source: mainline/uspace/srv/bd/hr/raid1.c@ 7debda3

/*
 * Copyright (c) 2025 Miroslav Cimerman
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup hr
 * @{
 */
/**
 * @file
 */

#include <bd_srv.h>
#include <block.h>
#include <errno.h>
#include <hr.h>
#include <io/log.h>
#include <ipc/hr.h>
#include <ipc/services.h>
#include <loc.h>
#include <task.h>
#include <stdatomic.h>
#include <stdio.h>
#include <stdlib.h>
#include <str_error.h>

#include "fge.h"
#include "io.h"
#include "superblock.h"
#include "util.h"
#include "var.h"

extern loc_srv_t *hr_srv;

static void hr_raid1_update_vol_status(hr_volume_t *);
static void hr_raid1_ext_state_callback(hr_volume_t *, size_t, errno_t);
static size_t hr_raid1_count_good_extents(hr_volume_t *, uint64_t, size_t,
    uint64_t);
static errno_t hr_raid1_bd_op(hr_bd_op_type_t, bd_srv_t *, aoff64_t, size_t,
    void *, const void *, size_t);
static errno_t hr_raid1_rebuild(void *);
static errno_t init_rebuild(hr_volume_t *, size_t *);
static errno_t swap_hs(hr_volume_t *, size_t, size_t);
static errno_t hr_raid1_restore_blocks(hr_volume_t *, size_t, uint64_t, size_t,
    void *);

/* bdops */
static errno_t hr_raid1_bd_open(bd_srvs_t *, bd_srv_t *);
static errno_t hr_raid1_bd_close(bd_srv_t *);
static errno_t hr_raid1_bd_read_blocks(bd_srv_t *, aoff64_t, size_t, void *,
    size_t);
static errno_t hr_raid1_bd_sync_cache(bd_srv_t *, aoff64_t, size_t);
static errno_t hr_raid1_bd_write_blocks(bd_srv_t *, aoff64_t, size_t,
    const void *, size_t);
static errno_t hr_raid1_bd_get_block_size(bd_srv_t *, size_t *);
static errno_t hr_raid1_bd_get_num_blocks(bd_srv_t *, aoff64_t *);

static bd_ops_t hr_raid1_bd_ops = {
        .open = hr_raid1_bd_open,
        .close = hr_raid1_bd_close,
        .sync_cache = hr_raid1_bd_sync_cache,
        .read_blocks = hr_raid1_bd_read_blocks,
        .write_blocks = hr_raid1_bd_write_blocks,
        .get_block_size = hr_raid1_bd_get_block_size,
        .get_num_blocks = hr_raid1_bd_get_num_blocks
};

errno_t hr_raid1_create(hr_volume_t *new_volume)
{
        errno_t rc;

        assert(new_volume->level == HR_LVL_1);

        if (new_volume->extent_no < 2) {
                HR_ERROR("RAID 1 array needs at least 2 devices\n");
                return EINVAL;
        }

        bd_srvs_init(&new_volume->hr_bds);
        new_volume->hr_bds.ops = &hr_raid1_bd_ops;
        new_volume->hr_bds.sarg = new_volume;

        /* force volume state update */
        atomic_store(&new_volume->state_changed, true);
        hr_raid1_update_vol_status(new_volume);

        fibril_rwlock_read_lock(&new_volume->states_lock);
        hr_vol_status_t state = new_volume->status;
        fibril_rwlock_read_unlock(&new_volume->states_lock);
        if (state == HR_VOL_FAULTY || state == HR_VOL_INVALID)
                return EINVAL;

        rc = hr_register_volume(new_volume);

        return rc;
}

errno_t hr_raid1_init(hr_volume_t *vol)
{
        errno_t rc;
        size_t bsize;
        uint64_t total_blkno;

        assert(vol->level == HR_LVL_1);

        rc = hr_check_devs(vol, &total_blkno, &bsize);
        if (rc != EOK)
                return rc;

        vol->nblocks = total_blkno / vol->extent_no;
        vol->bsize = bsize;
        vol->data_offset = HR_DATA_OFF;
        vol->data_blkno = vol->nblocks - vol->data_offset;
        vol->strip_size = 0;

        return EOK;
}

void hr_raid1_status_event(hr_volume_t *vol)
{
        hr_raid1_update_vol_status(vol);
}

errno_t hr_raid1_add_hotspare(hr_volume_t *vol, service_id_t hotspare)
{
        HR_DEBUG("hr_raid1_add_hotspare()\n");

        errno_t rc = EOK;

        fibril_mutex_lock(&vol->hotspare_lock);

        if (vol->hotspare_no >= HR_MAX_HOTSPARES) {
                HR_ERROR("hr_raid1_add_hotspare(): cannot add more hotspares "
                    "to \"%s\"\n", vol->devname);
                rc = ELIMIT;
                goto error;
        }

        size_t hs_idx = vol->hotspare_no;

        vol->hotspare_no++;

        hr_update_hotspare_svc_id(vol, hs_idx, hotspare);
        hr_update_hotspare_status(vol, hs_idx, HR_EXT_HOTSPARE);

        atomic_store(&vol->state_changed, true);
error:
        fibril_mutex_unlock(&vol->hotspare_lock);

        hr_raid1_update_vol_status(vol);

        return rc;
}

static errno_t hr_raid1_bd_open(bd_srvs_t *bds, bd_srv_t *bd)
{
        HR_DEBUG("hr_bd_open()\n");
        return EOK;
}

static errno_t hr_raid1_bd_close(bd_srv_t *bd)
{
        HR_DEBUG("hr_bd_close()\n");
        return EOK;
}

static errno_t hr_raid1_bd_sync_cache(bd_srv_t *bd, aoff64_t ba, size_t cnt)
{
        return hr_raid1_bd_op(HR_BD_SYNC, bd, ba, cnt, NULL, NULL, 0);
}

static errno_t hr_raid1_bd_read_blocks(bd_srv_t *bd, aoff64_t ba, size_t cnt,
    void *buf, size_t size)
{
        return hr_raid1_bd_op(HR_BD_READ, bd, ba, cnt, buf, NULL, size);
}

static errno_t hr_raid1_bd_write_blocks(bd_srv_t *bd, aoff64_t ba, size_t cnt,
    const void *data, size_t size)
{
        return hr_raid1_bd_op(HR_BD_WRITE, bd, ba, cnt, NULL, data, size);
}

static errno_t hr_raid1_bd_get_block_size(bd_srv_t *bd, size_t *rsize)
{
        hr_volume_t *vol = bd->srvs->sarg;

        *rsize = vol->bsize;
        return EOK;
}

static errno_t hr_raid1_bd_get_num_blocks(bd_srv_t *bd, aoff64_t *rnb)
{
        hr_volume_t *vol = bd->srvs->sarg;

        *rnb = vol->data_blkno;
        return EOK;
}

static void hr_raid1_update_vol_status(hr_volume_t *vol)
{
        bool exp = true;

        if (!atomic_compare_exchange_strong(&vol->state_changed, &exp, false))
                return;

        if (atomic_compare_exchange_strong(&vol->pending_invalidation, &exp,
            false)) {
                fibril_mutex_lock(&vol->deferred_list_lock);
                hr_process_deferred_invalidations(vol);
                fibril_mutex_unlock(&vol->deferred_list_lock);
        }

        fibril_rwlock_read_lock(&vol->extents_lock);
        fibril_rwlock_read_lock(&vol->states_lock);

        hr_vol_status_t old_state = vol->status;
        size_t healthy = hr_count_extents(vol, HR_EXT_ONLINE);

        fibril_rwlock_read_unlock(&vol->states_lock);
        fibril_rwlock_read_unlock(&vol->extents_lock);

        if (healthy == 0) {
                if (old_state != HR_VOL_FAULTY) {
                        fibril_rwlock_write_lock(&vol->states_lock);
                        hr_update_vol_status(vol, HR_VOL_FAULTY);
                        fibril_rwlock_write_unlock(&vol->states_lock);
                }
        } else if (healthy < vol->extent_no) {
                if (old_state != HR_VOL_REBUILD &&
                    old_state != HR_VOL_DEGRADED) {
                        fibril_rwlock_write_lock(&vol->states_lock);
                        hr_update_vol_status(vol, HR_VOL_DEGRADED);
                        fibril_rwlock_write_unlock(&vol->states_lock);
                }

                if (old_state != HR_VOL_REBUILD) {
                        if (vol->hotspare_no > 0) {
                                fid_t fib = fibril_create(hr_raid1_rebuild,
                                    vol);
                                if (fib == 0)
                                        return;
                                fibril_start(fib);
                                fibril_detach(fib);
                        }
                }
        } else {
                if (old_state != HR_VOL_ONLINE) {
                        fibril_rwlock_write_lock(&vol->states_lock);
                        hr_update_vol_status(vol, HR_VOL_ONLINE);
                        fibril_rwlock_write_unlock(&vol->states_lock);
                }
        }
}

static void hr_raid1_ext_state_callback(hr_volume_t *vol, size_t extent,
    errno_t rc)
{
        if (rc == EOK)
                return;

        assert(fibril_rwlock_is_locked(&vol->extents_lock));

        fibril_rwlock_write_lock(&vol->states_lock);

        switch (rc) {
        case ENOMEM:
                fibril_mutex_lock(&vol->deferred_list_lock);

                service_id_t invalid_svc_id = vol->extents[extent].svc_id;

                list_foreach(vol->deferred_invalidations_list, link,
                    hr_deferred_invalidation_t, di) {
                        if (di->svc_id == invalid_svc_id) {
                                assert(vol->extents[extent].status ==
                                    HR_EXT_INVALID);
                                goto deferring_end;
                        }
                }

                assert(vol->extents[extent].svc_id != HR_EXT_INVALID);

                hr_update_ext_status(vol, extent, HR_EXT_INVALID);

                size_t i = list_count(&vol->deferred_invalidations_list);
                vol->deferred_inval[i].svc_id = invalid_svc_id;
                vol->deferred_inval[i].index = extent;

                list_append(&vol->deferred_inval[i].link,
                    &vol->deferred_invalidations_list);

                atomic_store(&vol->pending_invalidation, true);
        deferring_end:

                fibril_mutex_unlock(&vol->deferred_list_lock);
                break;
        case ENOENT:
                hr_update_ext_status(vol, extent, HR_EXT_MISSING);
                break;
        default:
                hr_update_ext_status(vol, extent, HR_EXT_FAILED);
        }

        atomic_store(&vol->state_changed, true);

        fibril_rwlock_write_unlock(&vol->states_lock);
}

static size_t hr_raid1_count_good_extents(hr_volume_t *vol, uint64_t ba,
    size_t cnt, uint64_t rebuild_blk)
{
        assert(fibril_rwlock_is_locked(&vol->extents_lock));
        assert(fibril_rwlock_is_locked(&vol->states_lock));

        size_t count = 0;
        for (size_t i = 0; i < vol->extent_no; i++) {
                if (vol->extents[i].status == HR_EXT_ONLINE ||
                    (vol->extents[i].status == HR_EXT_REBUILD &&
                    ba < rebuild_blk)) {
                        count++;
                }
        }

        return count;

}

static errno_t hr_raid1_bd_op(hr_bd_op_type_t type, bd_srv_t *bd, aoff64_t ba,
    size_t cnt, void *data_read, const void *data_write, size_t size)
{
        hr_volume_t *vol = bd->srvs->sarg;
        hr_range_lock_t *rl = NULL;
        errno_t rc;
        size_t i;
        uint64_t rebuild_blk;

        fibril_rwlock_read_lock(&vol->states_lock);
        hr_vol_status_t vol_state = vol->status;
        fibril_rwlock_read_unlock(&vol->states_lock);

        if (vol_state == HR_VOL_FAULTY || vol_state == HR_VOL_INVALID)
                return EIO;

        if (type == HR_BD_READ || type == HR_BD_WRITE)
                if (size < cnt * vol->bsize)
                        return EINVAL;

        rc = hr_check_ba_range(vol, cnt, ba);
        if (rc != EOK)
                return rc;

        /* allow full dev sync */
        if (type != HR_BD_SYNC || ba != 0)
                hr_add_ba_offset(vol, &ba);

        /*
         * this is to allow adding hotspare or start a rebuild on
         * very busy array, because of how rwlocks are implemented
         * in HelenOS (no writer priority, so if there are multiple
         * continuos readers, writer will never own the lock)
         */
        if (vol->halt_please) {
                fibril_mutex_lock(&vol->halt_lock);
                fibril_mutex_unlock(&vol->halt_lock);
        }

        /*
         * extent order has to be locked for the whole IO duration,
         * so that workers have consistent targets
         */
        fibril_rwlock_read_lock(&vol->extents_lock);

        size_t successful = 0;
        switch (type) {
        case HR_BD_READ:
                rebuild_blk = atomic_load_explicit(&vol->rebuild_blk,
                    memory_order_relaxed);

                for (i = 0; i < vol->extent_no; i++) {
                        fibril_rwlock_read_lock(&vol->states_lock);
                        hr_ext_status_t state = vol->extents[i].status;
                        fibril_rwlock_read_unlock(&vol->states_lock);

                        if (state != HR_EXT_ONLINE &&
                            (state != HR_EXT_REBUILD ||
                            ba + cnt - 1 >= rebuild_blk)) {
                                continue;
                        }

                        rc = block_read_direct(vol->extents[i].svc_id, ba, cnt,
                            data_read);

                        if (rc == ENOMEM && i + 1 == vol->extent_no)
                                goto end;

                        if (rc == ENOMEM)
                                continue;

                        if (rc != EOK) {
                                hr_raid1_ext_state_callback(vol, i, rc);
                        } else {
                                successful++;
                                break;
                        }
                }
                break;
        case HR_BD_SYNC:
        case HR_BD_WRITE:
                if (type == HR_BD_WRITE) {
                        rl = hr_range_lock_acquire(vol, ba, cnt);
                        if (rl == NULL) {
                                rc = ENOMEM;
                                goto end;
                        }
                }

                fibril_rwlock_read_lock(&vol->states_lock);

                rebuild_blk = atomic_load_explicit(&vol->rebuild_blk,
                    memory_order_relaxed);

                size_t good = hr_raid1_count_good_extents(vol, ba, cnt,
                    rebuild_blk);

                hr_fgroup_t *group = hr_fgroup_create(vol->fge, good);
                if (group == NULL) {
                        if (type == HR_BD_WRITE)
                                hr_range_lock_release(rl);
                        rc = ENOMEM;
                        fibril_rwlock_read_unlock(&vol->states_lock);
                        goto end;
                }

                for (i = 0; i < vol->extent_no; i++) {
                        if (vol->extents[i].status != HR_EXT_ONLINE &&
                            (vol->extents[i].status != HR_EXT_REBUILD ||
                            ba >= rebuild_blk)) {
                                /*
                                 * When the extent is being rebuilt,
                                 * we only write to the part that is already
                                 * rebuilt. If IO starts after vol->rebuild_blk
                                 * we do not proceed, the write is going to
                                 * be replicated later in the rebuild.
                                 */
                                continue;
                        }

                        hr_io_t *io = hr_fgroup_alloc(group);
                        io->extent = i;
                        io->data_write = data_write;
                        io->data_read = data_read;
                        io->ba = ba;
                        io->cnt = cnt;
                        io->type = type;
                        io->vol = vol;
                        io->state_callback = hr_raid1_ext_state_callback;

                        hr_fgroup_submit(group, hr_io_worker, io);
                }

                fibril_rwlock_read_unlock(&vol->states_lock);

                (void)hr_fgroup_wait(group, &successful, NULL);

                if (type == HR_BD_WRITE)
                        hr_range_lock_release(rl);

                break;
        default:
                rc = EINVAL;
                goto end;
        }

        if (successful > 0)
                rc = EOK;
        else
                rc = EIO;

end:
        fibril_rwlock_read_unlock(&vol->extents_lock);

        hr_raid1_update_vol_status(vol);

        return rc;
}

/*
 * Put the last HOTSPARE extent in place
 * of first that != ONLINE, and start the rebuild.
 */
static errno_t hr_raid1_rebuild(void *arg)
{
        HR_DEBUG("hr_raid1_rebuild()\n");

        hr_volume_t *vol = arg;
        void *buf = NULL;
        size_t rebuild_idx;
        errno_t rc;

        rc = init_rebuild(vol, &rebuild_idx);
        if (rc != EOK)
                return rc;

        size_t left = vol->data_blkno;
        size_t max_blks = DATA_XFER_LIMIT / vol->bsize;
        buf = malloc(max_blks * vol->bsize);

        size_t cnt;
        uint64_t ba = 0;
        hr_add_ba_offset(vol, &ba);

        fibril_rwlock_read_lock(&vol->extents_lock);

        hr_range_lock_t *rl = NULL;

        while (left != 0) {
                if (vol->halt_please) {
                        fibril_rwlock_read_unlock(&vol->extents_lock);
                        fibril_mutex_lock(&vol->halt_lock);
                        fibril_mutex_unlock(&vol->halt_lock);
                        fibril_rwlock_read_lock(&vol->extents_lock);
                }

                cnt = min(max_blks, left);

                rl = hr_range_lock_acquire(vol, ba, cnt);
                if (rl == NULL) {
                        rc = ENOMEM;
                        goto end;
                }

                atomic_store_explicit(&vol->rebuild_blk, ba,
                    memory_order_relaxed);

                rc = hr_raid1_restore_blocks(vol, rebuild_idx, ba, cnt, buf);

                hr_range_lock_release(rl);

                if (rc != EOK)
                        goto end;

                ba += cnt;
                left -= cnt;
        }

        HR_DEBUG("hr_raid1_rebuild(): rebuild finished on \"%s\" (%lu), "
            "extent no. %lu\n", vol->devname, vol->svc_id, rebuild_idx);

        fibril_rwlock_write_lock(&vol->states_lock);

        hr_update_ext_status(vol, rebuild_idx, HR_EXT_ONLINE);
        /*
         * We can be optimistic here, if some extents are
         * still INVALID, FAULTY or MISSING, the update vol
         * function will pick them up, and set the volume
         * state accordingly.
         */
        hr_update_vol_status(vol, HR_VOL_ONLINE);
        atomic_store(&vol->state_changed, true);

        fibril_rwlock_write_unlock(&vol->states_lock);

        /*
         * For now write metadata at the end, because
         * we don't sync metada accross extents yet.
         */
        hr_write_meta_to_ext(vol, rebuild_idx);
end:
        if (rc != EOK) {
                /*
                 * We can fail either because:
                 * - the rebuild extent failing or invalidation
                 * - there is are no ONLINE extents (vol is FAULTY)
                 * - we got ENOMEM on all READs (we also invalidate the
                 *   rebuild extent here, for now)
                 */
                fibril_rwlock_write_lock(&vol->states_lock);
                hr_update_vol_status(vol, HR_VOL_DEGRADED);
                atomic_store(&vol->state_changed, true);
                fibril_rwlock_write_unlock(&vol->states_lock);
        }

        fibril_rwlock_read_unlock(&vol->extents_lock);

        hr_raid1_update_vol_status(vol);

        if (buf != NULL)
                free(buf);

        return rc;
}

static errno_t init_rebuild(hr_volume_t *vol, size_t *rebuild_idx)
{
        errno_t rc = EOK;

        fibril_mutex_lock(&vol->halt_lock);
        vol->halt_please = true;
        fibril_rwlock_write_lock(&vol->extents_lock);
        fibril_rwlock_write_lock(&vol->states_lock);
        fibril_mutex_lock(&vol->hotspare_lock);

        if (vol->hotspare_no == 0) {
                HR_WARN("hr_raid1_rebuild(): no free hotspares on \"%s\", "
                    "aborting rebuild\n", vol->devname);
                rc = EINVAL;
                goto error;
        }

        size_t bad = vol->extent_no;
        for (size_t i = 0; i < vol->extent_no; i++) {
                if (vol->extents[i].status != HR_EXT_ONLINE) {
                        bad = i;
                        break;
                }
        }

        if (bad == vol->extent_no) {
                HR_WARN("hr_raid1_rebuild(): no bad extent on \"%s\", "
                    "aborting rebuild\n", vol->devname);
                rc = EINVAL;
                goto error;
        }

        size_t hotspare_idx = vol->hotspare_no - 1;

        hr_ext_status_t hs_state = vol->hotspares[hotspare_idx].status;
        if (hs_state != HR_EXT_HOTSPARE) {
                HR_ERROR("hr_raid1_rebuild(): invalid hotspare state \"%s\", "
                    "aborting rebuild\n", hr_get_ext_status_msg(hs_state));
                rc = EINVAL;
                goto error;
        }

        rc = swap_hs(vol, bad, hotspare_idx);
        if (rc != EOK) {
                HR_ERROR("hr_raid1_rebuild(): swapping hotspare failed, "
                    "aborting rebuild\n");
                goto error;
        }

        hr_extent_t *rebuild_ext = &vol->extents[bad];

        HR_DEBUG("hr_raid1_rebuild(): starting REBUILD on extent no. %lu (%lu)"
            "\n", bad, rebuild_ext->svc_id);

        atomic_store_explicit(&vol->rebuild_blk, 0, memory_order_relaxed);

        hr_update_ext_status(vol, bad, HR_EXT_REBUILD);
        hr_update_vol_status(vol, HR_VOL_REBUILD);

        *rebuild_idx = bad;
error:
        fibril_mutex_unlock(&vol->hotspare_lock);
        fibril_rwlock_write_unlock(&vol->states_lock);
        fibril_rwlock_write_unlock(&vol->extents_lock);
        vol->halt_please = false;
        fibril_mutex_unlock(&vol->halt_lock);

        return rc;
}

static errno_t swap_hs(hr_volume_t *vol, size_t bad, size_t hs)
{
        HR_DEBUG("hr_raid1_rebuild(): swapping in hotspare\n");

        service_id_t faulty_svc_id = vol->extents[bad].svc_id;
        service_id_t hs_svc_id = vol->hotspares[hs].svc_id;

        /* TODO: if rc != EOK, try next hotspare */
        errno_t rc = block_init(hs_svc_id);
        if (rc != EOK) {
                HR_ERROR("hr_raid1_rebuild(): initing hotspare (%lu) failed\n",
                    hs_svc_id);
                return rc;
        }

        hr_update_ext_svc_id(vol, bad, hs_svc_id);
        hr_update_ext_status(vol, bad, HR_EXT_HOTSPARE);

        hr_update_hotspare_svc_id(vol, hs, 0);
        hr_update_hotspare_status(vol, hs, HR_EXT_INVALID);

        vol->hotspare_no--;

        if (faulty_svc_id != 0)
                block_fini(faulty_svc_id);

        return EOK;
}

static errno_t hr_raid1_restore_blocks(hr_volume_t *vol, size_t rebuild_idx,
    uint64_t ba, size_t cnt, void *buf)
{
        HR_DEBUG("REBUILD restoring blocks (ba: %lu, cnt: %lu)\n", ba, cnt);

        assert(fibril_rwlock_is_locked(&vol->extents_lock));

        errno_t rc = ENOENT;
        hr_extent_t *ext, *rebuild_ext = &vol->extents[rebuild_idx];

        for (size_t i = 0; i < vol->extent_no; i++) {
                fibril_rwlock_read_lock(&vol->states_lock);

                ext = &vol->extents[i];
                if (ext->status != HR_EXT_ONLINE)
                        continue;

                fibril_rwlock_read_unlock(&vol->states_lock);

                rc = block_read_direct(ext->svc_id, ba, cnt, buf);
                if (rc == EOK)
                        break;

                if (rc != ENOMEM)
                        hr_raid1_ext_state_callback(vol, i, rc);

                if (i + 1 >= vol->extent_no) {
                        if (rc != ENOMEM) {
                                HR_ERROR("rebuild on \"%s\" (%lu), failed due "
                                    "to too many failed extents\n",
                                    vol->devname, vol->svc_id);
                        }

                        /* for now we have to invalidate the rebuild extent */
                        if (rc == ENOMEM) {
                                HR_ERROR("rebuild on \"%s\" (%lu), failed due "
                                    "to too many failed reads, because of not "
                                    "enough memory\n",
                                    vol->devname, vol->svc_id);
                                hr_raid1_ext_state_callback(vol, rebuild_idx,
                                    ENOMEM);
                        }

                        return rc;
                }
        }

        rc = block_write_direct(rebuild_ext->svc_id, ba, cnt, buf);
        if (rc != EOK) {
                /*
                 * Here we dont handle ENOMEM, because maybe in the
                 * future, there is going to be M_WAITOK, or we are
                 * going to wait for more memory, so that we don't
                 * have to invalidate it...
                 *
                 * XXX: for now we do
                 */
                hr_raid1_ext_state_callback(vol, rebuild_idx, rc);

                HR_ERROR("rebuild on \"%s\" (%lu), failed due to "
                    "the rebuilt extent no. %lu WRITE (rc: %s)\n",
                    vol->devname, vol->svc_id, rebuild_idx, str_error(rc));

                return rc;
        }

        return EOK;
}

/** @}
 */