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 "qemu/osdep.h"
  15#include "trace.h"
  16#include "block/block_int.h"
  17#include "block/blockjob_int.h"
  18#include "qapi/error.h"
  19#include "qapi/qmp/qerror.h"
  20#include "qemu/ratelimit.h"
  21#include "sysemu/block-backend.h"
  22
  23enum {
  24    /*
  25     * Size of data buffer for populating the image file.  This should be large
  26     * enough to process multiple clusters in a single call, so that populating
  27     * contiguous regions of the image is efficient.
  28     */
  29    STREAM_BUFFER_SIZE = 512 * 1024, /* in bytes */
  30};
  31
  32#define SLICE_TIME 100000000ULL /* ns */
  33
  34typedef struct StreamBlockJob {
  35    BlockJob common;
  36    RateLimit limit;
  37    BlockDriverState *base;
  38    BlockdevOnError on_error;
  39    char *backing_file_str;
  40    int bs_flags;
  41} StreamBlockJob;
  42
  43static int coroutine_fn stream_populate(BlockBackend *blk,
  44                                        int64_t offset, uint64_t bytes,
  45                                        void *buf)
  46{
  47    struct iovec iov = {
  48        .iov_base = buf,
  49        .iov_len  = bytes,
  50    };
  51    QEMUIOVector qiov;
  52
  53    assert(bytes < SIZE_MAX);
  54    qemu_iovec_init_external(&qiov, &iov, 1);
  55
  56    /* Copy-on-read the unallocated clusters */
  57    return blk_co_preadv(blk, offset, qiov.size, &qiov, BDRV_REQ_COPY_ON_READ);
  58}
  59
  60typedef struct {
  61    int ret;
  62} StreamCompleteData;
  63
  64static void stream_complete(BlockJob *job, void *opaque)
  65{
  66    StreamBlockJob *s = container_of(job, StreamBlockJob, common);
  67    StreamCompleteData *data = opaque;
  68    BlockDriverState *bs = blk_bs(job->blk);
  69    BlockDriverState *base = s->base;
  70    Error *local_err = NULL;
  71
  72    if (!block_job_is_cancelled(&s->common) && bs->backing &&
  73        data->ret == 0) {
  74        const char *base_id = NULL, *base_fmt = NULL;
  75        if (base) {
  76            base_id = s->backing_file_str;
  77            if (base->drv) {
  78                base_fmt = base->drv->format_name;
  79            }
  80        }
  81        data->ret = bdrv_change_backing_file(bs, base_id, base_fmt);
  82        bdrv_set_backing_hd(bs, base, &local_err);
  83        if (local_err) {
  84            error_report_err(local_err);
  85            data->ret = -EPERM;
  86            goto out;
  87        }
  88    }
  89
  90out:
  91    /* Reopen the image back in read-only mode if necessary */
  92    if (s->bs_flags != bdrv_get_flags(bs)) {
  93        /* Give up write permissions before making it read-only */
  94        blk_set_perm(job->blk, 0, BLK_PERM_ALL, &error_abort);
  95        bdrv_reopen(bs, s->bs_flags, NULL);
  96    }
  97
  98    g_free(s->backing_file_str);
  99    block_job_completed(&s->common, data->ret);
 100    g_free(data);
 101}
 102
 103static void coroutine_fn stream_run(void *opaque)
 104{
 105    StreamBlockJob *s = opaque;
 106    StreamCompleteData *data;
 107    BlockBackend *blk = s->common.blk;
 108    BlockDriverState *bs = blk_bs(blk);
 109    BlockDriverState *base = s->base;
 110    int64_t offset = 0;
 111    uint64_t delay_ns = 0;
 112    int error = 0;
 113    int ret = 0;
 114    int64_t n = 0; /* bytes */
 115    void *buf;
 116
 117    if (!bs->backing) {
 118        goto out;
 119    }
 120
 121    s->common.len = bdrv_getlength(bs);
 122    if (s->common.len < 0) {
 123        ret = s->common.len;
 124        goto out;
 125    }
 126
 127    buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);
 128
 129    /* Turn on copy-on-read for the whole block device so that guest read
 130     * requests help us make progress.  Only do this when copying the entire
 131     * backing chain since the copy-on-read operation does not take base into
 132     * account.
 133     */
 134    if (!base) {
 135        bdrv_enable_copy_on_read(bs);
 136    }
 137
 138    for ( ; offset < s->common.len; offset += n) {
 139        bool copy;
 140
 141        /* Note that even when no rate limit is applied we need to yield
 142         * with no pending I/O here so that bdrv_drain_all() returns.
 143         */
 144        block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
 145        if (block_job_is_cancelled(&s->common)) {
 146            break;
 147        }
 148
 149        copy = false;
 150
 151        ret = bdrv_is_allocated(bs, offset, STREAM_BUFFER_SIZE, &n);
 152        if (ret == 1) {
 153            /* Allocated in the top, no need to copy.  */
 154        } else if (ret >= 0) {
 155            /* Copy if allocated in the intermediate images.  Limit to the
 156             * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).  */
 157            ret = bdrv_is_allocated_above(backing_bs(bs), base,
 158                                          offset, n, &n);
 159
 160            /* Finish early if end of backing file has been reached */
 161            if (ret == 0 && n == 0) {
 162                n = s->common.len - offset;
 163            }
 164
 165            copy = (ret == 1);
 166        }
 167        trace_stream_one_iteration(s, offset, n, ret);
 168        if (copy) {
 169            ret = stream_populate(blk, offset, n, buf);
 170        }
 171        if (ret < 0) {
 172            BlockErrorAction action =
 173                block_job_error_action(&s->common, s->on_error, true, -ret);
 174            if (action == BLOCK_ERROR_ACTION_STOP) {
 175                n = 0;
 176                continue;
 177            }
 178            if (error == 0) {
 179                error = ret;
 180            }
 181            if (action == BLOCK_ERROR_ACTION_REPORT) {
 182                break;
 183            }
 184        }
 185        ret = 0;
 186
 187        /* Publish progress */
 188        s->common.offset += n;
 189        if (copy && s->common.speed) {
 190            delay_ns = ratelimit_calculate_delay(&s->limit, n);
 191        }
 192    }
 193
 194    if (!base) {
 195        bdrv_disable_copy_on_read(bs);
 196    }
 197
 198    /* Do not remove the backing file if an error was there but ignored.  */
 199    ret = error;
 200
 201    qemu_vfree(buf);
 202
 203out:
 204    /* Modify backing chain and close BDSes in main loop */
 205    data = g_malloc(sizeof(*data));
 206    data->ret = ret;
 207    block_job_defer_to_main_loop(&s->common, stream_complete, data);
 208}
 209
 210static void stream_set_speed(BlockJob *job, int64_t speed, Error **errp)
 211{
 212    StreamBlockJob *s = container_of(job, StreamBlockJob, common);
 213
 214    if (speed < 0) {
 215        error_setg(errp, QERR_INVALID_PARAMETER, "speed");
 216        return;
 217    }
 218    ratelimit_set_speed(&s->limit, speed, SLICE_TIME);
 219}
 220
 221static const BlockJobDriver stream_job_driver = {
 222    .instance_size = sizeof(StreamBlockJob),
 223    .job_type      = BLOCK_JOB_TYPE_STREAM,
 224    .set_speed     = stream_set_speed,
 225    .start         = stream_run,
 226};
 227
 228void stream_start(const char *job_id, BlockDriverState *bs,
 229                  BlockDriverState *base, const char *backing_file_str,
 230                  int64_t speed, BlockdevOnError on_error, Error **errp)
 231{
 232    StreamBlockJob *s;
 233    BlockDriverState *iter;
 234    int orig_bs_flags;
 235
 236    /* Make sure that the image is opened in read-write mode */
 237    orig_bs_flags = bdrv_get_flags(bs);
 238    if (!(orig_bs_flags & BDRV_O_RDWR)) {
 239        if (bdrv_reopen(bs, orig_bs_flags | BDRV_O_RDWR, errp) != 0) {
 240            return;
 241        }
 242    }
 243
 244    /* Prevent concurrent jobs trying to modify the graph structure here, we
 245     * already have our own plans. Also don't allow resize as the image size is
 246     * queried only at the job start and then cached. */
 247    s = block_job_create(job_id, &stream_job_driver, bs,
 248                         BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED |
 249                         BLK_PERM_GRAPH_MOD,
 250                         BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED |
 251                         BLK_PERM_WRITE,
 252                         speed, BLOCK_JOB_DEFAULT, NULL, NULL, errp);
 253    if (!s) {
 254        goto fail;
 255    }
 256
 257    /* Block all intermediate nodes between bs and base, because they will
 258     * disappear from the chain after this operation. The streaming job reads
 259     * every block only once, assuming that it doesn't change, so block writes
 260     * and resizes. */
 261    for (iter = backing_bs(bs); iter && iter != base; iter = backing_bs(iter)) {
 262        block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 263                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED,
 264                           &error_abort);
 265    }
 266
 267    s->base = base;
 268    s->backing_file_str = g_strdup(backing_file_str);
 269    s->bs_flags = orig_bs_flags;
 270
 271    s->on_error = on_error;
 272    trace_stream_start(bs, base, s);
 273    block_job_start(&s->common);
 274    return;
 275
 276fail:
 277    if (orig_bs_flags != bdrv_get_flags(bs)) {
 278        bdrv_reopen(bs, orig_bs_flags, NULL);
 279    }
 280}
 281