Archipelago » qemu

/*

 * Image streaming

 *

 * Copyright IBM, Corp. 2011

 *

 * Authors:

 *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>

 *

 * This work is licensed under the terms of the GNU LGPL, version 2 or later.

 * See the COPYING.LIB file in the top-level directory.

 *

 */

#include "trace.h"

#include "block_int.h"

enum {

    /*

     * Size of data buffer for populating the image file.  This should be large

     * enough to process multiple clusters in a single call, so that populating

     * contiguous regions of the image is efficient.

     */

    STREAM_BUFFER_SIZE = 512 * 1024, /* in bytes */

};

#define SLICE_TIME 100000000ULL /* ns */

typedef struct {

    int64_t next_slice_time;

    uint64_t slice_quota;

    uint64_t dispatched;

} RateLimit;

static int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)

{

    int64_t delay_ns = 0;

    int64_t now = qemu_get_clock_ns(rt_clock);

    if (limit->next_slice_time < now) {

        limit->next_slice_time = now + SLICE_TIME;

        limit->dispatched = 0;

    }

    if (limit->dispatched + n > limit->slice_quota) {

        delay_ns = limit->next_slice_time - now;

    } else {

        limit->dispatched += n;

    }

    return delay_ns;

}

static void ratelimit_set_speed(RateLimit *limit, uint64_t speed)

{

    limit->slice_quota = speed / (1000000000ULL / SLICE_TIME);

}

typedef struct StreamBlockJob {

    BlockJob common;

    RateLimit limit;

    BlockDriverState *base;

    char backing_file_id[1024];

} StreamBlockJob;

static int coroutine_fn stream_populate(BlockDriverState *bs,

                                        int64_t sector_num, int nb_sectors,

                                        void *buf)

{

    struct iovec iov = {

        .iov_base = buf,

        .iov_len  = nb_sectors * BDRV_SECTOR_SIZE,

    };

    QEMUIOVector qiov;

    qemu_iovec_init_external(&qiov, &iov, 1);

    /* Copy-on-read the unallocated clusters */

    return bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, &qiov);

}

static void close_unused_images(BlockDriverState *top, BlockDriverState *base,

                                const char *base_id)

{

    BlockDriverState *intermediate;

    intermediate = top->backing_hd;

    while (intermediate) {

        BlockDriverState *unused;

        /* reached base */

        if (intermediate == base) {

            break;

        }

        unused = intermediate;

        intermediate = intermediate->backing_hd;

        unused->backing_hd = NULL;

        bdrv_delete(unused);

    }

    top->backing_hd = base;

}

/*

 * Given an image chain: [BASE] -> [INTER1] -> [INTER2] -> [TOP]

 *

 * Return true if the given sector is allocated in top.

 * Return false if the given sector is allocated in intermediate images.

 * Return true otherwise.

 *

 * 'pnum' is set to the number of sectors (including and immediately following

 *  the specified sector) that are known to be in the same

 *  allocated/unallocated state.

 *

 */

static int coroutine_fn is_allocated_base(BlockDriverState *top,

                                          BlockDriverState *base,

                                          int64_t sector_num,

                                          int nb_sectors, int *pnum)

{

    BlockDriverState *intermediate;

    int ret, n;

    ret = bdrv_co_is_allocated(top, sector_num, nb_sectors, &n);

    if (ret) {

        *pnum = n;

        return ret;

    }

    /*

     * Is the unallocated chunk [sector_num, n] also

     * unallocated between base and top?

     */

    intermediate = top->backing_hd;

    while (intermediate) {

        int pnum_inter;

        /* reached base */

        if (intermediate == base) {

            *pnum = n;

            return 1;

        }

        ret = bdrv_co_is_allocated(intermediate, sector_num, nb_sectors,

                                   &pnum_inter);

        if (ret < 0) {

            return ret;

        } else if (ret) {

            *pnum = pnum_inter;

            return 0;

        }

        /*

         * [sector_num, nb_sectors] is unallocated on top but intermediate

         * might have

         *

         * [sector_num+x, nr_sectors] allocated.

         */

        if (n > pnum_inter) {

            n = pnum_inter;

        }

        intermediate = intermediate->backing_hd;

    }

    return 1;

}

static void coroutine_fn stream_run(void *opaque)

{

    StreamBlockJob *s = opaque;

    BlockDriverState *bs = s->common.bs;

    BlockDriverState *base = s->base;

    int64_t sector_num, end;

    int ret = 0;

    int n;

    void *buf;

    s->common.len = bdrv_getlength(bs);

    if (s->common.len < 0) {

        block_job_complete(&s->common, s->common.len);

        return;

    }

    end = s->common.len >> BDRV_SECTOR_BITS;

    buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);

    /* Turn on copy-on-read for the whole block device so that guest read

     * requests help us make progress.  Only do this when copying the entire

     * backing chain since the copy-on-read operation does not take base into

     * account.

     */

    if (!base) {

        bdrv_enable_copy_on_read(bs);

    }

    for (sector_num = 0; sector_num < end; sector_num += n) {

retry:

        if (block_job_is_cancelled(&s->common)) {

            break;

        }

        s->common.busy = true;

        if (base) {

            ret = is_allocated_base(bs, base, sector_num,

                                    STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n);

        } else {

            ret = bdrv_co_is_allocated(bs, sector_num,

                                       STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE,

                                       &n);

        }

        trace_stream_one_iteration(s, sector_num, n, ret);

        if (ret == 0) {

            if (s->common.speed) {

                uint64_t delay_ns = ratelimit_calculate_delay(&s->limit, n);

                if (delay_ns > 0) {

                    s->common.busy = false;

                    co_sleep_ns(rt_clock, delay_ns);

                    /* Recheck cancellation and that sectors are unallocated */

                    goto retry;

                }

            }

            ret = stream_populate(bs, sector_num, n, buf);

        }

        if (ret < 0) {

            break;

        }

        ret = 0;

        /* Publish progress */

        s->common.offset += n * BDRV_SECTOR_SIZE;

        /* Note that even when no rate limit is applied we need to yield

         * with no pending I/O here so that qemu_aio_flush() returns.

         */

        s->common.busy = false;

        co_sleep_ns(rt_clock, 0);

    }

    if (!base) {

        bdrv_disable_copy_on_read(bs);

    }

    if (!block_job_is_cancelled(&s->common) && sector_num == end && ret == 0) {

        const char *base_id = NULL;

        if (base) {

            base_id = s->backing_file_id;

        }

        ret = bdrv_change_backing_file(bs, base_id, NULL);

        close_unused_images(bs, base, base_id);

    }

    qemu_vfree(buf);

    block_job_complete(&s->common, ret);

}

static void stream_set_speed(BlockJob *job, int64_t speed, Error **errp)

{

    StreamBlockJob *s = container_of(job, StreamBlockJob, common);

    if (speed < 0) {

        error_set(errp, QERR_INVALID_PARAMETER, "speed");

        return;

    }

    ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE);

}

static BlockJobType stream_job_type = {

    .instance_size = sizeof(StreamBlockJob),

    .job_type      = "stream",

    .set_speed     = stream_set_speed,

};

void stream_start(BlockDriverState *bs, BlockDriverState *base,

                  const char *base_id, int64_t speed,

                  BlockDriverCompletionFunc *cb,

                  void *opaque, Error **errp)

{

    StreamBlockJob *s;

    Coroutine *co;

    s = block_job_create(&stream_job_type, bs, speed, cb, opaque, errp);

    if (!s) {

        return;

    }

    s->base = base;

    if (base_id) {

        pstrcpy(s->backing_file_id, sizeof(s->backing_file_id), base_id);

    }

    co = qemu_coroutine_create(stream_run);

    trace_stream_start(bs, base, s, co, opaque);

    qemu_coroutine_enter(co, s);

}