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/qdict.h"
  20 #include "qemu/ratelimit.h"
  21 #include "sysemu/block-backend.h"
  22 #include "block/copy-on-read.h"
  23
  24 enum {
  25     /*
  26      * Maximum chunk size to feed to copy-on-read.  This should be
  27      * large enough to process multiple clusters in a single call, so
  28      * that populating contiguous regions of the image is efficient.
  29      */
  30     STREAM_CHUNK = 512 * 1024, /* in bytes */
  31 };
  32
  33 typedef struct StreamBlockJob {
  34     BlockJob common;
  35     BlockBackend *blk;
  36     BlockDriverState *base_overlay; /* COW overlay (stream from this) */
  37     BlockDriverState *above_base;   /* Node directly above the base */
  38     BlockDriverState *cor_filter_bs;
  39     BlockDriverState *target_bs;
  40     BlockdevOnError on_error;
  41     char *backing_file_str;
  42     bool backing_mask_protocol;
  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;
  58     BlockDriverState *unfiltered_bs_cow;
  59     BlockDriverState *base;
  60     BlockDriverState *unfiltered_base;
  61     Error *local_err = NULL;
  62     int ret = 0;
  63
  64     GLOBAL_STATE_CODE();
  65
  66     bdrv_graph_rdlock_main_loop();
  67     unfiltered_bs = bdrv_skip_filters(s->target_bs);
  68     unfiltered_bs_cow = bdrv_cow_bs(unfiltered_bs);
  69     bdrv_graph_rdunlock_main_loop();
  70
  71     /* We should drop filter at this point, as filter hold the backing chain */
  72     bdrv_cor_filter_drop(s->cor_filter_bs);
  73     s->cor_filter_bs = NULL;
  74
  75     /*
  76      * bdrv_set_backing_hd() requires that the unfiltered_bs and the COW child
  77      * of unfiltered_bs is drained. Drain already here and use
  78      * bdrv_set_backing_hd_drained() instead because the polling during
  79      * drained_begin() might change the graph, and if we do this only later, we
  80      * may end up working with the wrong base node (or it might even have gone
  81      * away by the time we want to use it).
  82      */
  83     bdrv_drained_begin(unfiltered_bs);
  84     if (unfiltered_bs_cow) {
  85         bdrv_ref(unfiltered_bs_cow);
  86         bdrv_drained_begin(unfiltered_bs_cow);
  87     }
  88
  89     bdrv_graph_rdlock_main_loop();
  90     base = bdrv_filter_or_cow_bs(s->above_base);
  91     unfiltered_base = bdrv_skip_filters(base);
  92     bdrv_graph_rdunlock_main_loop();
  93
  94     if (unfiltered_bs_cow) {
  95         const char *base_id = NULL, *base_fmt = NULL;
  96         if (unfiltered_base) {
  97             base_id = s->backing_file_str ?: unfiltered_base->filename;
  98             if (unfiltered_base->drv) {
  99                 if (s->backing_mask_protocol &&
 100                     unfiltered_base->drv->protocol_name) {
 101                     base_fmt = "raw";
 102                 } else {
 103                     base_fmt = unfiltered_base->drv->format_name;
 104                 }
 105             }
 106         }
 107
 108         bdrv_graph_wrlock();
 109         bdrv_set_backing_hd_drained(unfiltered_bs, base, &local_err);
 110         bdrv_graph_wrunlock();
 111
 112         /*
 113          * This call will do I/O, so the graph can change again from here on.
 114          * We have already completed the graph change, so we are not in danger
 115          * of operating on the wrong node any more if this happens.
 116          */
 117         ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
 118         if (local_err) {
 119             error_report_err(local_err);
 120             ret = -EPERM;
 121             goto out;
 122         }
 123     }
 124
 125 out:
 126     if (unfiltered_bs_cow) {
 127         bdrv_drained_end(unfiltered_bs_cow);
 128         bdrv_unref(unfiltered_bs_cow);
 129     }
 130     bdrv_drained_end(unfiltered_bs);
 131     return ret;
 132 }
 133
 134 static void stream_clean(Job *job)
 135 {
 136     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 137
 138     if (s->cor_filter_bs) {
 139         bdrv_cor_filter_drop(s->cor_filter_bs);
 140         s->cor_filter_bs = NULL;
 141     }
 142
 143     blk_unref(s->blk);
 144     s->blk = NULL;
 145
 146     /* Reopen the image back in read-only mode if necessary */
 147     if (s->bs_read_only) {
 148         /* Give up write permissions before making it read-only */
 149         bdrv_reopen_set_read_only(s->target_bs, true, NULL);
 150     }
 151
 152     g_free(s->backing_file_str);
 153 }
 154
 155 static int coroutine_fn stream_run(Job *job, Error **errp)
 156 {
 157     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 158     BlockDriverState *unfiltered_bs;
 159     int64_t len;
 160     int64_t offset = 0;
 161     int error = 0;
 162     int64_t n = 0; /* bytes */
 163
 164     WITH_GRAPH_RDLOCK_GUARD() {
 165         unfiltered_bs = bdrv_skip_filters(s->target_bs);
 166         if (unfiltered_bs == s->base_overlay) {
 167             /* Nothing to stream */
 168             return 0;
 169         }
 170
 171         len = bdrv_co_getlength(s->target_bs);
 172         if (len < 0) {
 173             return len;
 174         }
 175     }
 176     job_progress_set_remaining(&s->common.job, len);
 177
 178     for ( ; offset < len; offset += n) {
 179         bool copy;
 180         int ret;
 181
 182         /* Note that even when no rate limit is applied we need to yield
 183          * with no pending I/O here so that bdrv_drain_all() returns.
 184          */
 185         block_job_ratelimit_sleep(&s->common);
 186         if (job_is_cancelled(&s->common.job)) {
 187             break;
 188         }
 189
 190         copy = false;
 191
 192         WITH_GRAPH_RDLOCK_GUARD() {
 193             ret = bdrv_co_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
 194             if (ret == 1) {
 195                 /* Allocated in the top, no need to copy.  */
 196             } else if (ret >= 0) {
 197                 /*
 198                  * Copy if allocated in the intermediate images.  Limit to the
 199                  * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).
 200                  */
 201                 ret = bdrv_co_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
 202                                                  s->base_overlay, true,
 203                                                  offset, n, &n);
 204                 /* Finish early if end of backing file has been reached */
 205                 if (ret == 0 && n == 0) {
 206                     n = len - offset;
 207                 }
 208
 209                 copy = (ret > 0);
 210             }
 211         }
 212         trace_stream_one_iteration(s, offset, n, ret);
 213         if (copy) {
 214             ret = stream_populate(s->blk, offset, n);
 215         }
 216         if (ret < 0) {
 217             BlockErrorAction action =
 218                 block_job_error_action(&s->common, s->on_error, true, -ret);
 219             if (action == BLOCK_ERROR_ACTION_STOP) {
 220                 n = 0;
 221                 continue;
 222             }
 223             if (error == 0) {
 224                 error = ret;
 225             }
 226             if (action == BLOCK_ERROR_ACTION_REPORT) {
 227                 break;
 228             }
 229         }
 230
 231         /* Publish progress */
 232         job_progress_update(&s->common.job, n);
 233         if (copy) {
 234             block_job_ratelimit_processed_bytes(&s->common, n);
 235         }
 236     }
 237
 238     /* Do not remove the backing file if an error was there but ignored. */
 239     return error;
 240 }
 241
 242 static const BlockJobDriver stream_job_driver = {
 243     .job_driver = {
 244         .instance_size = sizeof(StreamBlockJob),
 245         .job_type      = JOB_TYPE_STREAM,
 246         .free          = block_job_free,
 247         .run           = stream_run,
 248         .prepare       = stream_prepare,
 249         .clean         = stream_clean,
 250         .user_resume   = block_job_user_resume,
 251     },
 252 };
 253
 254 void stream_start(const char *job_id, BlockDriverState *bs,
 255                   BlockDriverState *base, const char *backing_file_str,
 256                   bool backing_mask_protocol,
 257                   BlockDriverState *bottom,
 258                   int creation_flags, int64_t speed,
 259                   BlockdevOnError on_error,
 260                   const char *filter_node_name,
 261                   Error **errp)
 262 {
 263     StreamBlockJob *s = NULL;
 264     BlockDriverState *iter;
 265     bool bs_read_only;
 266     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
 267     BlockDriverState *base_overlay;
 268     BlockDriverState *cor_filter_bs = NULL;
 269     BlockDriverState *above_base;
 270     QDict *opts;
 271     int ret;
 272
 273     GLOBAL_STATE_CODE();
 274
 275     assert(!(base && bottom));
 276     assert(!(backing_file_str && bottom));
 277
 278     bdrv_graph_rdlock_main_loop();
 279
 280     if (bottom) {
 281         /*
 282          * New simple interface. The code is written in terms of old interface
 283          * with @base parameter (still, it doesn't freeze link to base, so in
 284          * this mean old code is correct for new interface). So, for now, just
 285          * emulate base_overlay and above_base. Still, when old interface
 286          * finally removed, we should refactor code to use only "bottom", but
 287          * not "*base*" things.
 288          */
 289         assert(!bottom->drv->is_filter);
 290         base_overlay = above_base = bottom;
 291     } else {
 292         base_overlay = bdrv_find_overlay(bs, base);
 293         if (!base_overlay) {
 294             error_setg(errp, "'%s' is not in the backing chain of '%s'",
 295                        base->node_name, bs->node_name);
 296             goto out_rdlock;
 297         }
 298
 299         /*
 300          * Find the node directly above @base.  @base_overlay is a COW overlay,
 301          * so it must have a bdrv_cow_child(), but it is the immediate overlay
 302          * of @base, so between the two there can only be filters.
 303          */
 304         above_base = base_overlay;
 305         if (bdrv_cow_bs(above_base) != base) {
 306             above_base = bdrv_cow_bs(above_base);
 307             while (bdrv_filter_bs(above_base) != base) {
 308                 above_base = bdrv_filter_bs(above_base);
 309             }
 310         }
 311     }
 312
 313     /* Make sure that the image is opened in read-write mode */
 314     bs_read_only = bdrv_is_read_only(bs);
 315     if (bs_read_only) {
 316         /* Hold the chain during reopen */
 317         if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
 318             goto out_rdlock;
 319         }
 320
 321         ret = bdrv_reopen_set_read_only(bs, false, errp);
 322
 323         /* failure, or cor-filter will hold the chain */
 324         bdrv_unfreeze_backing_chain(bs, above_base);
 325
 326         if (ret < 0) {
 327             goto out_rdlock;
 328         }
 329     }
 330
 331     bdrv_graph_rdunlock_main_loop();
 332
 333     opts = qdict_new();
 334
 335     qdict_put_str(opts, "driver", "copy-on-read");
 336     qdict_put_str(opts, "file", bdrv_get_node_name(bs));
 337     /* Pass the base_overlay node name as 'bottom' to COR driver */
 338     qdict_put_str(opts, "bottom", base_overlay->node_name);
 339     if (filter_node_name) {
 340         qdict_put_str(opts, "node-name", filter_node_name);
 341     }
 342
 343     cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
 344     if (!cor_filter_bs) {
 345         goto fail;
 346     }
 347
 348     if (!filter_node_name) {
 349         cor_filter_bs->implicit = true;
 350     }
 351
 352     s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
 353                          0, BLK_PERM_ALL,
 354                          speed, creation_flags, NULL, NULL, errp);
 355     if (!s) {
 356         goto fail;
 357     }
 358
 359     s->blk = blk_new_with_bs(cor_filter_bs, BLK_PERM_CONSISTENT_READ,
 360                              basic_flags | BLK_PERM_WRITE, errp);
 361     if (!s->blk) {
 362         goto fail;
 363     }
 364     /*
 365      * Disable request queuing in the BlockBackend to avoid deadlocks on drain:
 366      * The job reports that it's busy until it reaches a pause point.
 367      */
 368     blk_set_disable_request_queuing(s->blk, true);
 369     blk_set_allow_aio_context_change(s->blk, true);
 370
 371     /*
 372      * Prevent concurrent jobs trying to modify the graph structure here, we
 373      * already have our own plans. Also don't allow resize as the image size is
 374      * queried only at the job start and then cached.
 375      */
 376     bdrv_graph_wrlock();
 377     if (block_job_add_bdrv(&s->common, "active node", bs, 0,
 378                            basic_flags | BLK_PERM_WRITE, errp)) {
 379         bdrv_graph_wrunlock();
 380         goto fail;
 381     }
 382
 383     /* Block all intermediate nodes between bs and base, because they will
 384      * disappear from the chain after this operation. The streaming job reads
 385      * every block only once, assuming that it doesn't change, so forbid writes
 386      * and resizes. Reassign the base node pointer because the backing BS of the
 387      * bottom node might change after the call to bdrv_reopen_set_read_only()
 388      * due to parallel block jobs running.
 389      * above_base node might change after the call to
 390      * bdrv_reopen_set_read_only() due to parallel block jobs running.
 391      */
 392     base = bdrv_filter_or_cow_bs(above_base);
 393     for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
 394          iter = bdrv_filter_or_cow_bs(iter))
 395     {
 396         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 397                                  basic_flags, errp);
 398         if (ret < 0) {
 399             bdrv_graph_wrunlock();
 400             goto fail;
 401         }
 402     }
 403     bdrv_graph_wrunlock();
 404
 405     s->base_overlay = base_overlay;
 406     s->above_base = above_base;
 407     s->backing_file_str = g_strdup(backing_file_str);
 408     s->backing_mask_protocol = backing_mask_protocol;
 409     s->cor_filter_bs = cor_filter_bs;
 410     s->target_bs = bs;
 411     s->bs_read_only = bs_read_only;
 412
 413     s->on_error = on_error;
 414     trace_stream_start(bs, base, s);
 415     job_start(&s->common.job);
 416     return;
 417
 418 fail:
 419     if (s) {
 420         job_early_fail(&s->common.job);
 421     }
 422     if (cor_filter_bs) {
 423         bdrv_cor_filter_drop(cor_filter_bs);
 424     }
 425     if (bs_read_only) {
 426         bdrv_reopen_set_read_only(bs, true, NULL);
 427     }
 428     return;
 429
 430 out_rdlock:
 431     bdrv_graph_rdunlock_main_loop();
 432 }