block/stream.c

   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
  23 enum {
  24     /*
  25      * Maximum chunk size to feed to copy-on-read.  This should be
  26      * large enough to process multiple clusters in a single call, so
  27      * that populating contiguous regions of the image is efficient.
  28      */
  29     STREAM_CHUNK = 512 * 1024, /* in bytes */
  30 };
  31
  32 typedef struct StreamBlockJob {
  33     BlockJob common;
  34     BlockDriverState *bottom;
  35     BlockdevOnError on_error;
  36     char *backing_file_str;
  37     bool bs_read_only;
  38     bool chain_frozen;
  39 } StreamBlockJob;
  40
  41 static int coroutine_fn stream_populate(BlockBackend *blk,
  42                                         int64_t offset, uint64_t bytes)
  43 {
  44     assert(bytes < SIZE_MAX);
  45
  46     return blk_co_preadv(blk, offset, bytes, NULL,
  47                          BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH);
  48 }
  49
  50 static void stream_abort(Job *job)
  51 {
  52     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
  53
  54     if (s->chain_frozen) {
  55         BlockJob *bjob = &s->common;
  56         bdrv_unfreeze_backing_chain(blk_bs(bjob->blk), s->bottom);
  57     }
  58 }
  59
  60 static int stream_prepare(Job *job)
  61 {
  62     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
  63     BlockJob *bjob = &s->common;
  64     BlockDriverState *bs = blk_bs(bjob->blk);
  65     BlockDriverState *base = backing_bs(s->bottom);
  66     Error *local_err = NULL;
  67     int ret = 0;
  68
  69     bdrv_unfreeze_backing_chain(bs, s->bottom);
  70     s->chain_frozen = false;
  71
  72     if (bs->backing) {
  73         const char *base_id = NULL, *base_fmt = NULL;
  74         if (base) {
  75             base_id = s->backing_file_str;
  76             if (base->drv) {
  77                 base_fmt = base->drv->format_name;
  78             }
  79         }
  80         bdrv_set_backing_hd(bs, base, &local_err);
  81         ret = bdrv_change_backing_file(bs, base_id, base_fmt);
  82         if (local_err) {
  83             error_report_err(local_err);
  84             return -EPERM;
  85         }
  86     }
  87
  88     return ret;
  89 }
  90
  91 static void stream_clean(Job *job)
  92 {
  93     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
  94     BlockJob *bjob = &s->common;
  95     BlockDriverState *bs = blk_bs(bjob->blk);
  96
  97     /* Reopen the image back in read-only mode if necessary */
  98     if (s->bs_read_only) {
  99         /* Give up write permissions before making it read-only */
 100         blk_set_perm(bjob->blk, 0, BLK_PERM_ALL, &error_abort);
 101         bdrv_reopen_set_read_only(bs, true, NULL);
 102     }
 103
 104     g_free(s->backing_file_str);
 105 }
 106
 107 static int coroutine_fn stream_run(Job *job, Error **errp)
 108 {
 109     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 110     BlockBackend *blk = s->common.blk;
 111     BlockDriverState *bs = blk_bs(blk);
 112     bool enable_cor = !backing_bs(s->bottom);
 113     int64_t len;
 114     int64_t offset = 0;
 115     uint64_t delay_ns = 0;
 116     int error = 0;
 117     int64_t n = 0; /* bytes */
 118
 119     if (bs == s->bottom) {
 120         /* Nothing to stream */
 121         return 0;
 122     }
 123
 124     len = bdrv_getlength(bs);
 125     if (len < 0) {
 126         return len;
 127     }
 128     job_progress_set_remaining(&s->common.job, len);
 129
 130     /* Turn on copy-on-read for the whole block device so that guest read
 131      * requests help us make progress.  Only do this when copying the entire
 132      * backing chain since the copy-on-read operation does not take base into
 133      * account.
 134      */
 135     if (enable_cor) {
 136         bdrv_enable_copy_on_read(bs);
 137     }
 138
 139     for ( ; offset < len; offset += n) {
 140         bool copy;
 141         int ret;
 142
 143         /* Note that even when no rate limit is applied we need to yield
 144          * with no pending I/O here so that bdrv_drain_all() returns.
 145          */
 146         job_sleep_ns(&s->common.job, delay_ns);
 147         if (job_is_cancelled(&s->common.job)) {
 148             break;
 149         }
 150
 151         copy = false;
 152
 153         ret = bdrv_is_allocated(bs, offset, STREAM_CHUNK, &n);
 154         if (ret == 1) {
 155             /* Allocated in the top, no need to copy.  */
 156         } else if (ret >= 0) {
 157             /* Copy if allocated in the intermediate images.  Limit to the
 158              * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).  */
 159             ret = bdrv_is_allocated_above(backing_bs(bs), s->bottom, true,
 160                                           offset, n, &n);
 161             /* Finish early if end of backing file has been reached */
 162             if (ret == 0 && n == 0) {
 163                 n = len - offset;
 164             }
 165
 166             copy = (ret == 1);
 167         }
 168         trace_stream_one_iteration(s, offset, n, ret);
 169         if (copy) {
 170             ret = stream_populate(blk, offset, n);
 171         }
 172         if (ret < 0) {
 173             BlockErrorAction action =
 174                 block_job_error_action(&s->common, s->on_error, true, -ret);
 175             if (action == BLOCK_ERROR_ACTION_STOP) {
 176                 n = 0;
 177                 continue;
 178             }
 179             if (error == 0) {
 180                 error = ret;
 181             }
 182             if (action == BLOCK_ERROR_ACTION_REPORT) {
 183                 break;
 184             }
 185         }
 186
 187         /* Publish progress */
 188         job_progress_update(&s->common.job, n);
 189         if (copy) {
 190             delay_ns = block_job_ratelimit_get_delay(&s->common, n);
 191         } else {
 192             delay_ns = 0;
 193         }
 194     }
 195
 196     if (enable_cor) {
 197         bdrv_disable_copy_on_read(bs);
 198     }
 199
 200     /* Do not remove the backing file if an error was there but ignored. */
 201     return error;
 202 }
 203
 204 static const BlockJobDriver stream_job_driver = {
 205     .job_driver = {
 206         .instance_size = sizeof(StreamBlockJob),
 207         .job_type      = JOB_TYPE_STREAM,
 208         .free          = block_job_free,
 209         .run           = stream_run,
 210         .prepare       = stream_prepare,
 211         .abort         = stream_abort,
 212         .clean         = stream_clean,
 213         .user_resume   = block_job_user_resume,
 214     },
 215 };
 216
 217 void stream_start(const char *job_id, BlockDriverState *bs,
 218                   BlockDriverState *base, const char *backing_file_str,
 219                   int creation_flags, int64_t speed,
 220                   BlockdevOnError on_error, Error **errp)
 221 {
 222     StreamBlockJob *s;
 223     BlockDriverState *iter;
 224     bool bs_read_only;
 225     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
 226     BlockDriverState *bottom = bdrv_find_overlay(bs, base);
 227
 228     if (bdrv_freeze_backing_chain(bs, bottom, errp) < 0) {
 229         return;
 230     }
 231
 232     /* Make sure that the image is opened in read-write mode */
 233     bs_read_only = bdrv_is_read_only(bs);
 234     if (bs_read_only) {
 235         if (bdrv_reopen_set_read_only(bs, false, errp) != 0) {
 236             bs_read_only = false;
 237             goto fail;
 238         }
 239     }
 240
 241     /* Prevent concurrent jobs trying to modify the graph structure here, we
 242      * already have our own plans. Also don't allow resize as the image size is
 243      * queried only at the job start and then cached. */
 244     s = block_job_create(job_id, &stream_job_driver, NULL, bs,
 245                          basic_flags | BLK_PERM_GRAPH_MOD,
 246                          basic_flags | BLK_PERM_WRITE,
 247                          speed, creation_flags, NULL, NULL, errp);
 248     if (!s) {
 249         goto fail;
 250     }
 251
 252     /* Block all intermediate nodes between bs and base, because they will
 253      * disappear from the chain after this operation. The streaming job reads
 254      * every block only once, assuming that it doesn't change, so forbid writes
 255      * and resizes. Reassign the base node pointer because the backing BS of the
 256      * bottom node might change after the call to bdrv_reopen_set_read_only()
 257      * due to parallel block jobs running.
 258      */
 259     base = backing_bs(bottom);
 260     for (iter = backing_bs(bs); iter && iter != base; iter = backing_bs(iter)) {
 261         block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 262                            basic_flags, &error_abort);
 263     }
 264
 265     s->bottom = bottom;
 266     s->backing_file_str = g_strdup(backing_file_str);
 267     s->bs_read_only = bs_read_only;
 268     s->chain_frozen = true;
 269
 270     s->on_error = on_error;
 271     trace_stream_start(bs, base, s);
 272     job_start(&s->common.job);
 273     return;
 274
 275 fail:
 276     if (bs_read_only) {
 277         bdrv_reopen_set_read_only(bs, true, NULL);
 278     }
 279     bdrv_unfreeze_backing_chain(bs, bottom);
 280 }