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 bs_read_only;
  43 } StreamBlockJob;
  44
  45 static int coroutine_fn stream_populate(BlockBackend *blk,
  46                                         int64_t offset, uint64_t bytes)
  47 {
  48     assert(bytes < SIZE_MAX);
  49
  50     return blk_co_preadv(blk, offset, bytes, NULL, BDRV_REQ_PREFETCH);
  51 }
  52
  53 static int stream_prepare(Job *job)
  54 {
  55     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
  56     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
  57     BlockDriverState *unfiltered_bs_cow = bdrv_cow_bs(unfiltered_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 the unfiltered_bs and the COW child
  69      * of unfiltered_bs is drained. Drain already here and use
  70      * bdrv_set_backing_hd_drained() instead because the polling during
  71      * drained_begin() might change the graph, and if we do this only later, we
  72      * may end up working with the wrong base node (or it might even have gone
  73      * away by the time we want to use it).
  74      */
  75     bdrv_drained_begin(unfiltered_bs);
  76     if (unfiltered_bs_cow) {
  77         bdrv_ref(unfiltered_bs_cow);
  78         bdrv_drained_begin(unfiltered_bs_cow);
  79     }
  80
  81     base = bdrv_filter_or_cow_bs(s->above_base);
  82     unfiltered_base = bdrv_skip_filters(base);
  83
  84     if (bdrv_cow_child(unfiltered_bs)) {
  85         const char *base_id = NULL, *base_fmt = NULL;
  86         if (unfiltered_base) {
  87             base_id = s->backing_file_str ?: unfiltered_base->filename;
  88             if (unfiltered_base->drv) {
  89                 base_fmt = unfiltered_base->drv->format_name;
  90             }
  91         }
  92
  93         bdrv_set_backing_hd_drained(unfiltered_bs, base, &local_err);
  94
  95         /*
  96          * This call will do I/O, so the graph can change again from here on.
  97          * We have already completed the graph change, so we are not in danger
  98          * of operating on the wrong node any more if this happens.
  99          */
 100         ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
 101         if (local_err) {
 102             error_report_err(local_err);
 103             ret = -EPERM;
 104             goto out;
 105         }
 106     }
 107
 108 out:
 109     if (unfiltered_bs_cow) {
 110         bdrv_drained_end(unfiltered_bs_cow);
 111         bdrv_unref(unfiltered_bs_cow);
 112     }
 113     bdrv_drained_end(unfiltered_bs);
 114     return ret;
 115 }
 116
 117 static void stream_clean(Job *job)
 118 {
 119     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 120
 121     if (s->cor_filter_bs) {
 122         bdrv_cor_filter_drop(s->cor_filter_bs);
 123         s->cor_filter_bs = NULL;
 124     }
 125
 126     blk_unref(s->blk);
 127     s->blk = NULL;
 128
 129     /* Reopen the image back in read-only mode if necessary */
 130     if (s->bs_read_only) {
 131         /* Give up write permissions before making it read-only */
 132         bdrv_reopen_set_read_only(s->target_bs, true, NULL);
 133     }
 134
 135     g_free(s->backing_file_str);
 136 }
 137
 138 static int coroutine_fn stream_run(Job *job, Error **errp)
 139 {
 140     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
 141     BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs);
 142     int64_t len;
 143     int64_t offset = 0;
 144     int error = 0;
 145     int64_t n = 0; /* bytes */
 146
 147     if (unfiltered_bs == s->base_overlay) {
 148         /* Nothing to stream */
 149         return 0;
 150     }
 151
 152     WITH_GRAPH_RDLOCK_GUARD() {
 153         len = bdrv_co_getlength(s->target_bs);
 154         if (len < 0) {
 155             return len;
 156         }
 157     }
 158     job_progress_set_remaining(&s->common.job, len);
 159
 160     for ( ; offset < len; offset += n) {
 161         bool copy;
 162         int ret;
 163
 164         /* Note that even when no rate limit is applied we need to yield
 165          * with no pending I/O here so that bdrv_drain_all() returns.
 166          */
 167         block_job_ratelimit_sleep(&s->common);
 168         if (job_is_cancelled(&s->common.job)) {
 169             break;
 170         }
 171
 172         copy = false;
 173
 174         WITH_GRAPH_RDLOCK_GUARD() {
 175             ret = bdrv_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
 176             if (ret == 1) {
 177                 /* Allocated in the top, no need to copy.  */
 178             } else if (ret >= 0) {
 179                 /*
 180                  * Copy if allocated in the intermediate images.  Limit to the
 181                  * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).
 182                  */
 183                 ret = bdrv_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
 184                                             s->base_overlay, true,
 185                                             offset, n, &n);
 186                 /* Finish early if end of backing file has been reached */
 187                 if (ret == 0 && n == 0) {
 188                     n = len - offset;
 189                 }
 190
 191                 copy = (ret > 0);
 192             }
 193         }
 194         trace_stream_one_iteration(s, offset, n, ret);
 195         if (copy) {
 196             ret = stream_populate(s->blk, offset, n);
 197         }
 198         if (ret < 0) {
 199             BlockErrorAction action =
 200                 block_job_error_action(&s->common, s->on_error, true, -ret);
 201             if (action == BLOCK_ERROR_ACTION_STOP) {
 202                 n = 0;
 203                 continue;
 204             }
 205             if (error == 0) {
 206                 error = ret;
 207             }
 208             if (action == BLOCK_ERROR_ACTION_REPORT) {
 209                 break;
 210             }
 211         }
 212
 213         /* Publish progress */
 214         job_progress_update(&s->common.job, n);
 215         if (copy) {
 216             block_job_ratelimit_processed_bytes(&s->common, n);
 217         }
 218     }
 219
 220     /* Do not remove the backing file if an error was there but ignored. */
 221     return error;
 222 }
 223
 224 static const BlockJobDriver stream_job_driver = {
 225     .job_driver = {
 226         .instance_size = sizeof(StreamBlockJob),
 227         .job_type      = JOB_TYPE_STREAM,
 228         .free          = block_job_free,
 229         .run           = stream_run,
 230         .prepare       = stream_prepare,
 231         .clean         = stream_clean,
 232         .user_resume   = block_job_user_resume,
 233     },
 234 };
 235
 236 void stream_start(const char *job_id, BlockDriverState *bs,
 237                   BlockDriverState *base, const char *backing_file_str,
 238                   BlockDriverState *bottom,
 239                   int creation_flags, int64_t speed,
 240                   BlockdevOnError on_error,
 241                   const char *filter_node_name,
 242                   Error **errp)
 243 {
 244     StreamBlockJob *s = NULL;
 245     BlockDriverState *iter;
 246     bool bs_read_only;
 247     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
 248     BlockDriverState *base_overlay;
 249     BlockDriverState *cor_filter_bs = NULL;
 250     BlockDriverState *above_base;
 251     QDict *opts;
 252     int ret;
 253
 254     GLOBAL_STATE_CODE();
 255
 256     assert(!(base && bottom));
 257     assert(!(backing_file_str && bottom));
 258
 259     if (bottom) {
 260         /*
 261          * New simple interface. The code is written in terms of old interface
 262          * with @base parameter (still, it doesn't freeze link to base, so in
 263          * this mean old code is correct for new interface). So, for now, just
 264          * emulate base_overlay and above_base. Still, when old interface
 265          * finally removed, we should refactor code to use only "bottom", but
 266          * not "*base*" things.
 267          */
 268         assert(!bottom->drv->is_filter);
 269         base_overlay = above_base = bottom;
 270     } else {
 271         base_overlay = bdrv_find_overlay(bs, base);
 272         if (!base_overlay) {
 273             error_setg(errp, "'%s' is not in the backing chain of '%s'",
 274                        base->node_name, bs->node_name);
 275             return;
 276         }
 277
 278         /*
 279          * Find the node directly above @base.  @base_overlay is a COW overlay,
 280          * so it must have a bdrv_cow_child(), but it is the immediate overlay
 281          * of @base, so between the two there can only be filters.
 282          */
 283         above_base = base_overlay;
 284         if (bdrv_cow_bs(above_base) != base) {
 285             above_base = bdrv_cow_bs(above_base);
 286             while (bdrv_filter_bs(above_base) != base) {
 287                 above_base = bdrv_filter_bs(above_base);
 288             }
 289         }
 290     }
 291
 292     /* Make sure that the image is opened in read-write mode */
 293     bs_read_only = bdrv_is_read_only(bs);
 294     if (bs_read_only) {
 295         /* Hold the chain during reopen */
 296         if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
 297             return;
 298         }
 299
 300         ret = bdrv_reopen_set_read_only(bs, false, errp);
 301
 302         /* failure, or cor-filter will hold the chain */
 303         bdrv_unfreeze_backing_chain(bs, above_base);
 304
 305         if (ret < 0) {
 306             return;
 307         }
 308     }
 309
 310     opts = qdict_new();
 311
 312     qdict_put_str(opts, "driver", "copy-on-read");
 313     qdict_put_str(opts, "file", bdrv_get_node_name(bs));
 314     /* Pass the base_overlay node name as 'bottom' to COR driver */
 315     qdict_put_str(opts, "bottom", base_overlay->node_name);
 316     if (filter_node_name) {
 317         qdict_put_str(opts, "node-name", filter_node_name);
 318     }
 319
 320     cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
 321     if (!cor_filter_bs) {
 322         goto fail;
 323     }
 324
 325     if (!filter_node_name) {
 326         cor_filter_bs->implicit = true;
 327     }
 328
 329     s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
 330                          0, BLK_PERM_ALL,
 331                          speed, creation_flags, NULL, NULL, errp);
 332     if (!s) {
 333         goto fail;
 334     }
 335
 336     s->blk = blk_new_with_bs(cor_filter_bs, BLK_PERM_CONSISTENT_READ,
 337                              basic_flags | BLK_PERM_WRITE, errp);
 338     if (!s->blk) {
 339         goto fail;
 340     }
 341     /*
 342      * Disable request queuing in the BlockBackend to avoid deadlocks on drain:
 343      * The job reports that it's busy until it reaches a pause point.
 344      */
 345     blk_set_disable_request_queuing(s->blk, true);
 346     blk_set_allow_aio_context_change(s->blk, true);
 347
 348     /*
 349      * Prevent concurrent jobs trying to modify the graph structure here, we
 350      * already have our own plans. Also don't allow resize as the image size is
 351      * queried only at the job start and then cached.
 352      */
 353     if (block_job_add_bdrv(&s->common, "active node", bs, 0,
 354                            basic_flags | BLK_PERM_WRITE, errp)) {
 355         goto fail;
 356     }
 357
 358     /* Block all intermediate nodes between bs and base, because they will
 359      * disappear from the chain after this operation. The streaming job reads
 360      * every block only once, assuming that it doesn't change, so forbid writes
 361      * and resizes. Reassign the base node pointer because the backing BS of the
 362      * bottom node might change after the call to bdrv_reopen_set_read_only()
 363      * due to parallel block jobs running.
 364      * above_base node might change after the call to
 365      * bdrv_reopen_set_read_only() due to parallel block jobs running.
 366      */
 367     base = bdrv_filter_or_cow_bs(above_base);
 368     for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
 369          iter = bdrv_filter_or_cow_bs(iter))
 370     {
 371         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
 372                                  basic_flags, errp);
 373         if (ret < 0) {
 374             goto fail;
 375         }
 376     }
 377
 378     s->base_overlay = base_overlay;
 379     s->above_base = above_base;
 380     s->backing_file_str = g_strdup(backing_file_str);
 381     s->cor_filter_bs = cor_filter_bs;
 382     s->target_bs = bs;
 383     s->bs_read_only = bs_read_only;
 384
 385     s->on_error = on_error;
 386     trace_stream_start(bs, base, s);
 387     job_start(&s->common.job);
 388     return;
 389
 390 fail:
 391     if (s) {
 392         job_early_fail(&s->common.job);
 393     }
 394     if (cor_filter_bs) {
 395         bdrv_cor_filter_drop(cor_filter_bs);
 396     }
 397     if (bs_read_only) {
 398         bdrv_reopen_set_read_only(bs, true, NULL);
 399     }
 400 }