qemu/block/stream.c
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   1/*
   2 * Image streaming
   3 *
   4 * Copyright IBM, Corp. 2011
   5 *
   6 * Authors:
   7 *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
   8 *
   9 * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  10 * See the COPYING.LIB file in the top-level directory.
  11 *
  12 */
  13
  14#include "trace.h"
  15#include "block/block_int.h"
  16#include "block/blockjob.h"
  17#include "qemu/ratelimit.h"
  18
  19enum {
  20    /*
  21     * Size of data buffer for populating the image file.  This should be large
  22     * enough to process multiple clusters in a single call, so that populating
  23     * contiguous regions of the image is efficient.
  24     */
  25    STREAM_BUFFER_SIZE = 512 * 1024, /* in bytes */
  26};
  27
  28#define SLICE_TIME 100000000ULL /* ns */
  29
  30typedef struct StreamBlockJob {
  31    BlockJob common;
  32    RateLimit limit;
  33    BlockDriverState *base;
  34    BlockdevOnError on_error;
  35    char backing_file_id[1024];
  36} StreamBlockJob;
  37
  38static int coroutine_fn stream_populate(BlockDriverState *bs,
  39                                        int64_t sector_num, int nb_sectors,
  40                                        void *buf)
  41{
  42    struct iovec iov = {
  43        .iov_base = buf,
  44        .iov_len  = nb_sectors * BDRV_SECTOR_SIZE,
  45    };
  46    QEMUIOVector qiov;
  47
  48    qemu_iovec_init_external(&qiov, &iov, 1);
  49
  50    /* Copy-on-read the unallocated clusters */
  51    return bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, &qiov);
  52}
  53
  54static void close_unused_images(BlockDriverState *top, BlockDriverState *base,
  55                                const char *base_id)
  56{
  57    BlockDriverState *intermediate;
  58    intermediate = top->backing_hd;
  59
  60    /* Must assign before bdrv_delete() to prevent traversing dangling pointer
  61     * while we delete backing image instances.
  62     */
  63    top->backing_hd = base;
  64
  65    while (intermediate) {
  66        BlockDriverState *unused;
  67
  68        /* reached base */
  69        if (intermediate == base) {
  70            break;
  71        }
  72
  73        unused = intermediate;
  74        intermediate = intermediate->backing_hd;
  75        unused->backing_hd = NULL;
  76        bdrv_unref(unused);
  77    }
  78
  79    bdrv_refresh_limits(top);
  80}
  81
  82static void coroutine_fn stream_run(void *opaque)
  83{
  84    StreamBlockJob *s = opaque;
  85    BlockDriverState *bs = s->common.bs;
  86    BlockDriverState *base = s->base;
  87    int64_t sector_num, end;
  88    int error = 0;
  89    int ret = 0;
  90    int n = 0;
  91    void *buf;
  92
  93    if (!bs->backing_hd) {
  94        block_job_completed(&s->common, 0);
  95        return;
  96    }
  97
  98    s->common.len = bdrv_getlength(bs);
  99    if (s->common.len < 0) {
 100        block_job_completed(&s->common, s->common.len);
 101        return;
 102    }
 103
 104    end = s->common.len >> BDRV_SECTOR_BITS;
 105    buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);
 106
 107    /* Turn on copy-on-read for the whole block device so that guest read
 108     * requests help us make progress.  Only do this when copying the entire
 109     * backing chain since the copy-on-read operation does not take base into
 110     * account.
 111     */
 112    if (!base) {
 113        bdrv_enable_copy_on_read(bs);
 114    }
 115
 116    for (sector_num = 0; sector_num < end; sector_num += n) {
 117        uint64_t delay_ns = 0;
 118        bool copy;
 119
 120wait:
 121        /* Note that even when no rate limit is applied we need to yield
 122         * with no pending I/O here so that bdrv_drain_all() returns.
 123         */
 124        block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
 125        if (block_job_is_cancelled(&s->common)) {
 126            break;
 127        }
 128
 129        copy = false;
 130
 131        ret = bdrv_is_allocated(bs, sector_num,
 132                                STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n);
 133        if (ret == 1) {
 134            /* Allocated in the top, no need to copy.  */
 135        } else if (ret >= 0) {
 136            /* Copy if allocated in the intermediate images.  Limit to the
 137             * known-unallocated area [sector_num, sector_num+n).  */
 138            ret = bdrv_is_allocated_above(bs->backing_hd, base,
 139                                          sector_num, n, &n);
 140
 141            /* Finish early if end of backing file has been reached */
 142            if (ret == 0 && n == 0) {
 143                n = end - sector_num;
 144            }
 145
 146            copy = (ret == 1);
 147        }
 148        trace_stream_one_iteration(s, sector_num, n, ret);
 149        if (copy) {
 150            if (s->common.speed) {
 151                delay_ns = ratelimit_calculate_delay(&s->limit, n);
 152                if (delay_ns > 0) {
 153                    goto wait;
 154                }
 155            }
 156            ret = stream_populate(bs, sector_num, n, buf);
 157        }
 158        if (ret < 0) {
 159            BlockErrorAction action =
 160                block_job_error_action(&s->common, s->common.bs, s->on_error,
 161                                       true, -ret);
 162            if (action == BDRV_ACTION_STOP) {
 163                n = 0;
 164                continue;
 165            }
 166            if (error == 0) {
 167                error = ret;
 168            }
 169            if (action == BDRV_ACTION_REPORT) {
 170                break;
 171            }
 172        }
 173        ret = 0;
 174
 175        /* Publish progress */
 176        s->common.offset += n * BDRV_SECTOR_SIZE;
 177    }
 178
 179    if (!base) {
 180        bdrv_disable_copy_on_read(bs);
 181    }
 182
 183    /* Do not remove the backing file if an error was there but ignored.  */
 184    ret = error;
 185
 186    if (!block_job_is_cancelled(&s->common) && sector_num == end && ret == 0) {
 187        const char *base_id = NULL, *base_fmt = NULL;
 188        if (base) {
 189            base_id = s->backing_file_id;
 190            if (base->drv) {
 191                base_fmt = base->drv->format_name;
 192            }
 193        }
 194        ret = bdrv_change_backing_file(bs, base_id, base_fmt);
 195        close_unused_images(bs, base, base_id);
 196    }
 197
 198    qemu_vfree(buf);
 199    block_job_completed(&s->common, ret);
 200}
 201
 202static void stream_set_speed(BlockJob *job, int64_t speed, Error **errp)
 203{
 204    StreamBlockJob *s = container_of(job, StreamBlockJob, common);
 205
 206    if (speed < 0) {
 207        error_set(errp, QERR_INVALID_PARAMETER, "speed");
 208        return;
 209    }
 210    ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
 211}
 212
 213static const BlockJobDriver stream_job_driver = {
 214    .instance_size = sizeof(StreamBlockJob),
 215    .job_type      = BLOCK_JOB_TYPE_STREAM,
 216    .set_speed     = stream_set_speed,
 217};
 218
 219void stream_start(BlockDriverState *bs, BlockDriverState *base,
 220                  const char *base_id, int64_t speed,
 221                  BlockdevOnError on_error,
 222                  BlockDriverCompletionFunc *cb,
 223                  void *opaque, Error **errp)
 224{
 225    StreamBlockJob *s;
 226
 227    if ((on_error == BLOCKDEV_ON_ERROR_STOP ||
 228         on_error == BLOCKDEV_ON_ERROR_ENOSPC) &&
 229        !bdrv_iostatus_is_enabled(bs)) {
 230        error_set(errp, QERR_INVALID_PARAMETER, "on-error");
 231        return;
 232    }
 233
 234    s = block_job_create(&stream_job_driver, bs, speed, cb, opaque, errp);
 235    if (!s) {
 236        return;
 237    }
 238
 239    s->base = base;
 240    if (base_id) {
 241        pstrcpy(s->backing_file_id, sizeof(s->backing_file_id), base_id);
 242    }
 243
 244    s->on_error = on_error;
 245    s->common.co = qemu_coroutine_create(stream_run);
 246    trace_stream_start(bs, base, s, s->common.co, opaque);
 247    qemu_coroutine_enter(s->common.co, s);
 248}
 249