == 0) {
                error = ldi_open_by_devid(tmpdevid, minor_name,
                    FREAD, kcred, &vd_lh, zfs_li);
                ddi_devid_free(tmpdevid);
                ddi_devid_str_free(minor_name);
        }

        if (error && (error = ldi_open_by_name(devpath, FREAD, kcred, &vd_lh,
            zfs_li)))
                return (error);

        if (ldi_get_size(vd_lh, &s)) {
                (void) ldi_close(vd_lh, FREAD, kcred);
                return (SET_ERROR(EIO));
        }

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

        *config = NULL;
        for (l = 0; l < VDEV_LABELS; l++) {
                uint64_t offset, state, txg = 0;

                /* read vdev label */
                offset = vdev_label_offset(size, l, 0);
                if (vdev_disk_ldi_physio(vd_lh, (caddr_t)label,
                    VDEV_SKIP_SIZE + VDEV_PHYS_SIZE, offset, B_READ) != 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;
        }

        kmem_free(label, sizeof (vdev_label_t));
        (void) ldi_close(vd_lh, FREAD, kcred);
        if (*config == NULL)
                error = SET_ERROR(EIDRM);

        return (error);
}