[mirror_zfs.git] / module / zfs / zio_inject.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) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
 * Copyright (c) 2017, Intel Corporation.
 */

/*
 * ZFS fault injection
 *
 * To handle fault injection, we keep track of a series of zinject_record_t
 * structures which describe which logical block(s) should be injected with a
 * fault.  These are kept in a global list.  Each record corresponds to a given
 * spa_t and maintains a special hold on the spa_t so that it cannot be deleted
 * or exported while the injection record exists.
 *
 * Device level injection is done using the 'zi_guid' field.  If this is set, it
 * means that the error is destined for a particular device, not a piece of
 * data.
 *
 * This is a rather poor data structure and algorithm, but we don't expect more
 * than a few faults at any one time, so it should be sufficient for our needs.
 */

#include <sys/arc.h>
#include <sys/zio.h>
#include <sys/zfs_ioctl.h>
#include <sys/vdev_impl.h>
#include <sys/dmu_objset.h>
#include <sys/dsl_dataset.h>
#include <sys/fs/zfs.h>

uint32_t zio_injection_enabled = 0;

/*
 * Data describing each zinject handler registered on the system, and
 * contains the list node linking the handler in the global zinject
 * handler list.
 */
typedef struct inject_handler {
        int                     zi_id;
        spa_t                   *zi_spa;
        zinject_record_t        zi_record;
        uint64_t                *zi_lanes;
        int                     zi_next_lane;
        list_node_t             zi_link;
} inject_handler_t;

/*
 * List of all zinject handlers registered on the system, protected by
 * the inject_lock defined below.
 */
static list_t inject_handlers;

/*
 * This protects insertion into, and traversal of, the inject handler
 * list defined above; as well as the inject_delay_count. Any time a
 * handler is inserted or removed from the list, this lock should be
 * taken as a RW_WRITER; and any time traversal is done over the list
 * (without modification to it) this lock should be taken as a RW_READER.
 */
static krwlock_t inject_lock;

/*
 * This holds the number of zinject delay handlers that have been
 * registered on the system. It is protected by the inject_lock defined
 * above. Thus modifications to this count must be a RW_WRITER of the
 * inject_lock, and reads of this count must be (at least) a RW_READER
 * of the lock.
 */
static int inject_delay_count = 0;

/*
 * This lock is used only in zio_handle_io_delay(), refer to the comment
 * in that function for more details.
 */
static kmutex_t inject_delay_mtx;

/*
 * Used to assign unique identifying numbers to each new zinject handler.
 */
static int inject_next_id = 1;

/*
 * Test if the requested frequency was triggered
 */
static boolean_t
freq_triggered(uint32_t frequency)
{
        /*
         * zero implies always (100%)
         */
        if (frequency == 0)
                return (B_TRUE);

        /*
         * Note: we still handle legacy (unscaled) frequency values
         */
        uint32_t maximum = (frequency <= 100) ? 100 : ZI_PERCENTAGE_MAX;

        return (random_in_range(maximum) < frequency);
}

/*
 * Returns true if the given record matches the I/O in progress.
 */
static boolean_t
zio_match_handler(const zbookmark_phys_t *zb, uint64_t type, int dva,
    zinject_record_t *record, int error)
{
        /*
         * Check for a match against the MOS, which is based on type
         */
        if (zb->zb_objset == DMU_META_OBJSET &&
            record->zi_objset == DMU_META_OBJSET &&
            record->zi_object == DMU_META_DNODE_OBJECT) {
                if (record->zi_type == DMU_OT_NONE ||
                    type == record->zi_type)
                        return (freq_triggered(record->zi_freq));
                else
                        return (B_FALSE);
        }

        /*
         * Check for an exact match.
         */
        if (zb->zb_objset == record->zi_objset &&
            zb->zb_object == record->zi_object &&
            zb->zb_level == record->zi_level &&
            zb->zb_blkid >= record->zi_start &&
            zb->zb_blkid <= record->zi_end &&
            (record->zi_dvas == 0 ||
            (dva != ZI_NO_DVA && (record->zi_dvas & (1ULL << dva)))) &&
            error == record->zi_error) {
                return (freq_triggered(record->zi_freq));
        }

        return (B_FALSE);
}

/*
 * Panic the system when a config change happens in the function
 * specified by tag.
 */
void
zio_handle_panic_injection(spa_t *spa, const char *tag, uint64_t type)
{
        inject_handler_t *handler;

        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler)) {

                if (spa != handler->zi_spa)
                        continue;

                if (handler->zi_record.zi_type == type &&
                    strcmp(tag, handler->zi_record.zi_func) == 0)
                        panic("Panic requested in function %s\n", tag);
        }

        rw_exit(&inject_lock);
}

/*
 * Inject a decryption failure. Decryption failures can occur in
 * both the ARC and the ZIO layers.
 */
int
zio_handle_decrypt_injection(spa_t *spa, const zbookmark_phys_t *zb,
    uint64_t type, int error)
{
        int ret = 0;
        inject_handler_t *handler;

        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler)) {

                if (spa != handler->zi_spa ||
                    handler->zi_record.zi_cmd != ZINJECT_DECRYPT_FAULT)
                        continue;

                if (zio_match_handler(zb, type, ZI_NO_DVA,
                    &handler->zi_record, error)) {
                        ret = error;
                        break;
                }
        }

        rw_exit(&inject_lock);
        return (ret);
}

/*
 * If this is a physical I/O for a vdev child determine which DVA it is
 * for. We iterate backwards through the DVAs matching on the offset so
 * that we end up with ZI_NO_DVA (-1) if we don't find a match.
 */
static int
zio_match_dva(zio_t *zio)
{
        int i = ZI_NO_DVA;

        if (zio->io_bp != NULL && zio->io_vd != NULL &&
            zio->io_child_type == ZIO_CHILD_VDEV) {
                for (i = BP_GET_NDVAS(zio->io_bp) - 1; i >= 0; i--) {
                        dva_t *dva = &zio->io_bp->blk_dva[i];
                        uint64_t off = DVA_GET_OFFSET(dva);
                        vdev_t *vd = vdev_lookup_top(zio->io_spa,
                            DVA_GET_VDEV(dva));

                        /* Compensate for vdev label added to leaves */
                        if (zio->io_vd->vdev_ops->vdev_op_leaf)
                                off += VDEV_LABEL_START_SIZE;

                        if (zio->io_vd == vd && zio->io_offset == off)
                                break;
                }
        }

        return (i);
}


/*
 * Determine if the I/O in question should return failure.  Returns the errno
 * to be returned to the caller.
 */
int
zio_handle_fault_injection(zio_t *zio, int error)
{
        int ret = 0;
        inject_handler_t *handler;

        /*
         * Ignore I/O not associated with any logical data.
         */
        if (zio->io_logical == NULL)
                return (0);

        /*
         * Currently, we only support fault injection on reads.
         */
        if (zio->io_type != ZIO_TYPE_READ)
                return (0);

        /*
         * A rebuild I/O has no checksum to verify.
         */
        if (zio->io_priority == ZIO_PRIORITY_REBUILD && error == ECKSUM)
                return (0);

        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler)) {
                if (zio->io_spa != handler->zi_spa ||
                    handler->zi_record.zi_cmd != ZINJECT_DATA_FAULT)
                        continue;

                /* If this handler matches, return the specified error */
                if (zio_match_handler(&zio->io_logical->io_bookmark,
                    zio->io_bp ? BP_GET_TYPE(zio->io_bp) : DMU_OT_NONE,
                    zio_match_dva(zio), &handler->zi_record, error)) {
                        ret = error;
                        break;
                }
        }

        rw_exit(&inject_lock);

        return (ret);
}

/*
 * Determine if the zio is part of a label update and has an injection
 * handler associated with that portion of the label. Currently, we
 * allow error injection in either the nvlist or the uberblock region of
 * of the vdev label.
 */
int
zio_handle_label_injection(zio_t *zio, int error)
{
        inject_handler_t *handler;
        vdev_t *vd = zio->io_vd;
        uint64_t offset = zio->io_offset;
        int label;
        int ret = 0;

        if (offset >= VDEV_LABEL_START_SIZE &&
            offset < vd->vdev_psize - VDEV_LABEL_END_SIZE)
                return (0);

        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler)) {
                uint64_t start = handler->zi_record.zi_start;
                uint64_t end = handler->zi_record.zi_end;

                if (handler->zi_record.zi_cmd != ZINJECT_LABEL_FAULT)
                        continue;

                /*
                 * The injection region is the relative offsets within a
                 * vdev label. We must determine the label which is being
                 * updated and adjust our region accordingly.
                 */
                label = vdev_label_number(vd->vdev_psize, offset);
                start = vdev_label_offset(vd->vdev_psize, label, start);
                end = vdev_label_offset(vd->vdev_psize, label, end);

                if (zio->io_vd->vdev_guid == handler->zi_record.zi_guid &&
                    (offset >= start && offset <= end)) {
                        ret = error;
                        break;
                }
        }
        rw_exit(&inject_lock);
        return (ret);
}

static int
zio_inject_bitflip_cb(void *data, size_t len, void *private)
{
        zio_t *zio = private;
        uint8_t *buffer = data;
        uint_t byte = random_in_range(len);

        ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);

        /* flip a single random bit in an abd data buffer */
        buffer[byte] ^= 1 << random_in_range(8);

        return (1);     /* stop after first flip */
}

static int
zio_handle_device_injection_impl(vdev_t *vd, zio_t *zio, int err1, int err2)
{
        inject_handler_t *handler;
        int ret = 0;

        /*
         * We skip over faults in the labels unless it's during
         * device open (i.e. zio == NULL).
         */
        if (zio != NULL) {
                uint64_t offset = zio->io_offset;

                if (offset < VDEV_LABEL_START_SIZE ||
                    offset >= vd->vdev_psize - VDEV_LABEL_END_SIZE)
                        return (0);
        }

        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler)) {

                if (handler->zi_record.zi_cmd != ZINJECT_DEVICE_FAULT)
                        continue;

                if (vd->vdev_guid == handler->zi_record.zi_guid) {
                        if (handler->zi_record.zi_failfast &&
                            (zio == NULL || (zio->io_flags &
                            (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)))) {
                                continue;
                        }

                        /* Handle type specific I/O failures */
                        if (zio != NULL &&
                            handler->zi_record.zi_iotype != ZIO_TYPES &&
                            handler->zi_record.zi_iotype != zio->io_type)
                                continue;

                        if (handler->zi_record.zi_error == err1 ||
                            handler->zi_record.zi_error == err2) {
                                /*
                                 * limit error injection if requested
                                 */
                                if (!freq_triggered(handler->zi_record.zi_freq))
                                        continue;

                                /*
                                 * For a failed open, pretend like the device
                                 * has gone away.
                                 */
                                if (err1 == ENXIO)
                                        vd->vdev_stat.vs_aux =
                                            VDEV_AUX_OPEN_FAILED;

                                /*
                                 * Treat these errors as if they had been
                                 * retried so that all the appropriate stats
                                 * and FMA events are generated.
                                 */
                                if (!handler->zi_record.zi_failfast &&
                                    zio != NULL)
                                        zio->io_flags |= ZIO_FLAG_IO_RETRY;

                                /*
                                 * EILSEQ means flip a bit after a read
                                 */
                                if (handler->zi_record.zi_error == EILSEQ) {
                                        if (zio == NULL)
                                                break;

                                        /* locate buffer data and flip a bit */
                                        (void) abd_iterate_func(zio->io_abd, 0,
                                            zio->io_size, zio_inject_bitflip_cb,
                                            zio);
                                        break;
                                }

                                ret = handler->zi_record.zi_error;
                                break;
                        }
                        if (handler->zi_record.zi_error == ENXIO) {
                                ret = SET_ERROR(EIO);
                                break;
                        }
                }
        }

        rw_exit(&inject_lock);

        return (ret);
}

int
zio_handle_device_injection(vdev_t *vd, zio_t *zio, int error)
{
        return (zio_handle_device_injection_impl(vd, zio, error, INT_MAX));
}

int
zio_handle_device_injections(vdev_t *vd, zio_t *zio, int err1, int err2)
{
        return (zio_handle_device_injection_impl(vd, zio, err1, err2));
}

/*
 * Simulate hardware that ignores cache flushes.  For requested number
 * of seconds nix the actual writing to disk.
 */
void
zio_handle_ignored_writes(zio_t *zio)
{
        inject_handler_t *handler;

        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler)) {

                /* Ignore errors not destined for this pool */
                if (zio->io_spa != handler->zi_spa ||
                    handler->zi_record.zi_cmd != ZINJECT_IGNORED_WRITES)
                        continue;

                /*
                 * Positive duration implies # of seconds, negative
                 * a number of txgs
                 */
                if (handler->zi_record.zi_timer == 0) {
                        if (handler->zi_record.zi_duration > 0)
                                handler->zi_record.zi_timer = ddi_get_lbolt64();
                        else
                                handler->zi_record.zi_timer = zio->io_txg;
                }

                /* Have a "problem" writing 60% of the time */
                if (random_in_range(100) < 60)
                        zio->io_pipeline &= ~ZIO_VDEV_IO_STAGES;
                break;
        }

        rw_exit(&inject_lock);
}

void
spa_handle_ignored_writes(spa_t *spa)
{
        inject_handler_t *handler;

        if (zio_injection_enabled == 0)
                return;

        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler)) {

                if (spa != handler->zi_spa ||
                    handler->zi_record.zi_cmd != ZINJECT_IGNORED_WRITES)
                        continue;

                if (handler->zi_record.zi_duration > 0) {
                        VERIFY(handler->zi_record.zi_timer == 0 ||
                            ddi_time_after64(
                            (int64_t)handler->zi_record.zi_timer +
                            handler->zi_record.zi_duration * hz,
                            ddi_get_lbolt64()));
                } else {
                        /* duration is negative so the subtraction here adds */
                        VERIFY(handler->zi_record.zi_timer == 0 ||
                            handler->zi_record.zi_timer -
                            handler->zi_record.zi_duration >=
                            spa_syncing_txg(spa));
                }
        }

        rw_exit(&inject_lock);
}

hrtime_t
zio_handle_io_delay(zio_t *zio)
{
        vdev_t *vd = zio->io_vd;
        inject_handler_t *min_handler = NULL;
        hrtime_t min_target = 0;

        rw_enter(&inject_lock, RW_READER);

        /*
         * inject_delay_count is a subset of zio_injection_enabled that
         * is only incremented for delay handlers. These checks are
         * mainly added to remind the reader why we're not explicitly
         * checking zio_injection_enabled like the other functions.
         */
        IMPLY(inject_delay_count > 0, zio_injection_enabled > 0);
        IMPLY(zio_injection_enabled == 0, inject_delay_count == 0);

        /*
         * If there aren't any inject delay handlers registered, then we
         * can short circuit and simply return 0 here. A value of zero
         * informs zio_delay_interrupt() that this request should not be
         * delayed. This short circuit keeps us from acquiring the
         * inject_delay_mutex unnecessarily.
         */
        if (inject_delay_count == 0) {
                rw_exit(&inject_lock);
                return (0);
        }

        /*
         * Each inject handler has a number of "lanes" associated with
         * it. Each lane is able to handle requests independently of one
         * another, and at a latency defined by the inject handler
         * record's zi_timer field. Thus if a handler in configured with
         * a single lane with a 10ms latency, it will delay requests
         * such that only a single request is completed every 10ms. So,
         * if more than one request is attempted per each 10ms interval,
         * the average latency of the requests will be greater than
         * 10ms; but if only a single request is submitted each 10ms
         * interval the average latency will be 10ms.
         *
         * We need to acquire this mutex to prevent multiple concurrent
         * threads being assigned to the same lane of a given inject
         * handler. The mutex allows us to perform the following two
         * operations atomically:
         *
         *      1. determine the minimum handler and minimum target
         *         value of all the possible handlers
         *      2. update that minimum handler's lane array
         *
         * Without atomicity, two (or more) threads could pick the same
         * lane in step (1), and then conflict with each other in step
         * (2). This could allow a single lane handler to process
         * multiple requests simultaneously, which shouldn't be possible.
         */
        mutex_enter(&inject_delay_mtx);

        for (inject_handler_t *handler = list_head(&inject_handlers);
            handler != NULL; handler = list_next(&inject_handlers, handler)) {
                if (handler->zi_record.zi_cmd != ZINJECT_DELAY_IO)
                        continue;

                if (!freq_triggered(handler->zi_record.zi_freq))
                        continue;

                if (vd->vdev_guid != handler->zi_record.zi_guid)
                        continue;

                if (handler->zi_record.zi_iotype != ZIO_TYPES &&
                    handler->zi_record.zi_iotype != zio->io_type)
                                continue;

                /*
                 * Defensive; should never happen as the array allocation
                 * occurs prior to inserting this handler on the list.
                 */
                ASSERT3P(handler->zi_lanes, !=, NULL);

                /*
                 * This should never happen, the zinject command should
                 * prevent a user from setting an IO delay with zero lanes.
                 */
                ASSERT3U(handler->zi_record.zi_nlanes, !=, 0);

                ASSERT3U(handler->zi_record.zi_nlanes, >,
                    handler->zi_next_lane);

                /*
                 * We want to issue this IO to the lane that will become
                 * idle the soonest, so we compare the soonest this
                 * specific handler can complete the IO with all other
                 * handlers, to find the lowest value of all possible
                 * lanes. We then use this lane to submit the request.
                 *
                 * Since each handler has a constant value for its
                 * delay, we can just use the "next" lane for that
                 * handler; as it will always be the lane with the
                 * lowest value for that particular handler (i.e. the
                 * lane that will become idle the soonest). This saves a
                 * scan of each handler's lanes array.
                 *
                 * There's two cases to consider when determining when
                 * this specific IO request should complete. If this
                 * lane is idle, we want to "submit" the request now so
                 * it will complete after zi_timer milliseconds. Thus,
                 * we set the target to now + zi_timer.
                 *
                 * If the lane is busy, we want this request to complete
                 * zi_timer milliseconds after the lane becomes idle.
                 * Since the 'zi_lanes' array holds the time at which
                 * each lane will become idle, we use that value to
                 * determine when this request should complete.
                 */
                hrtime_t idle = handler->zi_record.zi_timer + gethrtime();
                hrtime_t busy = handler->zi_record.zi_timer +
                    handler->zi_lanes[handler->zi_next_lane];
                hrtime_t target = MAX(idle, busy);

                if (min_handler == NULL) {
                        min_handler = handler;
                        min_target = target;
                        continue;
                }

                ASSERT3P(min_handler, !=, NULL);
                ASSERT3U(min_target, !=, 0);

                /*
                 * We don't yet increment the "next lane" variable since
                 * we still might find a lower value lane in another
                 * handler during any remaining iterations. Once we're
                 * sure we've selected the absolute minimum, we'll claim
                 * the lane and increment the handler's "next lane"
                 * field below.
                 */

                if (target < min_target) {
                        min_handler = handler;
                        min_target = target;
                }
        }

        /*
         * 'min_handler' will be NULL if no IO delays are registered for
         * this vdev, otherwise it will point to the handler containing
         * the lane that will become idle the soonest.
         */
        if (min_handler != NULL) {
                ASSERT3U(min_target, !=, 0);
                min_handler->zi_lanes[min_handler->zi_next_lane] = min_target;

                /*
                 * If we've used all possible lanes for this handler,
                 * loop back and start using the first lane again;
                 * otherwise, just increment the lane index.
                 */
                min_handler->zi_next_lane = (min_handler->zi_next_lane + 1) %
                    min_handler->zi_record.zi_nlanes;
        }

        mutex_exit(&inject_delay_mtx);
        rw_exit(&inject_lock);

        return (min_target);
}

static int
zio_calculate_range(const char *pool, zinject_record_t *record)
{
        dsl_pool_t *dp;
        dsl_dataset_t *ds;
        objset_t *os = NULL;
        dnode_t *dn = NULL;
        int error;

        /*
         * Obtain the dnode for object using pool, objset, and object
         */
        error = dsl_pool_hold(pool, FTAG, &dp);
        if (error)
                return (error);

        error = dsl_dataset_hold_obj(dp, record->zi_objset, FTAG, &ds);
        dsl_pool_rele(dp, FTAG);
        if (error)
                return (error);

        error = dmu_objset_from_ds(ds, &os);
        dsl_dataset_rele(ds, FTAG);
        if (error)
                return (error);

        error = dnode_hold(os, record->zi_object, FTAG, &dn);
        if (error)
                return (error);

        /*
         * Translate the range into block IDs
         */
        if (record->zi_start != 0 || record->zi_end != -1ULL) {
                record->zi_start >>= dn->dn_datablkshift;
                record->zi_end >>= dn->dn_datablkshift;
        }
        if (record->zi_level > 0) {
                if (record->zi_level >= dn->dn_nlevels) {
                        dnode_rele(dn, FTAG);
                        return (SET_ERROR(EDOM));
                }

                if (record->zi_start != 0 || record->zi_end != 0) {
                        int shift = dn->dn_indblkshift - SPA_BLKPTRSHIFT;

                        for (int level = record->zi_level; level > 0; level--) {
                                record->zi_start >>= shift;
                                record->zi_end >>= shift;
                        }
                }
        }

        dnode_rele(dn, FTAG);
        return (0);
}

/*
 * Create a new handler for the given record.  We add it to the list, adding
 * a reference to the spa_t in the process.  We increment zio_injection_enabled,
 * which is the switch to trigger all fault injection.
 */
int
zio_inject_fault(char *name, int flags, int *id, zinject_record_t *record)
{
        inject_handler_t *handler;
        int error;
        spa_t *spa;

        /*
         * If this is pool-wide metadata, make sure we unload the corresponding
         * spa_t, so that the next attempt to load it will trigger the fault.
         * We call spa_reset() to unload the pool appropriately.
         */
        if (flags & ZINJECT_UNLOAD_SPA)
                if ((error = spa_reset(name)) != 0)
                        return (error);

        if (record->zi_cmd == ZINJECT_DELAY_IO) {
                /*
                 * A value of zero for the number of lanes or for the
                 * delay time doesn't make sense.
                 */
                if (record->zi_timer == 0 || record->zi_nlanes == 0)
                        return (SET_ERROR(EINVAL));

                /*
                 * The number of lanes is directly mapped to the size of
                 * an array used by the handler. Thus, to ensure the
                 * user doesn't trigger an allocation that's "too large"
                 * we cap the number of lanes here.
                 */
                if (record->zi_nlanes >= UINT16_MAX)
                        return (SET_ERROR(EINVAL));
        }

        /*
         * If the supplied range was in bytes -- calculate the actual blkid
         */
        if (flags & ZINJECT_CALC_RANGE) {
                error = zio_calculate_range(name, record);
                if (error != 0)
                        return (error);
        }

        if (!(flags & ZINJECT_NULL)) {
                /*
                 * spa_inject_ref() will add an injection reference, which will
                 * prevent the pool from being removed from the namespace while
                 * still allowing it to be unloaded.
                 */
                if ((spa = spa_inject_addref(name)) == NULL)
                        return (SET_ERROR(ENOENT));

                handler = kmem_alloc(sizeof (inject_handler_t), KM_SLEEP);

                handler->zi_spa = spa;
                handler->zi_record = *record;

                if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
                        handler->zi_lanes = kmem_zalloc(
                            sizeof (*handler->zi_lanes) *
                            handler->zi_record.zi_nlanes, KM_SLEEP);
                        handler->zi_next_lane = 0;
                } else {
                        handler->zi_lanes = NULL;
                        handler->zi_next_lane = 0;
                }

                rw_enter(&inject_lock, RW_WRITER);

                /*
                 * We can't move this increment into the conditional
                 * above because we need to hold the RW_WRITER lock of
                 * inject_lock, and we don't want to hold that while
                 * allocating the handler's zi_lanes array.
                 */
                if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
                        ASSERT3S(inject_delay_count, >=, 0);
                        inject_delay_count++;
                        ASSERT3S(inject_delay_count, >, 0);
                }

                *id = handler->zi_id = inject_next_id++;
                list_insert_tail(&inject_handlers, handler);
                atomic_inc_32(&zio_injection_enabled);

                rw_exit(&inject_lock);
        }

        /*
         * Flush the ARC, so that any attempts to read this data will end up
         * going to the ZIO layer.  Note that this is a little overkill, but
         * we don't have the necessary ARC interfaces to do anything else, and
         * fault injection isn't a performance critical path.
         */
        if (flags & ZINJECT_FLUSH_ARC)
                /*
                 * We must use FALSE to ensure arc_flush returns, since
                 * we're not preventing concurrent ARC insertions.
                 */
                arc_flush(NULL, FALSE);

        return (0);
}

/*
 * Returns the next record with an ID greater than that supplied to the
 * function.  Used to iterate over all handlers in the system.
 */
int
zio_inject_list_next(int *id, char *name, size_t buflen,
    zinject_record_t *record)
{
        inject_handler_t *handler;
        int ret;

        mutex_enter(&spa_namespace_lock);
        rw_enter(&inject_lock, RW_READER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler))
                if (handler->zi_id > *id)
                        break;

        if (handler) {
                *record = handler->zi_record;
                *id = handler->zi_id;
                (void) strlcpy(name, spa_name(handler->zi_spa), buflen);
                ret = 0;
        } else {
                ret = SET_ERROR(ENOENT);
        }

        rw_exit(&inject_lock);
        mutex_exit(&spa_namespace_lock);

        return (ret);
}

/*
 * Clear the fault handler with the given identifier, or return ENOENT if none
 * exists.
 */
int
zio_clear_fault(int id)
{
        inject_handler_t *handler;

        rw_enter(&inject_lock, RW_WRITER);

        for (handler = list_head(&inject_handlers); handler != NULL;
            handler = list_next(&inject_handlers, handler))
                if (handler->zi_id == id)
                        break;

        if (handler == NULL) {
                rw_exit(&inject_lock);
                return (SET_ERROR(ENOENT));
        }

        if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
                ASSERT3S(inject_delay_count, >, 0);
                inject_delay_count--;
                ASSERT3S(inject_delay_count, >=, 0);
        }

        list_remove(&inject_handlers, handler);
        rw_exit(&inject_lock);

        if (handler->zi_record.zi_cmd == ZINJECT_DELAY_IO) {
                ASSERT3P(handler->zi_lanes, !=, NULL);
                kmem_free(handler->zi_lanes, sizeof (*handler->zi_lanes) *
                    handler->zi_record.zi_nlanes);
        } else {
                ASSERT3P(handler->zi_lanes, ==, NULL);
        }

        spa_inject_delref(handler->zi_spa);
        kmem_free(handler, sizeof (inject_handler_t));
        atomic_dec_32(&zio_injection_enabled);

        return (0);
}

void
zio_inject_init(void)
{
        rw_init(&inject_lock, NULL, RW_DEFAULT, NULL);
        mutex_init(&inject_delay_mtx, NULL, MUTEX_DEFAULT, NULL);
        list_create(&inject_handlers, sizeof (inject_handler_t),
            offsetof(inject_handler_t, zi_link));
}

void
zio_inject_fini(void)
{
        list_destroy(&inject_handlers);
        mutex_destroy(&inject_delay_mtx);
        rw_destroy(&inject_lock);
}

#if defined(_KERNEL)
EXPORT_SYMBOL(zio_injection_enabled);
EXPORT_SYMBOL(zio_inject_fault);
EXPORT_SYMBOL(zio_inject_list_next);
EXPORT_SYMBOL(zio_clear_fault);
EXPORT_SYMBOL(zio_handle_fault_injection);
EXPORT_SYMBOL(zio_handle_device_injection);
EXPORT_SYMBOL(zio_handle_label_injection);
#endif