block/block-copy.c

/*
 * block_copy API
 *
 * Copyright (C) 2013 Proxmox Server Solutions
 * Copyright (c) 2019 Virtuozzo International GmbH.
 *
 * Authors:
 *  Dietmar Maurer (dietmar@proxmox.com)
 *  Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 */

#include "qemu/osdep.h"

#include "trace.h"
#include "qapi/error.h"
#include "block/block-copy.h"
#include "sysemu/block-backend.h"
#include "qemu/units.h"

#define BLOCK_COPY_MAX_COPY_RANGE (16 * MiB)
#define BLOCK_COPY_MAX_BUFFER (1 * MiB)
#define BLOCK_COPY_MAX_MEM (128 * MiB)

static void coroutine_fn block_copy_wait_inflight_reqs(BlockCopyState *s,
                                                       int64_t start,
                                                       int64_t end)
{
    BlockCopyInFlightReq *req;
    bool waited;

    do {
        waited = false;
        QLIST_FOREACH(req, &s->inflight_reqs, list) {
            if (end > req->start_byte && start < req->end_byte) {
                qemu_co_queue_wait(&req->wait_queue, NULL);
                waited = true;
                break;
            }
        }
    } while (waited);
}

static void block_copy_inflight_req_begin(BlockCopyState *s,
                                          BlockCopyInFlightReq *req,
                                          int64_t start, int64_t end)
{
    req->start_byte = start;
    req->end_byte = end;
    qemu_co_queue_init(&req->wait_queue);
    QLIST_INSERT_HEAD(&s->inflight_reqs, req, list);
}

static void coroutine_fn block_copy_inflight_req_end(BlockCopyInFlightReq *req)
{
    QLIST_REMOVE(req, list);
    qemu_co_queue_restart_all(&req->wait_queue);
}

void block_copy_state_free(BlockCopyState *s)
{
    if (!s) {
        return;
    }

    bdrv_release_dirty_bitmap(s->copy_bitmap);
    shres_destroy(s->mem);
    g_free(s);
}

BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
                                     int64_t cluster_size,
                                     BdrvRequestFlags write_flags, Error **errp)
{
    BlockCopyState *s;
    BdrvDirtyBitmap *copy_bitmap;
    uint32_t max_transfer =
            MIN_NON_ZERO(INT_MAX,
                         MIN_NON_ZERO(source->bs->bl.max_transfer,
                                      target->bs->bl.max_transfer));

    copy_bitmap = bdrv_create_dirty_bitmap(source->bs, cluster_size, NULL,
                                           errp);
    if (!copy_bitmap) {
        return NULL;
    }
    bdrv_disable_dirty_bitmap(copy_bitmap);

    s = g_new(BlockCopyState, 1);
    *s = (BlockCopyState) {
        .source = source,
        .target = target,
        .copy_bitmap = copy_bitmap,
        .cluster_size = cluster_size,
        .len = bdrv_dirty_bitmap_size(copy_bitmap),
        .write_flags = write_flags,
        .mem = shres_create(BLOCK_COPY_MAX_MEM),
    };

    if (max_transfer < cluster_size) {
        /*
         * copy_range does not respect max_transfer. We don't want to bother
         * with requests smaller than block-copy cluster size, so fallback to
         * buffered copying (read and write respect max_transfer on their
         * behalf).
         */
        s->use_copy_range = false;
        s->copy_size = cluster_size;
    } else if (write_flags & BDRV_REQ_WRITE_COMPRESSED) {
        /* Compression supports only cluster-size writes and no copy-range. */
        s->use_copy_range = false;
        s->copy_size = cluster_size;
    } else {
        /*
         * copy_range does not respect max_transfer (it's a TODO), so we factor
         * that in here.
         */
        s->use_copy_range = true;
        s->copy_size = MIN(MAX(cluster_size, BLOCK_COPY_MAX_COPY_RANGE),
                           QEMU_ALIGN_DOWN(max_transfer, cluster_size));
    }

    QLIST_INIT(&s->inflight_reqs);

    return s;
}

void block_copy_set_callbacks(
        BlockCopyState *s,
        ProgressBytesCallbackFunc progress_bytes_callback,
        ProgressResetCallbackFunc progress_reset_callback,
        void *progress_opaque)
{
    s->progress_bytes_callback = progress_bytes_callback;
    s->progress_reset_callback = progress_reset_callback;
    s->progress_opaque = progress_opaque;
}

/*
 * block_copy_do_copy
 *
 * Do copy of cluser-aligned chunk. @end is allowed to exceed s->len only to
 * cover last cluster when s->len is not aligned to clusters.
 *
 * No sync here: nor bitmap neighter intersecting requests handling, only copy.
 *
 * Returns 0 on success.
 */
static int coroutine_fn block_copy_do_copy(BlockCopyState *s,
                                           int64_t start, int64_t end,
                                           bool *error_is_read)
{
    int ret;
    int nbytes = MIN(end, s->len) - start;
    void *bounce_buffer = NULL;

    assert(QEMU_IS_ALIGNED(start, s->cluster_size));
    assert(QEMU_IS_ALIGNED(end, s->cluster_size));
    assert(end < s->len || end == QEMU_ALIGN_UP(s->len, s->cluster_size));

    if (s->use_copy_range) {
        ret = bdrv_co_copy_range(s->source, start, s->target, start, nbytes,
                                 0, s->write_flags);
        if (ret < 0) {
            trace_block_copy_copy_range_fail(s, start, ret);
            s->use_copy_range = false;
            s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER);
            /* Fallback to read+write with allocated buffer */
        } else {
            goto out;
        }
    }

    /*
     * In case of failed copy_range request above, we may proceed with buffered
     * request larger than BLOCK_COPY_MAX_BUFFER. Still, further requests will
     * be properly limited, so don't care too much.
     */

    bounce_buffer = qemu_blockalign(s->source->bs, nbytes);

    ret = bdrv_co_pread(s->source, start, nbytes, bounce_buffer, 0);
    if (ret < 0) {
        trace_block_copy_read_fail(s, start, ret);
        if (error_is_read) {
            *error_is_read = true;
        }
        goto out;
    }

    ret = bdrv_co_pwrite(s->target, start, nbytes, bounce_buffer,
                         s->write_flags);
    if (ret < 0) {
        trace_block_copy_write_fail(s, start, ret);
        if (error_is_read) {
            *error_is_read = false;
        }
        goto out;
    }

out:
    qemu_vfree(bounce_buffer);

    return ret;
}

/*
 * Check if the cluster starting at offset is allocated or not.
 * return via pnum the number of contiguous clusters sharing this allocation.
 */
static int block_copy_is_cluster_allocated(BlockCopyState *s, int64_t offset,
                                           int64_t *pnum)
{
    BlockDriverState *bs = s->source->bs;
    int64_t count, total_count = 0;
    int64_t bytes = s->len - offset;
    int ret;

    assert(QEMU_IS_ALIGNED(offset, s->cluster_size));

    while (true) {
        ret = bdrv_is_allocated(bs, offset, bytes, &count);
        if (ret < 0) {
            return ret;
        }

        total_count += count;

        if (ret || count == 0) {
            /*
             * ret: partial segment(s) are considered allocated.
             * otherwise: unallocated tail is treated as an entire segment.
             */
            *pnum = DIV_ROUND_UP(total_count, s->cluster_size);
            return ret;
        }

        /* Unallocated segment(s) with uncertain following segment(s) */
        if (total_count >= s->cluster_size) {
            *pnum = total_count / s->cluster_size;
            return 0;
        }

        offset += count;
        bytes -= count;
    }
}

/*
 * Reset bits in copy_bitmap starting at offset if they represent unallocated
 * data in the image. May reset subsequent contiguous bits.
 * @return 0 when the cluster at @offset was unallocated,
 *         1 otherwise, and -ret on error.
 */
int64_t block_copy_reset_unallocated(BlockCopyState *s,
                                     int64_t offset, int64_t *count)
{
    int ret;
    int64_t clusters, bytes;

    ret = block_copy_is_cluster_allocated(s, offset, &clusters);
    if (ret < 0) {
        return ret;
    }

    bytes = clusters * s->cluster_size;

    if (!ret) {
        bdrv_reset_dirty_bitmap(s->copy_bitmap, offset, bytes);
        s->progress_reset_callback(s->progress_opaque);
    }

    *count = bytes;
    return ret;
}

int coroutine_fn block_copy(BlockCopyState *s,
                            int64_t start, uint64_t bytes,
                            bool *error_is_read)
{
    int ret = 0;
    int64_t end = bytes + start; /* bytes */
    int64_t status_bytes;
    BlockCopyInFlightReq req;

    /*
     * block_copy() user is responsible for keeping source and target in same
     * aio context
     */
    assert(bdrv_get_aio_context(s->source->bs) ==
           bdrv_get_aio_context(s->target->bs));

    assert(QEMU_IS_ALIGNED(start, s->cluster_size));
    assert(QEMU_IS_ALIGNED(end, s->cluster_size));

    block_copy_wait_inflight_reqs(s, start, bytes);
    block_copy_inflight_req_begin(s, &req, start, end);

    while (start < end) {
        int64_t next_zero, chunk_end;

        if (!bdrv_dirty_bitmap_get(s->copy_bitmap, start)) {
            trace_block_copy_skip(s, start);
            start += s->cluster_size;
            continue; /* already copied */
        }

        chunk_end = MIN(end, start + s->copy_size);

        next_zero = bdrv_dirty_bitmap_next_zero(s->copy_bitmap, start,
                                                chunk_end - start);
        if (next_zero >= 0) {
            assert(next_zero > start); /* start is dirty */
            assert(next_zero < chunk_end); /* no need to do MIN() */
            chunk_end = next_zero;
        }

        if (s->skip_unallocated) {
            ret = block_copy_reset_unallocated(s, start, &status_bytes);
            if (ret == 0) {
                trace_block_copy_skip_range(s, start, status_bytes);
                start += status_bytes;
                continue;
            }
            /* Clamp to known allocated region */
            chunk_end = MIN(chunk_end, start + status_bytes);
        }

        trace_block_copy_process(s, start);

        bdrv_reset_dirty_bitmap(s->copy_bitmap, start, chunk_end - start);

        co_get_from_shres(s->mem, chunk_end - start);
        ret = block_copy_do_copy(s, start, chunk_end, error_is_read);
        co_put_to_shres(s->mem, chunk_end - start);
        if (ret < 0) {
            bdrv_set_dirty_bitmap(s->copy_bitmap, start, chunk_end - start);
            break;
        }

        s->progress_bytes_callback(chunk_end - start, s->progress_opaque);
        start = chunk_end;
        ret = 0;
    }

    block_copy_inflight_req_end(&req);

    return ret;
}