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 "qapi/qmp/qdict.h"
  21 #include "qemu/ratelimit.h"
  22 #include "sysemu/block-backend.h"
  23 #include "block/copy-on-read.h"
  24
  25 enum {
  26     /*
  27      * Maximum chunk size to feed to copy-on-read.  This should be
  28      * large enough to process multiple clusters in a single call, so
  29      * that populating contiguous regions of the image is efficient.
  30      */
  31     STREAM_CHUNK = 512 * 1024, /* in bytes */
  32 };
  33
  34 typedef struct StreamBlockJob {
  35     BlockJob common;
  36     BlockBackend *blk;
  37     BlockDriverState *base_overlay; /* COW overlay (stream from this) */
  38     BlockDriverState *above_base;   /* Node directly above the base */
  39     BlockDriverState *cor_filter_bs;
  40     BlockDriverState *target_bs;
  41     BlockdevOnError on_error;
  42     char *backing_file_str;
  43     bool bs_read_only;
  44 } StreamBlockJob;
  45
  46 static int coroutine_fn stream_populate(BlockBackend *blk,
  47                                         int64_t offset, uint64_t bytes)
  48 {
  49     assert(bytes < SIZE_MAX);
  50
  51     return blk_co_preadv(blk, offset, bytes, NULL, BDRV_REQ_PREFETCH);
  52 }
  53
  54 static int stream_prepare(Job *job)
  55 {
  56     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
  57     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
  58     BlockDriverState *base;
  59     BlockDriverState *unfiltered_base;
  60     Error *local_err = NULL;
  61     int ret = 0;
  62
  63     /* We should drop filter at this point, as filter hold the backing chain */
  64     bdrv_cor_filter_drop(s->cor_filter_bs);
  65     s->cor_filter_bs = NULL;
  66
  67     /*
  68      * bdrv_set_backing_hd() requires that unfiltered_bs is drained. Drain
  69      * already here and use bdrv_set_backing_hd_drained() instead because
  70      * the polling during drained_begin() might change the graph, and if we do
  71      * this only later, we may end up working with the wrong base node (or it
  72      * might even have gone away by the time we want to use it).
  73      */
  74     bdrv_drained_begin(unfiltered_bs);
  75
  76     base = bdrv_filter_or_cow_bs(s->above_base);
  77     unfiltered_base = bdrv_skip_filters(base);
  78
  79     if (bdrv_cow_child(unfiltered_bs)) {
  80         const char *base_id = NULL, *base_fmt = NULL;
  81         if (unfiltered_base) {
  82             base_id = s->backing_file_str ?: unfiltered_base->filename;
  83             if (unfiltered_base->drv) {
  84                 base_fmt = unfiltered_base->drv->format_name;
  85             }
  86         }
  87
  88         bdrv_set_backing_hd_drained(unfiltered_bs, base, &local_err);
  89
  90         /*
  91          * This call will do I/O, so the graph can change again from here on.
  92          * We have already completed the graph change, so we are not in danger
  93          * of operating on the wrong node any more if this happens.
  94          */
  95         ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
  96         if (local_err) {
  97             error_report_err(local_err);
  98             ret = -EPERM;
  99             goto out;
 100         }
 101     }
 102
 103 out:
 104     bdrv_drained_end(unfiltered_bs);
 105     return ret;
 106 }
 107
 108 static void stream_clean(Job *job)
 109 {
 110     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 111
 112     if (s->cor_filter_bs) {
 113         bdrv_cor_filter_drop(s->cor_filter_bs);
 114         s->cor_filter_bs = NULL;
 115     }
 116
 117     blk_unref(s->blk);
 118     s->blk = NULL;
 119
 120     /* Reopen the image back in read-only mode if necessary */
 121     if (s->bs_read_only) {
 122         /* Give up write permissions before making it read-only */
 123         bdrv_reopen_set_read_only(s->target_bs, true, NULL);
 124     }
 125
 126     g_free(s->backing_file_str);
 127 }
 128
 129 static int coroutine_fn stream_run(Job *job, Error **errp)
 130 {
 131     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 132     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
 133     int64_t len;
 134     int64_t offset = 0;
 135     uint64_t delay_ns = 0;
 136     int error = 0;
 137     int64_t n = 0; /* bytes */
 138
 139     if (unfiltered_bs == s->base_overlay) {
 140         /* Nothing to stream */
 141         return 0;
 142     }
 143
 144     WITH_GRAPH_RDLOCK_GUARD() {
 145         len = bdrv_co_getlength(s->target_bs);
 146         if (len < 0) {
 147             return len;
 148         }
 149     }
 150     job_progress_set_remaining(&s->common.job, len);
 151
 152     for ( ; offset < len; offset += n) {
 153         bool copy;
 154         int ret;
 155
 156         /* Note that even when no rate limit is applied we need to yield
 157          * with no pending I/O here so that bdrv_drain_all() returns.
 158          */
 159         job_sleep_ns(&s->common.job, delay_ns);
 160         if (job_is_cancelled(&s->common.job)) {
 161             break;
 162         }
 163
 164         copy = false;
 165
 166         WITH_GRAPH_RDLOCK_GUARD() {
 167             ret = bdrv_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
 168             if (ret == 1) {
 169                 /* Allocated in the top, no need to copy.  */
 170             } else if (ret >= 0) {
 171                 /*
 172                  * Copy if allocated in the intermediate images.  Limit to the
 173                  * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).
 174                  */
 175                 ret = bdrv_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
 176                                             s->base_overlay, true,
 177                                             offset, n, &n);
 178                 /* Finish early if end of backing file has been reached */
 179                 if (ret == 0 && n == 0) {
 180                     n = len - offset;
 181                 }
 182
 183                 copy = (ret > 0);
 184             }
 185         }
 186         trace_stream_one_iteration(s, offset, n, ret);
 187         if (copy) {
 188             ret = stream_populate(s->blk, offset, n);
 189         }
 190         if (ret < 0) {
 191             BlockErrorAction action =
 192                 block_job_error_action(&s->common, s->on_error, true, -ret);
 193             if (action == BLOCK_ERROR_ACTION_STOP) {
 194                 n = 0;
 195                 continue;
 196             }
 197             if (error == 0) {
 198                 error = ret;
 199             }
 200             if (action == BLOCK_ERROR_ACTION_REPORT) {
 201                 break;
 202             }
 203         }
 204
 205         /* Publish progress */
 206         job_progress_update(&s->common.job, n);
 207         if (copy) {
 208             delay_ns = block_job_ratelimit_get_delay(&s->common, n);
 209         } else {
 210             delay_ns = 0;
 211         }
 212     }
 213
 214     /* Do not remove the backing file if an error was there but ignored. */
 215     return error;
 216 }
 217
 218 static const BlockJobDriver stream_job_driver = {
 219     .job_driver = {
 220         .instance_size = sizeof(StreamBlockJob),
 221         .job_type      = JOB_TYPE_STREAM,
 222         .free          = block_job_free,
 223         .run           = stream_run,
 224         .prepare       = stream_prepare,
 225         .clean         = stream_clean,
 226         .user_resume   = block_job_user_resume,
 227     },
 228 };
 229
 230 void stream_start(const char *job_id, BlockDriverState *bs,
 231                   BlockDriverState *base, const char *backing_file_str,
 232                   BlockDriverState *bottom,
 233                   int creation_flags, int64_t speed,
 234                   BlockdevOnError on_error,
 235                   const char *filter_node_name,
 236                   Error **errp)
 237 {
 238     StreamBlockJob *s = NULL;
 239     BlockDriverState *iter;
 240     bool bs_read_only;
 241     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
 242     BlockDriverState *base_overlay;
 243     BlockDriverState *cor_filter_bs = NULL;
 244     BlockDriverState *above_base;
 245     QDict *opts;
 246     int ret;
 247
 248     GLOBAL_STATE_CODE();
 249
 250     assert(!(base && bottom));
 251     assert(!(backing_file_str && bottom));
 252
 253     if (bottom) {
 254         /*
 255          * New simple interface. The code is written in terms of old interface
 256          * with @base parameter (still, it doesn't freeze link to base, so in
 257          * this mean old code is correct for new interface). So, for now, just
 258          * emulate base_overlay and above_base. Still, when old interface
 259          * finally removed, we should refactor code to use only "bottom", but
 260          * not "*base*" things.
 261          */
 262         assert(!bottom->drv->is_filter);
 263         base_overlay = above_base = bottom;
 264     } else {
 265         base_overlay = bdrv_find_overlay(bs, base);
 266         if (!base_overlay) {
 267             error_setg(errp, "'%s' is not in the backing chain of '%s'",
 268                        base->node_name, bs->node_name);
 269             return;
 270         }
 271
 272         /*
 273          * Find the node directly above @base.  @base_overlay is a COW overlay,
 274          * so it must have a bdrv_cow_child(), but it is the immediate overlay
 275          * of @base, so between the two there can only be filters.
 276          */
 277         above_base = base_overlay;
 278         if (bdrv_cow_bs(above_base) != base) {
 279             above_base = bdrv_cow_bs(above_base);
 280             while (bdrv_filter_bs(above_base) != base) {
 281                 above_base = bdrv_filter_bs(above_base);
 282             }
 283         }
 284     }
 285
 286     /* Make sure that the image is opened in read-write mode */
 287     bs_read_only = bdrv_is_read_only(bs);
 288     if (bs_read_only) {
 289         int ret;
 290         /* Hold the chain during reopen */
 291         if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
 292             return;
 293         }
 294
 295         ret = bdrv_reopen_set_read_only(bs, false, errp);
 296
 297         /* failure, or cor-filter will hold the chain */
 298         bdrv_unfreeze_backing_chain(bs, above_base);
 299
 300         if (ret < 0) {
 301             return;
 302         }
 303     }
 304
 305     opts = qdict_new();
 306
 307     qdict_put_str(opts, "driver", "copy-on-read");
 308     qdict_put_str(opts, "file", bdrv_get_node_name(bs));
 309     /* Pass the base_overlay node name as 'bottom' to COR driver */
 310     qdict_put_str(opts, "bottom", base_overlay->node_name);
 311     if (filter_node_name) {
 312         qdict_put_str(opts, "node-name", filter_node_name);
 313     }
 314
 315     cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
 316     if (!cor_filter_bs) {
 317         goto fail;
 318     }
 319
 320     if (!filter_node_name) {
 321         cor_filter_bs->implicit = true;
 322     }
 323
 324     s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
 325                          0, BLK_PERM_ALL,
 326                          speed, creation_flags, NULL, NULL, errp);
 327     if (!s) {
 328         goto fail;
 329     }
 330
 331     s->blk = blk_new_with_bs(cor_filter_bs, BLK_PERM_CONSISTENT_READ,
 332                              basic_flags | BLK_PERM_WRITE, errp);
 333     if (!s->blk) {
 334         goto fail;
 335     }
 336     /*
 337      * Disable request queuing in the BlockBackend to avoid deadlocks on drain:
 338      * The job reports that it's busy until it reaches a pause point.
 339      */
 340     blk_set_disable_request_queuing(s->blk, true);
 341     blk_set_allow_aio_context_change(s->blk, true);
 342
 343     /*
 344      * Prevent concurrent jobs trying to modify the graph structure here, we
 345      * already have our own plans. Also don't allow resize as the image size is
 346      * queried only at the job start and then cached.
 347      */
 348     if (block_job_add_bdrv(&s->common, "active node", bs, 0,
 349                            basic_flags | BLK_PERM_WRITE, errp)) {
 350         goto fail;
 351     }
 352
 353     /* Block all intermediate nodes between bs and base, because they will
 354      * disappear from the chain after this operation. The streaming job reads
 355      * every block only once, assuming that it doesn't change, so forbid writes
 356      * and resizes. Reassign the base node pointer because the backing BS of the
 357      * bottom node might change after the call to bdrv_reopen_set_read_only()
 358      * due to parallel block jobs running.
 359      * above_base node might change after the call to
 360      * bdrv_reopen_set_read_only() due to parallel block jobs running.
 361      */
 362     base = bdrv_filter_or_cow_bs(above_base);
 363     for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
 364          iter = bdrv_filter_or_cow_bs(iter))
 365     {
 366         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 367                                  basic_flags, errp);
 368         if (ret < 0) {
 369             goto fail;
 370         }
 371     }
 372
 373     s->base_overlay = base_overlay;
 374     s->above_base = above_base;
 375     s->backing_file_str = g_strdup(backing_file_str);
 376     s->cor_filter_bs = cor_filter_bs;
 377     s->target_bs = bs;
 378     s->bs_read_only = bs_read_only;
 379
 380     s->on_error = on_error;
 381     trace_stream_start(bs, base, s);
 382     job_start(&s->common.job);
 383     return;
 384
 385 fail:
 386     if (s) {
 387         job_early_fail(&s->common.job);
 388     }
 389     if (cor_filter_bs) {
 390         bdrv_cor_filter_drop(cor_filter_bs);
 391     }
 392     if (bs_read_only) {
 393         bdrv_reopen_set_read_only(bs, true, NULL);
 394     }
 395 }